Hiya

My hat is off to the add-on providers here ..some of the work I have seen is as good as it gets. You guys have made MSFS fun for us airplane addicts

I have been havin problems with some of the add-on planes being a bit 'twitchy' and bouncing around while sitting stationary on various runways here an there ..even to the point of 'crashing' when they bounce to hard while taxiing.

I took one of the worst offenders, and have been wanderin thru the FS Edit program trying to smooth it out by changing wheel contact points so the wheels actually hit the ground where they are supposed to, the CG is actually where its supposed to be, and changed Max/Static damping ratios and all the other boxes in the Gear section to no avail so far.

I even thought it might be display settings/frame rate issues .. so I reduced the workload of the vid card a bit by reducing detail settings.. no change.

Plane still sits there, twitching.
I feel like I should poke it to make it stop
Once it gets up some speed the effect reduces ..with only an occasional massive bounce that catapults the plane into the air whether its ready to fly or not.

This happens on major metro runways and community municipal places. Forget about the little dirt strips here and there .. poor plane crashes through the ground more often than not just sitting there on the itty-bitty places.

My next trick is gonna be eliminating all the contact points except the landing gear only ..and gradually adding back scrape points .. perhaps one is not where it is supposed to be.

-Grayeagle
aka Frank P. Williamson (ex-actual 3d video game artist
type) -aka just another airplane nut

i had this same problem with the single nose gear of a bomber! the nose would bounce like a pogo stick! it would either bounce so high it would collape or flip over!
How big is your AC and whats the layout on the gear?

These issues can be resolved with a little effort and understanding.

First let me show you a technique I use when designing and setting up suspension.  I realize that if you do not have the mdl source files you cannot do this, but the technique once known will help understanding.

Basic steps to suspension setup can easily be accomplished with the design tool and cfg open.  

Before you start, ensure you have the aircraft properly positioned in your design program so that CoG/FS Reference are where you need them.  Example:
http://www.flightsimonline.com/tutorials/s0.JPG

The suspension setup steps are:
1.  Determine vertical distance from CoG/Ref point to ground.http://www.flightsimonline.com/tutorials/s1.JPG
2.  Determine suspension travel distance between frames 100 and 200 (total suspension travel)
http://www.flightsimonline.com/tutorials/s2.JPG
3.  Convert the vertical distance in meters to feet and update the cfg vertical distance.
http://www.flightsimonline.com/tutorials/s3.JPG
4.  Calculate static and max-to-static ratio and update cfg.
http://www.flightsimonline.com/tutorials/s4.JPG

Set the damping to your preference between .7 -1.0.
You may have to adjust vertical distance to ground by a tenth or so for proper tire-on-ground appearance.

Repeat the steps for the center gear.
When done, set static height and pitch so the aircraft tires are just a bit off the ground in slew mode, and drops gently when loaded.

Without gmax or FSDS source, what can you do?  

Well, you can use the navlight method to find where the CoG/Ref point(s) are, find where the contact points are saying the ground really is for each wheel, and from this you can reset the aircraft contact points using a basic method.

Bouncy, bouncy happens when the gear is too stiff.  That is, you have very little static compression (even at full gross weight) and a high value in max-static ratio.  That is like saying when at full gross, my suspension only compresses 2" of the available 10".  That is stiff suspension.

When your aircraft tire falls through the ground, the visual model is seeking the ground distance specified in the contact points (usually quite different from the visual model).

Setup a nav light in the Light section of the aircraft.cfg like this:
light.0=3,  13.00, 0.000,-8.100, fx_navred

Copy paste the contact point coordinates to the light statement.
point.0=1.0,  13.00, 0.000,-8.200, .........

Slew the aircraft up a bit so the light can be seen. (You may have to hit Y twice to get the gear to fully drop to hanging distance).  If you can't see the light, it may be inside the tire.  Adjust as necessary until you can see the light.
http://www.flightsimonline.com/tutorials/s5.JPG

Now, adjust the light so that it sits at the bottom of the tire tread (with light half embedded in the tire).  Now you have found the vertical "hanging" distance to ground for the contact point.  Plug this distance into the contact point statement. (where the -8.20 is shown in the example.)

Once you have the vertical distance to ground solved, you need to determine total suspension animation movement available to you for this aircraft.  Without that, it is purely guess work to get the suspension working near correctly.

We do this by "collapsing the suspension", that is getting total compression.  We use artificially high static compression to do this and make the max-to-static ratio = 1.  So, set the static compression to 2 or 3' and the ratio to 1.

Now you see the gear totally compressed.  Notice how far above the ground point light the tire is now.
http://www.flightsimonline.com/tutorials/s6.JPG

Now, using the nav light, adjust it so the light intersects the tire tread again at the bottom as you did earlier.  Once you accomplish this, you have distance to ground when gear is fully compressed.

Subtract this number from the earlier hanging distance to ground to get max animated suspension.  Now we have the number we need to set the suspension up correctly.

Now, go to step 4 in my earlier example above and set up your suspension to work just like it should have been done originally.  Use 75-80% of your total animated suspension distance for static compression.  i.e. total * .80 = static compression.

Then divide total animated distance by static compression to get the max-to-static ratio.

Set damping to your liking (typically .7 to 1.0).  Then set the static pitch to place the aircraft 2-4" above ground for slewing.  Set static pitch to level the aircraft wheels equi-distant from the ground in slew mode.

One last thing I do is change the .air file table entry for gear.
This may be overriden by the contact points but I'm not sure.
Table 1004 entries Main gear max spring load and center gear max spring load is computed to ensure accurate load calcs.

From Tom Goodrick's Flight Dynamic's:

Main Gear Spring Loading Factor = 2.72 * Gross weight
Main Gear Damping Factor = 0.34 * Gross Weight

Use 2.04 for center gear load factor and 0.24 for damping.

Hope this helps a bit.

#1 - Milton already gives free "clinics".  He frequently posts in this and other design forums, answering questions and pointing people - including other experts - in at least one direction.


#2 - Also - Get over the Jessy situation.  You're carrying too much of a chip on your shoulder for too long a time.  That matter was dealt with already.  That alone would be a reason to avoid working with you, no matter how good your vehicle FDEs are (and they are good!).

Quote:


It's better if the modeller and flight dynamics specialist work it out before release, rather than risk the modeller getting slammed for a "screwed up flight dynamics" or an "unfinished model".. etc.


Quote:

Ooo this could get really nasty, real fast .....

Just get a good Tree Doctor, chop out the bad wood, and if needed, get a Tree Stump Grinder.  Plant a new, solid oak tree, let it nurture and grow strong.