In an Embraer E170 at take off, there is only the faintest clue from the undercarriage that the wheels have left the ground.

In a Fokker F70, there is by contrast a loud mechanical "clonk" that can be heard and felt very distinctly.

What's different in the design of the undercarriage in these aircraft? And what's going on in the F70 that some component of the machinery is walloping around enough to produce such a noise?

  • $\begingroup$ Difference in hydraulic shock absorbers I would suppose. $\endgroup$ – SMS von der Tann Jul 20 '16 at 23:32
  • $\begingroup$ Can you proivde link to videos or sound records to illustrate the question? I cannot remember the sound of the undercarriage the last time I took a plane. $\endgroup$ – Manu H Jul 21 '16 at 10:53
  • $\begingroup$ @ManuH The Fokker's undercarriage sounds like a giant sprint being released. In fact it's not the only interesting noise it makes; when the engines are idling after a flight, they rattle like a huge metal box full of screwdrivers being shaken (I guess it's the slightly loose turbine blades). Sometimes passengers disembarking seem a bit startled when they realise where the racket's coming from. $\endgroup$ – Daniele Procida Jul 25 '16 at 18:24

Without hearing it I would imagine that what you are hearing is the landing gear reaching full extension and hitting it's mechanical limit. Think of it like one of those bicycle air pumps, and the sound it would make if you pull that handle all he way up. It's the same basic mechanism, except upside down, and the landing gear should be full of hydrolic fluid to support the force of the aircraft landing on it.

One aircraft has a mechanism that has a hard stop at the end of the stroke, and so you hear the extra forces being translated as that sound. The other aircraft has a softer end, so maybe there is a spring or rubber bumper pice or something that softens the end of the extension.

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    $\begingroup$ What is actually used is a pin of varying diameter inside the damper, so the resistance against movement (= damping) can be tailored along the stroke. I would expect the more modern aircraft uses this to decelerate the oleo strut extension near the maximum stroke. $\endgroup$ – Peter Kämpf Jul 21 '16 at 6:30

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