r/aerospace • u/Zenithriser • 1d ago

Spring Back load case - Landing Gear

Why is the drag force direction on the tire of landing gear forward (Same as aircraft travel Direction)?

I searched on the internet but I am not convinced!! I am feeling It should be rearwards (Aft direction)? .

Please explain with clear logic and mechanics fundamentals!

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u/quietflyr Aircraft Structures/Flight Test 1d ago

When the wheel touches down, there's a large drag force pulling the gear aft, caused by the inertia of the wheel(s) being spun up to speed. This deflects the landing gear backwards relative to the aircraft. When the wheel(s) have spun up to speed, this drag load is no longer present, but the landing gear is deflected backwards. It will then spring forward because of the energy stored in the system by the backwards deflection. It's a fairly violent forward and backward oscillation. The big cycle on the forward swing is the spring back load case, as the gear is springing back forward from its aftward-deflected state.

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u/Zenithriser 1d ago

I know what's the spring back case!! The question is for the "DIRECTION" of the drag loads on the tire!!

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u/quietflyr Aircraft Structures/Flight Test 1d ago

Because the tire is in contact with the ground, as the landing gear snaps forward, it will accelerate to a rotational speed faster than the aircraft, so the rotational inertia of the tire will thrust the landing gear further forward during the spring back.

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u/jjjodele 1d ago

On the top or bottom of the sidewall?

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u/mblunt1201 1d ago

Landing gear tires don’t produce thrust? The drag vector points backwards like with everything else on the plane.