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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?

max
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  • You may include what you think are the limiting factors, in particular why you think this differ from flying at high speed. – Manu H Apr 30 '20 at 06:48
  • 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. – KorvinStarmast Apr 30 '20 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) – KorvinStarmast Apr 30 '20 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 01 '20 at 01:40
  • @ManuH - possibly 1) during takeoff: 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 3) 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. Are you aware of methods for calculating these factors precisely? – max May 01 '20 at 01:54
  • @max, you should include those information in the question description. – Manu H May 01 '20 at 09:33
  • Max, you don't seem to have done enough research during takeoff: while the main rotor is spinning at less than flight RPM That is not correct. Helicopters go from engines off to flight RPM before they get off the ground. You get to flight RPM, then you leave the ground. – KorvinStarmast May 01 '20 at 12:44
  • @KorvinStarmast my apologies, "during takeoff" is superfluous (and incorrect) to the core statement, which could begin with "while the main rotor is spinning at less than flight RPM...". I was referring to the broader takeoff sequence of events, as compared with landing, and do understand the main rotor must reach flight RPM prior to the vehicle departing the ground. – max May 01 '20 at 15:46
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    @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 01 '20 at 15:53
  • @max including your current state of research helps us adapt the answers and if needed help you bring new elements to precise your question. – Manu H May 01 '20 at 15:56
  • "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" Why would the helicopter have to pitch forward? Usually you would just pitch the blade disc forward and there's no way it could come into contact with the ground (unless you were up against a hill)... – Ron Beyer May 01 '20 at 16:15
  • @RonBeyer -- the quote said "while inches above the ground", not while still on the ground. Is there not a tendency for the fuselage to tilt along with the rotor disk? See for example concepts in this related answer -- https://aviation.stackexchange.com/a/38904/34686 . It seems to me that there would indeed be some wind speed above which a helicopter could not hover inches above the ground without the rotor disk striking the ground. – quiet flyer May 01 '20 at 17:44
  • @max I'm guessing that in reality, by the time the wind is strong enough that even if it were 100% steady, take-off would be theoretically impossible for any of the reasons you suggest, any real-world wind would involve so much gustiness that no one in their right mind would even consider taking off or landing. May not always be true though, for example in stable marine air over cold ocean water, such as might be found at on oil platform landing site. Just a thought. Good questions though in my opinion. Perhaps could be improved by specifying a steady wind completely free of gusts? – quiet flyer May 01 '20 at 17:58
  • Max, have you ever flown a helicopter? If I were to be Flying directly into a 70 knot head wind I'd be almost level with the ground, pitch attitude wise, in the five helicopter models I can think of off the top of my head. Landing would be no problem at all. The harder thing would be trying to do pedal turns or sidewards flight. Most helicopters I am familiar with would not handle that well or at all. And then, as we turned off the engines and the rotors slowed down, I'd be looking at my manual and the limitations therein I'd wonder "uh, what happens next?" as I'd be outside of limits. – KorvinStarmast May 01 '20 at 19:30
  • Thanks @quietflyer - I have updated the question description to include clarify a theoretical wind environment without gusts. – max May 02 '20 at 17:50

1 Answers1

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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.

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Aaron Holmes
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