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Differential Braking


Thomasew

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Hi,

 

In Matt's video, .. An introduction to the L-39, .. he talks about the fact that there is no nose-wheel steering, .. and that ground handling is done using differential braking.

 

.. however, .. I can only find one wheel brake axis .. :helpsmilie:

 

Am I missing something?, .. besides the other wheel brake axis, that is ..

 

 

Cheers

Tom

He Who Will Not Risk Cannot Win

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Hi,

 

In Matt's video, .. An introduction to the L-39, .. he talks about the fact that there is no nose-wheel steering, .. and that ground handling is done using differential braking.

 

.. however, .. I can only find one wheel brake axis .. :helpsmilie:

 

Am I missing something?, .. besides the other wheel brake axis, that is ..

 

 

Cheers

Tom

 

You are missing rudder input, and maybe throttle.

There is only "one" break handle, in front of you stick.

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There are two main methods of differential braking. In the USA (among other places), differential braking is independent of rudder input, with the top of each pedal being depressed for the respective brake (as opposed to the normal sliding action for rudder input). In Russia (among other places), differential braking is tied to rudder input, with a single lever being pulled to activate the brakes, and then the rudder pedals being depressed (via the normal action for rudder inputs) to increase pressure on brake and decrease on the other.

 

The US system is superior for control (IIRC, Russian carrier fighters adopted it because of the high demand for fine control on carrier decks) but, as I understand it, the Russian system is superior for cost & ease of maintenance.

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and as i discovered in the manual, you have to move the rudder above 18° on each side to actually operate the differential braking !

 

so to turn it, give full rudder input, and map an axis on the brake (but it actually works well with keyboard too )

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  • 2 weeks later...
and as i discovered in the manual, you have to move the rudder above 18° on each side to actually operate the differential braking !

 

so to turn it, give full rudder input, and map an axis on the brake (but it actually works well with keyboard too )

 

18° of actual deflection seems to be close to 100% throw on my pedals, which makes taxiing a PITA. I wonder if there's a way to tune this engagement point.

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I squadron mate helped me with the brakes and my issues were solved instant. For me, it works with this brake settings:

 

screen_151006_183745zhuuo.jpg

 

For the rudders, I use the default settings.

 

 

Best regards,

Fire

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I squadron mate helped me with the brakes and my issues were solved instant. For me, it works with this brake settings:

 

...

 

For the rudders, I use the default settings.

 

 

Best regards,

Fire

 

So that makes my toebrakes more sensitive (as predicted) but is there any easy way to get the differential braking to engage before 18 degree rudder deflection (which is basically max, no?)

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for me - it seems to engage as soon as I apply any rudder - as long as I have the right amount of brake on & allow enough room for the nose wheel to castor around.

 

Well, this is strange - in my config, the left/right brake engages only when rudder is nearly fully deflected and brake depressed, otherwise both brakes work - you can check it in a window after pressing rctrl+enter. It works exactly as in the real thing, so I am happy with it. The technique I am using and works very well and reflects a real life technique is the following: Before initiating a turn apply full rudder in the direction of the intended turn and control the amount of turn by long/short press of the brake. When small corrections are needed, apply full rudder and only tap the brake, works great.

 

You can also read about it here for example; from a real pilot:

http://www.warbirdalley.com/articles/l39pr.htm

 

Taxiing is one of the more quirky aspects of operating the L-39. It's definitely a skill which can only be learned by doing -- no amount of mental preparation or studying can fully prepare you for it. After some practice it's not a big deal. Like the vintage MiG fighters and the Yak-52 and Nanchang CJ-6 trainers, the L-39 utilizes a stick-mounted wheel brake lever. There is no nosewheel steering -- the front wheel assembly castors freely. A selector valve sends hydraulic pressure to the left and right main wheel brakes in proportion to the rudder pedal deflection, and in proportion to how hard you squeeze on the handle. This means that if you need to make a left turn, no matter how small or large, you push the left pedal ALL the way down, then modulate the turn by squeezing either lightly (for a gentle turn) or more forcefully (to crank the nose around in a tight spot.) To stop a turn (again, no matter how small or large), you'll need full opposite pedal and some more carefully-modulated squeezing of the brake lever. You can actually do a 180-degree turn in the width of a narrow taxiway like this, but it takes a bit of momentum to do it. Careful speed management and anticipation are the keys to avoiding looking like a rank amateur, or worse, when maneuvering an L-39 on the ground. You can always spot a pilot who's trying it for the first time: They're the one who has decided to steer it like a "normal" airplane by holding down the brake lever a bit and simply steer using the pedals. This invariably results not only in prematurely-worn brakes, but a Pilot-Induced Oscillation and a lot of cussing.


Edited by Dr_Arrow
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The MiG-21 and MiG-15 use the same system but they seem to be easier to handle especially if you have wheel brake bound to an axis. I bound the L39 wheel brake to the same axis I used for 21 and 15 and it seems to be more 'On/Off' than the other planes making it hard to just where the sweet spot is for steering.

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Well, this is strange - in my config, the left/right brake engages only when rudder is nearly fully deflected and brake depressed, otherwise both brakes work - you can check it in a window after pressing rctrl+enter. It works exactly as in the real thing, so I am happy with it. The technique I am using and works very well and reflects a real life technique is the following: Before initiating a turn apply full rudder in the direction of the intended turn and control the amount of turn by long/short press of the brake. When small corrections are needed, apply full rudder and only tap the brake, works great.

 

You can also read about it here for example; from a real pilot:

http://www.warbirdalley.com/articles/l39pr.htm

 

This is how mine work. Still having trouble taxiing as I slowly learn...

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There are two main methods of differential braking. In the USA (among other places), differential braking is independent of rudder input, with the top of each pedal being depressed for the respective brake (as opposed to the normal sliding action for rudder input). In Russia (among other places), differential braking is tied to rudder input, with a single lever being pulled to activate the brakes, and then the rudder pedals being depressed (via the normal action for rudder inputs) to increase pressure on brake and decrease on the other.

 

The US system is superior for control (IIRC, Russian carrier fighters adopted it because of the high demand for fine control on carrier decks) but, as I understand it, the Russian system is superior for cost & ease of maintenance.

 

Braking is proportional to pedal displacement, but nobody does it this way IRL. Instead, full rudder input left or right, and modulate the amount of turn with the amount of pressure on the brake lever. A series of small squeezes on the brake lever gets the best result.

 

You would be flying solo in a real L-39 with 5-7 hours of instruction. To taxi it for style points requires at least another 15-20 hours of practice. :-) Keep speed above a walking pace and this makes it easier.

 

The Russian system is superior in some ways. Since the nose wheel is not connected to the tail you can use the crowning of a taxiway and the wind to "sail" the plane straight down the yellow line using only the rudder. Also, you cannot take off or land with full rudder deflection in a plane that has nose-wheel steering. This gives planes with differential braking a higher crosswind component rating.

 

When doing a formation takeoff in planes with differential braking, line up closer to abreast than you would with nosewheel steering. Usually dash-2 has to make some initial corrections during the takeoff roll and when those corrections are made he will drop back and be right on the bearing line.


Edited by jonboede
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It takes some getting used to. The bite for braking seems to be quite far down the wheel brake axis making it quite sensitive.

 

Also, you can't be sure which way your nose wheel is aligned, so if you stop and then move off you can end up veering in the wrong direction. Is there a way to re centre the nose wheel other than moving forward?

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I changed my rudder saturation to 80% instead of 100%, with no deadzone and no curve, and it seems to help a lot, since I need less pedal deflection to engage the differential braking. Thx for the suggestions!

 

(Oh, and I'm using the brake axis curve posted above as well)

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Interesting about having to turn rudder so hard initially. I use the handle on warthog stick for my brake seems to work ok :)

Same here. I tried one brake on physical rudder, though its analogue, my braking leg has to do this on right pedal with steering, which I find painful. Now mapped it to stick handle like you and small nudges seem to work fine. Of course its 1 or 0.

 

Sent from my SM-T231 using Tapatalk

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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The MiG-21 and MiG-15 use the same system but they seem to be easier to handle especially if you have wheel brake bound to an axis. I bound the L39 wheel brake to the same axis I used for 21 and 15 and it seems to be more 'On/Off' than the other planes making it hard to just where the sweet spot is for steering.

21 is not same as 39. In 21 the wheel turns as soon as rudder applied. In 39 it turns around extreme rudder.

 

Sent from my SM-T231 using Tapatalk

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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Same here. I tried one brake on physical rudder, though its analogue, my braking leg has to do this on right pedal with steering, which I find painful. Now mapped it to stick handle like you and small nudges seem to work fine. Of course its 1 or 0.

 

Sent from my SM-T231 using Tapatalk

 

I setup a custom brake curve as was mentioned elsewhere (earlier in this thread maybe?) such that the brakes reach 80% saturation at around 35% throw. This seems to give me much better toe-tap ability.

 

I also changed my rudder to saturate earlier, which limits how much rudder pedal deflection is needed to steer.

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I'll try this. Thanks

 

Sent from my SM-T231 using Tapatalk

AWAITING ED NEW DAMAGE MODEL IMPLEMENTATION FOR WW2 BIRDS

 

Fat T is above, thin T is below. Long T is faster, Short T is slower. Open triangle is AWACS, closed triangle is your own sensors. Double dash is friendly, Single dash is enemy. Circle is friendly. Strobe is jammer. Strobe to dash is under 35 km. HDD is 7 times range key. Radar to 160 km, IRST to 10 km. Stay low, but never slow.

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  • 2 weeks later...

One quick followup, in-case anyone brainfarts like I did.

 

I mapped both JOY_X and JOY_Y to the wheel brake, so I can use either toe to brake. I applied the curves from the post above, and all was happy... but only when making right turns.

 

Turns out that I forgot to apply the same curve to JOY_X as JOY_Y, leading to me rolling into the weeds (and having to do a mil-power taxi through the grass) a few times when attempting to turn left.

 

=P

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