Most modern helicopters have turbine engines.
Turbine engines eject lots of hot air.
All turbine engine inhale lots of air - from the immediate area - to state the obvious.
And helicopter main rotor blades agitate everybody's air.
Conclusion:
Depending on wind azmith, no matter how you design it, SOME of the ejected turbine engine air is gonna get into the engine inlet some of the time - which will cause higher Ng (N1) and T5 (T4.5, TOT, ITT, and FADEC problems, etc)
Get over it.
Last edited by oleary; 21st Feb 2013 at 06:15.