## Trending News

# physics: rotational motion?

The diameters of the main rotor and tail rotor of a single-engine helicopter are 7.63 m and 0.99 m, respectively. The respective rotational speeds are 459 rev/min and 4132 rev/min. Calculate the speeds of the tips of both rotors. Compare these speeds with the speed of sound, 343 m/s.

### 1 Answer

- 1 decade agoFavorite Answer
ok...

so, the first thing you want to do is turn those diameters into radii by dividing by 2

r(main rotor [MR]) = 3.815 m r(tail rotor [TR])= .495 m

now, convert rev/min of each into rad/sec. this is tricky, but this is what you do is multiply

1min/60secs to cancel the minutes

rot(MR) = 7.65 rev/sec rot(TR) = 68.87 rev/sec

next, you convert revs to radians by multiplying 2*Pii

angular speed of MR= 48.1rad/sec, TR= 432.7 rad/sec

finally, you multiply times their respective radii and you come up with

velocity of rotor tips (r*MR) = 183.37 m/s, (r*TR)= 214.19 m/s

Then compare it to 343m/s

Source(s): mechatronic engineer