Eli5: Why is it so hard to get the same results, suchas thrust/speed, with an engine that delivers power to a propeller instead of a wheel?

299 viewsOtherPhysics

So I’ve seen a couple of scenarios where somebody changes the traction from their bike/motorcyle from the wheels to a propeller and they get awful results – such as not being able to match the speed they get normally, or the “force”.

If the engine is the same, and its able to develop certain power, why does it gets so inneficient when using a propeller?

Simple example: we have a bike and by pedalling we can reach very interesting speeds (40km/h perhaps or even more). But I’ve seen videos with guys pedalling moving a propeller instead of the wheel and they are diying to get the same results.

In: Physics

3 Answers

Anonymous 0 Comments

Because propellers aren’t as efficient as wheels.

The same amount of energy is going in but less of it is getting converted to what you want (thrust) and more of it is getting converted to what you don’t want (heat, noise, thrust in directions you can’t use).

This is pretty much inherent to how propellers work, but it gets worse (much much worse) if the propeller is small or if it’s going really fast. Wheels don’t really have that issue…they basically have the same efficiency within a *very* wide range of sizes and speeds.

You are viewing 1 out of 3 answers, click here to view all answers.