3 ms·

Distilled: - Large rotors are more efficient than small rotors. - Because of the square-cube law, bigger, heavier aircraft require higher fuel energy densitie

Distilled: - Large rotors are more efficient than small rotors. - Because of the square-cube law, bigger, heavier aircraft require higher fuel energy densities than can be delivered by batteries. Therefore you need a relatively complex engine rather than simple motors, and you can't afford to replicate it four times. - A variety of handling and safety benefits of helicopters compared to quad rotors.

randallsquared 12y ago
As someone down the page mentions, hybrids seem like the obvious solution to this set of problems.
ObviousScience 12y ago
Trains require a HUGE engine, yet they relay their power via electrical linkage. This is actually more efficient than other systems, because it allows the engine to run at its optimum power generation cycle, without worrying about converting RPM down to the appropriate amount via mechanical linkage. An electrical linkage would be relatively straightforward to split in to 4 components.
- bdonlan 12y ago
  It's still a lot of weight to carry around a high-power generator, large-gauge power cables (or heavy transformers and smaller-gauge cables), and four electric motors. This is less of a problem on a train, because the train only has to deal with the additional friction, and doesn't have to worry about generating more lift to make up for the increased weight.
- dredmorbius 12y ago
  Being able to individually step wheels is also a big win -- if a given wheel starts to lose traction, it's much easier to cut electrical power than mechanical. Steel-wheel-on-steel-rail has fairly low static friction (which is why you find electrically-powered trains with many powered wheelsets, and virtually _all_ trains with track-sanding capabilities to increase traction).
IshKebab 12y ago
Most people are still missing the real reason, which is that quadrocopters vary thrust by changing the speed of the rotors. You can only do that with small rotors due to inertia, so with large rotors you'll need variable pitch to change the thrust. And if you have variable pitch you only need one rotor. The only exception to this is to have many small fixed pitch propellers, which has been done and is probably quite attractive from a price point of view, and to a certain extent safety (although you can't autogyro). But it is undoubtedly less efficient.

randallsquared 12y ago

As someone down the page mentions, hybrids seem like the obvious solution to this set of problems.

ObviousScience 12y ago

Trains require a HUGE engine, yet they relay their power via electrical linkage. This is actually more efficient than other systems, because it allows the engine to run at its optimum power generation cycle, without worrying about converting RPM down to the appropriate amount via mechanical linkage. An electrical linkage would be relatively straightforward to split in to 4 components.

bdonlan 12y ago
It's still a lot of weight to carry around a high-power generator, large-gauge power cables (or heavy transformers and smaller-gauge cables), and four electric motors. This is less of a problem on a train, because the train only has to deal with the additional friction, and doesn't have to worry about generating more lift to make up for the increased weight.
dredmorbius 12y ago
Being able to individually step wheels is also a big win -- if a given wheel starts to lose traction, it's much easier to cut electrical power than mechanical. Steel-wheel-on-steel-rail has fairly low static friction (which is why you find electrically-powered trains with many powered wheelsets, and virtually _all_ trains with track-sanding capabilities to increase traction).

IshKebab 12y ago

Most people are still missing the real reason, which is that quadrocopters vary thrust by changing the speed of the rotors. You can only do that with small rotors due to inertia, so with large rotors you'll need variable pitch to change the thrust. And if you have variable pitch you only need one rotor. The only exception to this is to have many small fixed pitch propellers, which has been done and is probably quite attractive from a price point of view, and to a certain extent safety (although you can't autogyro). But it is undoubtedly less efficient.