ORIGINAL: Flying freak
Q40 may already be breaking the sound barrier they really arnt that far from it and i havn't factored the speed of the aircraft.
Steven
When considering aircraft speed while calculating the actual tip speed use the formula below. The tip speed does go up with increasing aircraft speed but it is less then you might think.
The "helical" tip speed in flight Vtip is obtained by adding the airspeed V to the rotation tip speed Vr using the rule of vector addition.
Vtip = SQR( Vr ^ 2 + V ^ 2 )