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

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:

1. while the main rotor is spinning at less than flight RPM, and nonrigid, that it may come in contact with the fuselage.
2. 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:

1. 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?

• You may include what you think are the limiting factors, in particular why you think this differ from flying at high speed. Apr 30, 2020 at 6:48
• Is it your intention to fly in a hurricane? The problem with wind speed limits is (typically) in going from 0 RPM to flight RPM as the engine begins to turn the rotor, before the stiffness of the CF loads are fully realized. The transitional rotor speeds can lead to some unusual rotor blade behavior during high and / or gusty winds, depending on wind direction. Taking off and landing is less of a problem because you can always point into the wind. Which leaves me with: what problem are you trying to solve with this question? We seem to be missing something. The question makes no sense. Apr 30, 2020 at 13:36
• For example of what is missing - what is the highest airspeed that your model of helicopter can fly at? (An R-22 has a lower max speed than an S-92, for example) Apr 30, 2020 at 13:40
• Thanks @KorvinStarmast - I do not have any particular helicopter in mind (and do not own a helicopter), but would like to understand the math and physics that correlate rotor speed during startup with maximum tolerable winds. I do not intend that any pilot would fly in hurricane force winds. However, if instead the vehicle were automated, I would like to know what helicopters would be theoretically capable of flying in hurricane force winds. Because takeoff wind speed is a greater limiting factor than high winds during flight, I am asking about the theoretical limits of takeoff wind speed.
– max
May 1, 2020 at 1:40
• @ManuH I originally did not include my guesses to avoid potentially biasing answers, but have now edited the question description to include them.
– max
May 1, 2020 at 15:53

## 1 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.