• Which the release of FS2020 we see an explosition of activity on the forun and of course we are very happy to see this. But having all questions about FS2020 in one forum becomes a bit messy. So therefore we would like to ask you all to use the following guidelines when posting your questions:

    • Tag FS2020 specific questions with the MSFS2020 tag.
    • Questions about making 3D assets can be posted in the 3D asset design forum. Either post them in the subforum of the modelling tool you use or in the general forum if they are general.
    • Questions about aircraft design can be posted in the Aircraft design forum
    • Questions about airport design can be posted in the FS2020 airport design forum. Once airport development tools have been updated for FS2020 you can post tool speciifc questions in the subforums of those tools as well of course.
    • Questions about terrain design can be posted in the FS2020 terrain design forum.
    • Questions about SimConnect can be posted in the SimConnect forum.

    Any other question that is not specific to an aspect of development or tool can be posted in the General chat forum.

    By following these guidelines we make sure that the forums remain easy to read for everybody and also that the right people can find your post to answer it.

Friction coefficient of taxi/runways 0.023?

K

kand449170

Messages
37
Country
unitedkingdom
Greetings

Could somebody critique my logic here please!

I have a Boeing 777-300 perf chart

The chart details the amount of breakaway thrust required at sea level/ISA day. The 777-300 was loaded at 770,000lbs (max taxi weight) and has a 1% uphill slope

Idle power thrust produced (per engine) 4013 lbs

Breakaway thrust required 9125 lbs x 2 (18250 lbs) to get moving

Feed this into AJPC roll power requirements and reverse engineer the friction coefficient (thanks Herve) until approx 18250 lbs is required to move v friction coefficent. The value obtained here is the friction required to be set within the sim = 0.024 to get the aircraft moving at 18250 lbs thrust

Interpolate a little for the uphill slope so make it a little less draggy

0.023 is the correct coefficient of friction for a hard smooth surface to modify within SIM1.DLL? (offsets shared in my other post)

As the 777 is at max taxi weight. 40% N1 is generally the limit for apron maneuvering so in table 1506 0 mach I set idle N1 at around 4013lbs becasue I know this value (4013/115000) 0.034895

and at 40% N1 I set thrust to equal 9125lbs (9125/115000) 0.079347 because I know the aircraft needed more thrust than at idle and imagine %40 is probably the most to be used

Smooth out the thrust curve so its flatter at low N1 and with thrust ramping up exponential from %50 N1 onward

Power ground handling complete!

Any comments?

Aware that all other airfiles will be screwed up and taxi like rockets!

thanks
 
Heretic

Heretic

Resource contributor
Messages
6,830
Country
germany
Well done(?).

If you have a registered version of FSUIPC, you can use a LUA script (included in the package) that will set the friction realistically at low speeds (for correct breakaway behavior, provided the .air file is properly set up) and then switch back to the default behavior at higher taxi speeds. Could be a better compromise across the board.
 
K

kand449170

Messages
37
Country
unitedkingdom
I think Pete has removed that feature in FSUIPC 5 because the offsets keep changing every time the DLL is recompiled, I have just finished my editing and airfile work so about to test in P3d!
 
Roy Holmes

Roy Holmes

Resource contributor
Messages
1,803
Country
us-virginia
I'm not sure you can just
Interpolate a little for the uphill slope so make it a little less draggy
Click to expand...
With a 1% uphill slope at a weight of 777,000 lbs there is a potential energy force equivalent to 770,000*sin(slope) backwards or 7,700 lbs reverse thrust equivalent.
Your manual says it requires 18250 lbs thrust to get moving under those conditions.
I think that since you are not testing on a 1% slope you need to consider subtracting the 7700 from 18250 for level conditions.
Roy
 
K

kand449170

Messages
37
Country
unitedkingdom
Thanks Roy, that makes sense and I was hoping you would read this!

I have calculated a new coefficient of 0.014 (AJPC doesnt go this low so I have had to double the thrust and half the friction result)

The handling is very nice now, needs a bit of thrust to get moving but then rolls at idle at low MTW

Next part is to figure out the braking? is it now overbraked or underbraked?
 
K

kand449170

Messages
37
Country
unitedkingdom
Hi Herve, the issue was that as I lowered the friction past 0.016, AJPC reported that it was impossible to roll at idle thrust? This was a bit odd as you would expect it to become easier
 
hervesors

hervesors

Messages
89
Country
france
Hi Herve, the issue was that as I lowered the friction past 0.016, AJPC reported that it was impossible to roll at idle thrust? This was a bit odd as you would expect it to become easier
Click to expand...
Understand..In such a case, from AJPC calculation, it is indeed impossible to determine a proper thrust for taxiing since idle thrust is greater than what is required for an unaccelerated steady state move (that is you'll need braking from time to time)
 
K

kand449170

Messages
37
Country
unitedkingdom
Just an update to this and close out, I have just been reading through some Boeing performance data for the 787-9, they quote that the tyre static friction used in their maths equated to 0.0135!
Capture.PNG
 
E

efpg0708

Messages
12
Country
brazil
Hi guys. Sorry to dig an old post ...

I’m very newbie for these kind of things. I use PROSIM 737 with P3Dv4, and I really miss the old friction module from FSUIPC4.

Could anyone please help me modify the friction table on p3dv4 to help make taxiing more realistic ? I know that this requires work and time, so I’m willing to compensate for it.

I just can’t stand the default friction in P3dv4.

Thanks

Eduardo
 
J

jx_

Messages
555
Country
unitedstates
you could also use a fuel flow mod and add the additional ground drag to your thrust table under mach 0.2 If the real airplane requires 10000 pounds of thrust and the sim requires an extra 2%, adding 2% to your thrust tables from 0-0.2 mach would have the same effect on performance assuming you're not burning any extra fuel.

This is a solution that would work for anyone with a default P3D installation. If it's not something you'll be distributing to the masses, a SIM.DLL or FSUIPC hack would work just fine.
 
You must log in or register to reply here.
Top