Aviation Historian 35
M.Bearman - The other sound barrier
Perhaps unsurprisingly, German powerplant specialists experienced many of the same issues as their British counterparts when putting high power outputs through enormous propellers. The 16ft (4-87m)-diameter propellers of the Heinkel He 177 potentially caused the loss of a prototype when the pitch-change unit failed.
Bell P-39 serial 40-034 while up from Langley in 1943. The aim was to test the effects of compressibility on propeller blades, and required the aircraft to hold various level-speeds down to 200 m.p.h. (322km/h) at a constant blade angle-of-attack. The results were the first to measure a transonic drop in torque beyond the “barrier”.
In his article in TAH20, The Whirlwind Becalmed, the author explained how the second Whirlwind prototype, L6845, was fitted with experimental Rotol propellers for trials at the A&AEE, giving notably better performance than the thicker de Havilland propellers fitted to production machines such as P7048, seen here.
Built to Air Ministry Specification B.18/38 for a “Reconnaissance Bomber for Rapid Production”, the Armstrong Whitworth Albemarle was powered by a pair of Bristol Hercules radials of considerably less power than the Manchester’s Vultures - yet it was even noisier for its crew. Was the problem similarly propeller-based?
The Avro Manchester prototype L7246 with its original twin-finned tail, before a third central fin was added. The Manchester made its first flight in the hands of “Sam” Brown at Ringway on July 25, 1939, but suffered from recurrent powerplant problems and in total only 202 were ultimately built.
D.H. Propellers was forced to create the DP456250A prop-blade "in-house”, as there was nothing readily available that was big enough for the Manchester’s Vultures. Despite the scaled-up blades pushing into uncharted regions of power transmission, the Vulture has always taken the brunt of the blame for the type’s poor performance.