Simviation Forum - Nose gear compression when braking..

May 6^th, 2007 at 10:25am

f-16 Offline
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Here is my problem. My nose gear tires sit correctly on the ground. But when I try braking after landing, the tires sink through the ground up to the wheel rim (But does not crash). I assume this is some sort of compression problem. Here is the contact point for the nose gear:

point.0 = 1.000, 76.500, 0.000, -17.50, 2181.102, 0.000, 1.541, 65.000, 1.100, 0.650, 0.550, 9.000, 9.000, 0.000, 280.000, 300.000

I am trying to figure out which "Compression" value I have to change. Or do I have to adjust the "Dampening ratio" value? I'm not sure which one to adjust so that the nose wheels do not sink up to the rim when braking. The mains are fine.

Thanks for your help.
Scott

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Reply #1 - May 6^th, 2007 at 1:26pm

SkyNoz Offline
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Here is a link, Cool

http://www.oregon-coast.net/Tutorials/Contact_Points/index.htm

Project Kfir!&&&&My Gmax page&&Aircraft modeler/Aircarft painter&&&&Aye the key!&&[GeneralEngineData]&&//0=Piston, 1=Jet, 2=None, 3=Helo-Turbine, 4=Rocket, 5=Turboprop

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Reply #2 - May 6^th, 2007 at 4:12pm

Brett_Henderson Offline
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If you mean.. that it doesn't "look" like it's compressing properly (and the tire/wheel goes into the ground).. that's usually because the longitudinal number is off. Run it through the grass (set weather for day/summer/clear) and see where the dirt kicks up from. I'll bet it's either in front of, or behind where the models nose-wheel is. Once you get that sorted out.. you can fine tune the compression.

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Reply #3 - May 12^th, 2007 at 12:21am

Milton Offline
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f-16 wrote on May 6^th, 2007 at 10:25am:

Here is my problem. My nose gear tires sit correctly on the ground. But when I try braking after landing, the tires sink through the ground up to the wheel rim (But does not crash). I assume this is some sort of compression problem. Here is the contact point for the nose gear:

point.0 = 1.000, 76.500, 0.000, -17.50, 2181.102, 0.000, 1.541, 65.000, 1.100, 0.650, 0.550, 9.000, 9.000, 0.000, 280.000, 300.000

I am trying to figure out which "Compression" value I have to change. Or do I have to adjust the "Dampening ratio" value? I'm not sure which one to adjust so that the nose wheels do not sink up to the rim when braking. The mains are fine.

Thanks for your help.
Scott

I hope that you have this issue sorted out by now, but, in case you do not, here are some things to check.

First, understand that the max-static ratio should never be less than one, and should usually be at least 1.5. Yours is too low at .650.

The total suspension movement is represented by the static compression plus the remaining possible compression represented by the max-static ratio. If you have static compression of 12" and 6" remaining, your ratio is 1.5. The sum of these two, 18", must equal the animated distance in the model. If not, the model and the contact points will not agree and you will have appearance problems with the suspension and wheels.

You can read my step-by-step graphic tutorial here:
http://www.sim-outhouse.com/sohforums/showthread.php?t=13564

Damping should usually be high for nose gear, like .8 to 1.0. Additionally, nose gear should only carry around 20-25% of the weight. If you CoG is too far forward, the nose gear suspension cannot support it and make for a flattened suspension, sinking nosewheel, a rough ride, or too much "bite" on the tarmac, not to mention difficulty in rotating for liftoff.

It is important to setup all your contact points using coordinates from the model's design program. Then you know you have them correct. And while you are doing that, you can also get the coordinates for all you lights, your eyepoint, your engine and smoke effects, etc.

I hope this helps.

Milton&&Dash 7, Aero Commanders, Howard 500, D18S, Spartan, XP47J, Beechcraft A28 (Grizzly)

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