Abacus and Tom Goodrick put out a paper back in the FS98 days. Here is an excerpt regarding gear spring and damping that makes for an interesting read:
"9. LANDING GEAR DESIGN
Proper landing gear design is one of the most important things you can do using FDE.
Almost all aircraft converted from earlier versions of FS have poor landing
dynamics in FS98 because the conversion process does not properly set the landing gear parameters for spring constant and damping coefficient.
Evidently the FS designers made a significant change in the gear simulation and forgot to tell the aircraft designers. Even the original aircraft supplied with FS98 land poorly on stiff gear. This makes them bounce a lot. Curiously, the problem becomes worse the smoother the landing. Since all new designs must first be set up in the earlier version, FS5.1, and then converted to FS98, this is a big problem. For example, the XAS jet bounced so badly just taxiing, it could not be loaded without a crash. It could start parked with the engine off and it would rock fore and aft a lttle, then a lot and finally jump up and crash on its tail or nose!
Parameters
In FDEditor, someone identified two parameters, spring loading and damping, for the main gear and for the center gear. These parameters had been mis-identified in other editors. Shortly after seeing this listing of parameters, the author was able to fix all his hopping problems.
Though the mains only carry part of the static load, and during landing the wings are still contributing significant lift, the main gear springs are sized on the assumption they support the whole aircraft in a dynamic condition at landing. If they supported the entire aircraft in a static load, the force
would be W, the total landing weight of the aircraft.
But in a dynamic condition, we assume the springs are fully stretched and unloaded when the wheels touch.
Then the aircraft falls onto the springs which compresses them until their force has stopped the fall. In this motion problem the potential energy of the fall is W*z and the energy absorbed by the spring is 0.5*k*z^2 where z is the total compression.
Potential energy passing into the vehicle equals energy absorbed:
W*z = 0.5 * k* z^2 (k is the spring constant )
Define z1 where k * z1 = W, the static load deflection.
Then we find 2* W = W * z / z1 and 2 * z1 = z.
This means the dynamic load is twice the static load or 2*W since the deflection is twice the static deflection when the potential energy is absorbed. We can play safe, allowing for a little extra kinetic energy by
increasing the “spring loading” a little beyond twice the weight.
Flight Dynamics by Tom Goodrick
Stopping Hopping
Here’s the solution: First, figure the total weight by adding the fuel weight to the dry weight as found in the .air file. We’ll call that W. Then calculate and enter the following values in the Landing Gear Section of FDE:
Main Gear Spring Loading Factor = 2.72 * W
Main Gear Damping Factor = 0.34 * W
Center Gear Spring Loading Factor = 2.04 * W
Center Gear Damping Factor = 0.24 * W
You may want to adjust these values after trying some landings. However, these settings will be good enough for safe landings. These exact values were taken from the author’s Aerospatiale Trinidad.
Factors from a heavier jet are: 2.01, 0.34, 0.86 and 0.11 which are the values for the 35,000 lb Galaxy jet.
You have to watch for excessive compression or excessive stiffness. With excessive stiffness you will hear a series of strong chirps as the wheels barely touch the runway on a smooth landing. In bad cases the plane will bounce fore and aft or left and right (in roll) as the wheels chatter on the runway.
With these good values, any landing with touchdown velocity between 0 and -400 fpm will look and sound smooth.
