3 ms·

Honestly makes a lot of sense. Might be possible do do it as a ram jet too, that would get you a lot of efficiency upsides. Typical jet engines probably would

Honestly makes a lot of sense. Might be possible do do it as a ram jet too, that would get you a lot of efficiency upsides. Typical jet engines probably wouldn't work well however due to force but you get a fuel feed upside from the centrifugal force.

mnw21cam 6y ago
Ramjets work at supersonic airflow speeds. You really don't want your helicopter blade tips going supersonic.
- deleted 6y ago
  [deleted]
- AgloeDreams 6y ago
  Wouldn't it be possible to use a subsonic inlet but design the intake to allow for air to become super sonic in the flow?
- checker 6y ago
  Fair warning, this is probably a ridiculous idea because I'm nothing close to a mechanical/aerospace engineer. Would it be possible to mount the ramjets to a ring around the blades along with some sort of transmission in the ring? I'm thinking setup this would allow the ramjets to function supersonically at the edge of the structure to ensure the best airflow and limit the speed of the blades. However such a transmission might be overly complex or heavy and it's possible that the ring around the blades would cause some weird aerodynamic effects. Thanks for obliging my curiosity!
- chipsa 6y ago
  Ramjets do not require supersonic flow speeds. They require positive speed (they don't work at a standstill), and are usually tuned for a sweet spot. This is usually supersonic because most applications are military, where the supersonic capability is desired. That said,they usually don't produce much thrust until you get over M0.5.
jeffreyrogers 6y ago
There was a helicopter that used a ram jet IIRC. I guess the only problem there is you need a separate starter motor to get the rotor spinning fast enough for the ramjet to take over, but most helicopters have electric starters anyways. Edit: Here's one https://en.wikipedia.org/wiki/NHI_H-3_Kolibrie https://en.wikipedia.org/wiki/NHI_H-3_Kolibrie
GlenTheMachine 6y ago
One of the major issues with helicopter design is that the effective speed of the rotor tips vary by twice the forward speed of the helicopter as it swings around from back to front to back again. The rotor going from back to front experiences a speed that is the tip speed due to rotation plus the forward speed of the helicopter. As it swings around to the front and then towards the back it experiences a speed that is the speed of the tip due to rotation minus the forward speed of the helicopter. So if your helicopter is going at 200 mph and your rotors - which have been noted here several times need to stay below the speed of sound - are going at say 400 mph at the tip, then the rotor tip speed varies from 200 mph to 600 mph on every single rotation. It’s hard (for me) to imagine an air-breathing engine that could operate efficiently with its intake air speed changing that much that frequently. Much less a ramjet which has no turbines or anything to even out the intake velocity and which normally wants to operate well above the speed of sound.
stmw 6y ago
See my comment re: Hiller Aircraft

mnw21cam 6y ago

Ramjets work at supersonic airflow speeds. You really don't want your helicopter blade tips going supersonic.

deleted 6y ago
[deleted]
AgloeDreams 6y ago
Wouldn't it be possible to use a subsonic inlet but design the intake to allow for air to become super sonic in the flow?
checker 6y ago
Fair warning, this is probably a ridiculous idea because I'm nothing close to a mechanical/aerospace engineer. Would it be possible to mount the ramjets to a ring around the blades along with some sort of transmission in the ring? I'm thinking setup this would allow the ramjets to function supersonically at the edge of the structure to ensure the best airflow and limit the speed of the blades. However such a transmission might be overly complex or heavy and it's possible that the ring around the blades would cause some weird aerodynamic effects. Thanks for obliging my curiosity!
chipsa 6y ago
Ramjets do not require supersonic flow speeds. They require positive speed (they don't work at a standstill), and are usually tuned for a sweet spot. This is usually supersonic because most applications are military, where the supersonic capability is desired. That said,they usually don't produce much thrust until you get over M0.5.

jeffreyrogers 6y ago

There was a helicopter that used a ram jet IIRC. I guess the only problem there is you need a separate starter motor to get the rotor spinning fast enough for the ramjet to take over, but most helicopters have electric starters anyways. Edit: Here's one https://en.wikipedia.org/wiki/NHI_H-3_Kolibrie https://en.wikipedia.org/wiki/NHI_H-3_Kolibrie

GlenTheMachine 6y ago

One of the major issues with helicopter design is that the effective speed of the rotor tips vary by twice the forward speed of the helicopter as it swings around from back to front to back again. The rotor going from back to front experiences a speed that is the tip speed due to rotation plus the forward speed of the helicopter. As it swings around to the front and then towards the back it experiences a speed that is the speed of the tip due to rotation minus the forward speed of the helicopter. So if your helicopter is going at 200 mph and your rotors - which have been noted here several times need to stay below the speed of sound - are going at say 400 mph at the tip, then the rotor tip speed varies from 200 mph to 600 mph on every single rotation. It’s hard (for me) to imagine an air-breathing engine that could operate efficiently with its intake air speed changing that much that frequently. Much less a ramjet which has no turbines or anything to even out the intake velocity and which normally wants to operate well above the speed of sound.

stmw 6y ago

See my comment re: Hiller Aircraft