Re: How do rotor lengths affect how quickly a paper helicopter spins?

Hi Georgia,

That's a great observation you made!

There are a couple of reasons why smaller diameter rotors spin faster. The
first, and more dominant, is that smaller diameter rotors produce less
thrust for a given rotation rate. That means the smaller diameter rotor
must spin faster to produce the same thrust. This is more formally
described by momentum theory and blade element theory.

The second effect, which is not as great, is that smaller diameter rotors
have a smaller surface area, so their drag is lower.

madhu.com - blog