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# Landing gear problem

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3 replies to this topic

### #1LM-Crashy  Members

Posted 24 January 2014 - 10:55 AM

Hi Gamedev !

First, I'm not accustomed with the english math and physics terms so I may use wrong words to describe things.

I'm trying to simulate a landing gear using raycast, springs and dampers. I've got almost everything working, except one little but annoying problem.

Basically here are the forces I have right now:

In red, the weight and in blue the suspension forces, arrow lengths are not reflecting real magnitude values ;)

Now my problem is that my aircraft rolls backward. I understand why because the suspension forces have an horizontal compound.

What I don't understand is what am I missing ? What happens in real life in such a situation ?

I've thought about static friction (or something like a rolling resistance) but this doesn't seems to be the correct answer to my problem.

Thanks for any help !

### #2glechapelain  Members

Posted 24 January 2014 - 03:32 PM

Your suspension force should be upward:
The force is the one of the gravity against the ground at your wheels.
If the ground is flat, your force is upward.

For it to be tilted you would have to be on a slope.

Only when you represent the reaction (retractation or expansion) of the suspension to the ground would you then multiply against the suspension axis.

### #3Buckeye  GDNet+

Posted 25 January 2014 - 09:55 AM

glechapelain is correct wtih regard to the forces applied to the body (fuselage) of the plane.

If you're simulating the landing gear and torques in addition to forces, note that there will be a clockwise torque on the landing gear which must be accounted for.

The torque on the landing gear is shown in red and is proportional to the upward (blue) force x the moment arm ("d"). A torque in the opposite direction will be applied to the body of the plane.

Please don't PM me with questions. Post them in the forums for everyone's benefit, and I can embarrass myself publicly.

You don't forget how to play when you grow old; you grow old when you forget how to play.

### #4LM-Crashy  Members

Posted 25 January 2014 - 10:14 AM

Thank you guys, I've changed the force direction, now it is the same as the "contact" normal, and it works like a charm.

The torque thing was already done

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