F-18 NWS Hi

[bbrz]

I think bbrz meant the aircraft just stopping, not somehow getting stuck in a constant turn.

Exactly

[bbrz]

So in a phenomenal waste of time I downloaded and watched that track file. Not exactly earth shattering.

Why should taxiing around at less than 5kts be 'earth shattering?'

[Tom Kazansky]

I will test and see how well making a track file works through VR. I have no problems in showing the info as it will just give a visual representation of what I can always duplicate.

 

 

thank you.

[Greyman]

Let's say that the modelling of the turn of the front wheel used to determine the direction of travel does not exactly match the graphical representation of said front wheel, which is probably capped before it gets to 90degrees..

 

If the input to the front wheel would turn it beyond 90 degrees. which could be a function of the slider that the OP is using, then the back of the wheel becomes the front and the wheel will then roll the other way, causing the aircraft to move in the opposite direction. At, or very close to, 90degrees. the wheel would probably stop rolling altogether.

 

The solution would therefore either be for ED to set a limit for how tight the front wheel can move, to match that of the actual aircraft or for the OP to somehow calibrate the slider axis so that it doesn't try to turn the wheel so much.

 

simples :)

Edited September 25, 2019 by Greyman

[slug88]

Let's say that the modelling of the turn of the front wheel used to determine the direction of travel does not exactly match the graphical representation of said front wheel, which is probably capped before it gets to 90degrees.

 

I don't see any evidence that that is the issue. The actual situation was already perfectly explained by Deano:

 

The reason for turning in the wrong direction is because once the front tyres are sliding across the ground at almost 90 degrees to the direction of travel they are no longer providing any steering force only drag, but because of the offset of those wheels from the rotational axis they are actually stuck out to the side slightly. If you’re trying to turn right the wheels will be to the left of the nose, that drag on the left hand side of the nose is what turns the aircraft left.

 

https://forums.eagle.ru/showpost.php?p=4046610&postcount=26

 

I think Stubbie's issue is (as many people have been trying to point out) that he's putting the nosewheel into full deflection too rapidly. If you steadily and smoothly go into full deflection (while maintaining a quite low speed), the nosewheel will not slip.

[slug88]

I can duplicate the issue at such low speeds that the aircraft will stop itself.

 

The reason it stops itself is because when the nosewheel is slipping it's acting as a giant brake. So the fact that the aircraft stops on its own in this situation isn't saying much.

[Greyman]

So how else would you explain the aircraft travelling in the opposite direction to the way that the rudder pedals are telling it to go?

[slug88]

So how else would you explain the aircraft travelling in the opposite direction to the way that the rudder pedals are telling it to go?

 

Once again, this is the explanation:

 

The reason for turning in the wrong direction is because once the front tyres are sliding across the ground at almost 90 degrees to the direction of travel they are no longer providing any steering force only drag, but because of the offset of those wheels from the rotational axis they are actually stuck out to the side slightly. If you’re trying to turn right the wheels will be to the left of the nose, that drag on the left hand side of the nose is what turns the aircraft left.

 

https://forums.eagle.ru/showpost.php?p=4046610&postcount=26

 

In other words: when the nosewheel is in full deflection and skidding, there is an asymmetric braking force. This asymmetry causes the aircraft to turn. Due to the geometry of the landing gear, the asymmetry always pushes in the opposite direction of the commanded rudder input. The in-game behavior seems realistic and I'm sure the real aircraft would behave the same.

Edited September 26, 2019 by slug88

[Greyman]

Ah ok then. You believe that if you will and I'll stick to my theory.

 

Just look at the max angle that the graphical wheel can turn and a free spinning wheel would easily make that turn at the sorts of speeds we are talking about. It would certainly not stop spinning in a way that you describe and even at a higher speed I'd love to see a RL video of a stopped and skidding wheel travel in anything other than a straight line.

 

Either way, it will be any easy theory to prove or disprove, by the OP limiting the range of their slider axis to a point where the aircraft follows the track of the wheel at its maximum graphical deflection.

[Lex Talionis]

Interesting thread.

 

Aircraft with hi gain such as the 18, it is very possible that it can be engaged with too much momentum, at too high a relitive angle, such that the contact patch of the tires loose grip and slides.

 

Once sliding occors, the tire is no longer a "tire" and is simply a surface that is sliding on another surface with no bias to direction.

 

When at the boat, sliding on various surfaces with varying dagrees of worn out anti skid, it is very common to to slide in just about any direction. Once sliding occurs, it was anyones guess where you would go. After a rain at the field the same would be encountered. On a dry day, the full deflection of the front wheel at hi gain would be enough that it would act more like a brake than a wheel. Hi gain for a navy aircraft is designed to maneuver at slow speeds to stay on a confined flight deck. Often differential braking may be required to get the jet moving out of the LA if you caught the 4 wire to avoid conflict with the bow cats for whatever reason.

 

This is also why turning off the anti skid was part of your "feet wet" checks going to the boat as the anti skid would be in a perpetual state of "anti" such that you would get effectively no brakes.

 

Context is everything. Hope this helps:)

Edited September 26, 2019 by Lex Talionis

[slug88]

Ah ok then. You believe that if you will and I'll stick to my theory.

 

Theorize all you want, but this behavior is explained by basic highschool-level physics.

 

*When the wheel is skidding, it's creating drag.

*When the wheel is in full deflection, that drag is off to one side of the nose.

*This will cause the nose to turn in the direction with more drag.

 

Do you disagree with any of those statements?

Edited September 26, 2019 by slug88

[Greyman]

I have a fair bit of spare time, so I'll do a bit of experimentation with the axis curve on my rudder pedals, to see, if my theory is correct, whether I can match the modelled angle of turn with the direction of the graphical front wheel.

 

I'll report back, whether or not to eat humble pie. :)

 

Edit: by the way, how do you define "full deflection". Would that be 90 degrees or the deflection drawn on the visual model?

Edited September 26, 2019 by Greyman

[slug88]

Edit: by the way, how do you define "full deflection". Would that be 90 degrees or the deflection drawn on the visual model?

 

Actually, you can change my statement to read "any amount of deflection". If the front wheel is skidding and there is any amount of rudder input, you're gonna get asymmetric drag and the nose will turn. The effect is most pronounced when the deflection is exactly 90 degrees in either direction.

[Deano87]

Guys, Lex just answered your question for you.

 

https://forums.eagle.ru/showpost.php?p=4048613&postcount=60

[slug88]

Guys, Lex just answered your question for you.

 

https://forums.eagle.ru/showpost.php?p=4048613&postcount=60

 

Yes but Lex is talking about real life, we're talking about the idealized world of a video game that simulates newtonian physics :)

[Stubbies2003]

thank you.

 

 

Sigh. So right before I went into SP to make a track I had looked at the rudder controls to verify it didn't look like it was doing anything funky. All looked fine so I cancelled twice back to the main screen which *shouldn't* have changed anything and now I can hardly get this problem to occur at all. If DCS decides to start doing it again consistently then I will make a track showing the issue. As it is I have tried several times in SP on caucus and PG maps and NWS works just fine. I can see it rarely when in MP but not consistent at all.

[Stubbies2003]

The reason it stops itself is because when the nosewheel is slipping it's acting as a giant brake. So the fact that the aircraft stops on its own in this situation isn't saying much.

 

 

No. I know what you are referencing as during testing after this problem almost went away I can see the aircraft come to a sudden stop in tight turns but the problem isn't related to that at all.

 

When I could duplicate this just to prove to myself it wasn't an issue of going too fast I had the aircraft going VERY slow. I would fully deflect and it would start to go to the correct side, then after a bit straighten out then turn and start heading the wrong direction then it would stop due to lack of speed combined with friction/drag of the moving tires. That stop wasn't sudden at all unlike the ones I see now with big turns with it working properly.

[Greyman]

Sigh. So right before I went into SP to make a track I had looked at the rudder controls to verify it didn't look like it was doing anything funky. All looked fine so I cancelled twice back to the main screen which *shouldn't* have changed anything and now I can hardly get this problem to occur at all. If DCS decides to start doing it again consistently then I will make a track showing the issue. As it is I have tried several times in SP on caucus and PG maps and NWS works just fine. I can see it rarely when in MP but not consistent at all.

 

Did you check that you hadn't left your axis settings in their modified state. (Sorry, I have read your OP again and saw that you had already managed to get rid of the issue by tuning your rudder/slider axis.)

[Stubbies2003]

Once again, this is the explanation:

 

 

 

https://forums.eagle.ru/showpost.php?p=4046610&postcount=26

 

In other words: when the nosewheel is in full deflection and skidding, there is an asymmetric braking force. This asymmetry causes the aircraft to turn. Due to the geometry of the landing gear, the asymmetry always pushes in the opposite direction of the commanded rudder input. The in-game behavior seems realistic and I'm sure the real aircraft would behave the same.

 

 

The problem I have with this theory is when it is working correctly and the aircraft gives the sudden stop I can leave the rudder/NWS position the same and give it a fair amount of throttle to get it to move and it doesn't slide. It turns in the direction selected.

Edited September 26, 2019 by Stubbies2003

[Stubbies2003]

I think Stubbie's issue is (as many people have been trying to point out) that he's putting the nosewheel into full deflection too rapidly. If you steadily and smoothly go into full deflection (while maintaining a quite low speed), the nosewheel will not slip.

 

 

No it isn't even an issue of pushing it over too fast as I can do that and as long as the aircraft isn't going too fast then it behaves fine. If I did that with too much speed and it behaved badly I wouldn't be here talking about it.

[Stubbies2003]

Did you check that you hadn't left your axis settings in their modified state. (Sorry, I have read your OP again and saw that you had already managed to get rid of the issue by tuning your rudder/slider axis.)

 

 

That is why I specified that I hit cancel twice. I didn't change anything I simply went in and looked at the movement on the axis to verify it was going full one way then the other then I cancelled out back to the main menu. That shouldn't have changed anything.

[Greyman]

While you're here and possibly at a location where it isn't nearly 1am, have you tried watching the front wheel while adjusting your rudders? What I'll be looking at later today, if you haven't already, is whether the wheel stops turning before your pedals get to full deflection?

[Stubbies2003]

While you're here and possibly at a location where it isn't nearly 1am, have you tried watching the front wheel while adjusting your rudders? What I'll be looking at later today, if you haven't already, is whether the wheel stops turning before your pedals get to full deflection?

 

 

I was in F2 view but wasn't looking specifically for that but I can the next time I fly MP.

[Lex Talionis]

Theorize all you want, but this behavior is explained by basic highschool-level physics.

 

*When the wheel is skidding, it's creating drag.

*When the wheel is in full deflection, that drag is off to one side of the nose.

*This will cause the nose to turn in the direction with more drag.

 

Do you disagree with any of those statements?

 

This premise is not quite absolute. Direction bias is more a function of if the wheel has any rotation at all when it starts to skid. There is very little bias as to what direction once the wheels are no longer rotating. (all things equal i.e. tire pressure, side wall % etc) Wheels are imparting more friction while they are rolling and keeping positive directional traction, then when they slide and lose directional traction. Once a wheel is no longer rotating and is sliding, it has minimal bias to slid in the direction of rotation and more in the direction of inertia. If the inertia is great enough, probably as is the case when a 40,000lb chunck of aluminum (10x the weight of a car) is pushing two relatively tiny tires ( half the size of car tires), with two larger main gear tires creating a bias to go straight and activly fight what little turning tendinacy those smaller tires may have, it becomes very plasable if not probable. If a wheel had a propensity to slid in the direction of rotation even when locked, there would be no need for anti lock systems. The hi gain angles achieved in the hornet make locking up the front tire at full deflections relitively easy at anything other than taxi speeds. Deano gives a good explanation why the aircraft behaves the way it does given geometrical locations of the friction points once skidding. Once you stop the "slide" directional traction is regained and the wheel rolls again.

 

Context is infinantly important in these engineering thought experiments.

 

All that said, the game does slide a bit easy. But once sliding, it does what would be expected.

 

EDIT : just realized the primary concern was just that it rolls again after stopping. Sorry for all the excessive preamble to that explanation.

Edited September 27, 2019 by Lex Talionis

[Greyman]

Having spent a little time actually watching how far the nosewheel turns in NWS HI and confirming that it does stop turning at more or less the point at which my rudder pedals are at full deflection it looks like my theory about the causes of hornet "oversteer" was not correct/lacking in evidence/flawed/wrong. "It is no more, it is an ex" theory

 

Let's just say that this "humble pie" tastes a little salty, albeit not totally inedible. :)

 

Sorry all and thanks @Lex, for the reality check.