For the sake of a thought exercise let’s say Cold Fusion is finally unlocked, Yay mankind - free electricity. (just go with me on that alright? :D)
The vast majority of international air travel is conducted by aircraft using turbofan engines - ie they work by combining fuel and air and setting it on fire. (Gross oversimplification I know), but the essential point being that turbofans still require fuel to operate.
Even if, let’s say, we could create a small fusion reactor that could comfortably fit on a 767, so the aircraft can generate enough electricity for whatever it needs. Are there any other propulsion options out there that could be purely electrically driven, or would we see new passenger aircraft designs based on propellers?
Electrostatic propulsion is one option. One version of this is considered for space craft, but it can be done within the atmosphere. I don’t know if it would be very efficient. Plasma thrusters that generate air plasmas have also been considered. If you can generate enough heat from the fusion reactor then you can just make a hot air jet ramjet.
Well if some day we had fusion than air planes and space rockets will blur has every thing will have fusion reactor and the propellant would be plasma or ion .
The big thing why we don’t use plasma or ion drive is it does not have enough thrust to take any thing into space so can be only used in space.But with fusion reactor on craft you have enough heat for propellant of plasma or ion drive to take people and cargo into space.
Electric power has been practical for model aircraft for over a decade. I have seen some man-carrying self-launching gliders with electric power.
Batteries still have a long way to go with energy density though. Both of the cases above require only short duration power, and permit rather long charging times. Also, liquid fuels have an advantage that you burn them during the flight, and become lighter and more efficient. In some cases modern airliners take off with more fuel than they are permitted to land with. If they have to land early, they have to dump the fuel…not really practical to do that with batteries.
I worked on an aircraft that could fly weighing more than it could take off with! How was this possible? In-flight refueling on the F-111. As you mentioned, it had a fuel dump system for emergency landings.
The motors used in modern electric RC airplanes are already comparable if not better in power-to-weight ratio to the high bypass turbofan engines used on airliners. If you had a fusion power plant that was able to produce enough electric power to drive them, you could certainly make a large passenger aircraft that was electric powered. You wouldn’t even need to use propellers. Most of the thrust of a turbofan comes from the fan, the main job of the turbine is to make the fan turn. Replace the core turbine with a giant rare-earth brushless motor connected to your fusion plant, and you’ll have an electric-powered engine that looks mostly the same from the outside.
There might be some structural redesign involved. Modern planes spread the load of the fuel out along the wing spar. Your fusion plant is probably going to be a single large piece of heavily shielded machinery, which you’ll probably have to sit right on top of the wing spar in the middle of the plane for weight balance and structural reasons. On the other hand, you’re no longer having to worry as much about shaving every ounce off to save fuel costs.
What this technology might also do is make VTOL more practical. You know those little flying drones, the ones with 4-8 propellers in a ring and a camera or something underneath? They have horribly limited flight time due to battery limitations. There have been a few attempts to scale them up to be large enough to carry a person, and while it’s possible the severely limited range makes it impractical. If you can scale your fusion power plant down enough, you’ll make a new kind of personal transport aircraft possible.
If you are pushing yourself up by pushing air downwards, you are going to create a significant downdraft. It doesn’t matter if you’re doing it by propellers or by plasma thrusters, it’s just the unavoidable physics of it. To have a flying car without downdraft you’ll need some kind of magic antigravity system.
I have a book discussing ferrying small aircraft across the Atlantic and Pacific. It mentioned a special exemption to load up a small Cessna with extra fuel cans in the passenger seat(s) to fly from San Francisco to Honolulu, 2400 miles, the longest leg of the Pacific crossing. For some aircraft this was 25% over max gross weight -looooonnng runway for takeoff. Again, you probably want to burn off as much as you can if you have to land.
the question becomes somewhat similar if they ever go to hydrogen-powered jets. the ideal thermos jar for liquid hydrogen fuel would fill the fuselage over the wing spar (or under it?) rather than spread flat across a thin wing. Would also make for very chilly crashes.
A jet uses the expansion of burning fuel out the back to turn the turbine which compresses the incoming air; as mentioned above, presumably an electric engine would simply drive a few stages of progressive compression to produce a jet from motor-driven (ducted) fans. The compression would mean you don’t get the speed limitations of regular propellers.
IIRC too, NASA was experimenting with higher speed props with a dozen blades than looked like boomerangs, to help overcome the tyical speed limits of regular props.
That’s an interesting topic. Hydrogen already is a poor fuel for most types of aircraft. It doesn’t have as much energy by volume or weight as typical liquid fuels, and I think insulated containers would have to weigh more than non-cryogenic fuel tanks. It’s proposed for hypersonic flight because other fuels won’t burn as fast, but it might help turbine compressor efficiency through cooling. You’d already be at a disadvantage using hydrogen to power the typical airliner, so distributing tanks with high surface area to volume ratios around the plane would certainly make that worse. So you’re right that a crash scene might get very cold, but not for very long. It’s the huge fireball that follows that will get you.
Fusion does not directly generate electricity. It generates heat. Tremendous amounts of it. That heat is used to make steam to turn a turbine to turn a generator.
Depends on what kind of fusion, and how you capture the emitted energy. The easy types of fusion - D-D, D-T - generate mostly neutrons as energy output. Those you can’t do much more with than absorb with a blanket material and turn into heat. Some of the more difficult and exotic fusion reactions emit energy in the form of charged particles, and those you can decelerate through a series of grids to directly generate electrical power. Proton-Boron 11 fusion in particular produces three helium nuclei with about 14.7MeV of energy from each reaction. p-B11 fusion might well turn out to be technologically impossible, but if it could be somehow made to work would directly output DC electricity (at about 14.7 million volts!) from the collection grids.
If we’re dreaming of a fusion reactor small enough to put on an airplane, we might as well make it use advanced aneutrinic fusion. An airplane powered by a D-T reactor would probably be too radioactive for passengers anyway.
The US and Soviets both conducted research into aircraft powered by nuclear reactors in the 1950s (it was that sort of time). The Wikipedia article doesn’t really get into why the programs were canceled, but the general agreement is (1) they cost a lot for very little return, and (2) the risk of a plane carrying a reactor crashing was horrifying.