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Rudder/Aileron Coupling


104th_Money

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I noticed that whenever aileron input is applied, the rudder is also applied in the direction of the roll even though I am not applying rudder with pedals.

 

This seems to always give a bit of yaw when rolling somewhat to very aggressively.

 

I checked to see if I had rudder binding to roll commands but it was not.

 

I havent seen any video clips of the AV-8B doing this but there is a video from 2000 showing a GR7 making very crisp rolls and levels...

 

 

Any thoughts?

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I don't have the NATOPS right now so I can't double check; but IIRC this behavious is mentioned there and I think it can also be disabled.

 

As soon as I'm back I'll check and edit.

 

EDIT

2.16.1 Stability Augmentation System

The three SAS mode selection controls are the PITCH, ROLL and YAW switches which engage the stability

augmentation in the corresponding aircraft axes. The stability augmentation system increases aircraft stability and

improves the response to pilot inputs in maneuvering flight throughout the entire flight envelope. The yaw SAS also

provides a lateral stick to rudder interconnect for improved turn coordination.

The SAS switches may be engaged and disengaged individually to provide stability augmentation in any desired

combination of the three axes. Disengaging individual SAS switches degrades departure resistance (DEP RES) which

greatly increases the possibility of violent departure in certain flight regimes. An interlock between the yaw SAS

switch and the weight−on−wheels switch on the main gear inhibits the yaw stability augmentation when the aircraft

is on the ground.

Pressing the emergency SAAHS disengage switch (paddle switch) located on the control stick grip interrupts the

stability augmentation system in all three axes and also removes rudder trim. Releasing the paddle switch restores

stability augmentation to those axes selected by the SAS switches and restores the rudder trim.


Edited by Karon
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This coupling behavior is accurate.

 

The AV-8B is fairly susceptible to adverse yaw (yaw in the opposite direction of a roll due to increased drag on the upward-moving wing), and the SAAHS applies rudder in the direction of the roll to counteract the worst of these effects (I haven't tested whether this is true in DCS yet).

 

This affects the AV-8B's NATOPS roll limitations and it's important to make your rolls unloaded at higher IMN. At airspeeds < ~500 KCAS > 15,000' MSL or < ~400 KCAS < 15,000' MSL, rapid onset of AOA in a loaded roll can cause a wing rock condition or departure.

 

Disabling SAAHS doesn't increase roll performance at all, it just makes you more susceptible to departure.

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This coupling behavior is accurate.

 

The AV-8B is fairly susceptible to adverse yaw (yaw in the opposite direction of a roll due to increased drag on the upward-moving wing), and the SAAHS applies rudder in the direction of the roll to counteract the worst of these effects (I haven't tested whether this is true in DCS yet).

 

This affects the AV-8B's NATOPS roll limitations and it's important to make your rolls unloaded at higher IMN. At airspeeds < ~500 KCAS > 15,000' MSL or < ~400 KCAS < 15,000' MSL, rapid onset of AOA in a loaded roll can cause a wing rock condition or departure.

 

Disabling SAAHS doesn't increase roll performance at all, it just makes you more susceptible to departure.

 

Could you define 'loaded roll' and IMN please? Not applying G in the turn, or don't pull until your roll is complete? Or am I way off? :huh:

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IMN is your Indicated Mach Number on the HUD. A loaded roll is when you're pulling G during the roll itself, so don't pull until the roll is complete and you've captured the desired bank angle for the turn.

 

That's not to say you should never perform loaded rolls, just pay particular attention to doing them at high airspeeds. The aircraft is considered "Mach limited" at high altitude (>15,000' don't do loaded rolls > ~0.8 IMN) and "AOA limited" at the bands described above. At lower altitude and lower speeds the aircraft is "G limited" and you're more likely to over-G the airplane than depart controlled flight.


Edited by ChickenSim
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IMN is your Indicated Mach Number on the HUD. A loaded roll is when you're pulling G during the roll itself, so don't pull until the roll is complete and you've captured the desired bank angle for the turn.

 

That's not to say you should never perform loaded rolls, just pay particular attention to doing them at high airspeeds. The aircraft is considered "Mach limited" at high altitude (>15,000' don't do loaded rolls > ~0.8 IMN) and "AOA limited" at the bands described above. At lower altitude and lower speeds the aircraft is "G limited" and you're more likely to over-G the airplane than depart controlled flight.

 

Thank you for the explanation. On a similar vein, is it fair to say that if you want to do a level turn, with G applied, then you must have rolled through 90 degrees? Pulling the stick back in any shallower angle always results in a climbing turn, which isn't necessarily desired.

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Not quite, all level turns will have some G required to maintain level flight. otherwise they would be slipping or "slicing" into a descent.

 

The bank angle and amount of G pulled to maintain level flight are going to be related (Load Factor), but if you banked 90° you'd likely need more G than you could possibly pull to keep from descending.

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Thanks for the responses guys, guess thats the way its supposed to be...

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