VAF Forums - The Shrinking Exit

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- - The Shrinking Exit (http://www.vansairforce.com/community/showthread.php?t=68241)
DanH
02-08-2011 07:10 AM
The Shrinking Exit
Recall I've been experimenting with a different approach to cooling....large, low velocity inlets with a throttled exit (and a bunch of details). The
cowl was modified so I could swap exit panels and thus vary the exit area.
Started with the one on the left, changed to the middle one at 15 hours or so, and just started flying the one on the right. All are smaller than stock
by a good margin. I'll fly the latest into warmer weather, then consider the next step. I want to do some temperature and pressure measurements
when it gets really hot this summer. Plus, from a standpoint of break-in, I'm only at 70 hours or so.
This Sunday, with the smallest exit, a WOT/2700 climb at 105 knots from 200MSL to 5500 MSL at 50F OAT netted a highest CHT of 366F. CHT
spread is 20F. 60% cruise is 300F or less. No cylinder has ever seen 400F. Engine is an angle valve IO-390.
Stock exit for comparison:
zav6a
02-08-2011 09:02 AM
Shape
Hi Dan
I have come to the conclusion that your cooling strategy (exterior pressure recovery) is the best compromise ideal for the kind of flying RVs do and
and the limited space we have to work with under the cowl.
I could probably find pictures somewhere but I will just ask. What shape and how large of inlets?
I presume the desired effect of reducing the tunnel bump are less frontal area and better aerodynamics. It will also produce higher pressures in the
lower cowl to help kick the cooling air out at a higher velocity (less drag). Sealing the lower cowl then takes on a more critical role.
I am interested in your sealing measures around the prop and cowl seams. I think I recall a thread where you described what you did around the
prop. I have wondered at what point the lower cowl starts to distort as it does not have the the best shape to hold a lot of pressure. Have you
played with a manometer as you put the various subcowls sheets on?
DanH
02-08-2011 09:25 AM
Quote:
Originally Posted by zav6a (Post 511619)
Hi Dan
I have come to the conclusion that your cooling strategy (exterior pressure recovery) is the best compromise ideal for the kind of flying RVs
do and and the limited space we have to work with under the cowl.
Me too, which is why I went from theory to experiment.
Quote:
What shape and how large of inlets?
6" diameter. No claim of optimum size; my math could be wrong.
Quote:
I presume the desired effect of reducing the tunnel bump are less frontal area and better aerodynamics. It will also produce higher pressures
in the lower cowl to help kick the cooling air out at a higher velocity (less drag). Sealing the lower cowl then takes on a more critical role.
Didn't consider frontal area reduction; goal is to increase exit velocity. Cowl sealing is tricky and hardly perfect. I have a few tweaks in mind for the
future.
Quote:
I am interested in your sealing measures around the prop and cowl seams. I think I recall a thread where you described what you did around
the prop. I have wondered at what point the lower cowl starts to distort as it does not have the the best shape to hold a lot of pressure. Have
you played with a manometer as you put the various subcowls sheets on?
The flap seal shown above is doing fine. More or less as expected it has glazed a nice smooth strip on the ring gear casting after wearing itself to a
feather edge. Not perfect, but it's what I did. Tom Martin took a different approach with some foam rubber, but I don't have a prop extension.
I too am wondering about rising internal pressure, which is one reason I'm not going smaller than exit #3 until I install pressure and temperature
transducers. Real data will tell the tale.
hydroguy2
02-08-2011 09:57 AM
Once again....Nice work Dan.
RV8RIVETER
02-08-2011 11:20 AM
Truly nice work Dan!
Do you have an estimate as to what your exit area is now?
My first pass at my nozzle exit area is approx (6.1 inch dia) 29 sq inches. I will be making different size and configuration exit nozzles to test.
Danny7
02-08-2011 11:28 AM
what kind of airflow control have you done on the firewall corner where it comes down to that reflective ramp?
fatherson
02-08-2011 11:52 AM
Experimental!
Dan, I know the work you do is its own reward, and you hardly need any praise from the likes of me to motivate your efforts, but I want you to
know how much I am inspired by not only your experiments, but also by your willingness to share your progress with all of us.
There are so many disparate reasons each of us are doing this, but for so many of us, the claim to "Experimental" is just an FAA label, not a badge
of honor. We build to fly, standing on the shoulders of all those who came before us, learning ourselves, but not adding very much to the body of
knowledge in our community. Sure, I'm still proud of my participation in homebuilt aviation, but it's people like you who earn the right to put
"Experimental" on your airplane as an actual, bona-fide reward.
Thanks for helping us all expand our knowledge of the black magic that improves our craft.
--Stephen
DanH
02-08-2011 12:34 PM
You're in the ballpark Wade....I didn't build the latest exit to any precise dimension, but it should be between 25 to 30 sq in. Intake area is 56.5.
So much for those much-discussed intake-exit area ratios eh? ;)
Quote:
Originally Posted by Danny7 (Post 511672)
what kind of airflow control have you done on the firewall corner where it comes down to that reflective ramp?
A stock -8 has a rolled sheet aluminum radius on the firewall corner, 2", maybe 3" diameter. I elected to build a converging duct. Here you're
looking upward with the exit panel removed from the cowl:
Early concept sketch:
You've seen the reverse flow in the exit tuft video from an RV-6 (-7?). Here's what I think is happening:
To put the above in perspective.....you wouldn't put a square corner like that on the outside of the airframe would you? Well, the goal here is an
exit velocity of 200 knots....momentum loss is cooling drag.
Stephen, thank you....you're very kind.
Danny7
02-08-2011 01:06 PM
Thank you Dan, that photo helps me visualize much better. I would not expect a 90* corner on your airplane.
I also would like to say thank you for your explanations, photos and considerate attitude. I appreciate it.
it would be very interesting to have a camera and some smoke to see airflow inside the cowl..
zav6a
02-08-2011 01:52 PM
Exit area ratio
To Dan's point on rules of thumb for exit area ratio, there are so many factors to consider that there is simply no way a single ratio could be
considered ideal.
Dan has chosen external pressure recover so he has much bigger inlets than would be required for internal recovery. I will bet he will see nearly 100
percent velocity pressure in the plenum. The plenum will maintain more of that pressure. His lower cowl is sealed, so little pressure will be lost
there. Finally, he has the cleanest discharge tunnel I can remember seeing so that pressure will be efficiently converted back to velocity and
associated volume through a relatively small opening.
My bet is that all of those factors will add up to a record (low) outlet area/inlet area for RVs. And, low drag.
Dan, you probably could have save all of that streamlining on your pitot and just put a port in the plenum! Kidding but it will interesting to see your
pressure data!
Transporter
02-08-2011 02:34 PM
Converging Duct
Dan,
As always, great workmanship!
Do you have any photos of the converging duct with the cowl off?
Is the duct aluminum or stainless? I'm guessing you attached it to the engine mount at the leading edge?
Thanks,
Mike
elippse
02-08-2011 02:37 PM
Nice work, Dan! It's good to see that there are still experimenters around in Experimental aviation!
RV8RIVETER
02-08-2011 03:28 PM
Quote:
Originally Posted by DanH (Post 511696)
You're in the ballpark Wade....I didn't build the latest exit to any precise dimension, but it should be between 25 to 30 sq in. Intake area is
56.5.
So much for those much-discussed intake-exit area ratios eh? ;)
Dan. Thank you very much for sharing. It is the posters like you, Paul, and others that make experimenting rewarding. I don't think much of those
"ideal" ratios, just too many variables in individual installs.
In the interest of sharing, my inlet area is approx 12 sq inches per inlet, each one feeding a separate plenum. Plus 1.7" Dia oil cooler inlet.
DanH
02-08-2011 03:48 PM
Quote:
Originally Posted by Transporter (Post 511733)
Do you have any photos of the converging duct with the cowl off? Is the duct aluminum or stainless? I'm guessing you attached it to the
engine mount at the leading edge?
This from early in fabrication:
....and another from below:
2024T3.....in a former life, stock turtledeck skin. Finished duct has a 3/4" diameter transverse tube at the upper edge, attached to the motor mount
tubes with adels.
scsmith
02-08-2011 04:17 PM
intake lip shaping
Dan,
As you close down the exit, you get more spillage on the inlets. As long as the inlet lips are designed right, this spillage will cause negligible drag,
and the reduced frontal area and increased exit velocity will pay off.
The key is that the inlet lips need to be nicely radiused. The fairly sharp lip on Sam James inlets and LoPresti inlets are fine as long as they are sized
to match the exit and there is very little spillage, but lips that sharp will cause flow separation on the exterior of the lip when the exit area is closed
down. The separated flow around a sharp inlet lip is about like a leading-edge stall on a sharp leading edge airfoil. The flow will reattach, but you
pay a price in lost lip suction.
To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass flow,
and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.
gereed75
steve
Quote:
Originally Posted by scsmith (Post 511759)
The key is that the inlet lips need to be nicely radiused.
02-08-2011 05:38 PM
Would you say then the stock Van's intake lips are more forgiving of a mismatch between intake volume and exit size?? ie. less draggy when
spillage occurs??
This answer may help me formulate a plan as I begin to squeeze down my exit area using a vetterman type fairing. I have stock Van's openings,
mated to a Sam James plenum going to a stock cowl outlet (with a firewall exit ramp fairing). I have great cooling and my speeds indicate fairly low
drag. I plan some tuft tests to determine exit flow velocity/smoothness.
This may all fall into line with Dan's theory of slow, spill tolerant inlets matched to a correctly sized outlet to match outlet flow velocity.
Hmm, getting interesting!
AlexPeterson
02-08-2011 06:10 PM
That is the finest exit ever! I need to build a TD just to swipe your ideas! The large transition makes complete fluid flow sense. A masterpiece Dan.
I will bet you will do very well in an efficiency comparison (fly side by side with someone and see who uses less gas). In my book, that is the
comparison that ultimately matters.
DanH
02-08-2011 06:29 PM
Quote:
To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass
flow, and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.
I think the only way I could get closer would be to install some very tiny Norwegian folks:
(Thanks Alf!)
Transporter
02-08-2011 07:35 PM
Thanks
Dan,
Thanks for the photos with the cowl off. Again, beautiful work!
Mike
rocketbob
02-08-2011 09:26 PM
Quote:
60% cruise is 300F or less. No cylinder has ever seen 400F. Engine is an angle valve IO-390.
What's your cruise CHT's at 75%? At 60% at similar OATs I'm in the low 300's. This is with a stock RV-6 cowl.
elippse
02-08-2011 10:30 PM
Quote:
Dan,
As you close down the exit, you get more spillage on the inlets. As long as the inlet lips are designed right, this spillage will cause negligible
drag, and the reduced frontal area and increased exit velocity will pay off.
The key is that the inlet lips need to be nicely radiused. The fairly sharp lip on Sam James inlets and LoPresti inlets are fine as long as they
are sized to match the exit and there is very little spillage, but lips that sharp will cause flow separation on the exterior of the lip when the
exit area is closed down. The separated flow around a sharp inlet lip is about like a leading-edge stall on a sharp leading edge airfoil. The flow
will reattach, but you pay a price in lost lip suction.
To get an idea of what good intake lips should look like, look at the intake on a commercial transport nacelle. They are sized for take-off mass
flow, and at cruise, the spillage is often 30% or so. You are probably spilling almost that much with your smallest exit.
Keep in mind, too, that the airflow from the propeller, if the prop root has an airfoil shape and is producing some thrust will be flowing up into the
left, pilot-side inlet and down into the right inlet, so it is very important to have these nice, rounded lips, sorta like Angelina Jolie!
ccrawford
02-08-2011 11:07 PM
Dan,
Very nice work, good experimenting.
Have you considered shortening your 4-into-1 exhaust pipe to provide some exhaust driven velocity augmentation for your exiting cooling air?
DanH
02-08-2011 11:12 PM
Quote:
Originally Posted by ccrawford (Post 511910)
Have you considered shortening your 4-into-1 exhaust pipe to provide some exhaust driven velocity augmentation for your exiting cooling
air?
Nope. That's a whole different experiment.
Quote:
Originally Posted by rocketbob (Post 511875)
What's your cruise CHT's at 75%? At 60% at similar OATs I'm in the low 300's. This is with a stock RV-6 cowl.
So far only about 5 minutes at 75% with exit #3, and didn't pay much attention to CHT. I tend to focus on the critical case with a fixed exit; high
AOA, low airspeed, full power.
rocketbob
02-08-2011 11:22 PM
Quote:
So far only about 5 minutes at 75% with exit #3, and didn't pay much attention to CHT. I tend to focus on the critical case with a fixed exit;
high AOA, low airspeed, full power.
Sure, makes sense, but the real test will be 100 deg. OAT, with a passenger, on a long extended climb. That's the critical case. What's cool about
your setup (no pun intended) is you can switch exits for the cooler times of the year, or for a race.
Chris Hill
02-09-2011 04:31 AM
Dan, have you recorded any performance increase in speed with this modification?
Michael White
02-09-2011 06:56 AM
Quote:
<snip>100 deg. OAT, with a passenger, on a long extended climb. <snip>
Dan's gonna have to wait...we won't get those conditions until next month... :rolleyes:
Global Warming my foot...
Kevin Horton
02-09-2011 07:11 AM
Beautiful work Dan. I really appreciate the experimenting you are doing here. Bob Axsom is probably starting work on his new cowling as we speak
:)
What are you seeing for cruise TAS and fuel flow ROP or LOP?
DanH
02-09-2011 07:49 AM
Quote:
Sure, makes sense, but the real test will be 100 deg. OAT, with a passenger, on a long extended climb. That's the critical case.
Absolutely. So far the highest test OAT at 08A has been about 80F, as I didn't start flying until October. Those flights suggest a worst case of using
exit #2 for general fun flying in Alabama's hot months; WOT/85 knot field departures and 100 knot climbs to 10K.
Remember, this is an effort to reduce cooling drag, which is related to but not quite the same thing as reducing temperatures. I mention specific
temperatures and conditions only to communicate that nothing here has created a temperature problem. In the end, the very lowest drag system
will indicate rather high temps. I'll probably get to that in due course, but for now I'm looking for balanced performance.....the Vans mantra.
Quote:
Dan, have you recorded any performance increase in speed with this modification?
Well, obviously I didn't built an identical airplane with a stock cowl for comparison purposes, so here's the plan. With break-in done and these three
exits in hand I'll instrument the cowl for pressure and temperature, then swap 'em out for three quick back to back NTPS-method speed cal runs. I
figure I'll need to do it twice, the first morning running exits 1-2-3 and the second morning 3-2-1, so as to minimize the effect of OAT rise into the
day.
For now, no specific speed claims. The few early cal runs I did with exit#2 say it is not slow.
Quote:
What are you seeing for cruise TAS and fuel flow ROP or LOP?
Kevin, no valid data right now. Only balanced the restrictors a few weeks ago, and lately I've been shaving the static ports...need new airspeed
calibration.
lokobuff
02-10-2011 08:32 AM
Non scientific reply...
ALCON,
Guilt him into flying to Oshkosh this year, then go see it for yourselves. The airplane is beautiful, goes like ****, and is a hoot upside-down...
I think Dan's powered by beer, and I don't know if he's had New Glarus Spotted Cow Ale in a while.
Maybe he'll bring the small Norwegians with him.
Loko
scsmith
02-10-2011 05:58 PM
Yes, absolutely!
Quote:
Originally Posted by gereed75 (Post 511781)
Would you say then the stock Van's intake lips are more forgiving of a mismatch between intake volume and exit size?? ie. less draggy when
spillage occurs??
This answer may help me formulate a plan as I begin to squeeze down my exit area using a vetterman type fairing. I have stock Van's
openings, mated to a Sam James plenum going to a stock cowl outlet (with a firewall exit ramp fairing). I have great cooling and my speeds
indicate fairly low drag. I plan some tuft tests to determine exit flow velocity/smoothness.
This may all fall into line with Dan's theory of slow, spill tolerant inlets matched to a correctly sized outlet to match outlet flow velocity.
Hmm, getting interesting!
Yes - the stock cowl inlets are extremely tolerant of spillage. You could darn-near close the exit off entirely and the spillage drag on a stock cowl
would be small.
I am planning a cowl flap similar to what you would see on a C-182 or a Bonanza, mounted between my two exhaust pipes. When open, it will
match the stock cowl exit shape. When closed, it will form a surface in line with the basic fuselage shape, not counting the RV-8 exit ramp.
DanH
02-11-2011 03:53 PM
Steve, can you post some sketches or illustrations of spillage and flow separation?
Here's a fun paper...postwar research to rework the B-29 engine cowl.
http://ntrs.nasa.gov/archive/nasa/ca...1993093587.pdf
Interesting subject.
In the following illustration, which of the three lip profiles resulted in a cruise drag reduction of 60 hp, and 108 hp saved at 250 mph?
Scroll down
Surprise....it was the 43" opening with the smaller lip radius, in a Vi/Vo range of 0.256 to 0.144....indeed, a very large, very slow inlet.
gereed75
02-11-2011 04:11 PM
Dan
Facinating and needless to say, the profile of the 43" inlet should look pretty familiar to anyone that has banged around a Van's stock inlet.
Thanks for finding me some serious sleeping pill reading!
oh yea, and thanks Steve for the confirmation. Gives me the confidence to think my swag approach might prove effective.
scsmith
02-12-2011 03:21 AM
notional picture of spillage drag on sharp-lipped inlets
Here's a notional picture for you:
its a .pdf - maybe they don't post like a picture. Well, try the link:
http://www.hpaircraft.com/rv8/inlet_spillage.pdf
The B-29 cowl is interesting. It looks to me like the problem with the smaller inlets is the interior flow separation and incomplete pressure recovery.
It doesn't take much - the flow is trying to stop and the pressure is rising, but it will waste pressure on recirculation on the back side of an abrupt lip
like that. I think our cowls are "good enough" inside.
Looking forward to some speed data, Dan.
DanH
02-12-2011 08:13 AM
Quote:
Well, try the link:
http://www.hpaircraft.com/rv8/inlet_spillage.pdf
That bad inlet is indeed sharp-edged.
Quote:
The B-29 cowl is interesting. It looks to me like the problem with the smaller inlets is the interior flow separation and incomplete pressure
recovery. It doesn't take much - the flow is trying to stop and the pressure is rising, but it will waste pressure on recirculation on the back
side of an abrupt lip like that.
The old radial engine NACA papers are excellent for this stuff. Radial cowls are the ultimate large inlet, throttled exit systems.
Interior flow separation is not much of a concern given the interior velocity. Remember, in this case the Vi/Vo range (note for the non-engineers:
Vi/Vo = inlet velocity divided by freestream velocity, a measure of how much you slowed the air before it actually entered the inlet) is 0.256 to
0.144, thus the entire range of V behind the lip, inside the inlet, is something like 64 mph in the high speed case (250 mph with cowl flaps open)
and as low as 15 mph (100 mph, cowl flaps closed).
Inlets with very low Vi/Vo values require little or no flow control behind the inlet lip. Here's a late model example, the inlet on a Mooney Acclaim:
There's nothing inside the inlet....zip. It just dumps into the plenum.
Quote:
I think our cowls are "good enough" inside.
I think the the stock inlet is a bit better than the GA average, but hardly optimum for either internal or external recovery.
Quote:
Looking forward to some speed data, Dan.
Ok, but do remember the goal.....top speed AND good cooling at low speed/high power. That was the challenge with those ultimate piston powered
bombers, yes? ;)
Bob Kuykendall
Quote:
Here's a notional picture for you:...
Here it is converted to a .gif file:
02-12-2011 12:01 PM
DanH
02-12-2011 06:36 PM
Nice day here, so I went out and did some speed runs. Needed them to recalibrate the IAS anyway, as I've been shaving down the aluminum button
static ports (BTW, the method works and my thanks to whomever suggested it).
Exit #3, 2500 density altitude, 3-leg NTPS method, no taping, waxing, or prep, CG near forward limit:
All handles forward, 203.2 knots. About 6 minutes at WOT, highest CHT 317F, lowest CHT 298F, oil 187F.
Previous speed with exit #2 was 197.8 knots.
Kevin, you asked for some efficiency numbers. How would these compare with your benchmark -8?
22/2200, 50 LOP, 162.2 knots @ 7.5 GPH fuel flow (FF not fully calibrated but believed close), highest CHT 294F, lowest CHT 267F.
hydroguy2
02-12-2011 07:03 PM
nice numbers you got there. Keep up the good work.
what was the FF at WOT? :eek:
kcameron
02-12-2011 08:02 PM
Quote:
Great work as usual, Dan. I've been dreaming of reworking my cowl for awhile now. Maybe I'll copy your stuff. Not sure if I have the skills and/or
energy, though.
At what altitude did you get those numbers?
Thx.
Kevin Horton
02-12-2011 11:00 PM
Quote:
All handles forward, 203.2 knots. About 6 minutes at WOT, highest CHT 317F, lowest CHT 298F, oil 187F.
Very impressive speed - congratulations.
Quote:
Previous speed with exit #2 was 197.8 knots.
Nice increase, so the experiment is worthwhile.
Quote:
Kevin, you asked for some efficiency numbers. How would these compare with your benchmark -8?
My aircraft, with stock Van's cowling and a cooling plenum and a three-bladed MT prop would be burning around 8.2 gph at that speed at 50 deg
LOP at 8000 ft. My original old Hartzell (not the new blended airfoil Hartzell) was roughly five kt faster at the same power setting.
Chris Hill
02-12-2011 11:56 PM
Dan,
Is there a thread or website where you have listed your "mods" to achieve 200kts?
I'd sure like to get the kind of mileage out of my 8...
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DanH
02-13-2011 09:31 AM
Quote:
Originally Posted by hydroguy2 (Post 513084)
what was the FF at WOT? :eek:
Don't know....electric fuel pump is on for WOT runs, which skews the FF numbers.
Quote:
At what altitude did you get those numbers?
2500 ft density altitude for both data sets.
Quote:
My aircraft, with stock Van's cowling and a cooling plenum and a three-bladed MT prop would be burning around 8.2 gph at that speed at 50 deg LOP at 8000 ft.
Thanks Kevin. If I get out to the airport today I'll pop up to 8000 DA and record another run. Obviously a 22/2200 run at 2500 DA was throttled.
Quote:
Is there a thread or website where you have listed your "mods" to achieve 200kts?
Exclusive to VAF......scattered, but all here somewhere.
DanH
02-14-2011 03:30 PM
OK, took a few minutes and searched for some past posts.
The cowl inlets and the exit mods are obvious. Note the inlets are relocated upward and outward...diameter is 6".
The upper plenum is common practice, with the only significant difference being the rubber duct inlet experiment.
Less obvious is the detailed tweaks of baffle fit and sealing. Every molecule of air passes between cylinder fins or oil cooler fins.
The cowl is sealed, imperfectly but far better than average. Can't generate exit velocity if the pressure leaks away through 20 different "exits" all over the cowl.
It's a system. Capture lots of pressure. Maximize heat transfer. Maintain pressure to a clean exit.
http://www.vansairforce.com/communit...5&postcount=20
rv72004
02-15-2011 12:33 PM
I bow before you ,O Great Dan. You have taken workmanship to a whole new level. Ive been told Im a perfectionist, clearly "they" havent seen your work.
You have brought advanced technology to our RV species.
Absolutely fascinating .
DanH
02-20-2011 09:03 AM
Quote:
Sure, makes sense, but the real test will be 100 deg. OAT, with a passenger, on a long extended climb. That's the critical case. What's cool about your setup (no pun intended) is you can switch exits for the cooler times of the year,
or for a race.
Here ya go Bob....around 80F on the ground in south Alabama yesterday, so I logged a climb from 1000 MSL with the small exit (#3) and gross weight ~1840 lbs. This screenshot is just before an 8500 pushover.
The oil temperature is a new record for this airplane, but it was back to the usual 190 or less in 8 minutes. The CHT's are actually a little less here at the top of the climb than they were later at peak EGT and 22.1 hg (WOT) at 2200, 156
IAS.
Tom Martin
02-20-2011 01:27 PM
Interesting work Dan, and your engine temperature results echo what I was finding with my rocket. My goal with the rocket is to get exit air moving as smoothly as possible as straight back as possible. My converging duct is very similar
to what you have come up with. I have a cowl flap but have found that I have never had to open the flap in any flight condition.
As I continued in my cooling experiments CHTs continued to drop and oil temperature became my limiting factor, which is what I am seeing with your data as well. I have a personal maximum operating oil temp of 200F and that is where
I ran into a wall with the exit air size. The rocket cowling/firewall step, does not allow a nice way to duct the oil cooler air to the bottom of the cowling and so I am experimenting with ducting the oil cooler through the side of the cowling.
I followed some of the early NACA experiments in shaping a bluff body for that exit air and it seems to be working well. I can now independently work on the oil cooler exit air separate from the CHT exit air. This has allowed me to close
the exit duct a bit more and I finally have the cooling system that I was looking for. Ideally it would be nice to have a completely separate inlet and outlet for the oil cooler but that will have to wait for my next project.
In my case the only quantitative speed gains came with work to the inlets rather then exit air but as you have stated earlier it is a system and no one change will guarantee success in improved cooling or drag reduction. Improved cooling
has often resulted in reduced speed. It makes sense as more airflow will often result in increased drag.
elippse
02-20-2011 09:38 PM
Quote:
Originally Posted by Tom Martin (Post 515381)
The rocket cowling/firewall step, does not allow a nice way to duct the oil cooler air to the bottom of the cowling and so I am experimenting with ducting the oil cooler through the side of the cowling. I followed some of the early
NACA experiments in shaping a bluff body for that exit air and it seems to be working well. I can now independently work on the oil cooler exit air separate from the CHT exit air. This has allowed me to close the exit duct a bit more
and I finally have the cooling system that I was looking for. Ideally it would be nice to have a completely separate inlet and outlet for the oil cooler but that will have to wait for my next project.
How dare you, sir! I thought that I was the only Experimenter to go boldly where no one had gone before, and have a separate oil-cooler inlet and outlet, and here are you trying to steal my thunder. If this is kept up it will lead to others
doing the same thing and seeing their increased performance which should have been mine and mine alone! Please keep your results to yourself or I shall put a pox on you and your household! Pshaw!
hendrik
02-20-2011 09:49 PM
Quote:
Originally Posted by elippse (Post 515510)
I thought that I was the only Experimenter to go boldly where no one had gone before, and have a separate oil-cooler inlet and outlet, and here are you trying to steal my thunder.
Paul, I guess at least on the separate oil cooler inlet you're not alone (and he discusses the outlet, too):
http://www.vansairforce.com/communit...ad.php?t=12633 :p
DanH
02-21-2011 10:30 AM
Quote:
As I continued in my cooling experiments CHTs continued to drop and oil temperature became my limiting factor, which is what I am seeing with your data as well.
Yes Tom, I agree. Oil high, cylinders good. A separate oil cooler inlet would change one bit of CHT data. Cyl #3 runs warmer than the others with all exit sizes and all conditions. I pull oil cooler air with a 4"D duct from the baffle wall
behind #3. It's probably a local pressure loss at that cylinder. Don't consider it a problem at these CHT levels, but....
Here's another stressful condition, high power at what may be the highest altitude at which I can get 75% (have to check that detail). Anyway, 125-150 ROP for power, indicated true 183 knots. I could drop CHTs and oil temperature by
going richer or leaner, just like the theory says, but also went slower.
Paul, who you kidding? Clearly you stole the separate oil cooler inlet idea from that B-29 paper I referenced earlier ;)
elippse
02-21-2011 11:31 PM
Lots of WWII fighters had oil coolers installed under the wings with inlets and outlets; Hoerner covers a lot of them in Fluid Dynamic Drag. Here's something to consider. It seems to me the flat side of the cowling toward the rear on the
right or the left would make an ideal place to install an oil cooler, with a 6"W X 3/4" high inlet feeding it, and a 6"W X 1" outlet at the back. Kevin Eldredge had the oil cooler on Relentless NXT mounted on the bottom of the cowling, with a
separate inlet at the front and the regular engine outlet at the back. He used quick-disconnect hoses so that it was not a problem removing the cowl. The same Q-D set-up could be used with the cowling side mount. BTW; my OC IO was
on my plane when I got my airworthiness in 2001, so that trumps the one in 2006! :p
DanH
02-22-2011 05:19 PM
Quote:
Kevin Eldredge had the oil cooler on Relentless NXT mounted on the bottom of the cowling, with a separate inlet at the front and the regular engine outlet at the back. He used quick-disconnect hoses so that it was not a problem
removing the cowl.
Saw pictures of that somewhere, trick indeed.
I need several pressure measurements in the outlet area, then I'll make plans. Right now the oil cooler duct outlet is in the roof of the exit bell a few inches forward of the actual cowl outlet, which may not be the location with the lowest
pressure.
DanH
03-07-2011 09:37 AM
About 8 months ago Paul Lipps posted a recommendation for pressure and temperature sensors (thanks Paul):
Rainy weekend here, so I built a little board to go under the cowl:
The temperature probes are under the black heat shrink at the ends of the 3-wire shielded cables. No particular reason for the shields; I just had the cable in the spare wire box and the sensor needs at least two leads. The third lead
allows a calibration adjustment but I doubt I'll use it.
The two small differential pressure sensors have a range suitable for measurements like pressure drop across the cylinders or the oil cooler. The large sensor (Freescale MPX5010DP) is suitable for dynamic pressure in our speed range. I'll
hook one side of it to the aircraft static system and use it for velocity, in particular inlet and exit.
Primary goal is gathering data on this low velocity inlet/throttled exit system, but it would then be interesting to do the same with a standard RV-8 cowl and perhaps another with poor cooling performance.
RV8R999
03-07-2011 10:02 AM
Good stuff Dan!
Are the pressure sensors analog or digital output? Are you planning on recording the raw outputs and converting the data to pressure/velocities on the ground?
Ken
DanH
03-07-2011 10:57 AM
Quote:
Originally Posted by RV8R999 (Post 520651)
Are the pressure sensors analog or digital output? Are you planning on recording the raw outputs and converting the data to pressure/velocities on the ground?
Analog voltage proportional to pressure or temperature. Cockpit tools are just my trusty old Fluke and a clipboard, with conversions later. KIS is good.
rocketbob
03-07-2011 11:48 AM
Dan do you have any output filtering on the MPX sensors? It will be difficult to make readings with a multimeter without some sort of analog filter in-between the sensor output and your multimeter.
Bob Axsom
03-07-2011 12:55 PM
Oil Cooling
I have the inside of the cowl divided into three compartments - #1 is the area above the cylinders, #2 is the area under the cylinders leading back to the stock cowl outlet, #3 is the area above the lower cowl outboard of the plenum
baffling & valve covers continuing back to the area between the engine and firewall with a vent in the upper part of the stock outlet but separate from the exit path out of #2. In race configuration I mount closure plates over all of the
blast tube and heater ports at the rear of the plenum but the oil cooler continues to pass all of its cooling air into the large #3 compartment where it is vented through the small opening below the fuselage in the stock cowl cooling air
port.
The small zone #3 cooling air port is provided by continuing the curved baffle dividing compartments #2 and #3 down below the fuselage in the stock cooling air outlet and securing with screws to the flange of the fuselage skin and
firewall. The size of the opening ground adjustable and is controlled with AN960 washers stacked at the mounting points. The vent is approximately 3/16" tall and 7" wide. The oil temperature is stable at ~180 degrees under all
conditions. I experimented with opening the vent to 1/4" and detected a slight decrease in speed with no noticeable change in oil temperature. I see no need for a separate inlet for oil cooling in my O-360 application.
I just completed a difficult (messy) instrument panel change and have not been working on speed mods this winter but I have been going over that cooling air exit in my mind for many months (years?). I want to come up with something
that I feel confident will work which can be removed cleanly if it doesn't. I have the extra complication (opportunity) of the cowl and NLG strut support structure associated with the A model RV-6. The Larry Vetterman experiments add
conviction that speed can be gained in this area. I am currently thinking of a vertical "keel" structure with a bull nose or wedge inside the cowl behind the FAB and flat plates attached to the keel in the back that are flat against the keel in
ground and climb operations but the front deflects outward to seal against the leader bull nose or wedge in level flight.
Still not ready to commit but it is gnawing at me.
Bob Axsom
DanH
03-07-2011 12:58 PM
Quote:
Dan do you have any output filtering on the MPX sensors? It will be difficult to make readings with a multimeter without some sort of analog filter in-between the sensor output and your multimeter.
You'll have to help me Bob, I'm not an electronics guy. What sort of difficulty would you expect?
The data sheets suggest power supply and output filters for interfacing with the A/D input of a microprocesser. A quick bench check yesterday produced a stable meter reading without them.
Ted Johns
03-07-2011 03:13 PM
Dan,
Assuming you have a regulated 5v supply on-board to power the sensors, the supply decoupling circuit looks just fine from here. Just have to have clean power, so you aren't measuring alternator ripple. :)
T.J.
RV8R999
03-07-2011 04:16 PM
also, because the pressure changes are very small and the output range constrained to low value (5v spread) temperature stability can be a real challenge.
I used low pressure anologue sensors (0-1.0 psi and O-2.0 psi) in another project and found the output to vary significantly with temp requireing compensation.
I'd look at the sensor data sheet and see if it is supplied with a temp stability data. Also, all the components are affected by temperature to a certain extent - the power supply in particular. If the power supply voltage decreases as a
function of temperature then you can't rely upon the sensor output for conversion unless you can account for it. Make sense?
Ken
RV8R999
03-07-2011 04:20 PM
I should add... the other option is for you to remotely mount all the sensors keeping the components from being exposed to large changes in temp but the only accurate way to do this is to provide temp compensation - which is a course
all by itself :(
rocketbob
Quote:
You'll have to help me Bob, I'm not an electronics guy. What sort of difficulty would you expect?
The data sheets suggest power supply and output filters for interfacing with the A/D input of a microprocesser. A quick bench check yesterday produced a stable meter reading without them.
03-07-2011 04:27 PM
These sensors are very sensitive and they output even the tiniest of changes. What you'll see on a multimeter is a very erratic voltage and thus will be hard to read. Typically on a microcontroller one does filtering by taking something like
10 readings over X time and average them to get the real value.
Essentially this can be done in the analog world with whats called an RC (resistor/capacitor) low pass filter. There are many filters types that one could use but this is the easiest. I would try a 47K resistor in series and a 10uF resistor to
ground. This will give you a time constant of .47 seconds.
RV8RIVETER
03-07-2011 04:46 PM
I purchased the same sensors for my pressure measurements. The are fully temp compensating so that should not be an issue with them.
elippse
03-07-2011 09:40 PM
I agree with RocketBob about the filtering, since these sensors have a reponse time of 1 millisecond and can have an output that varies around somewhat with small changes in pressure due to minor oscillations in a plenum. Think of the
plenum of a car interior with a window slightly open where it wants to take out your eardrums! A-D converters often don't like variations during their conversion process, so they often incorporate a sample-hold circuit. These are good, but
due to Shannon-Nyquist sampling theorem they can often give strangely fluctuating readings.
I would suggest a very simple but easily accomplished filter of the data as it emerges from the A-D. A simple digital model of an RC network is to take the incoming value, subtract the previous filtered value from it, divide it by 2 or 4 or 8,
which can be accomplished by a shift instruction, and add the result to the filtered accumulator. Using 2 is similar to having a time-constant of 0.693, and using 4 is similar to having a time constant of 0.288 relative to the accumulation
interval and if you want more filtering, the 8 gives an equivalent time-constant of 0.134.
Where this kind of filtering works really well is if you are filtering data from a data set where the peridicity changes such as when counting rpm. That way the filtering is always a certain percentage of the periodicity, so whether the rpm is
low or high, you still get the same filtering.
rocketbob
03-08-2011 01:33 AM
Dan, I didn't see the image in your reply as some of them get blocked by the internet nazi's at work.
The power supply filtering that the datasheet mentions is a good start for the 5V lead, which will help you get stable readings. On the output side of the sensor, connect a 47K resistor in series, and a 10uF capacitor between the resistor
and your multimeter to ground. This will help eliminate noise and give you a more stable voltage to read.
As always my friend Paul is correct but it doesn't sound like Dan is ready to jump into writing code in assembler in the near term. :)
elippse
03-08-2011 12:19 PM
So, RB, Are you saying that fixed-point, fractional, binary machines are no longer derigeur? People no longer know octal notation? That they can't compute exactly the square root of a number in binary but must rely on the 1/2(X/A + A)
approximation?
Ted Johns
03-08-2011 02:16 PM
The DMM that the OP indicated he will use for data measurement already has a fair bit of signal integration. It may need a bit of analog filtering, it may not. As far as digital filtering, way beyond the scope of the task. But I wouldn't want
to slow down the fine mental mastur / err, the fine analysis going on here. :D
DanH
03-09-2011 10:33 AM
Here's the basic diagram for the sensor board, should some brave soul with a stock cowl want to follow along. (Wade's cowl is also non-stock.)
Currently no filters at all, but it's easy to add some later if necessary. As Ted mentioned, I've had good luck in the past using the old Fluke. We'll see; first step is to try the board while connected to ships power, alternator running, but
with the air ports capped. If the meter is jumpy I'll add filters.
On the air side, I expect to use aquarium bubbler rocks or similar to avoid dynamic pressure effects on the small sensors, and perhaps machined restrictors to smooth pressure fluctuations. On the flip side, I'm kinda curious about what
sort of flucuations may be present, so I don't want to start with a lot of damping.
Appreciate all the comments, keep 'em coming...very little electronics experience here.
Tom Martin
03-09-2011 12:51 PM
While you are at it, take a reading at your dipstick, to measure crankcase pressure. I had dumped the crankcase vent on the exhaust pipe, as per Van's recommendation, and found that that location pressurized the crankcase to the exact
same amount as the lower cowling, plus 1". By moving the crankcase vent outside, aft of the cowling outlet I was able to get a slightly negative number. Oil consumption, and oil on the bottom of the plane, did not change but all the little
drips in the engine compartment went away. It would be interesting to see if you get the same results that I did.
rocketbob
03-09-2011 01:00 PM
Quote:
So, RB, Are you saying that fixed-point, fractional, binary machines are no longer derigeur? People no longer know octal notation? That they can't compute exactly the square root of a number in binary but must rely on the 1/2(X/A
+ A) approximation?
Paul do you still have a rotary phone? :)
elippse
03-09-2011 03:29 PM
Quote:
Paul do you still have a rotary phone? :)
No, but every time I call a company and their recording says "You may dial your party's number now.", I always ask the person who answers if they still have a PBX with rotary phones. They have no idea what I'm talking about! I did work
for Ma Bell of Pa for 5 years after HS installing 'phones and teletypes and stuff.
RV8RIVETER
03-10-2011 12:17 PM
Quote:
(Wade's cowl is also non-stock.)
I will try and post some pict's of my cowl in another thread soon. I need to make them presentable, as my glass work is not up to par with Dan's. :)
FrankK90989
03-11-2011 10:03 AM
simple
Sorry Couldn’t resist.;)
DanH
03-11-2011 01:02 PM
Quote:
Originally Posted by FrankK90989 (Post 522124)
Sorry Couldn’t resist.;)
Resist? KIS is good. What are you measuring?
FrankK90989
03-11-2011 04:24 PM
I toyed with some VG;s fore of the cowl outlet. I did get a .5" more drop, in cruse using them.:eek: Saw some yarn tufting photos on this site. thought I would try smothing this turbulence out. burnt a bunch of gas measuring.:o
One of my last tests.
[IMG]
DanH
03-11-2011 06:59 PM
Frank, does "FWD of baffle" and "Aft of baffle" mean measurements taken above and below the cylinders? Put another way, upper plenum and lower plenum pressures?
DanH
03-15-2011 10:35 AM
Frank's KIS manometer got me thinking. I'm going to ditch the electronic pressure sensors with their electrical noise and calibration concerns.
Much of the driver for using sensors was a desire to bring the signal to the cockpit via wiring rather than tubing. However, for inlet and exit pressure measurements I really need to tap the aircraft static system, so there's one tube fitting
anyway.
Easy to make some small diameter steel "bulkhead fittings" for spaghetti tubing....old AN3 bolts and a few minutes each on the lathe.
Going over to direct pressure measurement offers a lot of options. About $60 will buy new differential pressure gauges calibrated in inches of water. There are handheld electronic manometers if you want to get fancy; China brands from
$50, USA from $140 or so. An old ASI will read velocity. And some tubing taped to a yardstick will do in a pinch ;)
BTW, anybody have an 0-200 knot ASI cheap?
Special Delivery
Quote:
03-15-2011 11:07 AM
BTW, anybody have an 0-200 knot ASI cheap?
If your interested, I have a used Falcon ASIT260MK that is yours for the asking. For accurate test results, it probably need to be calibrated. I've already benefited from your contributions WAY more that this instrument is worth! Keep up
the good work.
Tom Martin
03-15-2011 01:52 PM
I used tubing taped to a yardstick. I brought about six tubes into the cockpit through the heat box. I removed the hose and used aluminium tape to seal around the tubes. I just connected the tubes to the manometer one at a time. The
last test I did was a tube that was positioned at the opening of the engine cooing air inlet. There was WAY too much pressure there and it blew the water out the manometer all over me! I got a good reading from the upper mid and upper
back plenum and lower plenum, dipstick and cooling air outlet. Keep it simple, cheap and easy.
DanH
04-10-2011 09:12 AM
Tom (or others of course), have you ever measured air temperature at the oil cooler outlet?
Last night I moved a temperature probe into my cooler outlet duct and ran hard to push oil temperature up. At 209F oil temp and an OAT of 70F, outlet air temp was only 110F, which I found to be a huge surprise. Maybe I should pull and
test my vernatherm.
Postscript: Wrong...misread the chart, see below
Tom Martin
04-10-2011 09:19 AM
Dan
I have not taken any temperature or plenum pressures at the oil cooler. It would be interesting to get a pressure reading at the inlet of the oil cooler and outlet of the cooler. If there is not a duct on the outside of the cooler then you
would just be measuring the pressure of the lower plenum itself at that region.
With these two pressures you could determine the theoretical temperature drop and compare that to what you are actually seeing. I am sure that the supplier of your cooler would have charts with that data.
I would be very interested in your data of the oil cooler, especially if you have some before and after pressure readings on the out flow of the cooler, with and without a duct.
I ended up ducting my cooler to the side of the cowling, and it works, but I never did any actual measurements.
DanH
04-10-2011 11:05 PM
Whoops, misread my voltage-to-temperature conversion chart. Actual exit air temperature was 160F last night (not 110F) at 70F OAT and 209 OT.
This evening I rigged a manometer with one line to the oil cooler duct inlet and the other to the exit.
1" @1450 RPM warming up on the ground
7.5" climbing @100 knots IAS and 25/2500
12.25" @168 IAS (188 true) and 24/2400 (about 75%) 196F oil temp 66F OAT
3.34V 142F exit air
After a few minutes oil temp crept up to 208F @67 OAT
3.37V 147F exit air
So the exit air temp is more like expected, a heat transfer efficiency (temp rise/(oil temp - ambient temp) over 0.5, in this case between 0.57 and 0.65.
The 12.25" pressure differential across the cooler system suggests a mass air flow rate of about 44 lb/min per the Stewart Warner chart for a 10599 cooler. Hard to fault the duct design based on that chart, but does it really require
more? Tom, how about some pressure measurements for your dedicated duct system....how much mass are you flowing?
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DanH
04-24-2011 10:29 PM
Should be able to resume productive work shortly. Decided recent high oil temperatures didn't make
sense, so today I pulled and tested the vernatherm. Turned out to be dead as canned tuna.....zero
response in a hot water test:
RV8R999
04-24-2011 10:49 PM
interesting timing on your post Dan. Were you by chance having fluctuating oil temp issues? Last
couple of flights my OT steadily climbed to 210 in cruise flight having never been above 190 previously.
It cooled down with power/mixture management. Next flight OT stayed rock solid in the 180's where it
normally is. Was thinking maybe a vernatherm issue.
AlexPeterson
04-25-2011 08:30 AM
Quote:
Should be able to resume productive work shortly. Decided recent high oil temperatures didn't
make sense, so today I pulled and tested the vernatherm. Turned out to be dead as canned
tuna.....zero response in a hot water test:
Ahhh, homebuilding at its finest - I'm sure that setup passed Osha requirements,
much like when I did a similar thing with 400F peanut oil on an electric element
under the engine to test cht probes...
Look forward to seeing post-new-vernatherm data!
DanH
04-25-2011 08:44 AM
Ken, yes, oil temperature was inconsistent. Plus I had some high OAT conditions back in October and
no oil temp issues.
The first signs of high OT's were not long after switching to the smallest exit. Overall I would see
normal temps on the first flight then over 200 climbing out on the second. I assumed it was
heat-soaking on the ground and the system lacked capacity. What made me curious was swapping
back to a larger exit size with no change.....and then it started going over 200 on the first flight.
The little bugger was definitely working early on...good marking around the cone seat.
Round up an 1-1/4" socket. I set the camp stove so the water was gaining about 10 degrees per
minute and kept measuring the vernatherm length with a caliper. This one stayed at 72mm from
ambient to 210F.
Alex, gimme a break....the picture includes a fire extinguisher, and I wore my best boiling-waterresistant sneakers ;)
POSTSCRIPT: The vernatherm may not be bad after all. See below. Hmmmmm.....
Lars
04-25-2011 11:13 AM
Dan, that photo could spawn a whole host of off-topic responses. When I first glanced at it I assumed
you were working on the kitchen stove, and was formulating a snide remark about doing that sort of
thing while your wife was gone... until I looked closer. Myself, I mostly use my camp stove for making
beer these days, but that's a topic for yet another thread.
As for the vernatherm- nice to have that information in the back of my head, since it looks like I may
well fly my RV-7 before too long. In 40+ years of messing with cars, I've encountered plenty of
thermostats that were either DOA or suffered rapid infant mortality. Are vernatherms subject to similar
behavior? I'm not familiar with the technology (usually a wax pellet in automotive thermostats).
aerhed
04-25-2011 11:56 AM
Quote:
and I wore my best boiling-water-resistant sneakers
Try standing in jet fuel with your Converse All-Stars sometime.
Mike S
04-25-2011 12:04 PM
Quote:
Originally Posted by aerhed (Post 536491)
Try standing in jet fuel with your Converse All-Stars sometime.
As long as it is not on fire:eek:
DanH
04-26-2011 06:07 PM
Ahhh, the joy of education and recreation...
Take a close look at the vernatherm core in the boiling water. I've removed it from its machined
aluminum holder. Wrong, wrong, wrong....this is not how you check a vernatherm.
See post #12 here:
http://www.vansairforce.com/communit...ad.php?t=71409
flyvans.com
06-20-2011 11:50 AM
hi dan,
any news on your cowl exit progress?
what have you found to be the perfect size/shape?
any mods to the bottom of the firewall "lip"?
we did some tuft testing recently
http://www.flyvans.com/wordpress/ind...he-lower-cowl/
scroll down for a video of the tufts and a landing.
we do have some vibration in the cabin floor and lack a few knots top speed and it's all most likely due
to the fact that we had to enlarge the cowl opening to accomodate the special 4into4into1-muffler
exhaust system.
we also fitted louvers to the cowling precautiously to aid with temperatures and run "cool" during
breakin. this definitely proved to be working and the video would suggest, that the louvers also help to
maintain a smooth flow of air/are not the cause of the turbulence vibration.
we're now trying to come up with a plan to tackle that item without it becoming a never-ending
project...
regards,
bernie
DanH
06-20-2011 03:35 PM
Yes, Bernie, I've made progress, mostly measurements of temperature and pressure in a variety of
locations. Recall I don't have the slightest issue with CHT. I really want a little less cylinder cooling and
a bit more oil cooling.
Here's the rub...my system is not like yours, so the following may not apply well for you.
I'm running low velocity inlets and a throttled exit with a more-or-less sealed lower cowl. The lower
cowl volume runs almost 7" H20 higher than a measurement point just aft of the cowl exit, with the
medium exit panel, not the small one. With this cowl system I cannot dump the oil cooler into the
lower cowl volume per conventional methods. It must be ducted to the cowl exit.
The exit end of the oil cooler duct system is several inches inside the cowl exit (ie forward of the
firewall - see post #50). Pressure measurements tell me that location is roughly 3" H20 higher than the
aft-of-cowl-exit location. Thus the simple way to increase mass flow through the oil cooler is to extend
the oil cooler duct exit point rearward to the firewall plane and tap the lower pressure.
Another way would be to improve the oil cooler exit duct shape. Right now I think it chokes flow
because of the shape of the fiberglass transitions and because of the SCEET hose bent into a 90; the
interior wall is hardly smooth. I intend to build a new all-glass duct with a far better shape, with some
improvements at the point where it dumps at the exit. Initially I will not extend it rearward. If I can get
enough mass flow with duct shape improvement I will still be able to throttle cooler flow with cowl exit
area reduction. That will be desirable in winter. At the moment I vary exit size with swappable exit
panels. Later it may become a variable exit with cockpit control.
Right now temperatures are 95F to 105F on the ramp at midday in south Alabama, with 4000 ft OAT's
of 75 or more. As a temporary measure I've taken my mid-sized exit panel and cut a 4" half-moon
scallop out of the trailing edge. That moves the low pressure area at the cowl exit forward, meaning
lower pressure at the oil cooler duct end. Because of the aluminum exit bell it doesn't change cylinder
air exit area very much. A test climb yesterday at gross from 200 MSL to 6500, at 105 knots IAS and
full power, gave me a highest CHT of 355F and oil temp of 205F. Oil temp dropped of course as soon
as I leveled and allowed airspeed to increase. Quick fix; I may or may not get the new duct done
before OSH.
Like your tuft test video...I should do it at some point.
BTW, a probe on the oil cooler duct inlet (a 4" opening on the rear baffle wall) provided the most
surprising (to me anyway) temperature measurement; 15 to 18F higher than OAT. One obvious
conclusion; all our baffle mounted or ducted-from-the-baffle coolers start with an inlet air temp
disadvantage. A dedicated external oil cooler inlet is like a big drop in OAT.
L.Adamson
06-20-2011 03:57 PM
Quote:
BTW, a probe on the oil cooler duct inlet (a 4" opening on the rear baffle wall) provided the most
surprising (to me anyway) temperature measurement; 15 to 18F higher than OAT. One obvious
conclusion; all our baffle mounted or ducted-from-the-baffle coolers start with an inlet air temp
disadvantage. A dedicated external oil cooler inlet is like a big drop in OAT.
So far.............with summer oil temps in the 180-195 degree range, I wouldn't want a farther drop in
inlet temps. But then my 6A just cools well, with it's cooler mounted on the #4 baffle. I even have a
Van's slide damper. Others, sometimes, don't do as well........I see.
L.Adamson --- RV6A
DanH
06-20-2011 09:12 PM
Quote:
Originally Posted by L.Adamson (Post 551954)
So far.............with summer oil temps in the 180-195 degree range, I wouldn't want a farther
drop in inlet temps. But then my 6A just cools well, with it's cooler mounted on the #4 baffle. I
even have a Van's slide damper. Others, sometimes, don't do as well........I see.
Cooling in an absolute sense is easy.....just increase mass flow. Temps will drop and the airplane will
get slower.
To get 180-195F I install the "large" exit panel, which is about 77% of a stock exit.....but I don't want
to go that slow.
flyvans.com
06-21-2011 06:20 AM
hi dan,
thanks for the info...
i'm thinking about blocking some of the exit area initially without actually changing the outer shape of
the cowling... (major mod)
just to see what it changes.
in theory this should accelerate the outflow air and lessen the turbulence below the belly skin.
the oil cooler by the way is the default one from van's and we're even partly blocking it off to get
approx 190F in 80°F oat weather
regards, bernie
dessertire
06-21-2011 11:36 AM
Dan, this is a bit late, but just now seeing it... what a beautiful creation!
DanH
06-21-2011 03:41 PM
Quote:
Originally Posted by flyvans.com (Post 552139)
i'm thinking about blocking some of the exit area initially without actually changing the outer
shape of the cowling... (major mod) just to see what it changes. In theory this should accelerate
the outflow air and lessen the turbulence below the belly skin.
I have some reservations Bernie. Simply blocking exit area may or may not accelerate exit air at the
enlarged ramp (it may accelerate air from the louvers or may push more air out around the propshaft
opening), and will probably increase turbulence.
Want to do an easy experiment tailor made for your video camera? A lot of us think the -7's 90 degree
corner at the lower firewall / belly skin intersection is a problem. Add a simple sheet metal radius, large
as practical:
Quote:
the oil cooler by the way is the default one from van's and we're even partly blocking it off to get
approx 190F in 80°F oat weather
With both louvers and the enlarged exit ramp you have a HUGE total exit area. Perfect example of "just
increase mass flow". No surprise about blocking the cooler.
flyvans.com
06-21-2011 05:39 PM
i did not remove the cam mount yet... ;-)
the curved sheet metal is definitely an interesting idea, i've already thought about that as well, kind of
rv-8ish... the problem will be fitting it as the area is pretty tight if i remember correctly / close to the
exhaust. and it should be only semi permanent initially.
we did not actually intend to increase mass flow a gogo, it's more just a sum of fitting the louvers as
per a number of recommendations and only then finding out about / fitting the muffler system.
well, for the breakin phase this certainly didn't hurt the engine and the airplane is still plenty fast.
now it's just a matter of unlocking the potential.
cowl is standard van's and i'd say the front inlet seals are tighter than average. (including blocking off
the sides of the ramps in the top cowl etc...)
only problem is i'm having too much fun flying, and not enough time to tinker much at the moment.
cu bernie
DanH
07-05-2011 08:58 AM
With the store closed for the 4th I had some time to build a new cooler exit duct. The original was two
fiberglass transitions and a 4" SCEET hose, and I suspect rather restrictive:
The transitions were used as a tutorial example here:
The new duct is made the same way. So, start shaping foam:
Prep it and do the layups:
Then remove the foam...rough duct ready for some sanding and general cleanup:
Hopefully back in the air by next weekend for test. I may need something similar for the entry duct
from the plenum. Even SCEET (lined hose) is pretty bumpy on the inside ;)
David-aviator
07-05-2011 10:12 AM
Quote:
Cooling in an absolute sense is easy.....just increase mass flow. Temps will drop and the airplane
will get slower.
To get 180-195F I install the "large" exit panel, which is about 77% of a stock exit.....but I don't
want to go that slow.
I agree with this statement completely, based on personal experience - no science, no engineering data
- just experience.
The Van's cowl for the RV-7 has a exit to inlet ratio of about 107.69%.
My cowl, with a 5x16 exhaust exit area and 2 Bonanza side vents has a ratio of 219.51%
I also have a remote SW oil cooler with 4" scat duct from #4 aft baffle. It does not have the nice exit
flow device as per Dan, but simply dumps its air into the lower engine area just above the exit. I've
flown twice this past week with the OAT in the low 90's and oil temp ran at 168F! Yes, I have checked
the sensor in hot water and I can get warmer oil temperature by closing the air flow butter fly valve.
The point here being, good cooling is the result of mass air flow through the cowl.
OK, does the 219% exit ratio introduce a lot of drag? Very little if any. I've done several WOT runs at
75% at altitude and the machine moves along right at 200 mph, about the same as Vans RV-7A
numbers with a 180 HP engine.
Could be though, the extra drag is offset by the extra HP from BPE. The engine did crank out 187 HP
on the dyno. :)
DanH
07-05-2011 11:28 AM
Quote:
I also have a remote SW oil cooler with 4" scat duct from #4 aft baffle. It does not have the nice
exit flow device as per Dan, but simply dumps its air into the lower engine area just above the
exit. I've flown twice this past week with the OAT in the low 90's and oil temp ran at 168F!
I believe it. Understand why I need the exit duct and you don't...my lower cowl volume is pressurized,
while yours is near static due to the huge exit area. I must duct to low pressure at the cowl exit.
Quote:
OK, does the 219% exit ratio introduce a lot of drag? Very little if any.
Don't kid yourself.
RV8RIVETER
07-05-2011 03:26 PM
Dan beat me to it. ;)
To tweak it a little. Good cooling is efficient mass air flow thru the cylinder fins. The major driver of
that is pressure differential and making the air go where you want it to.
pierre smith
07-05-2011 03:57 PM
Say, Dan....
I'd like to build an exit duct for my -10's oil cooler as well. In case you don't know, they're mounted on
a firewall box that's angled about 30 deg downward, with the air coming in the top.
How do I determine the exit area? The cooler is fed by a 4" duct off the back of # 6 cylinder.
Thanks,
DanH
07-05-2011 07:52 PM
Quote:
Originally Posted by pierre smith (Post 556133)
I'd like to build an exit duct for my -10's oil cooler as well. In case you don't know, they're
mounted on a firewall box that's angled about 30 deg downward, with the air coming in the top.
I'm not so sure you can accurately calculate the exit area for a particular mass flow. Pressure
differential drives flow, friction reduces flow. There are equations for a theoretical perfect duct.....but
we build imperfect things. It's hard (for me anyway) to define the friction due to the duct wall, bends,
etc. Maybe one of the bright guys can chime in here?
The one I built this weekend is more-or-less a constant section area equal to the cooler face area,
roughly 25 sq in. The previous setup took the cooler outflow and squeezed it back into a 4" tube (12.5
sq in), ran it around a right angle bend with a bumpy minor radius, then into another fiberglass
transition whose outlet was partially blocked by the exhaust pipe. Surely the new one will flow more.
Pierre, the first thing to do is measure pressures. Run one leg of a manometer to the upper plenum.
Run the other to a few different locations; the cooler outlet face, a spot near the cowl exit (where your
duct might end), and perhaps just outside the cowl exit. Make a few flights and record the differential
pressures at your usual climb speed and at cruise. A cooler exit duct would be a waste of time if there
is no significant difference between the three locations.
David-aviator
07-05-2011 10:39 PM
Quote:
Originally Posted by RV8RIVETER (Post 556124)
Dan beat me to it. ;)
To tweak it a little. Good cooling is efficient mass air flow thru the cylinder fins. The major driver
of that is pressure differential and making the air go where you want it to.
If good cooling is efficient mass air flow, how is that efficiency defined?
There's plenty of air available in front of an air plane to affect cooling, so the amount used, as it is free,
can't be the answer. It has to be the amount of drag created as the air enters and moves through the
engine compartment. The basic premise here is that increasing air flow through the RV engine
compartment results in more drag. That may not be true at the speeds we fly at and the compromised
shape of the cowl itself to accommodate the engine.
Seems like if inlet air is restricted because of internal pressure caused by a small exit area, drag is
created in front of the engine compartment as oncoming air creates a wall of pressure at the inlets and
spills over the top, bottom and sides of the exterior of the cowl. It has no where to go so that's what
happens. The front of the cowl is not continuously smooth with its inlet holes, there is a radical cowl
shape change from near vertical to near horizontal, and there is a spinning prop stirring things up to
boot. This is not a drag free environment and there may be more drag with less air entering the engine
compartment.
If pressure within the cowl is low due to a large exit area, air enters the cowl, removes heat, and
passes on through. It is assumed this creates more drag than oncoming air deflected around the cowl
due to a restricted exit area and I question it. I have a hard time believing it makes much difference at
the speeds we fly.
The increased drag (if any) created by a 219% exit area is not significant. The airplane goes as fast as
the published numbers at Vans and the up side is very good cooling. It would be most disappointing to
close the cowl to original specs, not fly any faster, and maybe have cooling issues. Seems like a not
brainer to leave it alone as is.
pierre smith
I'm lost!
07-06-2011 06:50 AM
Quote:
.....Pierre, the first thing to do is measure pressures. Run one leg of a manometer to the upper
plenum. Run the other to a few different locations; the cooler outlet face, a spot near the cowl
exit (where your duct might end), and perhaps just outside the cowl exit. Make a few flights and
record the differential pressures at your usual climb speed and at cruise. A cooler exit duct would
be a waste of time if there is no significant difference between the three locations.
How in the world is this done? If a manometer is a piece of tubing with fluid in it, it'll all run out if one
end is at the plenum and the other down at the oil cooler exit??:confused: How do I record pressures
in flight if the manometer is under the cowl? I used to think that I'm not mechanically challenged but
this is confusing.
Thanks,
dedgemon
07-06-2011 09:28 AM
Airspeed indicator
An ASI is just a differential pressure gauge. You can measure the pressures in knots and then convert
that back to an engineering unit if needed. And not spill water on the interior!!
Quote:
How in the world is this done? If a manometer is a piece of tubing with fluid in it, it'll all run out
if one end is at the plenum and the other down at the oil cooler exit??:confused: How do I record
pressures in flight if the manometer is under the cowl? I used to think that I'm not mechanically
challenged but this is confusing.
Thanks,
RV8RIVETER
07-06-2011 10:47 AM
Quote:
Originally Posted by David-aviator (Post 556246)
The increased drag (if any) created by a 219% exit area is not significant. The airplane goes as
fast as the published numbers at Vans and the up side is very good cooling. It would be most
disappointing to close the cowl to original specs, not fly any faster, and maybe have cooling
issues. Seems like a not brainer to leave it alone as is.
I do not mean to say you should alter your airplane. Clearly you are happy with the way it performs,
which is what we all strive for.
I just think you under estimate the effect of drag on this configuration. Dan's experiments, Bonanza's
with cowl flaps open/closed, ect show there is clearly a measurable difference.
By efficient I merely mean get the highest cooling amount for the minimal amount of air. Air has mass
and the more air you take in the more mass you are decelerating, which is drag. If we could take the
air in and then send it out at the same speed and direction then we would not have drag. But alas, that
is not the case. An efficient cooling system is one that is taken as a whole. It is not one thing, exit
area, or inlet area, ect.
scard
07-06-2011 02:32 PM
Am I the only one silly enough to have a low scale digital manometer :).
Lars
07-06-2011 02:46 PM
Quote:
How in the world is this done? If a manometer is a piece of tubing with fluid in it, it'll all run out
if one end is at the plenum and the other down at the oil cooler exit??:confused: How do I record
pressures in flight if the manometer is under the cowl? I used to think that I'm not mechanically
challenged but this is confusing.
Thanks,
Pierre, imagine a piece of clear tubing oriented as in the drawing below. Fluid (water usually, I like
adding food coloring to make it easier to see) is added such that the upward facing "U" portion of the
tubing is half full up each leg. One end is routed to a point in the plenum, the other to one of the other
locations Dan mentions (for example). Obviously, in order to see this in flight, the tubing has to
penetrate the firewall somewhere. Also, the tubing has to be fastened to something (piece of wood,
aluminum sheet, hard plastic, whatever) so it doesn't just flop around, and the U has to be oriented
vertically as in the drawing, and you have to be able to see it while you are flying.
Without going into the nuts and bolts of the installation, now imagine flying with this. If there is a
pressure differential at the points of interest, then one leg of the fluid is exposed to a higher pressure
than the other, and so the fluid columns in each leg will be at different heights. The difference in height
is the pressure difference. Assuming you use water, the difference would typically be denoted in inches
(or millimeters if you prefer) of water.
Note that it's good to have an idea of what pressure differential you might expect to see prior to setting
this up. If the differential is greater than the water column height, you can wind up sucking the water
out of the manometer.
Lars
07-06-2011 02:47 PM
Quote:
Originally Posted by scard (Post 556403)
No............ (periods added for minimum character limit) :)
pierre smith
07-06-2011 03:08 PM
Thanks..
Quote:
Originally Posted by Lars (Post 556407)
Pierre, imagine a piece of clear tubing oriented as in the drawing below. Fluid (water usually, I
like adding food coloring to make it easier to see) is added such that the upward facing "U"
portion of the tubing is half full up each leg. One end is routed to a point in the plenum, the
other to one of the other locations Dan mentions (for example). Obviously, in order to see this in
flight, the tubing has to penetrate the firewall somewhere. Also, the tubing has to be fastened to
something (piece of wood, aluminum sheet, hard plastic, whatever) so it doesn't just flop
around, and the U has to be oriented vertically as in the drawing, and you have to be able to see
it while you are flying.
Without going into the nuts and bolts of the installation, now imagine flying with this. If there is
a pressure differential at the points of interest, then one leg of the fluid is exposed to a higher
pressure than the other, and so the fluid columns in each leg will be at different heights. The
difference in height is the pressure difference. Assuming you use water, the difference would
typically be denoted in inches (or millimeters if you prefer) of water.
Note that it's good to have an idea of what pressure differential you might expect to see prior to
setting this up. If the differential is greater than the water column height, you can wind up
sucking the water out of the manometer.
I've been mulling it over and fits what I thought..thanks.
I'll have to figure out how to penetrate the firewall....perhaps through the hot air valve with the heater
hose disconnected?
Best,
rv7boy
07-06-2011 03:17 PM
Quote:
You must be. I had access to one back in my college days (1971) to measure pressure drop across oil
and fuel filter samples, but it belonged to the university. It would surely be easier than messing with a
fluid manometer in an airplane.
gasman
07-06-2011 03:42 PM
Quote:
No........... your not.
Mine measures as low as .05 in-Wg.......... http://instrumentation2000.com/ueiem...20wcrange.aspx
scard
07-06-2011 04:20 PM
Quote:
Originally Posted by gasman (Post 556422)
No........... your not.
Mine measures as low as .05 in-Wg.......... http://instrumentation2000.com
/ueiem...20wcrange.aspx
It is nice to know I'm not the only one missing out on flying around with a tube filled with water,
tacked to a piece of plywood :). I've had many hours of engineering 'fun' with mine. Direct differential
measurement capability is useful. http://www.omega.com/pptst/HHP-90.html
Maybe this thread should be renamed "I'll show you mine if you show me yours."
rv6ejguy
07-06-2011 06:50 PM
We have used analog manometers from the HVAC industry for years to do this stuff. Cheap, steady,
accurate. You'll learn a lot!
DanH
07-06-2011 07:08 PM
Sorry, been out of town all day.
Looked at digital manometers, but I'm really cheap....had lots of vinyl tube and a yardstick.
You can't spill water in the cabin....the ends of the tubes are in the engine compartment.
The yardstick sits upright in the right passenger footwell of the RV8, taped to the canopy rail. No
problem, so surely there is enough room in an RV10.
I made miniature "firewall fittings" by chucking some 3/16" all-thread rod in the lathe, drilling the
center, and removing the threads from each end of a 2" length. Use an AN3 check nut on each side of
the firewall:
The yellow tubing is tygon, sold as "small engine fuel line" at the NAPA store. Tygon handles engine
compartment heat a little better than vinyl.
As I recall, Tom Martin ran his manometer tubes through the heater box.
FWIW, I also installed six "blank" wires in the wiring bundle through the firewall back when I was
rigging the engine. They can be used for any experimental purpose. Right now they are hooked to
temperature probes.
As Lars said, you should be aware of possible pressures, but if you screw up all you'll lose is water. The
maximum possible pressure is probably around 26" H2O, but that would require 100% of dynamic
pressure at 200 knots, at sea level. 100% dynamic pressure at RV cruise speed is more like 15" at
6000 ft, and you gotta hit 18" to lose water from a yardstick manometer. And you won't get 100%
recovery with a cooling plenum no matter what you do.
Fly tests in the AM before it gets bumpy. Variable G makes the water column bob up and down.
I would love to hear about your differential pressures as you move one leg closer and closer to the cowl
exit.
Ted Johns
07-07-2011 12:30 AM
Quote:
Direct differential measurement capability is useful.
Which you can do (of course) with the colored water and tube manometer. Just put each tube end
where you want the differential measurement. :)
DanH
07-07-2011 08:39 AM
Quote:
Originally Posted by David-aviator (Post 556246)
If good cooling is efficient mass air flow, how is that efficiency defined?
A serious question, so I dug around on my shelf for a reputable one-page reference. This from
Aerodynamics, Aeronautics, and Flight Mechanics, Barnes McCormick...the fundamentals:
Eq 4.45 spells out the most basic concept...mass x momentum loss = cooling drag.
Note the concept in the first paragraph about energy removed and energy added.
For any given power setting the quantity of heat you must carry away is fixed. The best way to
decrease required mass flow is to increase the quantity of heat transfered to the mass, ie heat the air
as much as possible during its pass through the engine compartment. Doing so requires less mass to
carry away the same quantity of heat. Measuring the air temperature increase following a pass through
the system (or an individual cylinder baffle, or an oil cooler) is one very real yardstick for cooling
efficiency. Heat exchanger efficiency = cooling air temp rise / (CHT-OAT)
Quote:
Seems like if inlet air is restricted because of internal pressure caused by a small exit area, drag
is created in front of the engine compartment as oncoming air creates a wall of pressure at the
inlets and spills over the top, bottom and sides of the exterior of the cowl.
Cowl and inlet shape can be done badly of course, but do realize that external diffusion is in itself
nearly frictionless.
David-aviator
07-07-2011 09:23 AM
Thanks for that bit of information, Dan. Very interesting.
I have a Dwyer magnehelic instrument and should be able to measure the differential from the inlet to
the exit. Next would be a couple temperature measurements to see how much heat is being extracted.
Then a moveable cowl flap could be installed to see how much things would change, including air
speed.
One thing leads to another. :)
Thanks again for the enlightened response to the original question, learn something new every day.
Bill Wightman
07-07-2011 09:56 AM
Duct Flow Analysis - How To
Quote:
I'd like to build an exit duct for my -10's oil cooler as well. In case you don't know, they're
mounted on a firewall box that's angled about 30 deg downward, with the air coming in the top.
Thanks,
Pierre and Dan, I'll give you the short course in how to size duct area to work for a given mass flow
and pressure drop. Its not hard to do, if you know the pressures and temps before and after the cooler
interface.
Cooling drag is analyzed as a momentum loss across the system. The "system" is composed of an
inlet; a heat exchanger; and an exit:
Flow conditions are denoted in the schematic. Ahead of the inlet plenum, we have free stream pressure
and velocity: P0 and V0. At the heat exchanger interface, there will be (most likely) a temperature rise
and pressure increase: Pb and Tb. Heat is added by the exchanger: Q in. Flow across the cooler
interface will lose pressure due to friction loss through the cooling fins. At the back side of the cooler,
we thus have an incremental loss of pressure and an increase in temp in the flow: Pb-dP and Tb+dT.
The "dP" and "dT" represent delta-P and delta-T across the cooler. At the duct exit, we have velocity Ve
and pressure Pe which will vary with duct design and exit area. Down stream of the exit, we once again
reach free stream conditions: Vinf and P0 (free stream velocity and static pressure).
The hard part in sizing the cooling duct system is knowing the flow conditions at the cooler face Pb and
Tb, and knowing how much heat is added to the flow and how much pressure is lost across the cooler.
But these can be measured with a little work.
The mass flow through the system can be found when we know the density of the flow, its pressure,
and the area across the cooler. More mass flow equals more cooling. The total drag of the system can
be found using compressible flow analysis (momentum loss). Inlet and outlet sizes can be optimized for
the mass flow needed.
Years ago, I had a spread sheet worked up that did the analysis, and sized the cowl system for Kestrel
Aircraft's KL-1C airplane. It worked great. I could do the spread sheet again, seeing there's probably
some interest in knowing how to size inlet and exit areas for optimum performance.
Bill Wightman
07-07-2011 09:58 AM
Dan, I see you have a source on how to do it. We must have posted at the same time!
Page 3 of 5 < 1 2 3 4 5 >
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Kinnerhatz
07-07-2011 11:09 AM
digital manometers
To you guys who are using digital manometers: How do you damp out the readings? I have one, but it is useless
because the displayed value does not settle down. I have tried using a fish tank air stone on the end of the line and
also adding some water to the tubing to no avail. The model I have is simple and has no filtering options.
DanH
07-07-2011 11:29 AM
Quote:
Originally Posted by Bill Wightman (Post 556602)
Dan, I see you have a source on how to do it. We must have posted at the same time!
Looks like it!
The McCormick text can be an example of a perfect duct, as I spoke of in post #102. It doesn't address frictional
issues due to duct shape or construction. As you say, with enough data you can back into the best duct dimensions.
I'm suggesting (to Pierre) that the first thing to do is gather enough pressure data to determine if a cooler outlet duct
would even be worth doing in the standard RV-10 cowl.
My own current duct experiment is a reversion to the cut-and-try tradition. It should be pretty easy to tell if duct
friction and area was cutting into cooler mass flow.
scard
07-07-2011 11:52 AM
Quote:
Originally Posted by Kinnerhatz (Post 556623)
To you guys who are using digital manometers: How do you damp out the readings? I have one, but it is
useless because the displayed value does not settle down. I have tried using a fish tank air stone on the end of
the line and also adding some water to the tubing to no avail. The model I have is simple and has no filtering
options.
Sorry, mine has a "smooth" function.
rv6ejguy
07-07-2011 12:27 PM
http://www.dwyer-inst.com/Products/P...eName=Ordering
These are the types we have used for years on race cars and aircraft for duct design experiments.
Kinnerhatz
07-07-2011 01:45 PM
The unit I'm using is the UEI EM201 Digital Manometer, but again, I need to figure out how to damp its readings.
RV8RIVETER
07-07-2011 04:09 PM
Quote:
Originally Posted by Kinnerhatz (Post 556671)
The unit I'm using is the UEI EM201 Digital Manometer, but again, I need to figure out how to damp its
readings.
According to the manual description you have a min/max function that will hold until you reset. You may want to try
that, set up your test condition and record max values only or record both and average for a particular test.
Kinnerhatz
07-07-2011 05:09 PM
Good idea; will try it. Thanks!
DanH
07-10-2011 07:17 PM
Got in a flight today to check the new cooler exit duct. Low layers and an overcast at 5000 so I was a bit limited; I'll
get more Tuesday when I fly to an auction in Chattanooga.
Looks like an incremental improvement, as expected. I climbed out of Wetumpka at 110 knots to 5000 then dived
into Alex City for cheap fuel (note to self: $4.75 is cheap...keep repeating, $4.75 is cheap..). I just wanted to get
everything hot. The real test was a departure at 185F oil temp on the runway before going forward with the throttle.
A 110 knot climb from 600 had the oil temp stabilized at 205F at 5000 with OAT at 79F. It came right back to 185
when level.
OSH in two weeks....I dropped down to 1500 and dragged the 20 miles back to Wetumpka at 80 knots, just like the
Ripon approach. Prop forward and 1950-2000 RPM did the trick; oil temp stabilized at 195F about 5 miles out. Yep,
we're ready!
DanH
10-07-2011 12:32 PM
Next experiment.
Cyl #3 has always been about 25F warmer than the coldest cylinder. I figure it's mostly a case of lower local pressure
in the right rear corner of the plenum; there's a 4" hole back there to feed the oil cooler. Take a look at the pressure
maps in CR3405.
In addition, the oil cooler air supply temperature has risen 15-20F (compared to OAT) by the time it gets to the oil
cooler face. No big surprise; the air passes lots of hot cylinder fins in the upper plenum on its trip to the cooler inlet
duct.
We all know what a difference 15-20 degrees reduction in OAT can make, so I started thinking about how to get some
unheated air back there for cyl #3 and the oil cooler supply. I'm going to try separating the air into two parallel
paths. One is conventional (the usual movement inside the plenum enclosure). The other is via a new duct attached
to the underside of the plenum roof. The duct does not extend all the way to the rear plenum wall, but rather just to
the rear edge of the #3 fins.
The goal is to deliver cool air, so the duct is insulated by laminating a sheet of ordinary 1/16" fiberfrax felt into the
surface. I did not want the fiberfrax to soak up resin, as that would both make it heavy and defeat some of its
insulation properties. So, to stick it in place I laid a thin coat of micro on the duct surface, then pressed the felt into
it. It then got a cover sheet of very light crowfoot glass.
Working on my annual now and hope to be back in the air in another week or so. The goal is to maintain low oil
temperature while running the very smallest exit at 100F OAT. I may not have any more really hot test days until
next spring, but you never can tell about fall weather in south Alabama.
Stewie
10-19-2011 04:21 PM
Hi guysMy first VAF post, other than the buying/selling on the classifieds. I'm a newbie so mostly I just sit back and absorb
information.
Accidentally wandered onto this thread (too easy to do on VAF... link to link was carbon fiber oil pan - Tom Aberle vernatherms - here...). Anyway, I think any of you interested in this topic would find Kays and London's Compact
Heat Exchangers an excellent resource. Expensive, but highly recommended.
Eric
DanH
11-26-2011 02:38 PM
The above experiment to direct cold air to the area of the oil cooler duct entrance reduced air temperature at the oil
cooler face by about 10 degrees F, with the expected effect on oil temperature.
There was no attempt to seal out hot plenum air. No point; the single duct only had a cross section area of about 7 sg
in, not large enough to supply all the required air. So next experiment; let's take all the oil cooler air from just inside
the cowl inlets, and send it to the cooler with a sealed system.
Recently in another thread I wrote about converting to two-part urethane for many of my mold and forming tasks.
Here's a pretty good example; a few minutes with some paper and tape for dams, mix, pour, and a half hour later
start carving and sanding. This form would have been very difficult with clay or block foam.
Should be flying again in a week or so.
jrs14855
11-26-2011 03:06 PM
Dan
Dan-I am not an RV builder/owner and probably never will be. With the loss of Paul Lipps, you are at the top of the
list of people generating ideas that are of interest to me. There is a lot of stuff here that is interesting and sometimes
entertaining but you are an idea guy and that is my primary focus. Do you remember the guy from nowhere,
Oklahoma a few years back that posted a lot of stuff on cowling/cooling. He had a controllable, external inlet for the
oil cooler. (RV6)
pierre smith
11-26-2011 03:53 PM
That would be Alan Judy.
Alan is another great innovator....a Naca type air inlet for his oil cooler and replacable inlet rings for summer or
winter cooling and so on.
Best,
jrs14855
11-26-2011 05:03 PM
Cooler
Thanks Pierre, I couldn't remember the name. He is on the OK panhandle, not the end of the world but if you stand
on a ladder you can see the end of the world from there.
RV8R999
11-26-2011 10:37 PM
Dan, how much space between the duct and top of cyl fins? Any thought to insulating the duct? ooking forward to
your results.
DanH
11-26-2011 11:40 PM
Quote:
Dan, how much space between the duct and top of cyl fins? Any thought to insulating the duct?
About 1-1/2" ~ 2" at the intakes and more towards the rear. I'll insulate like the previous duct.
Quote:
Do you remember the guy from nowhere, Oklahoma a few years back that posted a lot of stuff on
cowling/cooling. He had a controllable, external inlet for the oil cooler.
Yes, Alan Judy, as Pierre said. Beautiful work.
Air flowing through the cooler when the vernatherm is open is just drag, so flow control is smart. Others are doing it
with a butterfly or a shutter.
DanH
12-17-2011 12:31 PM
Ok, done, off to the airport. The black section with the flange gets riveted into the rear baffle wall. A slip fit (at the
arrows) allows plenum lid removal. The duct is insulated with 1/16" fiberfrax and Vans stick-on aluminum reflector
material.
Now if I can just arrange for some hot weather ;)
RV8R999
12-17-2011 02:56 PM
An artisan..
Very interested in your results. what area ratio did you use from duct inlet to entrance to the rear baffle slip joint?
Were the two duct inlets of equal area or did you try to balance based on CHT deltas in flight?
are you planning a full pressure survey of the ducting as well?
DanH
12-17-2011 08:19 PM
Quote:
what area ratio did you use from duct inlet to entrance to the rear baffle slip joint? Were the two duct inlets of
equal area or did you try to balance based on CHT deltas in flight? are you planning a full pressure survey of
the ducting as well?
The design approach is entirely TLAR. I did try to make the area total equal the 4" SCEET down to the cooler, a little
over 12 sq in. I recorded some pressures previously, so I'll no doubt make a comparison.
rvmills
12-17-2011 11:08 PM
Duct work looks great Dan! Couple pressure/temp related questions:
From the mention of 12 sq" of mini-duct inlet and outlet (to the oil cooler), I take it you're just trying to keep the
pressure the same throughout the duct, and you're just trying to get lower-temp cooling inlet air directly to the oil
cooler, versus air that has passed over the cylinders on its way to the oil cooler...correct?
IIRC, your CHTs have been great, but your oil T has been hotter than desired (correct?) so do you think you will be
trading a bit of higher CHT for cooler oil T? (Makes sense, just wondering if that is the logic.)
I know testing will reveal more, but do you have any concerns that the duct is eating up too much upper plenum
volume? I mention this because I am about to remake my baffles and install a new plenum, and one of my mentors
gave me a bit of a friendly lecture on how well the standard baffles (no plenum) cool if installed correctly. His
assertion was that installed plenums reduce the upper "plenum" volume normally provided by the cowl by too much. I
discussed Paeser a bit, and will stick with my plan of making a well-sealed plenum, but I wanted to ask if you feel
there is a point where your upper plenum volume will get too small.
If CHTs are impacted too negatively in the experiment, have you also considered a NACA duct on the cowl to feed the
cooler directly? Is that a later experiment, or is that too draggy to be beneficial?
I've been fortunate to have good cylinder cooling and low oil Ts, but I have a cavernous, draggy exit (2.25:1) and
hope to reduce that as you have. As I start down that road, this oil cooler work of yours is important to remember,
along with your exit work. Thanks for sharing it!
Cheers,
Bob
DanH
12-18-2011 08:27 AM
Quote:
Originally Posted by rvmills (Post 607011)
I take it you're just trying to keep the pressure the same throughout the duct,..
Yes. And on the practical side, larger takes up valuable space and smaller won't flow enough air.
Quote:
.. and you're just trying to get lower-temp cooling inlet air directly to the oil cooler, versus air that has passed
over the cylinders on its way to the oil cooler...correct?
Correct. Taking oil cooler air from the baffle wall behind #3 resulted in a temperature at the oil cooler face much
higher than OAT.
Quote:
IIRC, your CHTs have been great, but your oil T has been hotter than desired (correct?)...
Yes. I think of them as not properly balanced...the system needs less cylinder cooling and more oil cooling.
Quote:
... so do you think you will be trading a bit of higher CHT for cooler oil T?
I don't expect this experiment to change CHT at all (we'll see!). Lower oil temperature will allow another exit area
reduction later, which will increase CHT.
Quote:
...do you have any concerns that the duct is eating up too much upper plenum volume?......... His assertion
was that installed plenums reduce the upper "plenum" volume normally provided by the cowl by too much.
This plenum was built as large as possible. My humble student's understanding is aligned with your friend; larger is
better. However, I don't know of any published test data and remain open minded.
Realize I've not changed total cooling air quantity. And the exchange of dynamic for static is external in this scheme;
what I do up inside the entrance shouldn't matter very much. All I've done is segregate the oil cooler air so it doesn't
pick up so much heat before arriving at the cooler.
Quote:
... have you also considered a NACA duct on the cowl to feed the cooler directly? Is that a later experiment, or
is that too draggy to be beneficial?
If this doesn't do it the next step is probably a much larger oil cooler. I don't know if an external oil cooler intake
would add much drag, but it has to be more than not having one ;)
rvmills
12-18-2011 01:02 PM
Regrouped the replies a bit, some good notes there...thanks!
Quote:
And on the practical side, larger takes up valuable space and smaller won't flow enough air.
I think of them as not properly balanced...the system needs less cylinder cooling and more oil cooling.
Realize I've not changed total cooling air quantity. And the exchange of dynamic for static is external in this
scheme; what I do up inside the entrance shouldn't matter very much. All I've done is segregate the oil cooler
air so it doesn't pick up so much heat before arriving at the cooler.
I don't expect this experiment to change CHT at all (we'll see!). Lower oil temperature will allow another exit
area reduction later, which will increase CHT.
All makes sense, and the last note provided a bit of an ah-ha moment! Good thinking! So plenum + duct volume and
flow should remain equal to previous plenum flow and volume (or close, given the space occupied by the duct
material), and the air previously lost from the plenum back at the opening to the oil cooler, will now be lost at the
inlet. It'll be interesting to see if 1 & 3 creep up slightly, and 2 & 4 decrease slightly. Cool experiment (bad pun! ;))
Quote:
Taking oil cooler air from the baffle wall behind #3 resulted in a temperature at the oil cooler face much higher
than OAT.
If this doesn't do it the next step is probably a much larger oil cooler. I don't know if an external oil cooler
intake would add much drag, but it has to be more than not having one ;)
I figured you had measured temps into and out of the oil cooler (believe I've read it here), and that will be a telling
measurement in this experiment. When I purchased my plane, it took fresh air for the cockpit vents from the back of
the baffle (next to the oil cooler), into a mix valve, then into the cockpit vents (no naca scoops on the plane at all). I
didn't like that as the only source of fresh air, so I changed it, and blocked that opening in the back of the baffle. The
interesting thing is that the air was quite cool, even coming from the upper plenum. Pretty large plenum on the 540
in the six cowl though, so the smaller plenum required for an 8 cowl may be impacting (and sounds like your
measurements bear that out). I didn't take measurements back then, so its just offered as a data point of interest.
On the cooler, I have a baffle-mounted "double-wide", and rarely see over 185, and sometimes have to work to get it
up to that. I cover 1/2 in the winter, and it just cools and cools. Wreaks havoc on my aft baffle (another reason they
are getting replaced this winter...with more structure!), but I don't think I have room for a remote cooler of that
size...especially as I try to reduce firewall clutter for smoother exit flow. With that big cooler, the only times I've seen
over 200 is a multiple hop scenario on hot days (once in Las Vegas on a form hop, following a X-C there, and then on
the Mythbusters shoot day, on hops 6-9 wih OAT 100+). The big cooler really works well (another data point).
Quote:
This plenum was built as large as possible. My humble student's understanding is aligned with your friend;
larger is better. However, I don't know of any published test data and remain open minded.
Mine as well, though reading Paeser and others, and listening to many racers, the recommendation is "plenum...just
do it!". I know Mark (F1 Boss) is trying to cypher up a plenum for his 550 Rocket, and has had heat issues, so that
argument still seems to hold water. I've seen a lot of standard baffles leak (though some do very well), so I'm
guessing it's all about plenum sealing. As I jump into baffle/plenum work this winter, I'll try to go as large as I
can...thanks for the nudge in that direction!
Nice work, as always sir!
Cheers,
Bob
gereed75
12-18-2011 05:19 PM
Bob, My hangar mate just made a very nice plenum top by molding it up to the top of his Van's cowl (RV-7). This will
yield a shape that fits right under the cowl line and will maximize the plenum volume.
You could lay it up inside the cowl, but because of the bowl shape, you will get epoxy pooling in the center low spot
and this would be a pain to deal with.
Obviously the trick is protecting your cowl from epoxy. We used packing tape and sandwiched the glass and epoxy
betweem sheets of release plastic (maybe Visqueen will work).
This plenum top was then mated to Van's stock baffles. Came out nice.
He is now working on mating the stock Van's inlets to this plenum. We are using a "snorkel" kind of idea to get
complete sealing between the inlets and and the plenum.
The "snorkels" were laid up "female" inside the stock openings. As the cowls are taken off, the snorkels will remain
attached to the plenum via neoprene boots.
I think it will be pretty slick.
Glad to hear you got my outlet fairings and hope you get some use out of them. Focus boy focus, you have a full
plate going there!!
rvmills
12-18-2011 06:58 PM
Gary,
Right you are. Really need to focus on the baffles. The glass work will come one project at a time.
Hopefully I can get a layup or layer done on the glass projects each day (as they come up), then get baffled the rest
of each day.
Really glad I have a heater...it's gonna be a bit of a long winter in the hangar (lots to learn!!)
Thanks again for the loaner parts, and I'd love to see pics of the plenum and snorkels if or when ya got 'em!
Cheers,
Bob
DanH
12-18-2011 09:21 PM
Out flying around tonight. Works fine. No CHT change, spread is about 20 degrees across all four. Oil temperature
stayed on the vernatherm set point, hardly a surprise at 55F OAT. Not much else to say until the return of hot
weather. Until then I'll devote my experimental time to basic pressure and temperature measurement
DanH
12-21-2011 09:14 AM
Quote:
Originally Posted by rvmills (Post 607150)
I figured you had measured temps into and out of the oil cooler......When I purchased my plane, it took fresh
air for the cockpit vents from the back of the baffle (next to the oil cooler).....The interesting thing is that the
air was quite cool, even coming from the upper plenum.
Thought about that one Bob. It is interesting. Perhaps those parallel valve cylinder fins truly don't heat the plenum air
very much. Perception of temperature (as compared to measurement) can fool you; rigging a temperature probe or
two for moving around under the cowl is cheap, useful and fun. Add it to your winter list.
Here is a paste from my notes, temperatures recorded on a day trip to Jackson last summer, after settling into cruise.
Morning OAT 64F @ 8500 ft
Oil cooler inlet probe 81F
81-64= 17 degree rise
Afternoon OAT 86F @ 2500 ft
Oil cooler inlet probe 101F
101-86= 16 degree rise
The OAT and inlet temp probes agreed within 1 degree in the hangar before pullout. And the inlet probe is truly
isolated within the fiberglass duct at the cooler face....no radiant heating from some other source.
I'll get some new measurements shortly. A smaller temperature rise is pretty much a no-brainer.....that's not really
the experiment. The extended duct length surely adds some friction, which acting alone would reduce oil cooler mass
flow. I think the friction will be offset by the higher pressure at the cowl inlet source; see the plenum pressure map in
3405, 0.3F inlet, page 112.
DanH
11-12-2012 09:09 AM
Exit panel Ver.4 got its shakedown cruise last night. This one extends 4" further aft than previous, meaning 4" aft of
the firewall. The slope in the RV-8's inset exhaust ramp means the primary exit is again progressively smaller than
previous exit panels.....
....possible because this one incorporates additional exit area on demand.
The door is hinged just forward of its center, so the forward edge raises up into the cowl as it opens. The result is two
additional exit areas with the frontal area addition of one. Having eliminated the entire exit chute from the bottom of
the RV-8's cowl there just wasn't much virtue in frontal area addition, even in slow speed operation.
The center-hinged door also reduces mechanical loads on the operating mechanism, a linear actuator with a linkage
rigged to be over-center when the door is closed.
Ok, preliminary data, a shakedown cruise. I launched with the door open and climbed from 200 feet to 10,500, WOT,
2700 RPM, leaning in the climb, at 105 knots indicated, arriving with oil temperature on 197F and CHTs of 347, 330,
355, and 334. OAT was 70F on the ground and 49F at 10,500.
Pushed over and established the usual settings for fast cruise, WOT, set RPM, lean to 100-125 ROP for power, trim,
altitude hold on. Indicated TAS settled in at the usual 181 knots, which is what I had with the previous exit.
Now the good part.....thumbed the switch to close the door, and picked up four knots....
Me like.
I'll now move into an extension of the cowl pressure and temperature data gathering that Ken, Sonny, and myself
have been playing with since last winter. In the photos above you can see the brackets for an exit pitot-static and a
temperature probe taped and riveted into the exit. We'll publish here on VAF in due course. Probably rig a video
camera too. This one may be worth some yarn and tape.
jarvis
11-12-2012 10:17 AM
Awesome!
Simply awesome, Dan. Is everything glass--except the pushrods, bolts, nuts, etc.?
DanH
11-12-2012 10:32 AM
Quote:
Is everything glass--except the pushrods, bolts, nuts, etc.?
Yes. Fabrication details in this thread, post 67, 68, and 82:
Mike S
11-12-2012 10:48 AM
Congrats!!
Quote:
Dan, congratulations on this new setup, Expiremental aviation at its best:D
Bob A.----you watching this one???
zav6a
11-12-2012 10:30 PM
Drag
Man, that is pretty.
Hard to believe there was any drag to wring out of that configuration let alone 4kts.
Looking forward to seeing your data. I won't be surprise if someone buys the rights. Great R&D work.
erich weaver
11-12-2012 10:51 PM
"... a linear actuator with a linkage rigged to be over-center when the door is closed."
Cool stuff.. Minor detail: if it's truly over center, that means it would be jammed, right? I'm confused on why you
describe it this way.
Regards,
Erich
DanH
11-13-2012 12:26 AM
Quote:
... if it's truly over center, that means it would be jammed, right? I'm confused on why you describe it this
way.
Perhaps a poor choice of words. Let's try a picture.
The highest load on the door linkage would be when the door is closed, because that's when internal cowl pressure is
the highest.
If we arrange things so that the arm linked to the door becomes parallel to the link as the door reaches the closed
position, there is no resting load on the actuator. That's good for the plastic gears, which are subject to a bit more
heat than the designer intended. Even better, as the door nears closure and resistance rises, this sort of arrangement
provides a progressive increase in linkage ratio. Thus a little bitty actuator can pull the door shut without strain.
Top is door open, bottom is door closed.
erich weaver
11-13-2012 02:05 AM
Aha! Had to go back to your original photos and blow them up and compare with your diagrams, bit I get it now and
also see how the over center arrangement with the door closed relieves stress on the actuator.
Thanks
Erich
pierre smith
11-13-2012 07:09 AM
Sweet!
Brilliant invention, Dan.
Can I come and spend a week with my -10 and mess with its exit?
Best,
Kevin Horton
11-13-2012 07:32 AM
Great mod Dan. 4 kt increase is a pretty significant drag reduction. I think I know what Bob Axsom will be doing this
winter :)
rocketbob
11-13-2012 07:49 AM
Dan since you had your cowl manometer-ized I would be interested in knowing the cruise pressure differences
between iterations of the cowl exit.
DanH
11-13-2012 09:41 AM
Quote:
Originally Posted by erich weaver (Post 716071)
Aha! Had to go back to your original photos and blow them up and compare with your diagrams, bit I get it now
and also see how the over center arrangement with the door closed relieves stress on the actuator.
Here's one with the door more than half open. As the actuator pulls on its center arm to close, the arms on the ends
will eventually parallel the linkage rods. Linkage ratio goes to infinity.
The black heat shrink thing on a wire is a temperature probe. The actuator was subject to about 160F in this location.
As you can see the location shields it from radiant heating.
Quote:
Originally Posted by Kevin Horton (Post 716081)
Great mod Dan. 4 kt increase is a pretty significant drag reduction. I think I know what Bob Axsom will be
doing this winter :)
Thanks, but, well, let's remember this was a shakedown cruise. To use Bob's excellent example, accurate measuring is
needed. In addition to airspeed, it would be nice to cycle the door and measure a lower cowl pressure rise and an exit
velocity increase.
RV8R999
11-13-2012 12:30 PM
Point of clarification...
I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the previous
exit of same area without a door installed, correct Dan? Unless this exit has smaller area than previous??
Dan's idea, as was mine, was to shrink the exit as small as possible for cruise drag reduction with acceptable penalty
in CHT while adjusting the door open for the WOT climb condition to provide CHT margin.
Mike S
11-13-2012 12:51 PM
Quote:
I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the
previous exit of same area without a door installed, correct Dan?
I added the red for emphasis.
Quote:
Pushed over and established the usual settings for fast cruise, WOT, set RPM, lean to 100-125 ROP for power,
trim, altitude hold on. Indicated TAS settled in at the usual 181 knots, which is what I had with the previous
exit.
As I read this, he gained the 4k above his normal speed/power settings.
I wonder if there is going to be a max speed increase, and if so, how much.
Pretty sure that is what most folks are interested in :rolleyes:
Page 4 of 5 « First < 2 3 4 5 >
Page 5 of 5 « First < 3 4 5
DanH
11-13-2012 01:28 PM
Quote:
Point of clarification...
I believe the 4kt increase is from a door open to door closed position not an adidtional 4kt increase over the
previous exit of same area without a door installed, correct Dan?
Again, the numbers are preliminary, but with the door closed it appears to be faster than previous. A few GPS
triangles will tell the tale.
Remember, the fixed exit area (what remains with the door closed) has been reduced as compared to the previous
fixed exit. Even the tailpipe clearance bump has been reduced. I also added an internal flange to capture the trailing
edge of the horizontal intake fairing; you can see it below the actuator in the above photo. Sealing that joint means
one less loss of internal cowl pressure,as the previous exit panel was bulging outward along that line. Increased
internal pressure + smaller exit = increased exit velocity = less cooling drag.
RV8R999
11-13-2012 01:44 PM
yep, with smaller exit would expect speed increase.
So here is the test - how small will you go? I'm going to reduce mine an additional 15%.
AX-O
11-13-2012 02:36 PM
Dan, that is a very elegant solution. I appreciate the time and effort you have put into this “project”.
ppilotmike
11-13-2012 03:23 PM
+1 for Axel's sentiments
Dan,
Big thanks for your efforts in posting all of this, and for taking the time to educate the folks "in the back of the
classroom."
Steve Melton
11-13-2012 04:54 PM
sweet!
that's a sweet door. looks like a butterfly valve turned sideways. I'm impressed by both the thought and
workmanship. could you get by with only one actuator arm... like a butterfly valve?
DanH
11-13-2012 06:35 PM
Ya'll are quite welcome.
Steve, I doubt a single pushrod would work for long, at least not in this general configuration. I'd expect the hot
fiberglass door to warp torsionally.
Vlad
11-14-2012 10:41 AM
Another great invention
Dan I am amazed of your craftsmanship and inventiveness. You should have lived on the other side of the world :)
RV8R999
11-14-2012 08:59 PM
Force On Door
Quote:
Originally Posted by Steve Melton (Post 716214)
could you get by with only one actuator arm... like a butterfly valve?
My max measured lower cowl pressure was 6.75 " H20 (relative to ambient static at altitude) = .24 PSI at Vmax. My
door is 6" x 4" = 24 sq in. Force on the door at Vmax is about 5.76 lbs. Mine is hinged at the forward edge so the
hinge and door feel the full load . Because Dan's is hinged and actuated at the center, when the door is closed,
neglecting the slight pressure gradient across the span of the door, the force on his forward half should nearly oppose
the force on the aft half resulting in nearly zero moment about his neutrally located hinge line - elegant design for
sure! (the exit area begins to accelerate as it moves closer to the exit so static pressure in the cowl is not going to be
uniform but for purpose of illustration and in consideration of the short span of the door I'll call it uniform...I know, I
know)
Dan, your door may actually stay mostly closed without actuators since as the the door begins to open the dynamic
pressure of free stream will act mostly upon the aft portion of the door creating a closing moment. I cannot tell from
photos if the fwd and aft portion of the door are of equal area?
As Dan pointed out the heat on the glass plus the load will allow the door to warp. I saw this on the first iteration of
my setup when I only had one actuator. After a flight with the door fully closed on shutdown the side without the
actuator was still open about 1/2" my actuator arms are located near the aft edge of the door not at the hinge line.
My first actuator was simply a push-pull cable (standard Van's carb heat type). After a Vmax run with the door fully
open I returned to find the cable bent from dynamic pressure loads on the door when fully open.
This is super cool (no pun intended) - Dan really needs to start an engineering firm specializing in composite aircraft
modifications - maybe competition to LoPresti!
The Wizzard
11-16-2012 11:20 PM
Need more pic's
Please post more pictures!
DanH
11-26-2012 10:37 AM
Rigged my old lipstick camera on a pedestal mount under the belly and taped yarn everywhere.
Good news and bad news.
Bad: At this time the door does not fully close in flight. It appears be a combination of factors. Heat and internal
pressure is bulging the panel at the hinge line, and some of the deformation has become permanent despite using an
epoxy with a better Tg. I also think the aluminum pushrods are lengthening quite a bit in flight due to their location
very close to the exhaust pipe.
Good. The flows look excellent. With the door open you see some reversal just aft of the door chute. Nothing else
seems to be doing anything objectionable. There is a little disturbance in the primary exit (the big one with the
exhaust pipe), but watch how it smooths out when the door closes. The last 10 seconds or so is taken at 180
knots.....nice clean streamlines. Me like.
So, for now, don't copy the physical structure, but you might want to think about the aero stuff. It's all about exit
velocity.
http://youtu.be/nA5PY7PYBsU
AlexPeterson
11-26-2012 08:20 PM
Dan, excellent work! We'll be continuing to follow this project closely.
DanH
12-18-2012 10:37 PM
An examination of the cowl exit panel quickly located the problem. The pivot points lacked support; the edges of the
door opening were bowing outward due to internal pressure.
So, I added some ribs along the sides of the door opening to support the pivots. They are simple hardwood cores
covered with 2 plies of 9oz and aluminum reflector material:
Compare with the photo in post 147.
The weather cleared today and I had a chance to fly it. The door now stays shut as designed. Here's a short (boring)
clip from the Belly Cam:
http://youtu.be/aIBXAE2Ezn4
New speed numbers in the near future. I did have the opportunity to fly an NTPS triangle about 2 weeks ago, just to
confirm the TAS indication which was last calibrated during Phase 1. It's still accurate. 185 knots indicated calculated
at 184.9...cruise at 9500.
chaskuss
12-18-2012 10:42 PM
Quote:
Originally Posted by Vlad (Post 716389)
Dan I am amazed of your craftsmanship and inventiveness. You should have lived on the other side of the
world :)
Why, so they could send him to the gulag, like all of the brilliant Russian aircraft designers? We are Americans, we do
NOT live to suffer! :D Awesome work Dan.
Charlie
DanH
Follow up...this weekend I replaced the tiny Firgelli servo with a standard Ray Allen T2-7A.
06-10-2013 08:52 AM
Early in test I had noticed some freeplay developing within the Firgelli servo and expected it to strip a gear due to
heat, which measured at about 160F in the servo location. However, it has been hanging in there since Christmas, so
bravo to the designers.
That said, OSH is coming and I didn't want to chance a failed air door inbound from Ripon. The RAC servo is larger
and more powerful, meaning the load applied in this app should only be a small fraction of normal capacity, i.e. low
load on the gears when hot.
Figelli servo travel was 10mm (0.3937") and the T2-7A is 0.7", so the servo arm in the linkage was lengthened to
0.75". That gave me about 1/8" less door opening, good because the front edge of the door was contacting a pipe
when full open. The RAC servo takes a full 10 seconds to cycle end to end and has internal limit switches, so it's easy
to select partial openings. The Firgelli cycled so fast I pretty much just ran it full open or full closed.
More reports at OSH, over beer ;)
DanH
06-21-2013 12:18 PM
Playing around last weekend on a run to Oklahoma. Nothing much to do in cruise so I got some data.
Upper plenum - aircraft static delta vs exit door position in seconds of servo motor run. (picolo tubes in upper
plenum)
Exit velocity vs door position (exit pitot-static probe)
All pressures are inches H2O
position......pressure.....% of Potential Q....Exit delta
Open.........11.36........ 0.7126.................0.91
2..............11.63.........0.7296............... ..1.15
4..............12.03.........0.7547............... ..1.27
6..............12.3...........0.7716.............. ...1.35
8..............12.3...........0.7716.............. ...1.45
closed.......12.35..........0.7747................ .1.46
12.35 / 11.36 = 8.7% plenum pressure increase...pressure recovery rises when the exit is throttled.
1.46 / 0.91 = 60% exit velocity increase. Note that exit throttling is quite different as compared to the usual "cowl
flaps" concept.
RVbySDI
06-21-2013 01:10 PM
Dan,
Where in Oklahoma were you? Would have loved to talk with you when you were here.
Did you measure any speed changes from open to closed? Curious to know if there were any noticeable differences?
I am still very interested in the AirChia design for my exhaust exit but have not done anything besides think about it.
Tom Martin
06-21-2013 01:19 PM
Dan
Do you have the corresponding IAS and CHT numbers?
I am especially interested in the difference as you squeeze the opening the last few times.
On my plane there is a spot where IAS reaches a point where it actually will decrease slightly if I close it down too
much.
I have found that I never have to open or close the unit now that I have found that sweet spot, and I am considering
glassing the unit shut. (Now maybe if I lived in Alabama I might want to open it up occasionally in the summer!)
DanH
Quote:
Originally Posted by RVbySDI (Post 781579)
Dan, Where in Oklahoma were you? Would have loved to talk with you when you were here.
Just across the border from Ft Smith.
Quote:
06-21-2013 02:24 PM
Dan, Do you have the corresponding IAS and CHT numbers?
No...cross-country cruising, so I wasn't going to fly three leg circles. CHT goes up and down with cooling mass flow
and/or mixture adjustment, as you would expect.
Quote:
I am especially interested in the difference as you squeeze the opening the last few times. On my plane there
is a spot where IAS reaches a point where it actually will decrease slightly if I close it down too much.
I have found that I never have to open or close the unit now that I have found that sweet spot, and I am
considering glassing the unit shut. (Now maybe if I lived in Alabama I might want to open it up occasionally in
the summer!)
Door operation is non-linear; door motion is less and less per unit of servo run time as the door nears closed. Go back
a few posts to the door linkage discussion and you'll understand why. Speed increase appears to be proportional to
exit delta values.
Don't remember your exit configuration very well. Got a picture?
Yes, I want temperature control over a wide range of OAT and airspeed...an extension of Mr. VanGrunsven's mantra.
rv6ejguy
08-13-2013 11:10 PM
Just out of curiosity, did you ever measure the cooling air exit temperature at high speed? Door open vs. closed?
DanH
08-14-2013 06:24 AM
Quote:
Originally Posted by rv6ejguy (Post 797645)
Just out of curiosity, did you ever measure the cooling air exit temperature at high speed? Door open vs.
closed?
Not open vs closed.
I had done some preliminary measurements earlier with a fixed 4" extension, i.e. the same exit as with the door
closed.
TAS....... Exit Temp
knots..... F
133.7..... 228
154.5..... 221
170.6..... 221
191.9..... 209
Increasing airspeed means more mass through the system. Efficiency is reduced as mass flow rises; it's not heating
the air as much per unit quantity of air. I'd expect an across-the-board reduction if flown at the same airspeeds, door
open. It would simply be more mass flow. That's fine. I don't care about efficiency in initial climb, or when grinding
inbound on the Ripon approach. I just want low engine temperatures.
dealfair
Quote:
08-14-2013 08:39 AM
knots..... F
133.7..... 228
154.5..... 221
170.6..... 221
191.9..... 209
Increasing airspeed means more mass through the system. Efficiency is reduced as mass flow rises; it's not
heating the air as much per unit quantity of air. I'd expect an across-the-board reduction if flown at the same
airspeeds, door open. It would simply be more mass flow. That's fine. I don't care about efficiency in initial
climb, or when grinding inbound on the Ripon approach. I just want low engine temperatures.
Geez Dan, and I WAS feeling great about getting my temps down to 350 degrees. WOW!
rv6ejguy
08-14-2013 09:09 AM
Quote:
Not open vs closed.
I had done some preliminary measurements earlier with a fixed 4" extension, i.e. the same exit as with the
door closed.
knots..... F
133.7..... 228
154.5..... 221
170.6..... 221
191.9..... 209
Increasing airspeed means more mass through the system. Efficiency is reduced as mass flow rises; it's not
heating the air as much per unit quantity of air. I'd expect an across-the-board reduction if flown at the same
airspeeds, door open. It would simply be more mass flow. That's fine. I don't care about efficiency in initial
climb, or when grinding inbound on the Ripon approach. I just want low engine temperatures.
Fascinating data. I would have thought the temperatures would have been much higher given the heads are usually
well above 350F. I suppose the steel barrels have a large percentage of the total airflow running over them, are a lot
cooler than the heads and have a much lower K value than the aluminum heads. This would dilute the hotter air from
the heads somewhat.
DanH
08-14-2013 06:50 PM
Quote:
Fascinating data. I would have thought the temperatures would have been much higher given the heads are
usually well above 350F. I suppose the steel barrels have a large percentage of the total airflow running over
them, are a lot cooler than the heads and have a much lower K value than the aluminum heads. This would
dilute the hotter air from the heads somewhat.
The exit air is heated by the heads and the barrels, plus the oil cooler, hot exhaust system, the alternator, and even a
little heating from compression at the intakes. Due to the mixed nature of the heating you can't pay much attention
to the values by themselves. A better yardstick incorporates intake temperature and average CHT...
(Exit - OAT)/(CHT - OAT)
...the result being a decimal value. Work to push that value as high as possible; maximum heat transfer means less
mass flow for the same cooling.
Practical note; when measuring exit air temperature, be sure to shield the probe against radiant heat from the
exhaust system. You can see the shield to the right of the tailpipe in post 147. It's fiberglass with a reflective
aluminum tape surface. The probe is suspended behind it.
BillL
08-14-2013 07:59 PM
Dan, Great data, very useful. Now if we just knew the mass flow. One thing, is the heater bypass air also included in
your exit flow? I have been thinking about reducing it with an orifice on the heater valve rather than a full dump.
If we know ambient temp, pressure (density), fuel flow, manifold pressure, egt and engine rpm, we can make a good
approximation of heat balance for cooling mass flow purposes.
Thanks again.
dealfair
08-14-2013 09:09 PM
Oh - exit temperature
Please excuse me Dan & shame on me for not reading more closely. I mistook those numbers for cylinder head
temps. :(
DanH
08-15-2013 06:13 AM
Quote:
Originally Posted by BillL (Post 797986)
One thing, is the heater bypass air also included in your exit flow? I have been thinking about reducing it with
an orifice on the heater valve rather than a full dump.
Given the focus on efficiency, I'm rather anti-bypass. There is no forced air heater or heat muff; I wired the airplane
for electric vests. No blast tubes either.
Quote:
Originally Posted by dealfair (Post 798004)
Please excuse me Dan & shame on me for not reading more closely. I mistook those numbers for cylinder head
temps. :(
Jugs that cold would be poking little bumps in the baffling ;)
David-aviator
08-15-2013 09:12 AM
Quote:
The exit air is heated by the heads and the barrels, plus the oil cooler, hot exhaust system, the alternator, and
even a little heating from compression at the intakes. Due to the mixed nature of the heating you can't pay
much attention to the values by themselves. A better yardstick incorporates intake temperature and average
CHT...
(Exit - OAT)/(CHT - OAT)
...the result being a decimal value. Work to push that value as high as possible; maximum heat transfer means
less mass flow for the same cooling.
Practical note; when measuring exit air temperature, be sure to shield the probe against radiant heat from the
exhaust system. You can see the shield to the right of the tailpipe in post 147. It's fiberglass with a reflective
aluminum tape surface. The probe is suspended behind it.
Fascinating data indeed.
At some point you should arrive at an optimal entry-exit ratio that would achieve maximum heat transfer based on air
volume and speed through the compartment and with minimal drag factor based on TAS with a particular
configuration - or at least that is my interpretation of the effort - right?
Lots of stuff going on here....that's what makes it so interesting.
rv6ejguy
08-15-2013 09:31 AM
Dan, do you have a figure for the closed door exit area?
DanH
08-15-2013 07:36 PM
Quote:
Dan, do you have a figure for the closed door exit area?
13" x 2.625" less about half the tailpipe area, ballpark 22-25 sq in. Right at the moment I don't remember the exact
tailpipe diameter.
Postscript; measured the tailpipe..2.5" diameter, so (13 x 2.625) - (1.25^2 x 3.14) = 29.2 sq in. Call it 30.
DanH
06-06-2014 03:59 PM
Follow up....
The Ray Allen T2-7A servo has been operating the cowl door for about one year now. Recall that RA doesn't claim
their servos will hold up at the sort of temperatures typical for a well sealed cowl, but they don't say they won't either.
So far, I have not noticed the slightest reduction in performance, increase in noise, or any other symptom of a heat
issue. It is insulated with fiberfrax felt and aluminum tape, and it is shielded from exhaust pipe radiant heat. The
insulation just means it takes longer to reach the overall in-cowl temperature, so it's living with the heat.
The drag reduction is nice, although a fully closed door requires an OAT at 65F or so to maintain oil temp below 200 in
fast cruise. Here's a current example; yesterday, hauling back to the office after a truck sale in Mississippi. It was
warm at 7500, about 66F, and I'm at best power mixture, door closed, and 69% power per the EFIS. True airspeed
checks per the NTPS method say the EFIS is accurate.
With this exit geometry, door position has strong effect on oil temperature, or more precisely, oil cooler mass flow.
Given the above conditions, opening the door about 1/3 will lose 1~2 knots and drop oil temp 6~10 degrees. That's
rarely necessary if I get high enough, as OATs in the 10K ballpark tend to be low enough for a fully closed door.
Down low in a hot day, full open costs about 4 knots in cruise, and puts oil temperature under control of the
vernatherm, about 187F for mine. Obviously the door is full open for climb, or crawling around in slow flight.
Yesterday it was over 90F on the ramp at KPIB. With the door full open, taxi time and a WOT/2700 climb to 5500
@125 IAS didn't break 200F.
brad walton
06-06-2014 04:30 PM
Dan, what fuel flow are you at in th picture of your EFIS in post 190? I am trying to equate your 390 cubes to my 360
for the other parameters. Thanks.
DanH
06-06-2014 05:04 PM
Quote:
Originally Posted by brad walton (Post 886399)
Dan, what fuel flow are you at in the picture of your EFIS in post 190? I am trying to equate your 390 cubes to
my 360 for the other parameters. Thanks.
About 11.2; the EGT values are degrees ROP.
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VAF Forums - The Shrinking Exit

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