Originally Posted by
Ascend Charlie
...here is a gathering of Nick Lappos's Urban Myths, plus some notes from the late Shawn Coyle, both these gents being highly qualified test pilots:Helicopter Urban Myths
These Urban Myths pervade our understanding of helicopters and how they operate. Each is fundamentally incorrect, but most are generally held as gospel, because training, lore and reference documents have repeated them long enough that they are simply accepted.
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5) Winds affect the power we require when we are in forward flight...
At the risk of further "thread drift" from the original accident, I wanted to challenge this specific supposed 'myth'.
What was the original claim? Was it comparing identical helicopters achieving the same speed over the ground, one in still air, the others in a headwind or tailwind? Or was it comparing helicopters all achieving the same airspeed even if their ground speeds all differ? If the former, this wouldn't be a myth. If the latter, I would agree the statement is a myth. To elaborate for the case of constant ground speed:
* Helicopter A flying in still air at 110 knots ground speed hence airspeed also 110 knots. Resistance roughly proportional to velocity squared, so call this 100% resistance case.
* Helicopter B flying at 110 knots ground speed into 20 knot headwind, so airspeed 130 knots. Its resistance will be ~140% of Helicopter A.
* Helicopter C flying at 110 knots ground speed with 20 knot tailwind, so airspeed 90 knots. Its resistance will be ~67% of Helicopter A.
Power required from engine will be related to the combination of generating lift to support the helicopter and rotor thrust to overcome its resistance, so certainly changes. The differences in power demand are more stark the slower the helicopter ground speed and the higher the wind speed.
If I am wrong here, I would obviously like to be corrected.
I can't see an ideal solution for managing where discussions on SWP / VRS / LTE etc, etc, turn up. But I am learning regardless of which thread such exchanges appear in.