Mart [graviman]
"while rotational component of tip speed at cruise is
4.02m x ( 2pi x 360rpm / 60 ) = 152m/s (45% sound)
So if we let tip get up to 85% sound then machine can travel at
85% - 45% = 40% sound"
Check your algorithms. Do you not mean 2 x 4.02m x (pi x 360rpm / 60 )
_______________
"The limiting speed for X2 is likely to be from compressibility of the advancing tips."
Lets hope you are correct.
It appears that the limiting speed on the XH-59A was caused by the drag of the retreating blades. This high drag wanted to drive the rotors at a rotation speed faster then the engine was providing.
This appears to be the reason for the change in the X2's blade profile. They must now put up with the drag of the long 'spar' at the root of the blades, but they have eliminated the negative lift (and its drag) that was created by the reverse velocity causing a negative lift at the root of the XH-59A's retreating blades.
Dave