I’d noticed the skidding values before in the flight models, but it’s not something I’ve ever experienced in the SIM. When we experience the exaggerated xwind effect it’s more like veering than skidding, if that makes sense? So the wheels are tracking…just not in the direction you want them to go!
Going to be interested to find out what the changes in SU12 are like. I tried the CJ4 with friction scalars set to 12 the other night. Now that started to really feel more like it. But there is still definitely some threshold where once you exceed a certain ground speed the vaning becomes suddenly much stronger.
It was the humble 172. Assuming for a moment that after you land, and you start to veer of course, the nose wheel has not turned in that direction, then I assume by definition that the wheel is being forced across the surface sideways, which sounds like a skid to me. The movement is not in the direction the wheel is facing.
Assuming you haven’t tinkered with the static friction for a given plane, and with a left crosswind you have left aileron, and right rudder, and the plane still turns to the left, I would imagine that skidding value would be a pretty solid 1 at that point.
All very good points. In an unmodded slippery aircraft,I usually notice the nose starting to point the wrong way as soon as the mains touch, even though I’m wing low, cross-control, for a xwind landing as you describe.
But you should be able to track using the variables for aircraft heading (the nose) and ground track (the wheels).
I dream of the day when runway contamination and variables is a thing in the sim
This is what I see just sat on the runway with the engine running. Lateral forces is jumping as high as 25% at idle, which drops a little bit if you apply full power with parking brake left on. Note the “isskidding” variable.
The simvar watcher doesn’t seem to be able to observe those values, but SPAD can. I set up a takeoff in the stormy weather preset. As predicted I got blown straight off the runway, but persisted with the takeoff just to see what would happen. This is what SPAD saw:
Each one of those changes detected will be where it wasn’t skidding, then was, then back again. So halve them to find the number of times it actually skidded.
This was with a 15kt crosswind in a 172.
Note that I’m keyboard flying here, but even so, with full right rudder its was impossible to stay on the runway in the default “Stormy” weather preset, at least until airflow over the rudder had increased. But by then I was scaring the ramp staff with a very high speed taxi on two wheels.
Tried again with very little throttle at all, and did slightly better. What’s interesting is the amount of skidding detected.
To bring this data list current, these are the current setting (03/21/2023) for he WB-SIM C172SP Enhancement (all model variants)
ground_crosswind_effect_max_speed = -1000 ; 135 // feet per second, default is 80
ground_crosswind_effect_zero_speed = -1000 ; 15 // feet per second, default is 5 ground_high_speed_steeringwheel_static_friction_scalar = 1.0
ground_high_speed_otherwheel_static_friction_scalar = 1.0
If anyone has any better suggestion for values (and why) I would be most eager to hear them
Note: one would assume the static friction, (at least), would be different in the SKI & Float Planes, depending on if wheels are up or down, but since they are set in stone in a .cfg file, it is difficult to see how they can be changed dynamically for wheel up/down conditions ?
If a consensus was found on what the friction would be wheels up, perhaps a script could set those values?
if wheels_up static_friction = 0.5
else static_friction = 1.5
Something like that.
Those values of 1.0 are the defaults according to the SDK. I guess one process to work through would be set up a crosswind to meet the max demonstrated for a 172, and increase those values until its actually possible to stay on or near the centre line.
Last time I played with the AS1000 172, before the config files were unlocked for the steam 172, I think I had to have them up to 8, but I think it would be worth going over that whole thing again once SU12 drops.
I know if you set them too high the plane will decrab itself. I think I tested that in either the Kodiak or Caravan. I set very high values for the main gear, and as soon as those wheels touched down, the planes nose swung around to land on the centre line. No rudder input was necessary.
Now that I think on that silly scenario, shouldn’t the plane have instead just gone straight in the direction the wheels were facing, if they had say infinite friction? Or not infinite exactly as I guess that would have stopped it dead, but infinite resistance to lateral forces.
Yes, I tried using that. But for some reason those values didn’t appear…but now that I think of it I suspect what I’m really seeing is the built-in database of simvars, and I am merely picking from that list. If it lets me hand type the ones that SPAD can see, as it does pull the list from the sim, then perhaps I can.
Thanks - once SU12 drops I will update Post 1 and create a properly formatted list (keep putting it off).
Re: better values. You make an important point and I’ll restate what I said in another thread. We need a common yardstick to judge what is a good value. For me the best test scenario is to use take-offs rather than landings (too many other things going on in a landing that may skew the results):
1)Clear weather preset with a pure crosswind set to maximum demonstrated crosswind
2) Spawn on runway with default payloads
3) Control devices and settings noted
4) All assistances disabled and external apps like FSRealistic turned off.
5) If a take-off roll can be executed to rotation and wheels up, with runway centreline maintained without significant deviation, with the pilot using correct crosswind control inputs then the value is good.
6) If significant deviation occurs - say more than 3 degees from centreline, or maximum rudder authority is required with crosswind speeds less than maximum, then the value is too low.
7) If no deviation occurs and no significant rudder authority required at MDC, then the value is too high.
Vars should always be set to -1000 (for full realism, use of default or other values on these two vars is in effect enabling a hidden assistance option like the other pilot assistance options). Tuning should be done only using the two lateral friction vars:
Users should only submit suggested values if they:
a) Have properly configured their controls and curves for the aircraft type
b) Understand and can execute proper cross-wind take-off technique for the aircraft type
c) Are prepared to tell other users what their control settings are and ideally provide supporting evidence in the form of a video.
Just submitting a random number for an aircraft with no supporting evidence is not helpful and may get flagged by me!
If others agree this is a sound testing regime then I will update post 1, and may even make a YouTube video showing how to test effectively.
From nothing more than a point of logic, would it make sense that the static friction value for the main gear should be higher than the nose gear because of weight distribution? I know this will shift as the CoG does, but still. Also, there are two main gear, which in itself should mean more friction compared to a lone nose wheel.
So perhaps setting both values the same is not realistic either.
Good point. The Kodiak has 9.8 for the main and 4.9 for the front - so SWS clearly applied the same reasoning. WT have however put all at 5 for the CJ4 - but they themselves have admitted this was deficient and we can expect to see new values in SU12 release.
Will be interesting to see if any more Asobo aircraft have been upgraded with sticky tires!
For an aircraft landing at a slight crab, inertial forces should pull it straight when you land as you describe, overcoming the lateral friction - the force vector is down the Centreline and the wheels will pivot to align with the vector.
I understand that airliners often do this a little, as their undercarriage can easily take the resultant cross-loading. But not smaller GA aircraft where a decrab using the rudder just before touchdown is necessary.
Missing inertia is something else in the physics, but it seems like you were getting the correct behaviour for the wrong reasons…
Yes, it felt like the wheels had landed in a trench, or onto train tracks, and the nose was vigorously pulled to align with my flight path. Face hitting the glass kind of speed.
