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chabrier

Inherent flaw of FSX to give too much ground friction?

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I have searched the FSX forum unsuccessfully for solutions on the subject. I have been using FSX more lightly than FS9, mostly because my computer was only a dual core. Since building a new rig in October with an Ivy Bridge i7 and Windows 7 64, I've had a lot more opportunity to get a feel for FSX.

 

One thing that I have notice (old or new computer) is that FSX has an unrealistic ground drag, essentially with all aircrafts. Some are way worse than others, but the problem of excessive drag or friction is pervasive. I do have pedals, and yes, they are properly calibrated and are not the source of drag. One can easily check for the excessive drag by taking the default cessna one a runway, accelerating to say 50 kts, and bringing the throttle to idle (or shutting off the engine), letting the aircraft roll without using the brakes. The aircraft will come to a stop in a few hundred feet :excl: . A real aircraft will go to the end of the runway if the brakes are not used and if there is no up-slope. Once a real aircraft is moving, it essentially takes braking to stop it (I have been a real life PP since 1992 and have a goof feel for real aircraft ground handling by now :rolleyes:). Some third party aircraft are a bit better, others are a lot worse. I have FS9 and FSX installed on the same computer and using the same yoke/pedal/throttle. All aircrafts behave much better in FS9 in terms of ground drag. Many aircrafts in FSX need significant power to start moving and the associated engine revved-up sound is quite unrealistic.

 

FSX has so many improvments over FS9, especially in terms of scenery and cockpit design, but these ground handling issues seem like a step backward and are spoiling the enjoyment factor. Does anyone know if this is and aircraft design issue or a true inherent flaw of FSX?

 

Any insight would be appreciated. Thanks.

 

Pierre

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There was a post not long ago where someone complained about the opposite problem, that the aircraft didn't have enough friction.

 

I said at the time that I'm certain I once saw a parameter for tire pressure, and that would cause too much or too little ground friction. No one responded.

 

Hook

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Yeah there is some issues going on with friction. Would be nice if fsx simulated break away thrust on initial movement. Even after sitting in one spot for a while, it requires a little thrust to get moving again.

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The main problem has allways been side friction. MS FLIGHT corrected it... :-/

There are problems with exactly this same subject on other sims, including MSFS's direct competitor - X-Plane10.

 

Each has it's bad aspects, but I still preffer FSX's model, even if not perfect. I know X-Plane's one will probably get addressed during the current v10 cycle... MSFS's will not... Maybe Prepar3d v2.0 brings a ground physics model closer to what we have in MS FLIGHT (still not perfect but very good...) or almost perfect, like in DCS World, Condorsoaring...

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The problem with FSX is that the ground friction is only along the front-rear axis of the aircraft.

There is no lateral friction.

This results on some alarming situations when there is a crosswind, its like being on Ice.

 

ie. It's far too easy to do a 180, or a 360, when taxiing a C172 at high speed around a corner !!!

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One thing that I have notice (old or new computer) is that FSX has an unrealistic ground drag, essentially with all aircrafts. Some are way worse than others, but the problem of excessive drag or friction is pervasive. I do have pedals, and yes, they are properly calibrated and are not the source of drag. One can easily check for the excessive drag by taking the default cessna one a runway, accelerating to say 50 kts, and bringing the throttle to idle (or shutting off the engine), letting the aircraft roll without using the brakes. The aircraft will come to a stop in a few hundred feet :excl: . A real aircraft will go to the end of the runway if the brakes are not used and if there is no up-slope. Once a real aircraft is moving, it essentially takes braking to stop it

 

I think this must be to do with specific models. The 738 I use (based on the default FSX 738 but with modified AIR and CFG files), will roll forward with idle thrust (which is correct) and always needs braking to come to a stop.

 

All aircrafts behave much better in FS9 in terms of ground drag.

 

I always found FS9 to be very poor on the ground. Light aircraft would too easily veer into wind whilst taxiing, as if on ice rather than dry tarmac. That was much reduced in FSX, thankfully. But I think the drag you are talking about must be down to some parameters in either AIR or CFG file.

 

Regards

Pete

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I think this must be to do with specific models. The 738 I use (based on the default FSX 738 but with modified AIR and CFG files), will roll forward with idle thrust (which is correct) and always needs braking to come to a stop.

 

That would mean the PMDG NGX is incorrect, since it doesn't roll forard with idle thrust????

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Im pretty sure to to get an 800 moving initially you need 40% N1. Then you can reduce it/change it as required

 

lee

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Mind the GW. I'd say Pete has a point and the addon jets of mine do indeed start rolling on low GW and, often enough, only the slightest or no addition of thrust. So, some devs did try to work their way around. The 737-600 actually is hard to slow down at times. Just an example.

 

Same as others, I'd say ground friction is too high when it comes to start rolling and also when it comes to 'good' breaking, which is rendered too good by FSX. Just looking at the distances needed. At the same time, the comment on the axis is true, the nose wheel does not benefit from any friction enhancement in FSX, it actually skids along the tarmac and renders single engine taxi a no-go or just very annoying.

 

Try a small twin, decent FDE, and start rolling on one engine. You will start turning, yes. The bigger the plane and the larger the arm of the nosewheel, the better that becomes. But even large planes at slow speeds skid around. Geoff's comment on the lateral friction. Spot on in my eyes. 'Like on ice' sums it up in that regard. Wheel-barrowing in FSX? A hard thing to do.

 

Sounds far more severe than it is. It's the sim and I don't take it as a real thing nor do I plan to become a pilot by learning those elements from it. X-Plane is funny in that regard. Anyone heard that screaming nosewheel lately? ^_^

 

 

I could think of the issue being another example of 'fine tune the one element and spoil the others'. So while it may easily be possible to enhance the ground roll like mentioned, this may then lead to a wonky flight experience or just some more workarounds needed to not spoil other phases of sim flying.

 

We are also seeing that problem on some other ends. Take stall speeds on even the decent planes for example. With jets, being tuned to come in with realistic fuel burn and endurance values, those may end up being way off any charted values. The question being. What's more important when flying that one plane? By this, the devs may be forced to focus on the one thing and, knowingly, spoil the other one.

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The solution is in sim1.dll as it was in FS9.

There are frictions for side also in it, but it gave some side effects like small shakes at very low speed.

For FS9 there is an adjusted sim1.dll around, but nobody changed it for FSX.

Since I dont understand hex editing, it must be doable for one with the right knowledge.

Also, there is also an changed ATC.dll around for FS9 what stops the nagging due to baropressure difference on altimeter, and some more goodies.

I hope the same guru can do it for FSX too.

 

Who can hexedit is the major question!

 

EDIT:

http://www.fsdevelop...ad.php?t=376984

 

Here are the values, in the excel sheet. Now how to apply them is a different story.

 

EDIT:

Ok, found the old thread for FS9: http://www.gamehourz.com/Changing-Ground-Friction-Values-Translate-German-ftopict12513.html

With the excelsheet and the how to it must be doable, maybe even for me.

 

What values do we want or think must in it?

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Yes we are all referring to the 'sim1.dll' file. There was an addon altered file that was available on FS9.

 

The problem with this for FSX is that some devs (IFLY737ng) recognised this and altered their models to make them more realistic. If and when someone makes a realistic file for FSX, then owners of the IFL737 will have problems, methinks.

 

I do agree though with the OP that friction is WRONG in FSX.

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That would mean the PMDG NGX is incorrect, since it doesn't roll forard with idle thrust????

 

Well, the -800 anyway, yes. At least this is according to folks I know doing actual pilot training for the 738.

 

Im pretty sure to to get an 800 moving initially you need 40% N1. Then you can reduce it/change it as required

 

That would be the normal way to start taxiing after releasing the parking brake, yes. But if you just rellease your parking brake and just sit there with the thrust at idle it will start to slowly creep forward and eventually gather a little speed (depending on head/tail wind as well of course). I must admit I was surprised. I don't know whether it applies to the other models in the range.

 

Regards

Pete

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Its easily adjusted in the airfile, thrust at idle.

There is no way a developper can change the frictions on the plane alone, it needs involving into sim1.dll

They can only adjust the braking (see the cfg file) and thrust at idle.

However, changing thrust at idle gives you a different fuel consumption on the tarmac and probably also in the air, and the descend is changed also.

 

I am looking in the side frictions now, since that is the worst part imho.

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Thanks for all the responses. It looks like there is no trivial fix but interesting leads (I didn't know about the sim1.dll). I guess I am less bothered by the excessive friction itself than by the feeling that FSX has regressed from FS9 in that regard. Rolling down a runway in FS9 did require braking to stop. Not always the case in FSX ...

 

Thanks,

Pierre

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Well, the -800 anyway, yes. At least this is according to folks I know doing actual pilot training for the 738.

 

 

 

That would be the normal way to start taxiing after releasing the parking brake, yes. But if you just rellease your parking brake and just sit there with the thrust at idle it will start to slowly creep forward and eventually gather a little speed (depending on head/tail wind as well of course). I must admit I was surprised. I don't know whether it applies to the other models in the range.

 

Regards

Pete

 

 

I see what you mean now

 

Lee

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The main problem has allways been side friction. MS FLIGHT corrected it... :-/

There are problems with exactly this same subject on other sims, including MSFS's direct competitor - X-Plane10.

 

Each has it's bad aspects, but I still preffer FSX's model, even if not perfect. I know X-Plane's one will probably get addressed during the current v10 cycle... MSFS's will not... Maybe Prepar3d v2.0 brings a ground physics model closer to what we have in MS FLIGHT (still not perfect but very good...) or almost perfect, like in DCS World, Condorsoaring...

 

+1

 

:good:

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I'd say that the problem is that there is very little ground friction in FSX. It is ridiculously hard to get in trouble landing. Get a little off axis in a taildragger and you should know it immediately, with forces trying to throw you into a ground loop. It should be similar in a tri-gear, with side loads and tire deformation that you should feel in the motion of the aircraft. Others have mentioned the gliding on ice feeling. I think contact with the ground physics are almost non-existent. It's my biggest complaint with FSX. Some addons do get it better than others but none get that close in my experience.

 

So, I have no idea about the coding nuts and bolts but I'd guess that this lack of GROUND physics has been compensated for by unrealistic BRAKING in all planes. That's why people experience "friction" only along the inline axis of the aircraft, and why the OP and all of us sometimes experience silly deceleration rates on the ground at idle. I'd bet quite a bit that even with the brakes off, the code is always applying some braking when on the ground to SIMULATE friction without actually modelling any wheel to ground friction physics. I don't know, but that's my guess from over 1000 hours in many different FSX planes and trying to understand how FSX gets contact with the ground so wrong.

 

I also suspect that very little can be done about it outside of external physics modules on the line of what A2A does. And I'd LOVE for them to tackle this in their aircraft!!

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I think A2A should look into adding something like this to Accu-Feel

 

Obviously they can't fix the problems in fsx completely but I'm sure they could figure something out to make braking and friction more realistic

 

Lee

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Anyone cared to take a look in the excel sheet instead of rambling on ?

It CAN be done.

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As you mentioned above, looking at a set of hex values we don't understand doesn't tell us much. And I'm not sure what CAN be done without understanding what those values are used to do. I'm not sure there are many people outside the ACES team that know that.

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I have done it!. Now on to testing and tuning, but the first results are very nice!.

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Finding until now:

 

- sliding coefficient raised, saw no ill side effects like in fs9, like the shudder on start of roll.

- steering much more direct, great no more skid on normal taxi speeds.

- keeping runway centerline much better

- rolling friction lowered, little breakaway power needed, then taxi on idle, depending on weight of course

- much more difference on dry versus wet versus snowy runways and taxiways, as it should be.

- needed to adjust the brake value a bit in the aircraft cfg to compensate the lower friction. Easy.

 

Tests were with Cessna, DC3 and L749 and B737 at this moment.

 

AI doesnt seem to bother by the effects.

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no more skid on normal taxi speeds.

 

How fast are you guys taxiing anyway?? I've been able to get a skid in a turn on wet pavement by running way too fast. I like to keep about 12 knots ground speed on the straight and 8 knots in turns. I'll do 15 to get off the runway. I usually fly lighter aircraft, which may make a big difference.

 

Hook

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Finding until now:

 

- sliding coefficient raised, saw no ill side effects like in fs9, like the shudder on start of roll.

- steering much more direct, great no more skid on normal taxi speeds.

- keeping runway centerline much better

- rolling friction lowered, little breakaway power needed, then taxi on idle, depending on weight of course

- much more difference on dry versus wet versus snowy runways and taxiways, as it should be.

- needed to adjust the brake value a bit in the aircraft cfg to compensate the lower friction. Easy.

 

Tests were with Cessna, DC3 and L749 and B737 at this moment.

 

AI doesnt seem to bother by the effects.

 

Just tried it out.... I LOVE it...

 

I can realistically now simulate idle taxi on the NGX. Nosewheel is much more responsive. Thanks so much!!!

 

Also, single engine taxi on the NGX is MUCH more realistic... I can actually chug along at 15 kts without having to constantly leave the single engine at 40% N1.

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