3 ms·

I wonder how this equation would apply for electrical planes. And whether it could be useful to carry some water as fuel-mass (like in your saturn motor exampl

I wonder how this equation would apply for electrical planes. And whether it could be useful to carry some water as fuel-mass (like in your saturn motor example) that would be ejected via the use the electrical motor to convert more efficiently the energy that is stored in the batteries into the momentum needed to make the plane go forward. The other day I saw the TechIngredients video about afterburner https://www.youtube.com/watch?v=EP4Hf63zR6w https://www.youtube.com/watch?v=EP4Hf63zR6w that I found interesting. Edit: The wikipedia page about specific impulse https://en.wikipedia.org/wiki/Specific_impulse https://en.wikipedia.org/wiki/Specific_impulse and in particular its graph https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Specific-impulse-kk-20090105.png/1050px-Specific-impulse-kk-20090105.png https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Sp... helped me quantify the importance of air in the propulsion efficiency of a jet engine with respect to a rocket engine.

Gravityloss 4y ago
The kerosene plane is lighter towards the end of the flight, while the electric one's mass doesn't change. For rockets, there's Rocket Lab's Electron that uses electric pumps to pump the regular propellants to the combustion chamber. This was much easier to develop than a turbine for the turbopump. It drops some spent batteries along its flight. Could an electric airplane drop batteries at certain points? Like after climbing to target altitude. A lot of operational headaches there, so not likely. There have been some military planes that have used takeoff trolleys or takeoff rockets so there is some precedence there. Rocket engines are extremely inefficient, they just have to be used because of the very wide speed range they support. So it wouldn't really make sense to eject water with an electric pump. Batteries have such low energy density and the pumps are heavy too. It's the worst combination to carry your own reaction mass and propel it with battery stored energy! A rocket engine has tremendous trust to weight and power density, it can be gigawatts in a car sized package. This is enabled by the very energy dense liquid fuel and liquid oxidizer. Even a jet engine pales in comparison, as it has to use gaseous air as oxidizer which is not dense, and which is 80% "fluff" nitrogen. Hence the jet engine compressors have to be large, and the compression ratios are meager 10 to 20 bars. A rocket engine can run at 200 bars main chamber pressure. The compressors (pumps) can operate at hundreds of megawatts (this is actually not far from big jet engines). The thrust to weight ratio can be 100 to 1, while for jets it's 10 to 1.
- GistNoesis 4y ago
  Hopefully Sam Altman's Helion will pan-out and we will have fusion to have better energy density so that I can have my water propelled plane. https://en.wikipedia.org/wiki/Nuclear_thermal_rocket#/media/File:Nuclear_thermal_rocket_en.svg https://en.wikipedia.org/wiki/Nuclear_thermal_rocket#/media/... Until then we have to stay tethered to the sea with something like Zapata's Flyride / Flyboard https://www.youtube.com/watch?v=PCAvIHGylKo https://www.youtube.com/watch?v=PCAvIHGylKo Edit : (We just have to put an electric jetski inside a fire-fighting plane, and have the Flyride pull the plane forward until it reach lift-off speed, (no expensive fuel needed :) )

Gravityloss 4y ago

The kerosene plane is lighter towards the end of the flight, while the electric one's mass doesn't change. For rockets, there's Rocket Lab's Electron that uses electric pumps to pump the regular propellants to the combustion chamber. This was much easier to develop than a turbine for the turbopump. It drops some spent batteries along its flight. Could an electric airplane drop batteries at certain points? Like after climbing to target altitude. A lot of operational headaches there, so not likely. There have been some military planes that have used takeoff trolleys or takeoff rockets so there is some precedence there. Rocket engines are extremely inefficient, they just have to be used because of the very wide speed range they support. So it wouldn't really make sense to eject water with an electric pump. Batteries have such low energy density and the pumps are heavy too. It's the worst combination to carry your own reaction mass and propel it with battery stored energy! A rocket engine has tremendous trust to weight and power density, it can be gigawatts in a car sized package. This is enabled by the very energy dense liquid fuel and liquid oxidizer. Even a jet engine pales in comparison, as it has to use gaseous air as oxidizer which is not dense, and which is 80% "fluff" nitrogen. Hence the jet engine compressors have to be large, and the compression ratios are meager 10 to 20 bars. A rocket engine can run at 200 bars main chamber pressure. The compressors (pumps) can operate at hundreds of megawatts (this is actually not far from big jet engines). The thrust to weight ratio can be 100 to 1, while for jets it's 10 to 1.

GistNoesis 4y ago
Hopefully Sam Altman's Helion will pan-out and we will have fusion to have better energy density so that I can have my water propelled plane. https://en.wikipedia.org/wiki/Nuclear_thermal_rocket#/media/File:Nuclear_thermal_rocket_en.svg https://en.wikipedia.org/wiki/Nuclear_thermal_rocket#/media/... Until then we have to stay tethered to the sea with something like Zapata's Flyride / Flyboard https://www.youtube.com/watch?v=PCAvIHGylKo https://www.youtube.com/watch?v=PCAvIHGylKo Edit : (We just have to put an electric jetski inside a fire-fighting plane, and have the Flyride pull the plane forward until it reach lift-off speed, (no expensive fuel needed :) )