Change or roll rate

[tiopilotos]

Hi there! Can someone tell me how to change the roll rate of an aircraft? There are some modern aircrafts such as the versions of Mirage 2000 which have slow roll rate.

[Caesar]

Well, some modern aircraft actually DO have a slow roll rate, or can depending on the airspeed (more or less flow over a larger or smaller control surface will change how effective that surface is). I don't know the Mirage 2000's off the top of my head, but if you really want to modify it, I know that the RollDamper in the a/c data.ini has something to do with it, so check that line.

[Fubar512]

Roll rate is most effected by the following, in order:

 

1) Aileron/Elevon/Differential Stabilator values

2) Wing and fuselage values that pertain to roll resistance

3) Inertia values in the roll axis

4) Underwing ordnance, and how its positioned out from the roll center of the AC (depends on weight)

 

The large wing area of a delta, the wing's position in relation to the fuselage (mid wing verus low wing), and the position of the various masses inside the airframe, all have an effect on roll rate.

[FastCargo]

Listen to Ed, you should, hmmm?

 

FC

[Fubar512]

I find myself posting this about once every year or so.....

 

CL0 Lift coefficient at zero

angle of attack (AOA)

CLa Lift coefficient due to AOA

CD0 Zero-lift drag coefficient

CDL Drag coefficient due to lift

(induced drag effect)

Cmq Pitching moment due to pitch rate

(pitch damping)

Cmad Pitching moment due to AOA rate

(aero interaction between wings and horiz tail)

Cyb Side force due to sideslip

Cyp Side force due to roll rate

Cyr Side force due to yaw rate

Clb Roll moment due to sideslip

Clp Roll moment due to roll rate

(roll damping)

Clr Roll moment due to yaw rate

Cnb Yaw moment due to sideslip

Cnp Yaw moment due to roll rate

Cnr Yaw moment due to yaw rate

(yaw damping)

CLiftdc Lift due to control surface deflection

CDdc Drag due to control surface deflection

Cydc Side force due to control surface deflection

Cldc Roll moment due to control surface deflection

Cmdc Pitch moment due to control surface deflection

Cndc Yaw moment due to control surface deflection

DeltaStallAlpha Increase in max angle-of-attack before stall

Xmac X-location of aerodynamic center (represented as a table representing the migration of the Xmac backwards or forwards, as indicated air speed increases or decreases)

Ymac Y-location of mean aerodynamic chord at the leading edge (ideally at zero airspeed).

 

 

CLiftdc lift coefficient due to surface deployment

DeltaStallAlpha change in maximum alpha before stall due to surface deployment

AreaRatio increase in wing area due to surface deployment.

 

StallMoment is the additional pitching moment you get when the wing section starts to stall. positive pitch (+) makes it so it pitches up as you stall (making it more unstable), negative pitch (-) makes it so it pitches down when you stall (making it more stable). The default value, if you don't specify a value, I think, is -0.02, which I think would make for gentle mushing forward type stall I was looking for...

 

There are a couple of other stall/depart variables added, all of them have default values so if you don't specify, you just get the default behaviour you see...

 

PostStallCma=

 

determine the Cma (pitching moment due to Alpha) past stall. Pre-stall, the engine uses lift value and xac value to calculate the pitching moment. Once the wing stalls and departs, additional pitching moment of StallMoment + the PostStallCma * (AoA - AlphaDepart) is added. I think this defauls to -0.2 or something.

 

StallHysteresis= (should be from 0.0 to 1.0)

 

determine how far the AoA has to be reduced in order for the airflow to reattach itself. I think 0.0 means the wing section will be unstalled as soon as AoA goes back under the stall angle, 1.0 means wing will unstall only when AoA goes back to 0 deg. I think the default is 0.4 or something.

 

PostStallZeroLiftAlpha = this is the angle at which the lift goes down to zero. Post AlphaDepart, the lift is linearly reduced down to zero at this angle. I think this defaults to 90-deg...

Edited November 3, 2009 by Fubar512

[FastCargo]

Thanks for that Ed, I had seen those values in newer stock aircraft, but weren't quite sure what they meant...

 

Also, quick question...is it Xac or Xmac? I saw old FMs that had it as Xac (and they did have an effect). Also, unlike other table data which appear to be coefficients, the entries I saw seem to be absolute values.

 

FC

Edited November 3, 2009 by FastCargo

[Fubar512]

There's both an Xac and an Xmac.

Edited November 3, 2009 by Fubar512

[FastCargo]

Okay, if there's a Xac and Xmac...what's the difference. The old definition I read for Xac sounded just like the definition you wrote for Xmac....

 

FC

[Fubar512]

XAC = X Location of aerodynamic center (X-axis only).

 

XMAC table = X Location of mean area chord, though the table progression is in the Y axis.

[+Dave]

Hi I'm a Mac and I'm a PC....

 

 

Sorry wrong thread.

[Falcon1364]

Hi Guys,

I have a quick question about speed loss while pulling Gs. How do I eliminate the drag factor to keep my speed consent when pulling high Gs? Thanks a lot.