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Old 12-28-2017, 05:01 AM   #1
Lixma 06
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Default Rudder authority question

I've noticed that while the MiG's pitch and roll effectiveness decrease rapidly as the speed increases the rudder seems unaffected. So much so that even at speeds bordering on Mach 1 (and certain death) the rudder will swing the nose around as easily as if travelling half the speed causing the aircraft to flop about and the pilot to black-out.



Is this correct behaviour?
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Old 12-28-2017, 05:59 AM   #2
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Most likely not, as only ailerons were hydro-boosted on this plane . You might want to repeat the test with controls indicator turned on to see if the force limit modelling is absent completely, or just set too low.

The limit is modelled in F-86 by the way (unless it got glitched here as well, haven't flown both of them for quite a long time).
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Old 12-28-2017, 07:02 AM   #3
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Good idea about the controls indicator, thanks!



Apparently we're getting full deflection regardless of speed.

Perhaps even more worrying is at the start of the video at the aircraft continues swinging left to right like a pendulum for about 10 seconds after centering the rudder. That's not right is it? Shouldn't the air-flow dampen this kind of oscillation almost immediately?
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Old 12-29-2017, 10:21 AM   #4
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The main reason most jets nowadays have yaw dampers is reduction of Dutch roll so that passengers don't throw up all over the place . Back in late '40s when MiG was designed and nobody even dreamt of yaw dampers, Dutch roll had to be dealt with strictly by wings and empennage geometry design.

What we see on the clip above looks a bit excessive indeed, but unless we can dig up directional dynamic stability charts of this plane from some Russian source, there's nothing to report only by "feel".

I'd like the lack of ruddder force buildup to be fixed first, though. Lixma, you might want to create a relevant post in "bugs" section just to be sure (or at least hope ) someone notices it.
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Old 12-29-2017, 10:11 PM   #5
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I just picked up the Sabre yesterday and found its rudder stiffens up as you increase speed so following your advice I'll throw up a bug report in the other forum; see if it gets a look.
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Old 01-28-2018, 12:03 AM   #6
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Quote:
Originally Posted by Art-J View Post
The main reason most jets nowadays have yaw dampers is reduction of Dutch roll so that passengers don't throw up all over the place . Back in late '40s when MiG was designed and nobody even dreamt of yaw dampers, Dutch roll had to be dealt with strictly by wings and empennage geometry design.

What we see on the clip above looks a bit excessive indeed, but unless we can dig up directional dynamic stability charts of this plane from some Russian source, there's nothing to report only by "feel".

I'd like the lack of ruddder force buildup to be fixed first, though. Lixma, you might want to create a relevant post in "bugs" section just to be sure (or at least hope ) someone notices it.
That is not the main reason. The main reason is Dutch roll at altitude in a swept wing jet can get violent very quickly.

In the CRJ turning off the yaw damper and giving the rudder a kick quite often would result in you being upside down rather violently.
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