I wonder SpaceX Raptor engines could be cost-effectively used to make VTOL cargo planes. Three engines + a small fuel tank to service them should be enough for a single takeoff and landing and should fit within the existing fuselage. Obviously it would weigh a lot and cut down on cargo capacity, but maybe it’s still worth it? And you can still use the plane as a regular cargo plane when you have runways available, since the engines + empty tank don’t weigh that much.
[Googles a bit] OK so it looks like maximum thrust Raptors burn through propellant at 600kg/second. A C-17 Globemaster’s max cargo capacity is 77,000kg. So if you had three raptors (what, a ton each?) and were planning to burn two of them for 10 seconds to land, and two of them for 20 seconds to take off, you’d have about half your cargo capacity left! (Two raptors burning should provide almost twice as much thrust as a fully loaded C-17 weighs, if I’m reading Google facts correctly, so there should be plenty of acceleration and deceleration and ability to throttle up and down etc. I put in three raptors in case one breaks, just like SpaceX did with Starship.)
And when the tanks are empty, the engines+tanks would only use up a small fraction of cargo capacity, so the plane could still be used as a regular cargo plane when airstrips are available.
Good point. Probably even if you land in a parking lot there’d be pebbles and stuff shooting around like bullets. And if you land in dirt, the underside of the vehicle would be torn up as if by shrapnel. Whereas with helicopters the rotor wash is distributed much more widely and thus has less deadly effects.
I suppose it would still work for aircraft carriers though maybe? And more generally for surfaces that your ground crew can scrub clean before you arrive?
The problem isn’t in the power of the engine at all. The problem historically (pre-computers) has been precisely controlling the motion of the decent given the kinetic energy in the vehicle itself. When the flying vehicle is high in the air traveling at high speeds, it has a huge amount of kinetic and potential (gravitational) energy. By the time the vehicle is at ground level, that energy is either all in kinetic energy (which means the vehicle is moving dangerously fast) or the energy has to be dissipated somehow, usually by wastefully running the engine in reverse. The Falcon 9 is solving this problem in glorious fashion, so we know it’s possible. (They have the benefit of computers, which the original VTOL designers didn’t.) Read the book Where is my Flying Car?
Well if the Falcon 9 and Starship can do it, why can’t a cargo plane? It’s maybe a somewhat more complicated structure, but maybe that just means you need a bigger computer + more rounds of testing (and crashed prototypes) before you get it working.
My guess is that we don’t have passenger or cargo VTOL airplanes because they would use more energy than the airplanes we use now.
It can be worth the extra energy cost in warplanes since it allows the warplanes to operate from ships smaller than the US’s supercarriers and to keep on operating despite the common military tactic of destroying the enemy’s runways.
Why do I guess that VTOLs would use more energy? (1) Because hovering expends energy at a higher rate than normal flying. (2) Because the thrust-to-weight ratio of a modern airliner is about .25 and of course to hover you need to get that above 1, which means more powerful gas-turbine engines, which means heavier gas-turbine engines, which means the plane gets heavier and consequently less energy efficient.
Being able to land airplanes outside of formal airports would be valuable for civilian aircraft as well. I would however expect that you can’t legally do that with VTOL airplanes in most Western countries.
I wonder SpaceX Raptor engines could be cost-effectively used to make VTOL cargo planes. Three engines + a small fuel tank to service them should be enough for a single takeoff and landing and should fit within the existing fuselage. Obviously it would weigh a lot and cut down on cargo capacity, but maybe it’s still worth it? And you can still use the plane as a regular cargo plane when you have runways available, since the engines + empty tank don’t weigh that much.
[Googles a bit] OK so it looks like maximum thrust Raptors burn through propellant at 600kg/second. A C-17 Globemaster’s max cargo capacity is 77,000kg. So if you had three raptors (what, a ton each?) and were planning to burn two of them for 10 seconds to land, and two of them for 20 seconds to take off, you’d have about half your cargo capacity left! (Two raptors burning should provide almost twice as much thrust as a fully loaded C-17 weighs, if I’m reading Google facts correctly, so there should be plenty of acceleration and deceleration and ability to throttle up and down etc. I put in three raptors in case one breaks, just like SpaceX did with Starship.)
And when the tanks are empty, the engines+tanks would only use up a small fraction of cargo capacity, so the plane could still be used as a regular cargo plane when airstrips are available.
My understanding is that VTOL is not limited by engine power, but by the complexity and safety problems with landing.
Good point. Probably even if you land in a parking lot there’d be pebbles and stuff shooting around like bullets. And if you land in dirt, the underside of the vehicle would be torn up as if by shrapnel. Whereas with helicopters the rotor wash is distributed much more widely and thus has less deadly effects.
I suppose it would still work for aircraft carriers though maybe? And more generally for surfaces that your ground crew can scrub clean before you arrive?
The problem isn’t in the power of the engine at all. The problem historically (pre-computers) has been precisely controlling the motion of the decent given the kinetic energy in the vehicle itself. When the flying vehicle is high in the air traveling at high speeds, it has a huge amount of kinetic and potential (gravitational) energy. By the time the vehicle is at ground level, that energy is either all in kinetic energy (which means the vehicle is moving dangerously fast) or the energy has to be dissipated somehow, usually by wastefully running the engine in reverse. The Falcon 9 is solving this problem in glorious fashion, so we know it’s possible. (They have the benefit of computers, which the original VTOL designers didn’t.) Read the book Where is my Flying Car?
Well if the Falcon 9 and Starship can do it, why can’t a cargo plane? It’s maybe a somewhat more complicated structure, but maybe that just means you need a bigger computer + more rounds of testing (and crashed prototypes) before you get it working.
Yeah, to be honest I’m not sure why we don’t have passenger VTOLs yet. I blame safetism.
My guess is that we don’t have passenger or cargo VTOL airplanes because they would use more energy than the airplanes we use now.
It can be worth the extra energy cost in warplanes since it allows the warplanes to operate from ships smaller than the US’s supercarriers and to keep on operating despite the common military tactic of destroying the enemy’s runways.
Why do I guess that VTOLs would use more energy? (1) Because hovering expends energy at a higher rate than normal flying. (2) Because the thrust-to-weight ratio of a modern airliner is about .25 and of course to hover you need to get that above 1, which means more powerful gas-turbine engines, which means heavier gas-turbine engines, which means the plane gets heavier and consequently less energy efficient.
Being able to land airplanes outside of formal airports would be valuable for civilian aircraft as well. I would however expect that you can’t legally do that with VTOL airplanes in most Western countries.