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.

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  • 1 decade ago
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    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
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