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The XF-84H is said to be the world's loudest aircraft .

 

Two XF-84H aircraft were built,  Their concept was to combine the acceleration of a propeller plane with the top speed of a jet fighter.  The J35 jet engine of the F- 84 Thunderchief was replaced with an Allison  XF-40- A-1  turboprop engine. The propeller blades were only about four times longer than wide.

 

The results was a failure.  The  XF-84H  was  plagued with excessive drive shaft  vibrations.    Between  July 22, 1955 and Oct 9, 1956 the prototype made  twelve flights of which only one was successful.  

 

At idle the propeller of the  XF-84H  had  a  tip  speed faster than the speed of sound.   It made  the  XF-84H one of the loudest aircraft in the world earning it the un- official nickname "Thunderscreech."

 

Maiden flight 22 July 1955

 

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The XF-84H, a joint Air Force/Navy project based on the Republic F-84F, was originally designed to combine the speed of jet aircraft with the long range, low fuel consumption and low landing speed of propeller-driven aircraft. The XF-84H used an Allison XF-40-A-1 turboprop engine in a modified F-84 fuselage. Additional changes included a T-type tail and a triangular fin on the top of the fuselage to reduce the high torque produced by the propeller.

Between July 22, 1955 and Oct. 9, 1956, two XF-84H made 12 test flights. Eleven of the 12 flights ended in emergency landings. Sounds produced by the aircraft’s turboprop engine caused nausea and headaches among ground crews, earning the XF-84H the unofficial nickname “Thunderscreech.” Though the XF-84H was the fastest single-engine propeller-driven aircraft ever built, it never approached supersonic speed. Due to poor performance and high maintenance requirements, the XF-84H never became operational.

The aircraft on display (S/N 51-17059) was the first of the two prototypes produced by Republic. It flew eight of the 12 test flights. The museum obtained the aircraft from Kern County, Calif., in February 1999. 

SPECIFICATIONS:

• Crew: 1
• Length: 51 ft 5 in (15.67 m)
• Wingspan: 33 ft 5 in (10.18 m)
• Height: (4.69 m)
• Wing area: 30.75 m ()
• Empty weight: 17,892 lb (8,132 kg)
• Loaded weight: 27,046 lb (12,293 kg)
• Engine: Allison XF-40-A-1 turboprop of 5,850 shaft hp
   

Performance

• Maximum speed: 670 mph (1,069 km/h)
• Range: 2,000 mi
• Service ceiling: 40,000 ft (14,630 m)
• Rate of climb: 5,000 ft/min (3,810 m/min)

Armament

None

 

The XF-84H

 

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Prototype FS-059 underwent ten hours of flight testing.

The Republic Aviation Company XF-84H Thunderscreech was an experimental American-built turboprop aircraft based on the the F-84F Thunderstreak. Its turbine engine drove the plane with a supersonic propeller as well as its exhaust. Although only one ever flew, it set the unofficial air speed record for propeller-driven craft.

Originally designated XF-106 ^[1], the project and its resultant prototype aircraft were renamed XF-84H, a designation that retained the original F-84 origins although the USAF Wright Air Development Center was the key sponsor of the project ^[2].

 

Design and development

The XF-84H was created by modifying F-84F Thunderstreak aircraft. The engine was changed to an Allison XT-40-A-1, capable of 5,850 horsepower. An afterburner was installed but never used, which could increase power to 7,230 hp. The propeller was a square blade turning at a constant 3,000 rpm, with the tips traveling at approximately Mach 1.18. Thrust was adjusted by changing the blade pitch. The tail was modified to a T-tail to avoid turbulent airflow flow over the horizontal stabilizer/elevator surfaces from propeller wash.^[3] The XF-84H was the first plane to carry a ram air turbine. In the event of failure of the engine, it would automatically swing out into the airstream to provide extra hydraulic and electrical power.

 

Testing

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The Thunderscreech was destabilized by the powerful torque from the propeller, as well as inherent problems with supersonic propeller blades. It was plagued with engine related problems that affected other aircraft of the time with similar Allison T40 engines such as the Douglas XA2D Skyshark and the North American A2J Super Savage attack aircraft.

It flew a total of 12 test flights. One test pilot flew in it once and refused to ever fly in it again. Test pilot Hank Baird took the craft up 11 times and ten of these flights ended in forced landings.

 

Noise

The Thunderscreech was possibly the loudest plane ever built, earning the nickname "Thunderscreech."^[4] On the ground, they were reportedly audible 25 miles away.

The propeller blades were supersonic even while the airplane was running up on the ground. Each blade shed a shock wave that spiraled outward. It was more than just sound but also the shock waves created that were detrimental. Sound is a series of smooth waves of variable frequency and amplitude. Shock waves change the nature of the air carrying them, a fundamental difference from sound waves. They are typified by a nearly instantaneous pressure increase, which causes an impact upon reaching a solid surface. Ground crew reported that wearing standard ear protectors "made no difference" and a person standing some distance from the airplane was subjected to rapid fire shock waves. The shock waves acted on the body, causing spasms, nausea and loosening of the bowels. Even epileptic seizures were reported.

In short order, the Air Force Flight Test Center directed Republic to tow the XF-84H out on Rogers Dry Lake, far from the flightline, before running up its engine.

 

Historical significance

It holds the record in the Guinness Book of Records as the fastest propeller-driven plane ever built.^[5] With a design top speed of 670 mph (Mach 0.9), it is reported to have reached 623 mph (Mach 0.83).

It was only ever flown by the Republic test pilots, making it possibly the only USAF plane to be never flown by a USAF pilot.

 

Survivors

Two prototypes were built (FS-059 and FS-060) and only the FS-059 ever flew, logging only ten hours.

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FS-059 (pictured) was retired and spent many years mounted on a pole outside Meadows Field Airport, Bakersfield, California. It was taken to the 178th Fighter Wing of the Ohio Air National Guard whose volunteers spent over 3,000 hours bringing the Thunderscreech back into display condition. It is now on show at the National Museum of the United States Air Force at Wright-Patterson Air Force Base near Dayton, Ohio.

FS-060 (currently unknown) is assumed to have been scrapped, along with the plans, when the project was cancelled in 1956.

 

 

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References

1. ^ http://www.designation-systems.net/usmilav/duplications.html
2. ^ Keaveney 1987, p. 19, 27. Note: The initial inception for the program came from a US Navy requirement for a fighter that would not require catapult assistance.
3. ^ http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2296
4. ^ Knaack, Marcelle Size. Encyclopedia of US Air Force Aircraft and Missile Systems: Volume 1 Post-World War II Fighters 1945–1973. Washington, D.C.: Office of Air Force History, 1978. ISBN 0-912799-59-5.
5. ^ Young, Mark C., ed.The Guinness Book of Records 1997. North Sakem, New York: Mint Publishers Group, 1997, p. 137. ISBN 0-85112-014-8.

• Bowers, Peter M. and Angellucci, Enzo. The American Fighter. New York: Orion Books, 1987. ISBN 0-517-56588-9.
• Keaveney, Kevin. Republic F-84 (Swept-Wing Variants). Arlington, Texas: Aerofax Inc., 1987. ISBN 0-942548-20-5

 

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The XF-84H

 

 

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