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Even in the mid-1950s the superiority of the jet powerplant for combat
aircraft was questioned by some. A modern technology propeller driven
by a turbine (a turboprop) offered high speeds, long endurance and low landing
speeds. To test this concept the USAF commissioned two XF-84Hs from
Republic. Powered by the troublesome T-40 turboprop, the noise the F-84H
made has been described as an 'unholy shriek', leading to the nickname
'Thunderscreech'. Resonance off the ground made groundcrew physically
sick. The two aircraft only made a dozen test flights, all but two of which
resulted in emergency landings and the USAF refused to accept it for their
own tests, cancelling the programme in 1956.
The first XF-84H spent 40 years on a pole at Bakersfield Airport,
California, its propeller slowly (and quietly) rotated by an electric motor.
| CREW | 1 |
| ENGINE | 1 x 585Ohp Allison XT40-A-1 turboprop |
| WEIGHTS |
| Take-off weight | 8123 kg | 17908 lb |
| DIMENSIONS |
| Wingspan | 10.18 m | 33 ft 5 in |
| Length | 15.67 m | 51 ft 5 in |
| Height | 4.67 m | 15 ft 4 in |
| PERFORMANCE |
| Max. speed | 837 km/h | 520 mph |
| Costas Tsaganas, costanbarbarian(@)yahoo.com, 22.08.2008 The noise because most of each propeller blade was supersonic when spinning (e.g. the T-6 Texan makes a distinctive buzzsaw noise because the prop tips are supersonic). Even with the engine idling and the prop feathered the noise was awful, as it is a constant speed unit and thrust variations are made by pitch change. IT would cause extreme discomfort and nausea to anyone near it, and there is at least one instance of a man collapsing to the ground with (epileptic?) convulsions a fair distance from the Thunderscreech. |
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COMPANY
PROFILE
FACTS AND FIGURES© The turboprop engine
was mounted behind
the cockpit and drove
the propeller through a
long extension shaft. © A small auxiliary fin
behind the cockpit
helped yaw control. © The XF-84H had a T-tail
arrangement rather than a
mid-set tailplane as on the
F-84F Thunderstreak. This
kept it out of the propwash. © Various changes were needed to
counteract the massive torque
from the propeller. The left engine
intake was mounted a foot further
forward than the right and the
flaps had differential operation.
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