Taxiing, brakes, rudder - how does it work (technically)?

[159th_Viper]

Courtesy of a fellow tester, Weta43:

 

It has a system where the rudder also controls a valve which applies more of whatever level of brake is applied to the side you turn the rudder towards ?

You can't apply one brake by pushing one pedal, but you do control how the stopping force is distributed across the wheels.

[MBot]

Well I think we all understood that. What we are asking is why the plane still turns at low speed (almost no airflow over the rudder) an *no* brakes applied.

[Sceptre]

Because it has nose wheel turning? Kind of like the sabre's, except you use brakes to get moving, once you are moving you can turn it. Just turn off nose wheel braking

[159th_Viper]

Well I think we all understood that. What we are asking is why the plane still turns at low speed (almost no airflow over the rudder) an *no* brakes applied.

 

See, I thought the quote was clear: The valve applies brake pressure to whatever side the rudder is turned towards, thus facilitating a turn with brake pressure via the valve without resorting to the main brake.

[MBot]

Your quote says: "more of whatever level of brake is applied to the side you turn the rudder towards".

 

So if no level of brake is applied, none is applied to the side you turn the rudder towards. So this is of no help for the question at hand.

[159th_Viper]

Your quote says: "more of whatever level of brake is applied to the side you turn the rudder towards".

 

So if no level of brake is applied, none is applied to the side you turn the rudder towards. So this is of no help for the question at hand.

 

:megalol:

 

OK then I tried.

 

Still do not see what the issue is: Apply left rudder, valve applies pressure to left wheel and facilitates turn to left. Apply right rudder, valve applies pressure to right wheel and facilitates turn to right, all the above without touching brake.

 

Apparently it is rocket science :D

Edited September 23, 2014 by 159th_Viper
Eliminate uncertainty

[MBot]

:megalol:

Still do not see what the issue is: Apply left rudder, valve applies pressure and facilitates turn to left. Apply right rudder, valve applies pressure and facilitates turn to right, all the above without touching brake.

 

Apparently it is rocket science :D

 

Ok, so this is different than what Weta said (he just explained the braking-turning mechanic). Is this secured knowledge or are you just stating this? Because this is nowhere to be found in the manual.

 

I am not saying it doesn't work like this (it would explain the the observed behaviour), but I would appreciate the confirmation that this is how the real jet works.

[159th_Viper]

It's no different: It's a matter of interpretation. I interpreted it correctly and you interpreted it incorrectly it would seem. Yes, one could pick apart the linguistics to suit one's particular interpretation but the explanation Weta proffered and I relayed at least three times now is correct, as confirmed by a member of the Dev team.

Edited September 23, 2014 by 159th_Viper

[Flagrum]

Richtungsänderungen werden mit Hilfe des Bremshebels am Steuerknüppel und den Seitenruderpedalen bewerkstelligt. Das funktioniert so: bei Neutralstellung der Seitenruderpedale und Ziehen des Bremshebels werden beide Hauptfahrwerksräder gleichmäßig abgebremst. Will man nun um die Kurve rollen, so tritt man das Seitenruder in die entsprechende Richtung aus und zieht gleichzeitig die Bremse. (also für rechts herum - rechtes Bein langmachen und bremsen). Dabei wird die entsprechend andere Radbremse entlüftet (bei einer Rechtskurve die linke Bremse).

source: http://www.mig-21-online.de/

 

My (crude) translation:

Directional changes are performed with help of the braking lever at the flight stick and the rudder pedals. This works like this: if the rudder pedals are in neutral position and the braking lever is actuated, both wheels are braked equally. To perform a turn, the rudder pedal on the appropriate side is to be pushed and the brake lever to be actuated (i.e. for a right turn - push right pedal and pull the brake lever). The opposite wheelbrake is then vented (i.e. the left wheel brake when performing a right turn).

 

The interesting part is, that it is not the wheel on the side of the turn is braked, but instead when you brake, the opposite wheel is braked less! That means, the rudder pedals are only responsible to open a venting valve, but not for actually applying/re-directing brake forces to any wheel. That makes sense as there would be no need for special precautions when using the rudder pedals in flight (to prevent that constantly pressure is applied to the brakes when it is totally unnecessary).

 

But, hrm, but this still does not explain how it all works when you turn without actuating the brake lever... Given the information above, one would suspect that during taxi constantly some ammount of air pressure is applied to the brakes (so that the venting valve can have an effect) - very unlikely, right?

[Tango]

It's still no clearer.

 

The "no brake turning" ability seems to be airspeed derived. I tried applying a high power setting (80%) with the brakes fully applied, released the brakes, then applied rudder before the aircraft accelerated, and I didn't see any turning until the aircraft passed ~25 kph.

 

In the posts above, was the suggestion that differential wheels brakes are automatically applied with rudder, and that the turn is still brake induced even though we are not pulling the brake lever ourselves?

 

Best regards,

Tango.

[[DBS]TH0R]

In the posts above, was the suggestion that differential wheels brakes are automatically applied with rudder, and that the turn is still brake induced even though we are not pulling the brake lever ourselves?

 

Correct. For me, the plane turns with rudder movement only at 60-80% power starting at 10 km/h (measured from the external view).

 

I did not use the brake lever, and I did not see any of the pneumatic pressure gauges move.

[swe_badger]

I have the Sibwings Antonov AN-2 for FSX and it uses a very similar pneumatic system to power the breaking and turning.

[MBot]

I did not use the brake lever, and I did not see any of the pneumatic pressure gauges move.

 

The fact that the pneumatic pressure gauges don't move is very interesting. This indicates that brakes are not used in "non-braked rudder input", opposite to what was explained to us above.

[159th_Viper]

This indicates that brakes are not used in "non-braked rudder input"

 

Exactly. I said all along it was a valve which applied necessary pressure to have a 'braking' effect facilitating a turn in whatever direction the rudder is applied. Nowhere was it stipulated that the brake is used, obviously common cause to the discussion I thought.

 

Will teach me to assume the obvious I suppose.

[Buzzles]

Exactly. I said all along it was a valve which applied necessary pressure to have a 'braking' effect facilitating a turn in whatever direction the rudder is applied. Nowhere was it stipulated that the brake is used, obviously common cause to the discussion I thought.

 

Will teach me to assume the obvious I suppose.

 

Eh? How does it actually work then?

 

How you can you have a braking effect but not use a brake?

 

Either the wheel brakes are being used, or they are not.

 

The impression I think a lot of us take from the manual is that the brakes are *only* actuated when you pull the lever, and how much differential braking is down to rudder control as part of that.

 

What you're saying is that *any* rudder input uses the brakes, regardless of the lever being pulled, and that's opposite to what people are actually experiencing where the rudder has no affect at all at slow speeds.

[KaspeR32]

Exactly. I said all along it was a valve which applied necessary pressure...

 

According to what Flagrum posted, what you've been saying all along is wrong. :music_whistling:

[Esac_mirmidon]

I understand Valve-pressure vs brakes.

 

Different things for me

[[DBS]TH0R]

What you're saying is that *any* rudder input uses the brakes, regardless of the lever being pulled, and that's opposite to what people are actually experiencing where the rudder has no affect at all at slow speeds.

 

Apparently so. Rudder as in air moving over it isn't effective at 10 km/h, but the plane turns anyway without using the brake lever. For me rudder has effect at very slow speeds.

 

Clearly a valve which applies necessary pressure to have a 'braking' effect facilitates a turn in whatever direction the rudder is applied - at very slow speeds and minimum ~70% power.

[Corrigan]

There's something fishy here still.

 

If rudder activates diff braking without us touching the brakes, why don't we see it on the manometer? Why doesn't the manual (or anything else I've ever read) explain this?

 

If, when no brakes are manually applied, we are turning just by aerodynamics, why can we turn so sharply at unphysically low speeds?

 

There has to be something amiss with the sim's behaviour, IMO.

[AndyHill]

I think it's just over-effectiveness of the rudder at low speeds or too little friction in the front wheel mechanism (if friction is 0, any small force, even one over a rudder at 10km/h is easily enough to turn the wheel). As mentioned earlier the suspension stuff is being looked at anyway, so maybe this behavior will change as well.

[Dejjvid]

You are mixing multiple things.

 

At high speed (let's say 100 kph) then NOSE WHEEL STEERING is available.

 

I'm very intrigued as to why it doesn't have full-time nose wheel steering, and how the system works.

 

Best regards,

Tango.

 

@Tango

No, you are the one mixing things up and assume stuff. There is no active nose wheel steering. The nose wheel is pivoting freely.

 

@Everyone that care

If you MUST apply brakes in order to turn, then the model is wrong in the current state. But IF a movement of the rudder actuate the brakes (both), and venting the opposite cylinder. The current implementation is correct, and explain why the aircraft behave like it does.

[Flagrum]

@Tango

No, you are the one mixing things up and assume stuff. There is no active nose wheel steering. The nose wheel is pivoting freely.

 

@Everyone that care

If you MUST apply brakes in order to turn, then the model is wrong in the current state. But IF a movement of the rudder actuate the brakes (both), and venting the opposite cylinder. The current implementation is correct, and explain why the aircraft behave like it does.

 

Current situation: you CAN turn without applying brakes IF your speed is higher than about 10 km/h - although the turn radius is large...ish.

You CAN turn with applying the brakes and using the rudder pedals, with minimum turn radius.

 

When turning without manually applying the brakes, there is no evidence that pressure air is used up (according to the pressure gauge). This indicates that no braking of the wheels happen at all in this case.

 

If it is correct - as the consent in this thread seems to be - that the nose wheel is pivoting freely and can not be steered, then the only remaining force is induced by the deflected rudder. Which would mean, that there is a bug as the airflow of 10 km/h can not realistically cause a direction change of the aircraft so easily (mind you: even smallest rudde pedal inputs result in a [small] direction change).

 

What AndiHill suggested, that the nose wheel is not modelled correctly (friction) seems to be the most plausible explanation for me atm.

[Irregular programming]

maybe it's a very heavy pilot, and he is just leaning?

[sydost]

...then the only remaining force is induced by the deflected rudder. Which would mean, that there is a bug as the airflow of 10 km/h can not realistically cause a direction change of the aircraft so easily.

 

How about testing if it is aerodynamic force by setting a 20 km/h wind and taxiing downwind at a speed of 20 km/h. If it still turns it shouldn't be aerodynamic force in the model which causes the turning.

[Corrigan]

How about testing if it is aerodynamic force by setting a 20 km/h wind and taxiing downwind at a speed of 20 km/h. If it still turns it shouldn't be aerodynamic force in the model which causes the turning.

 

Good idea, do it!

Of course, the devs might have "cheated" and used actual rudder input as a proxy for rudder deflection and subsequent aerodynamic forces, if you see what I mean. But your test can still tell us something.