Hanger 11 Harpoon - ROCKETS Magazine

Volume 6, Issue 1
April 2011
8
MAGAZINE
ARG
Coast Optimization System
Part 4
Let the Bungee take the HEAT
Hanger 11 Harpoon
Build a Jeff Jakob’s Nozzle
MAD DOG DRAG-RACER
Testing Estes’s
Thrust Claims for the
A10-PT motor
Backup Charges
News and Review
$6.95 US
$8.95 Canada
Photo by Neil McGilvray
Kerbel Geoffrey’s Solar Sailor 2.22x Upscale at ARG8
April 2011
Volume 6 Issue 1
4
EDITORIAL
6
ROCKETRY PLANET NEWS
46
By Jeff Jakob
Now you can make a great nozzle
50
By Darrell Mobley
8
COAST OPTIMIZATION SYSTEM PART 4
53
56
BACKUP CHARGES
By David Chance
Photo by Phil Tomeo
How rocketry relates to life
ARG 8
By Neil McGilvray
Photos by Neil McGilvray
First big launch of the year
36
MAD DOG DRAG-RACE
By Justin Farrand
Review of Wildmans Mad Dog Kit
ROCKET TRICKS:
LET THE BUNGEE TAHE THE HEAT
By John Ritz
How to not burn your recovery
16
TESTING ESTES’S THRUST CLAIMS FOR
THE A10-PT MOTOR
By Garrett R. Hedrick, Elliott E. Beski,
Timothy R. Lopez and Michael Courtney
Students give the results to their testing
By Frank Hermes
Get more altitude with this system
14
BUILD A JEFF JAKOB’S NOZZLE
58
NCR LAUNCH
Photos by Ray LaPanse
HANGER 11 HARPOON
60
By Rod and Paula Thrasher
The build and flight of this rocket kit
NARAM 52
Photos by Ray LaPanse
Corrections:
Volume 5 Issue 6
Firgure 6, on page 23 was taken
by Mike Ficco not Mike McBurnett
THE OFFICAL MAGAZINE OF THE TRIPOLI ROCKETRY ASSOCIATION
BOARD OF DIRECTORS
TERRY MCCREARY - PRESIDENT
PAT GORDZELIK - V. PRESIDENT
STU BARRETT SECRETARY
BRUCE LEE TREASURER
ROCKETS MAGAZINE APRIL 2011
KEN GOOD
ROBIN MEREDITH
BOB SCHONER
DICK EMERY
DEBRA KOLOMS
3
Coast Optimization System
Part 4
By Frank Hermes
Photos by Frank Hermes
Photo by Neil McGilvray
Implementation
Trying to actually implement the integration formula from
Part 3 on the integer-only math of the Parallax BASIC Stamp
was a bit onerous. I was using fractional conversion factors
and performing division that resulted in remainders. I had
some difficulty obtaining the gyro rate integration using this
approach and the relatively simple, inter-only-math Parallax
BS2pe. There are integer-only conversions you can make to
do so, but the accuracy is limited and the processing power
to do so is lacking with that microcontroller. I decided I really
needed to move to floating point math capability. I would
learn much later that a lot of my difficulty at this point was
not due to these constraints, but rather another problem I did
not recognize at the time.
In addition to the integer-only difficulty, there is no convenient
way to accurately set the sample rate of the BASIC Stamp
since there is no access to timer control or interrupts on
the BS2pe. I had to essentially set up my code, then insert
some programming feedback indicator loops (e.g., turn on
an LED via my code, run a hundred samples, then turn off
the LED and use a stopwatch to see how long it took to run
the 100 samples. Then I would divide the stopwatch time by
the 100 samples in order to know what the sample rate was.
Then I would go into the code and change the sample rate
factor in my calculations – but I was always playing with the
sample rate factor because any time I modified the code, the
execution time changes and therefore the time to take 100
samples changes - tedious.
8
Even when I got the sample rate routine sort of figured
out, I was still having little success in generating angles. The
angles I got were very erratic and always greatly less than
the actual observed orientation of my setup. If I changed one
of the formula factors by an order of magnitude I could almost
get there, but it was very inconsistent in nature. It was very
frustrating. Though I thought I was doing things correctly,
my calculated angles always seemed to be about a third of
the actual observed angle. I went over things in my setup
and code a hundred times and did more research to confirm
that my integration formula was right. I concluded that the
“looseness” of the integer-only, non-interrupt processing of
the BS2pe was the culprit. So, I searched the Parallax site
for an alternative.
Floating Point Unit - FPU
I came across the microMega Floating Point Unit, or
uMFPU. Cam Thompson has produced a great chip and
created a great web site at microMega. At Cam’s site you
can find support for using his uMFPU with a variety of
microcontrollers. With the uMFPU, I felt would be home free
since I would be able to implement floating point math, as
well as precise sample rates.
The uMFPU contains, in addition to its built in floating
point support, a couple of channels of 12-bit ADC, so it was
a relatively simple process to attach my IDG gyro to one of
the ADC inputs on the FPU, and then connect the FPU to
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Rocket Tricks:
Let the Bungee take the HEAT
By John Ritz
Ever had one of those heavy rockets (especially at the front end) that kept popping the main chute out at apogee
and drifting away into the sunset? I am talking about the usual recovery method of dual deployment recovery (at least on
the east coast with the tree infested lands). Sometime we end up having to put a lot of weight in the nosecone to stabilize
the rocket or for other reasons. At apogee when the payload section deploys, a heavy nosecone can sometimes get yanked
out prematurely with the main chute. Even when main chute deployment is intended at apogee, a heavy nose cone being
kicked out like a cannon ball from a good size ejection charge can rip of the shock cord and fall loose into the ground. The
kinetic energy can be quite tremendous in some big sized rockets and it is necessary to divert most of this kinetic energy
somewhere else. One solution is to use a “sacrificial lamb”, in this case a short piece of bungee cord attached as in figure
1. This is the only good use of bungee cord in rocketry that I know of; to tear it apart.
Figure 1: Attach a piece of bungee cord (Home Depot) between the payload section and the shock cord (tubular) at a point
that is two to three times the length of the bungee.
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8
ARG
By Neil McGilvray
Photos by Neil McGilvray
16
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Hanger 11 Harpoon
By Rod and Paula Thrasher
First flight of Harpoon
.Statistics:
half-scale AGM-84 Harpoon Missile
5.5″ diameter × 6′ 3″ tall
54mm motor mount
Dual-deployment built-in altimeter bay
Background of the Real Harpoon:
The Harpoon is an all-weather anti-ship missile.
Originally developed for the U.S. Navy to serve as its
basic anti-ship missile for fleet-wide use, the AGM84 Harpoon also has been adapted for use on U.S. Air
Force B-52s.
36
Harpoon Parts:
Two 5.5″-diameter sections of body tube
One body-tube coupler
One nose cone, with bulkhead and coupler.
Three sets of four fins, totaling twelve fins.
One 54mm motor tube
One 38mm altimeter tube
Four lower centering rings
Three upper centering rings
Two sections of ½″ shock cord
Two extreme rail buttons
Altimeter bay and pre-drilled mounting
board
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Build a Jeff Jakob’s Nozzle
Nozzle Carrier
bulk material
trim befor turning
drill hole for tool
attach to tool
cut to size X 4
center and mark for turning
46
after turning
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ROCKETS MAGAZINE APRIL 2011
49
Testing Estes’s
Thrust Claims for the
A10-PT motor
By Garrett R. Hedrick, Elliott E. Beski,
Timothy R. Lopez and Michael Courtney
Abstract: This article describes the thrust curve for Estes model
A10-PT rocket motors. The rocket-motor thrusts were measured
using a force plate. Key findings are: 1) The propellant mass in the
rockets is significantly less than what Estes publishes. 2) The rocket
thrust curve is less than what Estes has published. Failure to meet
the published impulse specification is due, in part, to less than the
expected efficiency, but is mainly due to putting less propellant in
the rocket motors than the published specification.
Keywords: peak thrust, impulse, thrust curve, model rocket,
rocket propellant
I. Introduction
This article presents measurements of the thrust curves (force
vs. time) and propellant mass of the Estes A10-PT rocket
motor and compares them with the company’s published
specifications. Rocket-motor thrust curves play a significant
role in rocket performance. Impulse and specific impulse are
important rocket-motor performance parameters. Impulse is
the total area under the force vs. time thrust curve in units of
Newtons times seconds (Ns). Specific impulse is the impulse
(Ns) divided by the weight of propellant (N), thus it has units
of seconds. The lower the rocket-motor impulse, the lower
the velocity and the lower the peak altitude attained.
50
Figure 1: Force plate for measuring rocket-engine thrust
curves. The rocket motor is attached to the bolt extending out
of the plate on the right, which is set on top of the three force
sensors on the left. (The photo shows one aluminum-cased
rocket motor attached to the bolt and two other aluminum
cased motors on the lower left corner of the plate, as well as
two brown paper–cased Estes A10-PT rocket motors.)
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MAD DOG DRAG-RACER
By Justin Farrand
Photo courtesy of Brent Hill
ROCKETS MAGAZINE APRIL 2011
53
Backup Charges
By David Chance
Photo courtesy of Phil Tomeo
Have you ever noticed that rocketry can teach
you lessons about life? Do you realize that the hobby itself
teaches us things that many of us might never have come to
appreciate? High Power, Low Power, Mid Power, Odd-Roc,
Hybrid, or Experimental, they all have something in common.
Whether your rocket flies low and slow, or zips to the nether
regions while being chased by a thin wisp of smoke, each
and every rocket teaches us a very important lesson. No
matter how much planning went into the design, how much
detail went into the construction, how meticulously the
rocket has been prepped . . . once that button is pushed; it is
one part science and one part luck. The best-laid plans are
only a memory when the electrical current passes through
the igniter. As the rocket glides up the rod or rail, it leaves
behind all control that has been exercised over it. All we can
hope for is that this object with no mind of its own will follow
the path that has been laid for it.
A few days ago, the festival affectionately known as Red
Glare concluded. The smoke trails had cleared, the rockets
were packed, the trailers were loaded, and a peaceful quiet
returned to Higgs Farm. This ninth iteration, hosted by those
big dogs of MDRA, is but one launch out of many that have
taken place over the past few months across the country.
There was LDRS in California, Oktoberfest in Colorado,
Rocktober Skies in Alabama, Freedom Launch in South
Carolina, Balls in Nevada, and many others. All of these
launches, even in different parts of the country, had one
thing in common. They all had a guy like me.
During Red Glare IX, I was one of those guys of whom you
would say,” If he didn’t have bad luck, he wouldn’t have any
luck at all.” All launches seem to have a guy like that, and
during this particular weekend I drew the short straw. I flew
five rockets, and out of those, four were heavily damaged
56
and the fifth barely escaped certain destruction. Although
each rocket had already boasted a successful track record,
this launch was different. All of the planning, all the prepping,
and that one part science all left town for the weekend,
leaving only the bad luck.
The first rocket crashed to the ground, breaking a fin,
when the parachute got charred by hot ejection gases. The
second crashed to the ground when the shock cord broke
away from the centering ring. The third suffered the same
fate as the second, plus the added insult of a nasty zipper.
The fourth broke a fin, due either to the landing itself or to
the wind using the parachute to drag the rocket over some
uneven ground. All of these rockets had flown successfully
before, but on this day a stroke of bad luck or unforeseen
events would mar each one.
The fifth rocket was Buttercup. This is the one I want to tell
you about. At 9 feet 11 inches tall, she was to blast off with
one of my experimental M-1700 loads. The detailed planning
of this launch had to be meticulously thought out. A rocket
this size under that much power using a homemade motor
must be given respect. Each detail of the prep work was
checked and double-checked until the moment she sat on
the pad and the electronics chirped. When the preparations
were complete, it was now time for that one part science and
one part luck to determine if she would fly successfully.
When the button was pushed, the ignition flash was instant.
A split second later, the motor chamber was pressurized,
and Buttercup was lifting. The roar was remarkable, and
the flames blasted the launch tower as she quickly flew
heavenward. Other than some pieces of casting tube being
spit out the nozzle end, the flight was beautiful and majestic.
It was a moment to behold.
Buttercup achieved apogee at over 3000 feet, and the
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Brad Morse’s Liberty L2 on a J-240

Chris LaPanse’s L3
on an M-3400
Sean Serell’s It’s Awesome Time Baby
on an M-2505
58
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Al Zelnick’s Icarus L1 H-90


Dwayne Schmel’s Lets Get Kracken on a J-350
60
Boyd and Ryder’s FatMan on a H-400
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