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markk71

New tire-force modelling for beta3

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Here is a quote I found at the X-Plane.org forum from Austin about new features for beta 3:

 

 
 
 
 
COMING LATER THIS WEEK IN BETA 3, PUBLISH THIS WHEN YOU SEE BETA 3 IS HERE:
 

this is new for beta-3 and really fun and cool to see it in action

 
 
Tire-force modelling.. WHEN THE PLANE IS NOT MOVING!!!
 
OK maybe my sense of humor is all screwed up after 2 weeks of straight coding but this one is just too funny:
 
For X-Plane 11 beta-3, I just solved a bug (pointed out by Vit Zenisek) that has actually been in X-Plane for 20 years… and only affects the motion of the airplane when it isn't moving.
 
Got it?
 
Here’s the dynamics of the non-dynamic situation:
 
The tire force model in X-Plane is good enough to use in a driving racing simulator, as it actually gets right down to the vector along which the rubber is dragged across the pavement on the contact-patch of the tire. The dynamics are really quite good, especially in X-Plane 11 where I have taken tire-modelling updates from Stradale.
 
BUUT, this physical model has  fatal flaw: The model that simulates the detail right down to how the rubber interacts as it is being dragged across the pavements….  only works WHEN THE RUBBER IS BEING DRAGGED ACROSS THE PAVEMENT! DUH! So when does it NOT work? WHEN YOU ARTE STOPPED!!! HAR!!!
 
So, whenever an aircraft in X-Plane has been STOPPED, I simply ‘locked the airplane down’, bypassing the tire model altogether.
 
No motion? No flight model!
 
This SOUNDS fine, right?
 
WRONG!!!!!!
 
During the run-up, the plane is indeed motionless, but the forces acting on the airplane, via the landing gear, are HUGELY important!
As you add power, for example, the force opposing propeller thrust is COMING FROM THE TIRE CONTACT PATCH FAR BELOW THE PROPELLER!
This aft force, far BELOW the prop, opposing the forward motion of the prop, creates a torque that LOWERS THE NOSE when power is applied with the brakes on!
You sure feel this on short-field take-offs, when you add power, holding the brakes, and the nose hunkers DOWN
Then, when you release the brakes, the nose POPS up as the nose-gear strut is unloaded and it is off you go!
So, even though the airplane is NOT EVEN MOVING during the run-up or power application before brake-release, the forces on the landing gear and resulting aircraft dynamics are CRITICAL to making the X-Plane aircraft behave, and feel, like the real airplane!
 
SOOOO, how do we BUILD a tire model that is based on MOTION, so that it works when the plane is STOPPED?
 
SIMPLE!
 
We simulate a WELD!
 
When the plane is stopped and the tire forces are adequate to HOLD it there, we imagine that the tire contact patch is WELDED DOWN TO THE GROUND right at the center of the tire contact patch! The force on the airplane from the tires is a damped spring that opposes any displacement of the aircraft from that welded-down spot! Any (small) displacement from that world-point of the tire contact patch is due to the flexing of the tire sidewall, allowing the axle to move ever so slightly fore and aft as the tire flexes under the loads of the engine, wind, a sloped runway, or whatever else it is that is trying to move the airplane!
 
SO, when STOPPED, we weld the tire contact patch to the ground with a damped spring simulating the tire sidewall that holds you in place with, indeed, some FLEX!
Then, as the brake are released OR the forces on the aircraft EXCEED the braking allowed by the tires… we switch over to the rolling or dragging dynamic tire models as needed!
 
Cool!
 
The whole thing happens seamlessly, and the effect is really quite amazing.
With the Cessna 172, for a short-field take-off, get all the way on the brakes and go to full power.. the nose starts to dive under the thrust!
Then, get OFF the brakes and the nose POPS up and oscillates as the nose strut unloads, over-extends from the aircraft inertia, and oscillates a few times until the motion is damped out, as the airplane starts to accelerate down the runway!
 
It feels JUST like the real plane!
 
You will get this starting in X-Plane 11 beta-3, and I am really annoyed we have not had this for the last 20 years!
(Because in the version of X-Plane you have right now, all of this is missing which SUUUUUUUUCKS!)
 
So grab X-Plane 11 beta-3 when it comes out (soon) and try some of these brakes-on, full-power, brakes-off short-field take-offs in light airplanes.. it finally feels real!
 
 
 
 
 
and this is also largely improved for beta 3
 
 
 
 
In my REAL airplane, when you turn ON electrical system stuff, it DRAGS DOWN the speed of the compressor.
The compressor provides the cooling air that keeps the engine from destroying itself!
This is a BIG DEAL for pt-6 airplanes!
So as the generator load comes up, the turbine Ng does DOWN, and the ITT comes up… possibly enough to destroy the engine!
One day when it was really hot and I was taxiing with the air conditioning on and I taxied into a tailwind, the ITT start to go to REDLINE!!!!!
I quickly turned off the air conditioning and the ITT quickly came down!
I said “whew”, advanced from LO IDLE to HI IDLE to get enough compressor speed to support the electrical draw of the air conditioner, and THEN turned the AC back on!
 
Now, at this moment in X-Plane, I am making all of this DEFAULT behavior.
It's SO EASY!
The user ALREADY enters the electrical load in plane-maker for each system.
The user ALREADY enters the generators and what engines they attach to.
The user ALREADY enters the horsepower of the engine.
 
So now, as I am coding right this moment, X-Plane looks at the amperage and voltage of each generator hooked to each engine.
What is amperage times voltage? POWER!
So we can MATHEMATICALLY FIND the power that is sucked from the compressor by the generator!
And, yes, as you turn stuff on, the generator load will go up, the Ng will come down from the drag, and the ITT will go up!
 
So it is all baked right into the model.. no user-mods needed.
As you increase electrical load on the airplane, that load will be passed to any turned-on generators which will drag down any engine attached to those generators,
changing power output and temperatures accordingly! COOL!!!!
 
While this is surely most noticeable on the PT-6, I have applied the affect to the pure jets and recip-engine airplanes as well, and also applied the drag on the engine from the pressurization system as well, when applicable.
 
 
So we now have accessory drag on the engines.
 
this is real, and very important.
 
in free-turbine airplanes, especially, turning on the air conditioning requires you to advance to hi idle BEFORE you turn on the air conditioning or you will destroy the engine!
 
here is what happens:
 
-at low idle, the air conditioning drag on the generators slows the compressor
-the compressor slowing causes the ITT to rise
-the ITT ride can DESTROY the engine!
 
this is problem on lancair evolutions AND EVERY KING AIR IN THE WORLD.
 
king-airs must go to a VERY HIGH IDLE to be able to run their air conditioning or the air conditioning will snap OFF to prevent it from destroying the engine!
 
in the jet stream javier you entered a free turbine (this is wrong! that plane has a FIXED turbine!) and the electrical load is so high that it is dragging the compressor down
 
you need to have lower electrical system load, or a higher idle!
 
right now, the plane is in an emergency: not enough compressor speed and power to turn those generators!
 
this is NOT a bug in x-plane.. it is a new system simulation that makes the sim better!
 
but you and perhaps others will need to tun down you electrical amperage in the systems pages in plane-maker or go to hi idle, or turn up your low or hi idle, to turn the generator (which is hooked to the compressor) fast enough to make your needed generator amperage!
 
now the story:
in my evo this summer when it was hot, i turned on the ac when i had the plane at a very LO idle with a tailwind during taxi… the ITT in my airplane started to go to redline!
i almost ruined my engine!
i saw it and instantly turned off the generators!
the ITT fell as the generator turned off and freed the compressor to turn as it liked and send the cooling blanket of air through the engine
then i went to HI idle to get plenty of power from the compressor, and generator back on… no problem!
 
why did this only just happen after i had the plane for 2 years?
 
because i had just had the idle adjusted to be lower… IN OREGON, WHERE IT IS COLD, AND THEY DON'T NEED AIR CONDITIONING! HAR!!!!!!!!!!
 
so, that is what is going on!

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Good, a rewriting of the tire model was long overdue. Crosswind T/O and landings became unrealistically difficult since X-Plane 10. Hopefully things will improve.

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Good, a rewriting of the tire model was long overdue. Crosswind T/O and landings became unrealistically difficult since X-Plane 10. Hopefully things will improve.

 

I don't think this will be affecting that. Austin seems to be very happy with the current tire model as is judging by this post.

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Awesome now fix the banding and night sky textures and I will be very happy - you would think this would not even be an issue in a flight sim

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It looks cool indeed, but none of the listed features / fixes directly impacts that overdone weathervane effect when taxiing or taking off with a slight quarterly 5knot wind...

 

Maybe it's also going to be addressed... Let's wait and see...

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Awesome now fix the banding and night sky textures and I will be very happy - you would think this would not even be an issue in a flight sim

Did you try the LUA fix? PM me.

 

BTW: I came here to post what I read at the .org forums, only to find that someone beat me to it. :smile:

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Oh wow. Tire modelling? Hmm. Are we getting a bit lost in detail here???

 

Never mind, must have been my right brain talking to my left brain...

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Did you try the LUA fix? PM me.

 

BTW: I came here to post what I read at the .org forums, only to find that someone beat me to it. :smile:

 

Yes I have that but banding still there just not as bad - thanks 

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Will this new feature solve the problem with the "dancing ground" that us GA flyers see?

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Would like to see them carry this same enthusiasm towards Clouds, ATC, Framerate, and Sky texture gradients as well. 

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Would like to see them carry this same enthusiasm towards Clouds, ATC, Framerate, and Sky texture gradients as well. 

Since we're still in Beta, anything is possible. :)

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Will this new feature solve the problem with the "dancing ground" that us GA flyers see?

 

No, that has literally nothing to do with the tire model. Also it's not limited to GA flying either.

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No, that has literally nothing to do with the tire model. Also it's not limited to GA flying either.

 

I theorized that it is the rotation of the earth causing that.  I agree it is annoying , wish they'd fix that.

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This fix will add a small but nice level of realism and immersion. Aircraft should 'hunch dow'n on their forward suspension when you apply power with the brakes on. XP aircraft don't seem to exhibit this behavior.

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Maybe this fix could be applied in one last update for XP-10, since it appears to be in the old code - overlooked for years.

 

John

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Maybe this fix could be applied in one last update for XP-10, since it appears to be in the old code - overlooked for years.

 

I kinda doubt it. It's not a serious flaw in the flight model like the torque effect that was fixed during the XP10 run. It's more of an extension of the existing static tire model. It almost qualifies as eye candy in my view, compared to all the other things they could be working on.

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hmmm, this fix may also help with the moon's transition-friction, finally we will see the moon where it should be at 8:00pm.   :blink:

 

Jose will be very happy indeed! 

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It's not a serious flaw

 

Seems pretty serious to Austin.  Don't think I ever saw/read him more excited!

 

John

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Seems pretty serious to Austin.  Don't think I ever saw/read him more excited!

 

 

We get things in the sim that Austin is excited about, so that's good, but I still doubt we're going to see this ported to XP10. It would mean a new XP10 beta and release candidate cycle, and they're already running one for XP11. 

 

Meanwhile, I wish Austin would get that excited about a full 3D weather model that would give us vertical convection and thunderstorms. 

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Austin does get excited about stuff pretty easily - then it takes month and years or forever to scale whatever he gets excited about (undulating terrain runways, vortex ring state in helicopters, turbulence, slippery runways in "icy" conditions...) back to a realistic level.

 

I am convinced that the current lack of tire friction in the "rolling model" (and the associated screeching sound) is absolutely due to the fact that he thinks it looks cool how the airplanes skid and swerve in strong crosswind.

 

I would also not be surprised if the new implementation of static flexn on ground will make the prop strike the ground on even the slightest bit of power application or make the plane buck down the runway like a young bronco. Mark my words. :blink:

 

He gets pretty excited about stuff - but he does not like to listen to people. X-Plane could be years ahead in commercial success if he did.

 

Jan

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Austin does get excited about stuff pretty easily - then it takes month and years or forever to scale whatever he gets excited about (undulating terrain runways, vortex ring state in helicopters, turbulence, slippery runways in "icy" conditions...) back to a realistic level.

 

I am convinced that the current lack of tire friction in the "rolling model" (and the associated screeching sound) is absolutely due to the fact that he thinks it looks cool how the airplanes skid and swerve in strong crosswind.

 

I would also not be surprised if the new implementation of static flexn on ground will make the prop strike the ground on even the slightest bit of power application or make the plane buck down the runway like a young bronco. Mark my words. :blink:

 

He gets pretty excited about stuff - but he does not like to listen to people. X-Plane could be years ahead in commercial success if he did.

 

Jan

 

Couldn't agree more with this description of the State of Affairs, since I use XP ( and that's since v2... )

I got tired of sending Austin emails...

It would be great if at least Laminar Research looked at the impact XP11 is having on the users community and see a great chance for advances like never before in sales, 3pds interest, etc...

 

Let's hope for the best.

 

Using a "zillion" of invisible undercarriages to cope with the silly implementation of ground physics isn't really the way, right Janov ? :-)

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Got to agree with the comments here, AM does come across as if in the playground it is my sim and you can play with it but I control it.

 

While I deeply admire the talent of AM and the team he has, would it not be better to concentrate on the basic fundemaentals of the sim to ensure it runs well rather that tyre friction or whatever.

 

I like a lot of users am seriously thinking of ditching esp for good and have been caught up,in the Beta, however the XP FS is lacking in a lot of good basic stuff weather atc etc.

 

Get this right and XP will be a great success generating income not only for LR but also all add on software companies, this is a golden opportunity so they should jump at it and Listen to the community....

 

We shall see I hope I am proved wrong...but it is an easy switch to jump back to other platforms if they ignore us the potential buyers...

 

Said my bit..

 

Wishing all a good xmas

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Got to agree with the comments here, AM does come across as if in the playground it is my sim and you can play with it but I control it.

 

While I deeply admire the talent of AM and the team he has, would it not be better to concentrate on the basic fundemaentals of the sim to ensure it runs well rather that tyre friction or whatever.

 

I like a lot of users am seriously thinking of ditching esp for good and have been caught up,in the Beta, however the XP FS is lacking in a lot of good basic stuff weather atc etc.

 

Get this right and XP will be a great success generating income not only for LR but also all add on software companies, this is a golden opportunity so they should jump at it and Listen to the community....

 

We shall see I hope I am proved wrong...but it is an easy switch to jump back to other platforms if they ignore us the potential buyers...

 

Said my bit..

 

Wishing all a good xmas

 

Well, to be fair, a lot of the good stuff in X-Plane is also due to Austin being so stubborn and detached from user feedback. And X-Plane has been blessed with some very talented additions to the team, Ben Supnik alone is worth his weight in platinum, in my opinion. One of his dogmae is to "do it right", though. And doing it right requires a lot of planning and work (-> time).

 

Just think of the new "European buildings". The framework for regionalized autogen has been in the sim for YEARS - that is the kind of foresight that Ben applies to his scenery system. He has it all figured out in his head, just give him a few years to lay it down in solid code...and enjoy flying while you wait.

 

Jan

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[...] Ben Supnik alone is worth his weight in platinum, in my opinion. One of his dogmae is to "do it right", though. And doing it right requires a lot of planning and work (-> time).

 

Just think of the new "European buildings". The framework for regionalized autogen has been in the sim for YEARS - that is the kind of foresight that Ben applies to his scenery system. He has it all figured out in his head, just give him a few years to lay it down in solid code...and enjoy flying while you wait.

 

Jan

 

I totally agree with you, Jan !

 

Cheers,

Pascal

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