Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throttle

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gonzman
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Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throttle

Post by gonzman »

I've noticed this behavior a few times with the p47 mostly , to mr it feels like the plane "lost" its friction with the ground, like that part of simulator code stopped working , landing on pure ice with no tread on the tires, the p47 would drift off to the left quite badly, not sure about the p51 yet but if I notice I'll post again

VulcanB2
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by VulcanB2 »

Hi,

I changed the saved flight, and the aircraft tracked the center line perfectly!! :D

Best regards,
Robin.
A2A/AccuSim. 'nuff said!

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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by VulcanB2 »

gonzman wrote:I've noticed this behavior a few times with the p47 mostly , to mr it feels like the plane "lost" its friction with the ground, like that part of simulator code stopped working , landing on pure ice with no tread on the tires, the p47 would drift off to the left quite badly, not sure about the p51 yet but if I notice I'll post again
Exactly! It is like the aircraft is on the ground visually, but acts like it is still flying. With the aircraft being kept level by the landing gear, rudder input results in a slip, instead of a turn as would be expected if the tyres had grip.

The question then becomes: does the sim_on_ground variable read ZERO when it is faulting?

Best regards,
Robin.
A2A/AccuSim. 'nuff said!

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DHenriques_
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by DHenriques_ »

VulcanB2 wrote:Nice find!!!

I have a saved situation involving an aircraft with a castoring NOSEWHEEL. Now I'm not sure if it is technically a tail dragger in order for this to function in FSX??? That aircraft never experiences oddities in landing, BUT the flight WAS saved after it had flown and landed again. :idea:

I'll change the default flight file back to the FSX default and shall try what you suggest.

Note that even when selecting an MP flight that the default flight file is still loaded, so any quirks as a result will be present at that point as well.

Best regards,
Robin.
I've been watching this thread progress with great puzzlement as I can not even come close to replicating what's being discussed on my system. In fact I have never seen this issue as discussed in FSX with any aircraft default or add on.
I will comment that we worked the Mustang's roll out carefully to duplicate the real aircraft's roll out behavior and to my eye here on my system this behavior is extremely close to the real Mustang.

Just to reiterate on the actual Mustang roll out specifically, on a normal roll out after touchdown what you get is a steadily decreasing rudder response as the roll out progresses. This can be quite surprising and takes some getting used to. For those used to a light tail dragger I will comment that it's a much different scenario. The landing weight of a P51 can be in the area of 9 to 10K lbs. There's a LOT of mass and inertia there. The Mustang isn't a Decathlon or a J3. Although the 51 will track straight if handled properly on the ground, with all that mass coupled with the decreasing dynamic pressure on the rudder, as speed decreases down to around 50mph and under, the Mustang could very well require a soft touch of intermittent differential brake (but not much and very carefully).
To put it another way, under 50mph, it's a soft "tap dance" on the rudder pedals if you're doing it right.
The trick to controlling the Mustang on roll out is in anticipating the SLIGHTEST diversion from the centerline. The earlier the response on the pedals the better. If the nose is allowed to wander more than a few degrees either way under 50mph, recovering it back to the centerline just using rudder can be difficult.

Aside from the above, if those having a directional control issue with the Mustang feel it's an FSX issue, just be advised I can not duplicate the issue here and have not seen it before in FSX as an issue.
My landings in the A2A Mustang are routine and straight on the runway consistently so whatever might be causing these issues I can't duplicate here.
This leaves us with the fact that there is an issue being reported and the issue has affected several different people. Whatever it turns out to be these threads are useful and I hope helpful to those affected.

Dudley Henriques

VulcanB2
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by VulcanB2 »

Hi Dudley,

Thanks for the response!

I greatly appreciate the info regarding the rudder and its effectiveness, but it is not a rudder effectiveness issue. :( The rudder is more than capable of creating a 40 degree slip angle during the problem occurrence. The problem is that the aircraft suddenly and unexpectedly starts slipping to the left without the nose moving at all. It is like you touched down with zero wind, then a 100 kt, 90 degree crosswind hits you - that's the only way I can describe what I'm seeing. :(

Best regards,
Robin.
A2A/AccuSim. 'nuff said!

Nico081
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by Nico081 »

That is my opinion, too. Thats what i wanted to say posts before. This is an issue apart from real aerodynamic logic and individual P51 flying techniques as nobody can better describe than Dudley due to his "on type" real expierience, this is an simulator issue.

I will also try to find a solution inside FSX itsself when my computer is back and available to fly.

Kind regards,

Nico
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by VulcanB2 »

Interesting... changing the save file did help a bit, but then I had the problem again.

Note that the aircraft was asymmetrically loaded (left tank near empty, right tank 35 gals). The reason for the massive asymmetry was due to racing and not balancing the tanks deliberately.

Note that if I refuel so the tanks are balanced, I will still see the problem once it has started. Maybe massive asymmetric fuel loading is triggering it?

Best regards,
Robin.
Last edited by VulcanB2 on 15 Jun 2012, 17:25, edited 1 time in total.
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DHenriques_
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by DHenriques_ »

Nico081 wrote:That is my opinion, too. Thats what i wanted to say posts before. This is an issue apart from real aerodynamic logic and individual P51 flying techniques as nobody can better describe than Dudley due to his "on type" real expierience, this is an simulator issue.

I will also try to find a solution inside FSX itsself when my computer is back and available to fly.

Kind regards,

Nico
I have to admit I'm at a loss to figure what could be causing this. Power or anything connected with power shouldn't be an issue in the equation as power should be at idle when this happens. Almost sounds like a flat tire. Trim shouldn't be a factor either.
Check the maintanence hangar for control issues. I'm thinking an assymetrical flap deployment.
Beats me fellas. Let me know if you find it. :-)
Dudley Henriques

Hobart Escin

Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by Hobart Escin »

It has to do with something flaky in the FSX engine itself I would have to say, definitely. Remember how goofy and unstable the default FSX Piper Cub is at full realism settings - it way over-exaggerates the natural instability of a tailwheel aircraft and will ground loop at times for no real reason at all. It defies physics.

I'm wondering if this hard coded goofiness inherent in the legacy FSX tailwheel coding is somehow seeping through to add-on aircraft like the A2A Mustang. However, if this were the case, I sure don't understand why only some of us experience it.

So far in my testing I'm starting a fresh session of FSX, selecting and positioning the default FSX C172 at an airport with clear weather, then switching to the A2A Mustang afterwards. I've not encountered the yaw bug YET so far by using this startup method, but who knows. I'll keep testing and report back. I do know for almost certain though that I can guarantee using certain previously saved .flt files will bring on the yaw bug behavior. Unless I'm crazy and delusional (a possibility too).....

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bigjuicyspider
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by bigjuicyspider »

Hobart, VulcanB2:

I just had a thought. Next time you experience this, immediately pause the sim, switch to external view, and let the sim roll again as you pay attention to the Left Tire. See if its rolling or if its locked up....
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Hobart Escin

Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by Hobart Escin »

bigjuicyspider wrote:Hobart, VulcanB2:

I just had a thought. Next time you experience this, immediately pause the sim, switch to external view, and let the sim roll again as you pay attention to the Left Tire. See if its rolling or if its locked up....
Will do Spiderfriend. Man, I really want to solve this.

Nico081
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by Nico081 »

As i sad before, at my system this issue has nothing to do with flat tires, unbalanced fuel or wrong flying techniques. I sometimes had it with the P40, P47, Cub, P51 and even with the B17 an B377 !??.
This required "nose right" effect short before touchdown has also nothing to do if i perform an high or low power approach. After touchdown massive slide sideways to the left of the runway. Yaw angle is same as short before touchdown which has to be around 20-40° nose right to maintain runway track, you additionally have do add engine power to become the nose more to the right. Massive right rudder and right hand wheel brake on maximum required to hold centerline track. At lower roll out speeds issue is solved. Normally the tires or landing gear should get damaged from that slide while on ground.

->Short before touchdown massive nose right required to maintain required track
->After touchdown massive nose right required to maintain requires track on the runway.
->Is rollout speed below a certain value, everything becomes normal.

It is nearly unable to control the aircraft against that "unknown" aerodynamic forces acting from right direction.

Kind regards,

Nico
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Hobart Escin

I'm done...no solution that I can find

Post by Hobart Escin »

Well, happened to me again just now after some extensive testing. There does not seem to be a solution guys; at least none that I can conceive of. I stopped flying the P-47 because of this issue, and now I'm afraid the P-51 is going to have to follow suite. I'm certainly not blaming A2A and I certainly appreciate the help of Dudley Henriques on this thread, as well as the other A2A customers who have tried in vain like myself to find a fix for this.

The problem of course is the hopelessly flawed coding somewhere deep inside FSX itself. I'm too frustrated with the unrealistic and flawed physics modeling that is a limitation inherent in FSX to want to even try to fly taildraggers in the sim anymore.

A2A will hopefully be releasing some nice jets in the near future, and when they do I'll eagerly come back to using their fine products. For now at least the Mustang gets uninstalled on my computer. I just can't justify trying to fight this issue without some clear concept of what is actually happening. Too many ruined flights for this old soldier.

Bye and thanks again everyone.

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bigjuicyspider
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by bigjuicyspider »

Hobart, this is an awesome plane that was released less than 3 weeks ago. Don't you think that it is a little early to just quit?
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whiic
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Re: Adverse Yaw Durring Rollout/Highspeed Taxi W/ Zero Throt

Post by whiic »

bigjuicyspider wrote:Hobart, this is an awesome plane that was released less than 3 weeks ago. Don't you think that it is a little early to just quit?
I think his reasoning was: P-47 has been around for YEARS and it still not has been fixed.
...and possibly can't be fixed as the problem might as well be within FSX's all too buggy core, instead of A2A's addon planes.

Since it might be a core FSX issue, and not everyone can replicate the bug, is it limited to some specific combination of FSX core & Microsoft expansion? FSX Deluxe, Gold, SP2, Acceleration, etc.?

On a side note, I don't think I've had this bug surface on my system. My FSX installation has Acceleration. I dunno if it's FSX Gold + Acceleration or some other variant. There's just too many to keep track...

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