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chabrier

Inherent flaw of FSX to give too much ground friction?

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It would seem that the current preferred way for users to alter these Friction parameters is by using Luna script, through FSUIPC. (Thanks -- Peter to the rescue once again !!)

 

However, I've never written anything in LUNA, and I suspect I am not alone here.

 

Would someone proficient in Luna, like to write a couple of template scripts: One that has the original Sim1.dll parameters for reference, and one that has the modified values that FSUIPC has.

These would provide a consistent reference for anyone, experimenting with values, as well a forming some good documentation of theses parameters.

 

Before someone says "Why not learn to write it yourself" -- here is one good reason.

 

Even if I, and others do finally learn enough to write this script, if there are any errors, resulting in the expected values are NOT getting correctly patched, then we will be providing feedback on suggested values that are incorrect .. resulting in a massive amount of misinformation.

 

A standard template for this particular script would be the most efficient and accurate way to get everyone on the same page.

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Yes, Capish -- Thanks, but this leads to another question.

 

 

Is there any modeling of tyres that have grip on the surface, then loosing grip and skidding, and the associated modeling of "automatic breaking systems" with anti-skid ?

Planes with Anti-skid options -- is this really simulated, or just approximated somehow ?

 

Maybe, if LUNA can patch these parameters in Real time, Luna could be used to help simulate more complex braking systems ?

 

 

Hmm, good question. I actually, and you can do that too, that with max braking you can see the wheel skid over the tarmac.

With autobrakes, you dont.

 

One can do just a test to see what is the difference.

You can put the autobrake to zero in the aircraft.cfg to see it skidding. Test also with snow and rain and observe any difference. If not then its cosmetic, but I think it does something.

But its not adjustable as far as I could see.

 

Please note that this has nothing todo with the autobrake on your panel.

Some designers even put the autobrake ON in the cfg to have it in spotview not skidding.

So double check on your testing. I will do it too, but later this week.

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It would seem that the current preferred way for users to alter these Friction parameters is by using Luna script, through FSUIPC. (Thanks -- Peter to the rescue once again !!)

 

I think you mst mean Lua?

 

However, I've never written anything in LUNA, and I suspect I am not alone here.

 

In version FSUIPC 4.859j, which I will release probably tomorrow, there will be a new function in Lua called "SetFriction" which can be used to simply set any specific friction value, anywhere in the whole of SIM1's tables. I will provide an example -- in fact Johan's values being set, and it will be easy to see how to do it and how to make it different for different aircraft.

 

I will be removing the offset mapping in that version as it then will not be needed, and only covered the Wheel and Brake classes in any case. There's also Water Rudder, Scrape, Skid, Ski and Float sets. All can be changed in the next update.

 

A standard template for this particular script would be the most efficient and accurate way to get everyone on the same page.

 

Just wait a while, less than a whole day, and I'll be packaging the "template" for Johan's current values with the next FSUIPC update.

 

Pete


Win10: 22H2 19045.2728
CPU: 9900KS at 5.5GHz
Memory: 32Gb at 3800 MHz.
GPU:  RTX 24Gb Titan
2 x 2160p projectors at 25Hz onto 200 FOV curved screen

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I patched my sim1.dll and tested the new ground handling and I love the "new" feel.

 

I had stopped using flight sim for over a year out of frustration with the ground behavior. I found it very dissapointing to end a carefully planned flight, wich had gone well, with the airplane skidding off the runway due to a moderate crosswind.

 

I'd like to take a minute and thank the people who made this improvement.

 

THANK YOU!

 

Alejandro Gutierrez

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Do you think this could fix a similar problem with the float/amphibian planes? For instance the Aerosoft Beaver needs 60% throttle just to make it move on the water. Because of this, the engine overheats after 5 minutes of water-taxiing.

 

Yes I will look in them too.

But I have no idea how it should behave.

So here are the questions:

 

- How much throttle would you prefer? So I can adjust it to that, or just give your feelings/idea, like half the friction ?

- Side/lateral friction: is this already okay? or too much or too less?

 

Since there is no brake in a water plane, it wouldnt do anything of course to adjust that.

But there is an entry for the floats, and the water rudder, so if you can tell if the rudder causes friction, thus using it slowing the plane down then also tell about that.

 

Oh, I have to post some settings information here:

 

The rolling resistance of an aircraft on the ground is usually assumed to be proportional to (W-L),
the net downward load exerted by the aicraft of the undercarriage. Thus the rolling resistance is expressed as Ur(W-L)
where Ur is a constant coefficient of rolling restistance and is usually taken to be about [b]0.025[/b] for a concrete runway.
Collingbourne (1970) has shown that Ur depends to some extent on the forward speed
and on the inflation pressure and other characteristics of the tyres, but the exact value of Ur that is used in
estimating the length of the ground run is not very important because the rolling resistance is usually small in comparison to
the thrust. An important exceptional case occurs when the runway is covered with snow or slush, giving a large increase
of Ur wich has a substantial effect on the takeoff ground run.

 

 

http://books.google....quation&f=false

 

The normal force will be the difference between Weight of aircraft and Lift, the friction coefficient 
will be typically of a magnitude of [b]0.02[/b] for a standard tarmac runway.

 

http://www-mdp.eng.c...f/to/index.html

 

http://en.wikipedia.org/wiki/Friction

http://en.wikipedia....ling_resistance

 

Above values have been used as a starting point, and MS have been using the same format, but doubled the friction, and halved the sliding friction, better did it the other way around, and we shouldnt have done this. Lol..

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I just want to say that I LOVE Pete's solution for how to experiment with these friction values in FSX. The fact that nothing is actually changing in the FSX files, and that we can adjust values on the fly for each plane we are flying and set them up in profiles makes this a worry free way to try to find better ground handling for our aircraft. Even if we can't improve the actual ground contact physics of the sim, the ability to "fiddle" with the brake and friction values offers the chance of improving "realism" some at least. Bravo.

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One of the reasons I taxi slowly is that I've had several times in the Grumman Goose where a turn during a too-fast taxi on pavement caused me to tip over and scrape a wingtip float on the ground. How would such a thing be possible if there's insufficient lateral friction? No, I wasn't using brakes at the time.

 

I'm not saying people aren't getting decreased friction, just that I don't seem to have the problem, and I'm wondering why.

 

Two possible causes: The SP1 version of the sim1 file had normal friction. I can't absolutely guarantee that I dragged a wing after installing SP2, guess I'll need to test that. The other possible cause is that someone else changed the file.

 

Hook


Larry Hookins

 

Oh! I have slipped the surly bonds of Earth
And danced the skies on laughter-silvered wings;

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I think the Goose has a high centre of gravity.

Friction is for all the same, but wheelspan and centre of gravity differ, and have an effect of course. Not all planes handle the same of course.

Wheel diameter is also taken in account, but I have no idea if this is connected in any way to the frictions.

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A (minor) side effect of modifying the Sim1 dll seems to be, at least in my case, that when shutting down FSX, Windows reports a damaged fsx exe and advises to execute a 'chkdsk'. This looks like a false alarm; both Windows Maintenance Center and my own maintenance program (Advanced System Care) do not report any problems. Only the Windows Event Manager confirms this 'fault'.

 

I tried Pete's solution as well as Johan's replacement file (with the NGX 737-600) and they both improve the taxi and rolling behaviour a lot. So yes, a bravo for both of them! For the time being I'm having a preference for Johan's file though, as with the FSUIPC approach I'm experiencing a slight hesitation, sort of micro stutter, just before rotation and at the end of the rollout after landing.

 

Don't know whether this is linked to the NGX: When taxying with idle throttle, the taxi speed slowely but surely increases, so regular braking is necessary. But then this might be the case in the real world as well, can't judge that.

 

Regards,

Rene

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A couple of Boeing manuals state that this happens, and you don't ride the brakes, to prevent heat build up.

They advise to firmly brake, and accellerate again.

So I think we are getting mor as real as it gets.

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I think the Goose has a high centre of gravity.

 

Especially with a ton of fuel in the wing; that's almost 1/4 of the max gross weight. The main gear are close to the body as well, which would make it easier to tip.

 

I'd like to test the side friction on my system. Given the stock C-172 and the clear weather theme, which airport (the runway surfaces are different at different airports), which runway, and what ground speed to I need to experience skidding? You can get the ground speed from the GPS.

 

Edit: it needs to be a stock airport too, not one from any add-on scenery or a custom airport. Thanks.

 

Hook


Larry Hookins

 

Oh! I have slipped the surly bonds of Earth
And danced the skies on laughter-silvered wings;

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I tried Pete's solution as well as Johan's replacement file (with the NGX 737-600) and they both improve the taxi and rolling behaviour a lot. So yes, a bravo for both of them! For the time being I'm having a preference for Johan's file though, as with the FSUIPC approach I'm experiencing a slight hesitation, sort of micro stutter, just before rotation and at the end of the rollout after landing.

 

Unless you are setting the option for mapping the offsets, there is no difference between replacing the SIM1.DLL with a ready-patched version and using the Patch facility in FSUIPC, because the patching is done just once, when FSUIPC and SIM1 are first loaded into memory.

 

In FSUIPC 4.859j, which i am just finalising, there is no offset mapping. I've withdrawn that. Instead, via Lua, every single friction setting (water etc too) can be changed, and by Lua files which can be actvated separately for each aircraft profile. Here's an example Lua plug-in which sets Johan's currently released changes:

 

ipc.RestoreFriction()

ipc.SetFriction(WHEEL, CONCRETE, ROLLING, DRY, 0.030)
ipc.SetFriction(WHEEL, GRASS, ROLLING, DRY, 0.060)
ipc.SetFriction(WHEEL, GRASS_BUMPY,ROLLING, DRY, 0.070)
ipc.SetFriction(WHEEL, ASPHALT, ROLLING, DRY, 0.025)
ipc.SetFriction(WHEEL, SHORT_GRASS,ROLLING, DRY, 0.050)
ipc.SetFriction(WHEEL, LONG_GRASS, ROLLING, DRY, 0.060)
ipc.SetFriction(WHEEL, DIRT, ROLLING, DRY, 0.050)
ipc.SetFriction(WHEEL, GRAVEL, ROLLING, DRY, 0.060)
ipc.SetFriction(WHEEL, BITUMINUS, ROLLING, DRY, 0.030)
ipc.SetFriction(WHEEL, MACADAM, ROLLING, DRY, 0.030)
ipc.SetFriction(WHEEL, TARMAC, ROLLING, DRY, 0.030)

ipc.SetFriction(WHEEL, CONCRETE, SLIDING, DRY, 1.000)
ipc.SetFriction(WHEEL, GRASS, SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, GRASS_BUMPY,SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, ASPHALT, SLIDING, DRY, 0.950)
ipc.SetFriction(WHEEL, SHORT_GRASS,SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, LONG_GRASS, SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, DIRT, SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, GRAVEL, SLIDING, DRY, 0.800)
ipc.SetFriction(WHEEL, BITUMINUS, SLIDING, DRY, 1.000)
ipc.SetFriction(WHEEL, MACADAM, SLIDING, DRY, 0.950)
ipc.SetFriction(WHEEL, TARMAC, SLIDING, DRY, 1.000)

ipc.SetFriction(BRAKE, CONCRETE, ROLLING, DRY, 0.900)
ipc.SetFriction(BRAKE, GRASS, ROLLING, DRY, 0.700)
ipc.SetFriction(BRAKE, GRASS_BUMPY,ROLLING, DRY, 0.650)
ipc.SetFriction(BRAKE, ASPHALT, ROLLING, DRY, 0.900)
ipc.SetFriction(BRAKE, SHORT_GRASS,ROLLING, DRY, 0.650)
ipc.SetFriction(BRAKE, LONG_GRASS, ROLLING, DRY, 0.650)
ipc.SetFriction(BRAKE, GRAVEL, ROLLING, DRY, 0.650)
ipc.SetFriction(BRAKE, BITUMINUS, ROLLING, DRY, 0.900)
ipc.SetFriction(BRAKE, MACADAM, ROLLING, DRY, 0.900)
ipc.SetFriction(BRAKE, TARMAC, ROLLING, DRY, 0.900)

 

The "RestoreFriction" function at the start makes sure the patching starts from the defalut settings, in case different profiles change different parts of the complete set of values.

 

Here's the description of the SetFriction function:

 

 

x = ipc.SetFriction(class, surface, type, condition, value)

 

[Not WideClient]

[FSUIPC4 only]

 

This is a rather specialist function which specifically changes the rolling, sliding and braking coefficients within FSX's SIM1.DLL. It operates on-the-fly at run time so different plug-ins ca be used to tailor these for different aircraft models. It operates with all versions of FSX plus Prepar3D version 1.4.

Class = one of:

BRAKE, WHEEL, SCRAPE, SKID, FLOAT, WRUDDER, SKI

 

(where WRUDDER is short for Water Rudder).

 

Surface = one of:

CONCRETE, GRASS, WATER, GRASS_BUMPY, ASPHALT, SHORT_GRASS, LONG_GRASS, HARD_TURF, DIRT, CORAL, GRAVEL, OIL_TREATED, STEEL_MATS, SNOW, ICE, URBAN, FOREST, BITUMINUS, BRICK, MACADAM, PLANKS, SAND, SHALE, TARMAC, WRIGHT_FLYER_TRACK

 

Type = one of:

ROLLING, SLIDING (but only ROLLING for the BRAKE class)

 

Condition = one of:

DRY, RAIN, ICE, SNOW

 

Value should be a number between 0 and 1 inclusive, but this is not checked.

The Boolean result x is True if this was done, False if there's something wrong.

 

I've got some more testing to do and documentation to update, but meanwhile comments on this approach are welcomed. I am out tonight so this won't get released till Thursday morning (UK time).

 

Regards

Pete


Win10: 22H2 19045.2728
CPU: 9900KS at 5.5GHz
Memory: 32Gb at 3800 MHz.
GPU:  RTX 24Gb Titan
2 x 2160p projectors at 25Hz onto 200 FOV curved screen

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Well guys I am very happy thanks very much Johan and Pete. Just taken all my aircraft out for a test flight and have to say things are a lot better for taxying, takeoff run and landing. Makes one look like a pro instead of weaving down the runway!

 

Cheers

 

Clive Northrop

OEAB

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Great work. Once again FSX is improved thanks to great people at great communities like this one. Fabulous. FSX taxi almost feels like rw now. Awesome.

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