Placing the Bell P39 Aircobra.

[Kutscha]

Had Fedden not spent so much time on the sleeve-valve, then perhaps a poppet-valve Hercules or Centaurus could have been available much sooner, and the story completely different.

Both the Hurc and Centaurus were sleeve valves. Are you saying they could have been re-designed with poppets?

The Soviets did not leave the P-39s stock (as shipped from the USA).

[Graham Boak]

Originally Posted by Kutscha

Both the Hurc and Centaurus were sleeve valves. Are you saying they could have been re-designed with poppets?

The Soviets did not leave the P-39s stock (as shipped from the USA).

No: I am saying that if Fedden had not gone down the route of sleeve valves then powerful British radial engines could have been made available sooner. On the other hand, Napier could not have debugged the Sabre without the Bristol experience.

The Soviets did not make major changes to the P-39s, mainly removing wing-mounted weaponry. Where the P-39 did differ from other Lend-Lease types was that strenuous efforts were made to maintain the supply of fuel additives so that the P-39 units operated with 100 octane fuel. Perhaps somewhat higher opinions would have been held of the Hurricane had the higher boost usable with 100 octane been available.

[Jukka Juutinen]

Originally Posted by Graham Boak

No: I am saying that if Fedden had not gone down the route of sleeve valves then powerful British radial engines could have been made available sooner. On the other hand, Napier could not have debugged the Sabre without the Bristol experience.

The Soviets did not make major changes to the P-39s, mainly removing wing-mounted weaponry. Where the P-39 did differ from other Lend-Lease types was that strenuous efforts were made to maintain the supply of fuel additives so that the P-39 units operated with 100 octane fuel. Perhaps somewhat higher opinions would have been held of the Hurricane had the higher boost usable with 100 octane been available.

Graham, the sleeve valves are the very one feature that made the Hercules and Centaurus so excellent engines. With poppet valves they would have been mediocre engines with much shorter TBO, higher fuel consumption and substantially increased diameter for the same capacity. The same applies for the Sabre. The sleeve valve is vastly superior to the poppet valve. Now you ask why it hasn´t been adopted universally. The answer is the same as why the significantly inferior VHS system won over the Beta system: whims of commercialism.