Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

A helicopter's main rotor has blades that are $2.75$ meters long. If it rotates at $400$ rev/min, how fast is the tip of one of the blades moving in m/s?

share|improve this question

2 Answers 2

The velocity is a vector quantity given by $ \vec{v} = r \vec{\omega} $ in tangential direction.

Therefore, $ \vec{v} = 2.75 * 400 $ m/min $ = \frac{1100}{60} $ m/s $ = 18.33 $ m/s.

share|improve this answer

For clarity assume the helicopter is not moving.

Then the rotor tip travels in a circle. The circumference of that circle is $\pi$ times the diameter, that is, $2.75\pi$ metres. Thus in $1$ minute the rotor tip travels through $(2.75\pi)(400)$ metres.

If we want the speed in metres per second, divide by $60$.

share|improve this answer
    
Are helicopter blades measured hub-to-tip, or tip-to-tip? –  User58220 Mar 21 '13 at 2:57
    
I believe that for airplane blades, it is tip to tip. Don't know whether the same applies to helicopters. Assumed that it did. –  André Nicolas Mar 21 '13 at 3:04

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.