What methods are used for calculating maximum takeoff windspeed of a helicopter?

Question

I would like to calculate the maximum windspeed in which a helicopter may safely take off and safely land, assuming a theoretical wind environment with constant wind direction and no gusts.

I understand that Effective Translational Lift is generated when taking off into the wind, which increases the climb rate.

However, I would like to understand at what windspeed taking off and landing into the wind is theoretically no longer possible for a given main rotor RPM.

Some factors I have considered include:

while the main rotor is spinning at less than flight RPM, and nonrigid, that it may come in contact with the fuselage.
during takeoff or landing: if the vehicle must pitch forward to compensate for extremely strong headwinds while inches above the ground, the main rotor may strike the ground

While not relevant to the theoretical wind environment described above: if there are gusts, I have also considered:

during takeoff or landing: while hovering inches above the ground, a strong crosswind may roll the vehicle above a threshold which causes the main rotor to strike the ground.

What methods might I use to calculate these (and any other factors I have not considered) precisely?

Aaron Holmes · Answer

The simple (and probably unsatisfying) answer would be:
The maximum headwind into which a helicopter can land will be somewhat less than it’s listed maximum operating speed.
Flying at Vmo into a headwind of equal speed should lead to a stationary velocity relative to the ground. In theory, the aircraft could gently lower itself all the way the ground like this (although, I certainly wouldn’t try it). The problem is, most helicopters will be in a very pitch-forward attitude at this point and the skids or landing gear may not be in the proper orientation to safely put the aircraft on the ground. This will vary from model to model and would need to be tested on a case-by-case basis.
It should be noted that landing and shutting the engine down are 2 separate problems. Many helis have a maximum wind speed for startup/shutdown, like this BK117 which has a listed limit of 50 knots in its POH.

What methods are used for calculating maximum takeoff windspeed of a helicopter?

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