This is way too difficult to explane..
You will need to open the.mat file for the plane you use,
Then you need to open your materials.cfg And copy\paste for example this :
<Materials>
<Material
Name = "Concrete"
Elasticity = "0.1"
KineticFriction = "0.35"
StaticFriction = "0.35"
Priority="0"
ElasticityMode = "Average"
FrictionMode = "Average"
StepType="tarmac"
MinScrapeSpeed = "1"
MinScrapeFreq = "0.9"
MinScrapeFreqSpeed = "1.2"
MaxScrapeFreq = "1.1"
MaxScrapeFreqSpeed = "2.2"
MiddleScrapeSpeed = "2"
MinScrapeContacts = "3"
ScrapeSoundName = "step_Walk_Tarmac"
>
<Impact MinSpeed="2" SoundName="wettarmac_1"/>
<Impact MinSpeed="2" SoundName="wettarmac_2"/>
<Impact MinSpeed="2" SoundName="wettarmac_4"/>
<Impact MinSpeed="2" SoundName="wettarmac_5"/>
<Impact MinSpeed="2" SoundName="wettarmac_7"/>
<Impact MinSpeed="2" SoundName="wettarmac_8"/>
<Impact MinSpeed="2" SoundName="wettarmac_9"/>
<Impact MinSpeed="2" SoundName="wettarmac_10"/>
<Hit MinSpeed="3" SoundName="" PSName="ps_hit_hard" PSPrio="10" />
<Hit MinSpeed="1" SoundName="" PSName="ps_hit_hard" PSPrio="10" />
</Material>
Then...
Change this name -> Name = "Concrete" into whatever Name = "MyNewConcrete" or whatever you want,
Then the Name = "MyNewConcrete" need to be replaced into the .mat file your plane uses..
ALso there are 8 defferent stepsounds in the example above.
SO <Impact MinSpeed="2" SoundName="wettarmac_1"/>
Need be changed as well (wettarmac_1) <-- Is the soundfile in your mod\folder.
---
As i said, VERY hard... THis is NOT for beginners.
If you want to try, try like mine, and COPY THE ORIGINAL FILES as backup.
Good luck.