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Old 24th Nov 2019, 20:43
  #24 (permalink)  
JimEli
 
Join Date: Dec 2006
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IMHO, best case would have the 2 Apaches at flat pitch creating some possible turbulence in the immediate area downwind of them. Worst case, with the Apaches holding near taxi power (20-24% Q as recommended by the RFM), they would be producing ~16 mph of turbulent wind (see analysis below). Ultimately, it’s always left to the PIC to accept or decline a clearance.

Assume 75% power to hover and using 24% for taxi = ~1/3 of hover thrust. Assuming a GWt of 15000, means each Apache would create about 4950 lbs. of thrust. Therefore, the downwash velocity (at the disc) is SQRT((GWt)/(DA*2*rho)), or SQRT(4950/1809*2*0.002378), at SL. So, each Apache is making 24 f/s, or 16mph of wind.
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