I'd imagine the props are sufficiently short as to allow the tips to remain subsonic. Maybe it's an aerodynamic improvement on the propellers themselves. Rounded tips cause less induced drag than square ones so it's a bonus really.
Also Flying INTO wind is better on take off because it increases the indicated airspeed.
In other words. if the aircraft is travelling up a north pointing runway at 80 knots and the wind speed is 80 knots in a southerly direction, the indicated air speed (IAS) will be 160 knots. If it can take off at 130 knots, then the aircraft could actually take off at the 80 knots it is actually travelling at (Ground speed)
Clearly if the opposite happens..i.e northerly wind of 80K and the aircraft is heading down a northerly runway, then it would have to take off at 210K (ground speed) which would be 130K (indicated air speed) I don't know how the engines react in this situation. I can't imagine them haing many problems with either.
(I don't know if that's what you were asking or whether you wanted information only on the engines.)
[This message has been edited by Ceppo (edited 02 August 2000).]