Supersonic Propellers

November
1996
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St. Louis has launched into the current
Program Year with lots of energy and plans
for informative, interesting, and useful programs
for all members. Already we have hosted presentations dealing with Smart Structures, UFO's,
the JASSM program, and the affordability initiatives of JDAM. Donn Gruensfelder is once again
preparing for his annual Tour-de-force in the "Pilots Super Safety Seminar"* to be held in January
1997.
The local members who are affiliated with the
AIAA Nation Technical Committee (TC's) have
been contacted and told to promote our Section
as host site for future conferences and seminars.
The St. Louis visitors and convention bureau
has been contacted and is assisting us in preparation of proposals to offer the TC's, showing
why St. Louis is an ideal place to host large,
annual meetings. Planning and executing these
meetings take a lot of time and effort, but the
payoff is worth it. More of our members will be
able to attend the conferences if held locally, and
many more will be able to deliver papers at the
conference. Our Student Chapters also benefit
from being able to attend a locally held National
Conference. These meetings are booked several
years in advance (Just like the Olympics), so the
advanced "Marketing" the Council is doing now
begins to payoff in 1999 and later years. If you are
interested in helping land and plan for one or more
of these please feel free to contact me at 314/
234.6483 or e-mail at [email protected].
Once again your Section is underwriting Pam
Luetkemeyer's effort in decorating a Christmas
Tree to be auctioned off at a charity gala benefiting
autistic children. This is one activity of providing
service to our community stemming from Dianne
Cheng's service projects committee.
Our hats are off to Bill Bernzott and Dick
Pinkert for Leading last year's young member and
public policy committees to Third and Second place
Awards in the AIAA large section category Nationally. Each of the committee chairs put in a lot of
effort representing our Section and it's great to see
that effort recognized. Please feel free to contact
any section chair and offer your services. With
YOU, we can sweep the awards table next time
around! •
Supersonic Propellers
s
by John M. Leonard
upersonic propellers interest developed in
the early 50's with the advent of turboprop engines coupled with speed limitations of
traditional propellers. Several aircraft had
pushed their propeller tips through the sound
barrier during dives. For example, in August
of 1943 an instrumented P-47C reached a
Mach number of 0.86 in a dive from about
33,000 feet (Ref. 1). Assuming a 13 foot diameter conventional prop turning at 1260 rpm,
the tip Mach number would be approximately
1.15. However, a static supersonic prop would
have a tip Mach number as high as 1.89 due to
the high rotational speed. Flying at Mach 0.8
with a supersonic prop would produce a tip
Mach number slightly in excess of Mach 2. A
correlation of aircraft maximum velocity versus the engine horsepower for 150 propeller
driven fighters, mostly of WWII vintage, is
shown in Figure 1. Flight velocity increases
with horsepower up to about 1500 hp; thereafter, more power does not result in additional
speed. Shock waves on the transonic and
continued on page 2
continued from page
Maximum 600Velocity
-mph _—
400300200100-
0
1000 2000
3000 4000
Horsepower
5000
6000
7000
Figure 1 - Speed Limit of Propeller Driven Aircraft
supersonic sections of the propeller blade
ncrease the local drag and reduce efficiency.
Studies conducted by NACA and U.S. propeller companies identified propeller designs
;hat could operate more efficiently at supersonic speeds. These propellers were character.zed by: (1) thin blade sections and (2) high
rotational speeds. Supersonic propellers
;ypically have a rotational Mach number of 1.0
at the hub and 1.7 at the tip. Thin blade
sections are a requirement for supersonic
operation; however, high rotational speeds
induce large centrifugal stresses. Consequently, supersonic propellers require blades
constructed of high strength steel. Efficiency
ifthese supersonic propellers designs vs.
traditional World War II fighters can be seen
in figure 2.
Propeller
Efficiency
100 <
Supersonic
Propeller
8060-
40-
World WarH
Propeller
Two research aircraft, XF-88B and XF-84H,
were developed to investigate the validity of
supersonic propeller concepts. The McDonnell
XF-88, predecessor to the F-101 Voodoo, was
the prime testbed for NACA development. Air
Force investigations used the prolific F-84
airframe, with engines provided by the U.S.
Navy. Characteristics of these two unique test
aircraft are summarized in Table 1 and illustrated in Figures 3 and 4.
The XF-88 was modified by McDonnell to
incorporate an Allison XT-38 turboprop engine, while retaining the two main turbojet
engines. An offset nose landing gear was
required to provide necessary turboprop room.
An engine inlet was added on the left and a
smaller oil cooler inlet on the right side of the
nose. Gearbox ratios could be altered to provide 1700, 3600, and 6000 propeller rpm's.
Propeller flight characteristics were gathered
by blade strain gages, a nose mounted pressure rake, and fuselage microphones (Figure
5). To accommodate the instrumentation, one
fuel cell was removed.
Table 1 - Aircraft with Supersonic Propellers
Parent Airframe
Number Suit/ Flown
Length /Span -Ft
Wing Sweep Q C/4 - deg
Engine for Propeller
Engine Horsepower
Number of Blades
Prop Diameter - ft
Propeller RPM
Auxiliary Engines
Test Organization
First Flight Date
Last Flight
Number of Flights
20-
Number of Flight Hours
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Mach Number
Figure 2 - Comparison of Propeller Efficiency
2
Max Speed Achieved
XF-88B
McDonnell XF-68A
XF-64H
Republic RF-84F
1/1
2/1
58.0/39.67
51.5/33.5
35
40
Allison XT-38- A- 5
2650
4or3
10.0, 7.2, and 6.85
1700 or 3500
2xJ-34'swithA/B
NACA
Jets only -April 14, 1953
Prop also- April 24, 1953
1956
16 (8 with prop turning)
by McDonnell. T? by
NACA
9.25 (2.07 with prop
turning) by McDonnell. 77
by NACA
M=0.94(Q,97 with prop
feathered) by McDonnell,
M=1.1inadivebyNACA
Allison XT-40-A-1
5850
3
12.0
3000
none
USAF
July 22. 1955
FTotetty 1955
11
7.5
about 600 mph
Figure 4 - USAF XF-84H
Figure 3 -NACAXF-88B
Root
Roof 6tade~o'«j!«
recorder
S*ot«c ere Mure er
YO* aT9-« pfoces
Figure 5 - XF-88B Instrumentation
When the XF-88, S/N 1, returned to St.
Louis for modification it had flown 126 hours
and 49 minutes. After modification,
McDonnell performed acceptance flight evaluations to check its suitability as a high speed
turboprop research aircraft. Each of the 16
flights lasted between 23 and 48 minutes, due
to reduced fuel tankage. Inflight turboprop
operation took place on 8 flights, with 24
minutes being the longest inflight operation of
the propeller. The XF-88 sister aircraft, S/N 2,
became the NACA parts support vehicle for
the research program.
Low speed testing, with the XT-38 turbo-
prop running, required about 3/4 rudder and
some aileron to counteract the engine torque.
Flight tests conducted in St. Louis discovered
that the modification had reduced the longitudinal and directional stability. Thus, it was
concluded that the turboprop should not be
operated during takeoff. Typical takeoffs and
landings were made with the propeller feathered and clocked in the X position to provide
the maximum propeller blade ground clearance. This unique configuration was one day
reported to the Lambert tower: saying an
aircraft had taken off without the engine
running. Since fuel tank volume was reduced
for instrumentation and test time limited; the
XT-38 was used to climb to the test altitude.
Flight tests noted that aileron control was
marginal during cross wind landings and
takeoff distances long in warm weather. First
generation afterburners frequently quit working during the takeoff run.
NACA was aware of the unacceptable noise
created by the propeller from USAF investigations with the XF-84H. Accordingly the first
test NACA performed with the XF-88B centered on static noise evaluation. In addition to
propellers, NACA tested various spinner
shapes, advance ratios, and gearbox drive
ratios. Two of the test propellers and spinners
are illustrated in Figures 6 and 7. It is interesting to note that of the three 3-bladed propellers tested by NACA each had a lower tip
Mach number than the one previously tested.
This must have been an attempt to deal with
the noise problem.
NACA intended to test a family of supersonic propellers. Five different propellers were
constructed, of which four were flown(see
Table 2).
III
GP69AO€Q05
Figure 6 - XF-88B With 60° Spherical Spinner
Figure 7 - XF-88B With 60° Conical Spinner
Table 2 - XF-88B Test Propellers
No of
Blades
Diameter
-R
Propeller
RPM
4
10.0
3
3
3
4
7.2
1675
3500
1700
1700
6000
10.0
6.85
4.0
Static
Tip
Mach
No.*
0.88
1.33
0.89
0.61
1.26
Max.
Mo
Reporte
d
0.94
1.01
0.95
0.96
not
flown
Max.
Tip
Mach
No.'
1.29
1.67
1.30
1.14
* Mach numbers are affected by the air temperature.
Exact flight test are not known, so these numbers are
computed for a typical flight condition of 30,000 ft,
standard day.
Air Force supersonic propeller flight tests
were carried out with the Republic XF-84H.
This F-84 conversion was created by replacing
the single J-65 turbojet, 7,800 Ib. thrust, with
an Allison XT-40. This turboprop engine
produced 5,850 shaft horsepower along with
1000 Ib. of residual jet thrust. Other XT-40
engine installations turned a 6-bladed counter
rotating propeller (Douglas XB2D Skyshark,
Convair XFY, & Lockheed XFV VTOL research aircraft); however, this version turned
only a three bladed single disk propeller. This
engine conversion made the XF-84H the most
powerful single disk propeller driven aircraft
in the world. The next most powerful would
be the Goodyear F2G Corsair or Martin AM-1
Mauler at 3000 hp. Propeller torque was so
high that Republic added an anti-torque fin to
the upper fuselage just behind the cockpit. A
raised horizontal tail was incorporated to
presumably keep the control surfaces out of
the prop wash. Takeoff with high propeller
torque required gradual throttle input, as
speed and rudder power increased.
The XT-40 turboprop consisted of two T-38
turbine units connected to the propeller
through a gearbox. Typically a 3 or 4 foot
extension shaft connected the turbine units
and the gearbox. On the XF-84H the T-38
power units were located behind the wing
leading edge connected to wing root inlets.
This midship installation necessitated long
extension shafts to the nose mounted gearbox/
combiner.
Two XF-84rFs were built; however, only one
actually flew. Continual problems with the
hydraulic system, engine, and power transmission, resulted in 11 emergency landings.
Noise generated by the propeller caused
ground crew members within several hundred
feet to experience acute nausea. Ground crews
unofficially nicknamed the aircraft
Thunderscreech." Currently this aircraft is
located on a pedestal at Meadow's Field,
Bakersfield, California.
Although the theory for supersonic propellers indicated improved high speed performance, operational considerations made them
impractical. Also, about this time turbojet
engines began replacing propellers for all high
performance applications.
References in Article
1. Journal of Aircraft, July-Aug 1970,
page 297
2. NACA Misc. Report L57C14-15
3. NACARML55I21
4. NACARML56D20a
5. NACARML57E20
6. NACA TN 3422
7. NACA TN 3535
8. NACA TN 4059
9. NACA TN 4172
10 NACA TN 4389
11 NASA Memorandum 4-18-59L
12. NASA Memorandum 4-19-59L
13. Air Enthusiast 48 dated Dec 1992 to
Feb 1993
14. X-Fighters, USAF Experimental and Prototype Fighters, XP-59 to YF-23
Creve Coeur Airport Rises Again
By Dr. Marty Ferman and Albert Stix
Several years ago the Great Midwest Floods
of 1993-1995 damaged Creve Coeur Airport.
Since then the airport has been rebuilt
through much hard work. Creve Coeur Airport is located on the Missouri River flood
plain, west of Lambert St. Louis International
Airport. This classic general aviation field was
once part of the Dauster Farm which still
ajoins the airport.
Currently, the airport is home to 60-80
flyable antique aircraft. There are some 180
aircraft in current residence now at Creve
Coeur Airport. Expansion plans are underway
to accommidate 220 aircraft in the next few
years. More hangars and an expanded "Shade
Port" open side storage area will accommodate
new aircraft.
The St. Louis Historical Aircraft Restoration Museum hangar was heavily damaged by
the raging flood waters (figure 1). The repaired museum building is now open and
construction is underway to double the display
area.
An example of a refurbished aircraft, a
Russian Shavrov (Sh-2), is shown in figure 2.
This aircraft is on display at the Museum
along with 75 other vintage aircraft of interest.
Figure 1 - Antique Aircraft Museum After the Flood and After Reconstruction
Figure 2 - Rehabbed Antique Russian Seaplane
Other airport activities include assembly of
Russian YAK 55 acrobatic aircraft. Figure 3
shows some of these aircraft in various stages
of assembly. Major subassemblies arrive from
Russia with final assembly here. This aircraft
is in high demand by acrobatic groups because
the design can withstand flight maneuvering
loads of 9-G's.
Creve Coeur Airport has become increasingly more important to local aviation with the
closing of Weiss Airport. Recognizing these
constraints on local aviation, the FAA has
recently designated Creve Coeur Airport as a
6
Figure 3 - Russian YAK 55's in
Various Assembly Stages
feeder Airport for the St. Louis area.
A visit to this quaint general aviation airport will be well worth while. It is located
west of Lambert St. Louis Airport, at the bend
in Creve Coeur Mill road just south and west
of 1-70 and the Earth City interchange. For
those wishing to accomplish two things at
once, the December AIAA dinner meeting will
take place at the Restoration Museum. A
casual pizza dinner is planned before a guided
tour of the museum and workshop area. Attendance is limited, so call early! •
Awards
Bob Krieger presents the '95 - '96 AIAA Technical Management
Award to Charlie Dillow for his JDAM Program Leadership
Congratulations to the following Section V
members promoted to associate fellow:
Richard M. Andres
Mark D. Bass
Kevin D. Citurs
John F. Donovan
Edward A. Eiswirth
Wayne L. Ely
Kakkattukuzhy M. Isaac
Swami Karunamoorthy
Leslie R. Koval
Linda D. Krai
Frank Laacke
Martin J. Morris
Gary P. White
Web Sites of Interest
International Plastic Modellers
http://ssnet.com/~hpyralph/ipmsusa.html
Aircraft Design Information Sources
http://www.aoe.vt.edu/Mason/ACinfoTOC.html
300° Below Cryogenic Tempering
http://www.tecsolv.com/cryo/
Have some interesting Web Sites of your own??
Share them with the membership. Send your
inputs to:
Dave Morgan,
MDA m/s S064-2904,
e-mail: [email protected]
phone 314/234.1919 or fax 314/233.9997.
St. Louis Branch of International Plastic Modellers,
December Meeting
Brighton Trails County Library, McKelvy Rd.
Tues, Dec. 10 @ 7:30 p.m.
Send us your e-mail address - Save A Tree
Address to:
[email protected]
Non-Profit
Organization
Bulk Rate
U.S. POSTAGE
PAID
Florissant, MO
Permit No. 121
Future AIAA Events
St Louis Aircraft Restoration
Museum at Creve Coeur Airport
Thursday, 5 December
5:30 pm
Pizza Dinner
Limited Capacity
AIAA CouncU Meeting
Monday, 2 December
5:00 pm - 7:00 pm
MDA HQ, Level 2S
Conference Room