BACK TO THE DRAWING BOARD – The Republic XF-84H ‘Thunderscreech’

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Just over 75 years ago, the world’s loudest ever aircraft took to the skies for its first test-flight. When the US Navy voiced its need for a carrier fighter that did not require catapult assistance, Republic Aviation started experimenting with the USAF/Republic XF-84H experimental turboprop fighter.

A variant of Republic Aviation’s F-84 Thunderstreak, this novel aircraft used an Allison XT40-A-1 turboprop engine which drove the propeller at 3,000 rpm. Thrust level was changed by varying the blade pitch. However, there was one immediate drawback which gave rise to the aircraft’s nickname: the shock-waves created by the prop engine were so powerful and the sound level so extreme that it induced intense nausea and raging headaches among the ground crew. The ‘Thunderscreech’ was born.

Two XF-84H prototype aircraft were built by Republic Aviation. The use of a T-tail was required to keep the horizontal tail and elevator in clean air flow. In flight, they were destabilised by the powerful torque from the propeller, hindered by problems with the supersonic propeller blades, and plagued by engine-related glitches.

When it came time to begin testing prototypes, Lin Hendrix – one of Republic Aviation’s test pilots assigned to the program – stepped up. One flight in prototype Ship Number 2 was all it took. He vowed not to fly it again, claiming ‘it never flew over 450 knots indicated, since at that speed, it developed an unhappy practice of “snaking”, losing its longitudinal stability.’ That prototype never left the ground again.

For prototype Ship Number 1, test pilot Henry G ‘Hank’ Beaird Jr. volunteered himself. Although he achieved a slightly more successful 11 test-flights, the majority of these, including the craft’s maiden flight, experienced forced landings. The sorry flight-time clocked up by these experiments was a mere six hours and 40 minutes. It quickly became obvious that the Thunderscreech was an unreliable, unsafe, vomit-inducing waste of time.

In the face of such blatant failure, the USAF was left with little choice but to cancel the XF-84H Program in September of 1956. But although the Thunderscreech may have nose-dived as an idea, although its flaws may have literally made people sick, it achieved one redeeming accolade. Between 1956 and 1989, it held the speed record for single-engine prop-driven aircraft. Every cloud has a silver lining…

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