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Lateral Friction. skidding, when moving on Ground

Geoff_D

Geoff_D

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unitedstates
During Taxi, or during takeoff/landing, when on the ground, the "Lateral Friction" between wheels and the ground surrface seem to be unrealistically low.

Even on dry tarmac or Concrete, if there is any crosswind, the plane tends to slide ACROSS the runway, as if on ice, and does not follow the wheel directions, as expected.

IS there any way to adjust this "lateral friction" between the wheels and the ground surface. ?

Depending on how this is modeled in FSX, either in the Plane's model, or maybe, more ideally, for individual surfaces.

I would have expected different surfaces have different Friction Values ?
If so, is there any way a user can alter that, to make this modeling more realistic. ??

At the monent, it seems like all FSX aircraft have very worn tyres, with no tread, and very little ability to keep the plane on track with the wheel heading, especially in a crosswind situation, or when turning shaply when in the taxi.

It's most unrealistic.

Fingers crossed !!

Geoff
 
Lateral friction

Geoff,
Unless you are seeing this with every FS airplane, you might want to look at your contact point values. Under some conditions the tires are continually reacting with the surface (hopping) and this certainly reduces their braking power and would also reduce lateral friction. For instance it you get more or less continuous smoke from wheels on landing they are making numerous contacts, in between which they are in the air. I have one aircraft that moves in azimuth with parking brakes on and I'm sure the wheels are hopping. Not got round to fixing it yet. Another thing to check is whether fuel load makes any difference.

Best way to see the effect is to operate the aircraft as an AI because then any bad contact point values really show up. I had one airplane which positively quivered when active but parked and once it started taxying it performed amazing gymnastics, leaped into the air, did back flips and then buried itself underground. I fixed it by increasing the static compression in stages and put the damping at around 0.95.

Different surfaces do have different frictions.

Just think that since the contact points are what governs the airplane/surface interface, that they could be the key to improving the lateral friction.

Roy
 
Geoff_D said:
... IS there any way to adjust this "lateral friction" between the wheels and the ground surface. ?
.....
Click to expand...

Yes and no.
Yes, the values for roll, braking and skid friction on 25 different surface types are stored in the SIM1.DLL
And no, because if you edit this file you will change the ground behavior for all your planes. And people who use your aircraft have to edit the own SIM1.DLL too. Furthermore there is no editor for the SIM1.DLL and you have to edit it manually with an hex editor.

Yves Guillaume, the guy who discovered all this, had written a tutorial about it, but I have no link to it.
 
sergio said:
Yes and no.
Yes, the values for roll, braking and skid friction on 25 different surface types are stored in the SIM1.DLL
And no, because if you edit this file you will change the ground behavior for all your planes. And people who use your aircraft have to edit the own SIM1.DLL too. Furthermore there is no editor for the SIM1.DLL and you have to edit it manually with an hex editor.

Yves Guillaume, the guy who discovered all this, had written a tutorial about it, but I have no link to it.
Click to expand...

Anyone got the link -- I would like to read what Yves had to say.

OK, so lets "ASSUME" the values in the dll are correct and approprate.

Then, from what I am hearing, for Individual planes, there is some adjustment in the "Contact Points" that can make these Frictions LESS, and thus give the effect of excessive skidding.

So, is there a process to adjust these contact point values, to arrive at Optimum (maximum) Friction, short of a continual tweeking and testing, that is both time consuming and frustrating.

ie. Assuming (again) there is an Optimum value to set in the Contact Points, is there a definitive procedure to arrive at that "optimum" value.

Then, having got these values Optimized for planes, if the resulting Frictions are incorrect, I guess one can start looking at a correction for ALL planes in the dll, but that would oviously be on a "per system" basis.

For example, the Default C172, It's taxxing performace on a dry runway, seems to be very "slippery" (for want of a better word). It "feels" like one is taxiing on ICE. Certainly not like any REAL C172 I have ever taxied on dry Concrete or Tarmac.

If there was a way to at least fix this for MY system, I would welcome the opportunity.

Geoff
 
C 172 taxying

Geoff,
A good test of lateral friction is to put on full rudder and about half throttle then full brake. Do it in front of the tower in tower view.

Tried this in the FSX C172 and managed to tip it over on its wingtip after doing several tight circles. No lack of lateral friction there! Not flown a 172, but have flown similar single pistons and the FS C172 seemed real to me from its ground handling perspective. The tail wheel airplanes seem a little over enthousiastic to ground loop, though their differential braking is realistic, but the nose wheel airplanes simulation is hard to fault.

I have several FS models with narrow track, Spitfire, TA-7C, F-104G and I have to be very careful when turning hard during fast taxying or they will tip over, which says the lateral friction is OK or even too high.

In my last, I mentioned that contact point performance in an AI airplane shows up faults you do not normally see. The C172 as AI is faultless, so it is nothing to do with contact points. The Extra 300 is a joke, bounces continually when landing and takes forever to stop.

So I am not finding the same issues you have. What else is there? Perhaps it is your rudder control system? I have a Saitek X52 Pro, I have set all deadbands to zero and get immediate response in yaw. Rudder deadbands will give an impression that nothing is happening as far as turning on the ground is concerned.

You did mention flying in crosswinds and that may be the issue. Any "wind" setting in FS causes abnormal behaviour if the sim thinks it should cause windshear. I have found it sometimes impossible to land in FS at Roanoke because it is surrounded by mountains and you get violent changes in roll (simulated windshear) just before landing. Moved 40 nm NE to Lynchburg where it is flatter and the problem went away. Usually fly from TNCM and when passing over the ridge east of the airfield I always had uncommanded inputs. I have also noticed that flying fast and low in autopilot near mountains will often cause violent departures beyond the capabilities of the autopilot to handle (causes crashes). I made a gauge that showed me ACCELERATION BODY X, Y, Z data and they went bananas when I was experiencing departure symptoms. Means the sim is injecting uncommanded flight control inputs.

To fix these issues, in Options/Settings Display/Weather I disabled "turbulence and thermal effects on aircraft" and life has been a lot more pleasant and realistic since then! The thermal stuff is designed to give ridge lift with sailplanes and is all very well, but about as unrealistic for normal aircraft as that stupid DynamicHeadMovement section in the FSX.cfg file!

Try turning off turbulence and thermal effects and see if you still have the same problem. Or move to a nice flat area well away from any hills!

Roy
 
Geoff_D said:
“Anyone got the link -- I would like to read what Yves had to say.”
Click to expand...

This all started about 8 years ago when people complained about the breakaway thrust needed with various transport category jets in FS2002 and FS2004. One explanation was that starting with FS5 the game no longer had two physics models, one for ground, and one for air, but relied on one model only, the airborne one, and vastly increased ground friction to compensate. Is that true? I have no idea.

The ground friction is high, but even so, and as you’ve noticed, the effect of wind on ground handling is grossly over modeled. Exacerbating that are any problems that may exist with the contact points.

They can be tricky and time consuming to get right. The relationship between the Longitudinal Position, Lateral Position, Vertical Position, and the static_pitch and static_cg_height is crucial to stability and contact patch; then you have to work out the compression and damping too. The longitudinal position of the nose gear or tail wheel also affects steering -- I’ve seen many examples of MSFS aircraft that will slide straight ahead with max steering angle inputs.

Improper W & B can cause steering problems too -- reference_datum and station_loads can give you fits with distributed MOIs if done wrong, since the effect of any given weight and arm is overdone, and the resulting moment is too high. But enough about that, you wanted a link to the Sim1.dll thing.

I have no idea how this will work in FSX; the “fix” was for FS2004, but here’s a link to a discussion on it:

http://www.gamehourz.com/Changing-Ground-Friction-Values-Translate-German-ftopict12513.html

The problem with the Sim1.dll hack is that it fixes a problem that wasn’t unsolvable in the first place -- it’s an easy airfile fix for the break away thrust problem -– but the Sim1.dll hack introduces an even worse ground handling problem than that which already existed. I suppose some people used it in conjunction with the FSUIPC Taxi Wind button, congratulating themselves on the realism of the ground surface friction, but somehow ignoring the lack of effect of wind on ground handling.

I edited the Sim1.dll when this idea came out, tried it, and quickly discarded it.
 
Geoff,

I truly believe the unrealistic effects of FS wind are what cause these issues. Wind begats turbulence which begats uncommanded inputs. I have seen an AI F104 on an approach be flipped inverted and crash when "turbulence and thermal effects on aircraft" was not false, the F-104 has lousy stability, but even so it should not have happened.

Interested in your conclusions since you started this thread.
Roy
 
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