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I would like to know what vertical descent rate a Huey or other helicopter with skids can land safely at. What would be considered a "hard" landing that would require air frame inspection? What would the descent rate be for a running landing? Thanks.

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  • $\begingroup$ You won't get a hard number and will only get opinions. In the end, a landing that doesn't bend anything permanently is fine. If you touchdown unusually hard, it'll be an airmanship issue for the pilot to decide what is "hard" and whether or not an inspection of the skids or some other structure is appropriate. I'd probably get out and look for bent skids with a touchdown more than 100 or 200 fpm, or whatever just felt rough. If you really do it hard, you will either collapse the skids, or chop the tail boom off and it won't require any judgement. $\endgroup$
    – John K
    Jan 21, 2021 at 23:44
  • $\begingroup$ The manufacturer should have some specifications on how hard a landing the gear can take, although that's also dependent on weight. A 100fpm descent with a full load is more force on the gear than a light load. $\endgroup$
    – GdD
    Jan 21, 2021 at 23:56
  • $\begingroup$ @JohnK the airframe is designed and manufactured to an ultimate descent rate, above which there will be deformations. $\endgroup$
    – Koyovis
    Aug 27, 2021 at 14:29

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I don't have descent rate numbers, but many years ago I trained on a Bell 206. In the engine/transmission compartment, I recall there being a spike which was attached to the drivetrain, the drive train having some freedom of movement within the compartment. As the drivetrain wiggled around, this spike would move with it, and there was a plate with an opening within which the spike moved. If there was a hard landing, the spike could contact the sides of the opening. This could leave a mark, deform and in extreme cases could even break off. I Googled and found a manual for the 206, it mentions the skids and crosstubes will deform at 2.5G of load. It also mentions if the cabin fuselage reaches the ground, it is considered to have sustained a 10G load. Link to the document: https://www.bellcustomer.com/Bulletins/Download?FileName=206AB-Inspection_and_Airworthiness_Limitations.pdf&CategoryID=139

Neat, I wouldn't have thought the manual for the 205 (aka Huey for the military version UH-1) was also available but it is: See page 95 for the information on hard landing. No specific descent rates mentioned, but rather procedures to check for specific types of damage are spelled out. https://www.bellcustomer.com/Bulletins/Download?filename=205A1-Inspection_and_Airworthiness_Limitations.pdf

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A particular issue is a hard landing in which one skid or wheel touches the ground first and the rotor has drag hinges. This can cause the blades to bunch up on one side of the rotor so it develops an asymmetry and starts to wobble. If the frequency of this wobble resonates with the eigenfrequency of the landing gear, ground resonance will develop. What follows can be watched here.

I would be less concerned about the sink rate and more about the symmetry of ground contact. To give only a single number is not sufficient for characterizing a safe landing.

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A descent rate of over 240'/min on landing is considered hard. It may damage the skids and is supposed to prompt an inspection of the skids before further use.

Touching down with a descent rate above 720'/min (at 16,700lb GW) risks damaging the airframe as well as the skids.

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    $\begingroup$ The precision in this answer is good, but could you include references as well? Possibly those values only apply to certain helicopters (such as the Huey), but I could see an argument that they're generic to all skids. $\endgroup$
    – Kenn Sebesta
    Jun 16, 2021 at 14:45
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In an EC135T1 you can "land" with around 1000ft/min and you should survive it according to Airbus. So this is not an opinion but a fact.

Source: Crash Safety Documents EC135T1 Airbus

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  • $\begingroup$ could you provide a link to said document? or is it not public? $\endgroup$
    – Federico
    Aug 27, 2021 at 9:33

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