Although there isn’t any documentation yet of how the new ground contact model or new parameters work, I’ve noticed an issue I’d like to point out. The following test was conducted on the default Asobo A320NEO with the following lines added to the [FLIGHT TUNING] section of the flight_model.cfg:
ground_crosswind_effect_zero_speed = -1000; default = 5, -1000 means crosswind is never cancelled out
ground_crosswind_effect_max_speed = -1000; default = 80, -1000 means crosswind is never cancelled out
ground_new_contact_model_rolling_stickyness = 0.5; default = 1.0
ground_new_contact_model_up_to_speed_lateral = 1000.0 ; default = 0.1
ground_new_contact_model_up_to_speed_longitudinal = 1000.0 ; default = 1.0
ground_new_contact_model_gear_flex = 0.005 ; default = 0.0
ground_new_contact_model_gear_flex_damping = 5 ; default = 0.0
The new contact model with these parameters prevents skidding of the nose gear tires in the presence of a strong crosswind (at least up to about 35 knots crosswind) at low speed. WIth the previous ground contact model, the parameters to cancel the crosswind at low speeds must be used to prevent skidding of the nose wheel that results in the airplane weather vaning and moving in the direction of the wind, even with the nose gear tires being turned to the max steering angle. Here is an example of the skidding with the “old” ground contact model with no cancellation of the crosswind: Default A320NEO Crosswind turn on runway current MSFS 100% Crosswinds.mp4
With the default values for the cancellation of the crosswind at low speeds, this sliding of the nose tires does not occur.
With the new ground contact model and parameters set as above (including no cancellation of the crosswind at low speed), the nose wheel sliding does not occur, but another interesting issue come up. Once thrust is applied to get the airplane turning against the wind, if thrust is removed, the wind will cause the airplane to turn in the reverse direction. I don’t think 35 knots of wind should cause an A320neo to turn in the opposite direction from which it is attempting to turn.
This appears to be a mismatch between the rolling friction and the force or torque needed to cause the airplane to move/turn. If standing still (static friction), the wind does not cause the airplane to move/turn. Only when thrust is applied to start the airplane moving/turning does it end up turning in the opposite direction when thrust is removed.
Here is a video this effect showing the wind simvar values and the wheel debug window: Default A320NEO Crosswind turn on runway SU15 beta 100% Crosswinds.mp4
This can be countered by using the crosswind cancelling variables to cancel out the crosswind at low speeds, so the new ground contact model does not remove the need for this capability.
Is this a known characteristic of the new ground contact model, and is it intended?
Edit: It turns out this isn’t a totally new issue. It appears to be an existing issue that has changed form. What I mean is that previously, the airplane would weathervane into the wind by sliding the nose tires until the airplane is pointing into the wind and moving straight even though the nose tires are turned completely in one direction. For a turn against the wind (nose tires turned against the wind direction), when the wheel starts to skid, it does so in the opposite direction from which it is turned until the airplane is fully weather vaned. After that point, the airplane continues straight, skidding on the turned nose wheel.
With the rolling stickiness applied, the nose gear does not skid, so once the airplane is turning against the wind by applying thrust, once that thrust is removed, the airplane starts turning in the opposite direction that the nose wheels are turned and weather vanes without skidding the nose wheels.
I am unsure as to the exact cause and solution, but it is hard to believe that a 25 knot wind would cause an A320 to start turning in the opposite direction to which a turn was begun if the force used to turn the airplane (thrust) is reduced or removed.