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Very interesting, thanks for this. Do you suppose a hybrid system might be useful in special applications, like providing a power boost to rescue helicopters t

Very interesting, thanks for this. Do you suppose a hybrid system might be useful in special applications, like providing a power boost to rescue helicopters trying to hover above mountains?

MaxBarraclough 6y ago
Rather beyond my knowledge but I'll take a stab at it: I don't think tip jets (the name for this design, oddly absent from the article) [0] are generally thought to be of practical value in modern helicopters. They have the neat advantage that they don't require a tail-rotor (the main rotor isn't driven by a drive shaft from the main body of the helicopter so there's no torque trouble) but I don't think they're all that practical. This article dates from 2010 after all. We already have a reliable means of increasing a helicopter's power: bigger engines. Alternatively, more engines. Heavy-lifting helicopters tend to be powered by twin turbine engines. [1][2] Even if they use unusual designs [2] the power-plant is the same as for any other serious helicopter. The enormous Super Stallion military helicopter went even further: 3 turbine engines! [3] I imagine a hybrid design would greatly increase complexity. Helicopters use a 'sprag clutch' to permit the rotor RPM to exceed the engine RPM, but not the other way around. This allows the rotor to keep spinning in case of an engine failure. (This is the reason helicopters don't drop like bricks when their engines fail.) Perhaps there would be a way to modify the design so that the conventional engine could still contribute power even as the rockets are firing, but I imagine it would be very high in complexity. Also, tail rotors can suffer if they aren't working in clean air, and of course this can threaten the helicopter's safety. [4] It's not something I know anything about but I imagine rockets on the main rotor could be troublesome in that regard. For yet another wacky (but likely impractical) alternative design with no need for a tail rotor, see [5] Lastly, google tells me rockets have been used to assist fixed-wing aircraft in takeoff. [6] [0] https://en.wikipedia.org/wiki/Tip_jet https://en.wikipedia.org/wiki/Tip_jet [1] https://en.wikipedia.org/wiki/Sikorsky_S-64_Skycrane https://en.wikipedia.org/wiki/Sikorsky_S-64_Skycrane [2] https://en.wikipedia.org/wiki/Kaman_K-MAX https://en.wikipedia.org/wiki/Kaman_K-MAX [3] https://en.wikipedia.org/wiki/Sikorsky_CH-53E_Super_Stallion#Specifications_(CH-53E) https://en.wikipedia.org/wiki/Sikorsky_CH-53E_Super_Stallion... [4] https://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectiveness https://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectivene... [5] https://youtu.be/0Z2Rr39hiUs https://youtu.be/0Z2Rr39hiUs [6] https://en.wikipedia.org/wiki/JATO https://en.wikipedia.org/wiki/JATO

Very interesting, thanks for this. Do you suppose a hybrid system might be useful in special applications, like providing a power boost to rescue helicopters trying to hover above mountains?

MaxBarraclough 6y ago

Rather beyond my knowledge but I'll take a stab at it: I don't think tip jets (the name for this design, oddly absent from the article) [0] are generally thought to be of practical value in modern helicopters. They have the neat advantage that they don't require a tail-rotor (the main rotor isn't driven by a drive shaft from the main body of the helicopter so there's no torque trouble) but I don't think they're all that practical. This article dates from 2010 after all. We already have a reliable means of increasing a helicopter's power: bigger engines. Alternatively, more engines. Heavy-lifting helicopters tend to be powered by twin turbine engines. [1][2] Even if they use unusual designs [2] the power-plant is the same as for any other serious helicopter. The enormous Super Stallion military helicopter went even further: 3 turbine engines! [3] I imagine a hybrid design would greatly increase complexity. Helicopters use a 'sprag clutch' to permit the rotor RPM to exceed the engine RPM, but not the other way around. This allows the rotor to keep spinning in case of an engine failure. (This is the reason helicopters don't drop like bricks when their engines fail.) Perhaps there would be a way to modify the design so that the conventional engine could still contribute power even as the rockets are firing, but I imagine it would be very high in complexity. Also, tail rotors can suffer if they aren't working in clean air, and of course this can threaten the helicopter's safety. [4] It's not something I know anything about but I imagine rockets on the main rotor could be troublesome in that regard. For yet another wacky (but likely impractical) alternative design with no need for a tail rotor, see [5] Lastly, google tells me rockets have been used to assist fixed-wing aircraft in takeoff. [6] [0] https://en.wikipedia.org/wiki/Tip_jet https://en.wikipedia.org/wiki/Tip_jet [1] https://en.wikipedia.org/wiki/Sikorsky_S-64_Skycrane https://en.wikipedia.org/wiki/Sikorsky_S-64_Skycrane [2] https://en.wikipedia.org/wiki/Kaman_K-MAX https://en.wikipedia.org/wiki/Kaman_K-MAX [3] https://en.wikipedia.org/wiki/Sikorsky_CH-53E_Super_Stallion#Specifications_(CH-53E) https://en.wikipedia.org/wiki/Sikorsky_CH-53E_Super_Stallion... [4] https://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectiveness https://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectivene... [5] https://youtu.be/0Z2Rr39hiUs https://youtu.be/0Z2Rr39hiUs [6] https://en.wikipedia.org/wiki/JATO https://en.wikipedia.org/wiki/JATO