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P3D v4 Ground friction

J

jeehell

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43
Country
france
Hello everyone,

Pete Dowson indicated in his initial FSUIPC5 release notes that LM has changed the ground friction model in P3D V4.
I have been looking around for some time in the SDK, and have been doing tests as well in the sim, and I cannot find any difference in this aspect (and also, all other aerodymanics behvior are unchanged).
The same tables apply, and it is still possible to patch them...
Any one else has some input?

Cheers
JL
 
Agree
From what I analyzed by now in the current P3Dv4 sim1.dll, it seems table structure and coefficients are strictly identical to those of previous P3D versions and FSX
Note that rolling friction coefficient table (with scalars) is at offset 0x148500 and Braking coefficient table is at offset 0x1497C0
Now it could be that math behind has changed (but it is unlikely). May be Pete has additional info and you could ask him on his forum

Hervé

[Edit: offset values that were incorrect]
 
Last edited:
Any HEX editor as far as you know which values you're looking for (I searched for previously known HEX representations of coefficients)
 
Hi Hervé,

Well I have the same findings as you have... So I think either Pete doesn't want to add this feature in FSUIPC5 or he has info others don't have...
I'll try his forum..

Jean Luc
 
Not available anymore indeed. Give me a few days to build an Excel sheet with offsets/values. I will provide a link here
 
even I didn't know much yet how to use it, but that table would be useful. many thanks
 
even I didn't know much yet how to use it, but that table would be useful. many thanks
Click to expand...
Quite simple
Suppose you wish to reduce rolling friction coefficient for wheel aircrafts on asphalt surface. Default value is 0.05
Locate in the table the rolling friction coefficient offset in the P3Dv4 sim1.dll file for wheel category/asphalt surface. Offset (hex) is 0x148580
With any hex file heditor, load your sim1.dll file (MAKE A BACKUP FIRST) then go to offset 0x148580. The 4 bytes at this position (32-bit float value) are CD CC 4C 3D. It is the 32-bit float representation of the value 0.05. Note that bytes are in a reverse order (hex value is 3D 4C CC CD)
You'll find a converter here
http://babbage.cs.qc.cuny.edu/IEEE-754.old/Decimal.html
If you enter 0.05 as decimal value you will obtain the single precision hex representation above

Suppose you want to decrease the friction coefficient to 0.03
Use the convertor to obtain the 32-bit hex value that is 3C F5 C2 8F
Change the bytes at position 0x148580 to -> 8F C2 F5 3C (reverse order)

Save the file. You're done

Note that future versions of P3Dv4 may change the position of these tables inside the DLL. So take care. Provided offsets are only valid for the 4.0.23.21469 version of the file (the current one)
 
Am I going mad? just started to make my changes and I see this with the latest sim1.dll hotfix1

btw using hexeditor neo with the columns set to decimal floating point as opposed to hex


fEJzBwT.png
 
Well, this picture doesn't make sense at all for the searched tables. What is the sim1.dll version number? Could be that the tables are now at different adresses in the latest version or the decimal conversion doesn't work properly (but probably it does)
 
Yep..and it may change again in the future. That's the reason why Pete Dowson didn't wish to implement it again in FSUIPC5
http://forum.simflight.com/topic/83542-p3dv4-ground-friction/

Okay. I may look again and possible relent on this and implement via offsets, but there will be a limit on how many times I do this. I expect P3D4 to keep developing and I doubt that these offsets will stay the same. That's the main problem.
And it would still be better if folks would apply pressure to L-M for such things to be accessible either via functions or simple exported pointers (the latter only if they never expect the structure to change).
Click to expand...
 
fs1 said:
Is this the one?
http://www.fsdeveloper.com/forum/threads/sim1-dll-in-fsx.376984/
Click to expand...
Thank you for making this reference! I found the link to the spreadsheet with instructions to edit sim1.dll surface friction in both FS2004 and FSX SP2 (different instructions for each). I appreciate hervesors' posts on this thread also, for the concept of the hex value edits. I have been wondering for a long time how to resolve the excessive sliding in crosswinds in both FS2004 and FSX SP2, both of which I use regularly. Significant improvement by simply changing the coefficient for sliding friction on concrete and asphalt from the default value of 0.64 to a new value of 1.92 (i.e. I just figured about three times the effect would be about right). No other bad things happened as a result, as I can see so far. Tested using C172, DC-3 in both FS versions.
 
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