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

[Flagrum]

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.

Done. :o)

 

Wind itself seems to have no influence - tail wind, head wind, no difference.

 

But I noticed that the actual speed when the steering is possible, is 5-6 km/h (F2 view). As soon as you reach 5+ km/h, the steering capabilities suddenly set in and then don't really change any more with increasing speed. You start to skid and the aircraft banks until it tips over the side eventually - as one would expect. But besides that the turn radius that is possible, don't really change. You can turn 360 deg. on the Kobuleti runway, without applying brakes, with 5 km/h or with 10...15 km/h (then it becomes a bit trickier - as mentioned above).

 

I haven't measured it exactly, but you need the whole runway width for 360 deg without brakes, and about 2/3 of that if brakes are applied.

[Corrigan]

Ok, so the physics appears to suggest rudder input actually applies diff. braking on its own, since there's no airspeed dependence according to the above.

 

Now, if this is the case, why doesn't the pressure meter show anything? Are these valves not monitored? Has it been mistakenly left out in the sim?

Also, why hasn't the literature been clearer? As I said before, everything I've read on the subject suggests that you can turn only when you apply brakes.

 

And that's including what Viper posted (and probably misunderstood...)

 

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.

Edited September 23, 2014 by Corrigan

[Flagrum]

Ok, so the physics appears to suggest rudder input actually applies diff. braking on its own, since there's no airspeed dependence according to the above.

 

Now, if this is the case, why doesn't the pressure meter show anything? Are these valves not monitored? Has it been mistakenly left out in the sim?

Also, why hasn't the literature been clearer? As I said before, everything I've read on the subject suggests that you can turn only when you apply brakes.

 

And that's including what Viper posted (and probably misunderstood...)

Well, physics suggest that there is a bug. :o)

 

From the DCS manual (was probably quoted already?):

allow the aircraft to gather about 40-60km/h (20-30nmi/h) then decrease the power to maintain that speed (~65%). At this speed you will be able to use the rudder to maintain direction, so you’ll avoid wasting compressed air when braking to maintain direction. However, if you are making turns, you need to decelerate to 15-20km/h (9-11nmi/h) and use rudder controls and brakes to turn the aircraft.

And that is not what is happening in game. Either the nose wheel friction is incorrect or/and the effects of the rudder are exaggerated. Probably the latter is the real cause (rudder authority sets in way too early, according to what the DCS manual states).

[Corrigan]

Right, but it has to be more than exaggerated rudder authority since it doesn't care about wind.

[ObvilionLost]

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).

 

 

Just though I should add a little illustration of the process, from MIg-21bis maintenance manual.

 

[portman]

Just got feedback from a former GDR (East Germany) MiG-21 pilot, and he stated that you could NOT turn just by using the rudder pedals. Even at high taxiing speed you always had to apply the breaks to turn.

Another interesting aspect he mentioned is that you could adjust braking power (like on a bike) by pulling the lever just a bit. In game you only can "brake" or "not brake".

[Dejjvid]

Nice! But does this info apply to the Bis? We need input from LN. Their coder is an actual pilot, so I'd take his word.

 

And btw, you can map the brake to an axis. :)

[portman]

And btw, you can map the brake to an axis. :)

 

Cool! :doh:

[Frischi234]

Just got feedback from a former GDR (East Germany) MiG-21 pilot, and he stated that you could NOT turn just by using the rudder pedals. Even at high taxiing speed you always had to apply the breaks to turn.

 

Nice! But does this info apply to the Bis? We need input from LN. Their coder is an actual pilot, so I'd take his word.

 

Same way in the Bis.

[Brun]

Another interesting aspect he mentioned is that you could adjust braking power (like on a bike) by pulling the lever just a bit. In game you only can "brake" or "not brake".

You can assign the brake lever to an axis. It works exactly as it should.

[portman]

You can assign the brake lever to an axis. It works exactly as it should.

 

Done. But it doesn't sound as good as if you press and release "W" :music_whistling::D Hope that's going to be fixed.

[[DBS]TH0R]

Well, physics suggest that there is a bug. :o)

 

From the DCS manual (was probably quoted already?):

And that is not what is happening in game. Either the nose wheel friction is incorrect or/and the effects of the rudder are exaggerated. Probably the latter is the real cause (rudder authority sets in way too early, according to what the DCS manual states).

 

Unless someone provides documentation that the plane can turn with rudders only (not using the brake lever), it definitely looks like a bug.

[Fishbreath]

As I posted earlier in the thread, the document in this thread remarks that the MiG has rudder authority at 20-30 knots. Turning on the ground with the rudder is definitely possible, it's just possible too slow right now, apparently.

[SilentEagle]

While I don't know how LN have modeled the suspension system and I haven't tested it myself, I had a terrible time trying to model a free castoring nose wheel with rudder based differential braking on the L-39, which works in the same fashion as the Mig-21. Eventually I just added a bit of nose wheel steering (temporary cheat) for low speeds to assist the horrible turn radius we were experiencing, because the nose wheel refused to turn sufficiently when differential brakes were applied.

[Corrigan]

I suspect that's what's happened here. To be honest, I think they overdid it.

[Azrayen]

Thanks SE, that looks like a probable scenario.

 

Would be nice to get some confirmation from LN guys, though, as soon as they had time to rest a little from the release-frenzy :)

[ff4life4]

Well its been nerfed :noexpression:

 

http://forums.eagle.ru/showthread.php?p=2192715#post2192715

[Krebs20]

Please leatherneck, make it a checkbox or option to use the steering the right way!

[Snarf]

I am having a lot of difficulty with the steering of the Mig 21, following the manuals instructions to the letter I can barely get the aircraft to turn. There is no mention of differential brakes in the manuals or commands for them. There seems to be a lot of talk of valves attached to the rudder system which allow you to differentially brake however once again no mention in the manual. I have seen some people complain that the aircraft turns to easily on rudder alone, this has not been my experience at all. I would prefer it to operate realistically but that manual should be updated with clearer instructions on how to turn the aircraft as the present ones don't explain at all.

[[DBS]TH0R]

Do you enable nose wheel catering before you start turning?

[Snarf]

Castoring is not something you can enable, at least in real aircraft. It simply pertains to the geometry of the gear. Castored wheels can be locked in tail draggers but normally the most a castored non steering nose wheel would have is light spring centring. The Mig nose wheel does turn so is not locked even if that is possible. I've got it working with the brake application, but the manual should be updated to reflect that requirement.

Edited May 4, 2015 by Snarf

[Buzzles]

I am having a lot of difficulty with the steering of the Mig 21, following the manuals instructions to the letter I can barely get the aircraft to turn. There is no mention of differential brakes in the manuals or commands for them. There seems to be a lot of talk of valves attached to the rudder system which allow you to differentially brake however once again no mention in the manual. I have seen some people complain that the aircraft turns to easily on rudder alone, this has not been my experience at all. I would prefer it to operate realistically but that manual should be updated with clearer instructions on how to turn the aircraft as the present ones don't explain at all.

 

First of all is to make sure the nose wheel brake is off. Normally it starts off, so you don't have to touch it.

Second, page 81 has some instructions under the Taxi section. I'd agree that they're not very clear though, and there's no real description of the braking system.

 

The aircraft does operate as per the real world manual though, which is where the talk of the valves has come from.

 

You've already figured this out going by your later post but: single brake lever on joystick. Brakes are operated by compressed air. Rudder while applying lever releases the opposite brake.

 

Ie, lever + left rudder releases the right brake, making plane rotate around the left wheel (which is still braked). There's the differential braking.

 

As for the previous complaints about people having no problem with using just the rudder, that was a problem at launch, LN did revisit it with a patch it so it behaves as per the real world now.

Edited May 4, 2015 by Buzzles

[[DBS]TH0R]

I meant nose wheel brake, sorry. Haven't flown the thing in a while.