Uncontrolled roll out to 0° of bank.

[Kobal]

Hi,

When you roll in to 30° of bank for example, and you put the stick in neutral position to maintain the bank angle,  the plane roll out to 0°.

[WTFCSon]

How fast, how high and in what configuration(stores, flaps, gear, etc.)? After enter 30 degree of bank, how long does it take for the jet to roll back to 0? Does it roll all the way back to 0? Does it roll past 0?

I'm going to go out on a limb and say this is expected behavior. Most analog jets are inherently stable and thus will generally want to return to wings level flight. Not until you hop in s FBW jet will you be able to "set" a degree of bank with the stick and then be able to go hands off.

I will acknowledge that there are exceptions and some jets are more stable than others.

Edited December 20, 2023 by WTFCSon
Correction

[Dragon1-1]

Actually, for most part, a stable aircraft will stay where it is, in roll. A jet aircraft that is stable in roll will maintain the roll rate commanded by the stick, and when that rate is zero, it'll stay where it is. Anything that doesn't have prop torque effects will behave the same at smaller bank angles.

[WTFCSon]

1 minute ago, Dragon1-1 said:

Actually, for most part, a stable aircraft will stay where it is, in roll. A jet aircraft that is stable in roll will maintain the roll rate commanded by the stick, and when that rate is zero, it'll stay where it is. Anything that doesn't have prop torque effects will behave the same at smaller bank angles.

Thank you for your correction...

[Dragon1-1]

No problem. In fact, the aircraft that is worst in roll in DCS is an FBW jet, namely the Hornet. It has a completely inappropriate uncommanded roll when in landing configuration, a major bother when lining up with the boat. Given that even a Piper Cub holds a steady bank angle pretty well, that's rather egregious.

Indeed, that's why aileron trim is not a universal feature. You only need it if you expect to have asymmetric loads, as in a fighter aircraft or a bomber. If you want to trim an aircraft to hold a steady turn (say, at a holding point), you just set bank, add a little power and trim the nose up. On props, you'll see rudder trim more often than aileron trim (rudder is used to offset prop effects), and if you've got the latter, you almost certainly have all three.

[WTFCSon]

Interesting, I've got some testing to do to prove this to myself. I refrain from commenting further until OP provides more details.

 

[Bremspropeller]

On 12/20/2023 at 7:50 PM, WTFCSon said:

Thank you for your correction...

You weren't incorrect at all.

Static roll stability has your aircraft return to zero bank, within the boundaries of non-extreme bank angles and attitudes.

Different kinds of aircraft will have different kinds of stability requirements. What's good for an IFR cross-country aircraft (high static and dynamic stability) isn't always what you'd opt for in fighter/ attack aircraft, which also want a degree of maneuverability. The dynamic stability part can partially be taken care of by a well-designed SAS. The static part is a bit harder to tune.

I'd expect the aircraft to have positive static roll stability at small bank angles, but I'd be surprised if it really had that much dihedral-effect at greater bank-angles. If it had, I'd expect more roll-due-to-yaw with rudder-inputs.

[Bremspropeller]

Just did a quick and dirty test on the Caucasus Take Off quick mission. Some data-points:

At 2500ft and ~310KIAS/ Mach 0.5, the aircraft will take about 15s from a 30° bank to 10° bank and another 30s to reach almost zero bank. Heading change not observed. (R bank)

At 3000ft and M0.6, starting at 30° she took 5s to get to 20°, another 10s (15 total) to 10° and didn't quite reach upright before the minute. Heading change not obsserved (L bank)

At 15.000ft and M0.8 (~400KIAS) at 90° bank, she took 8s to get back to 60°, rolled through 30° at about 18s and never reached less than 10° of bank before I had to jank her out of the dive that had developed. The nose went through about 40 degrees of heading change. (L bank)

Power = iso, same for all trims.

[Bremspropeller]

One additional observation:

The aircraft will roll upright, when overbanked past 90°.

[Snappy]

On 12/27/2023 at 11:33 PM, Bremspropeller said:

Just did a quick and dirty test on the Caucasus Take Off quick mission. Some data-points:

At 2500ft and ~310KIAS/ Mach 0.5, the aircraft will take about 15s from a 30° bank to 10° bank and another 30s to reach almost zero bank. Heading change not observed. (R bank)

At 3000ft and M0.6, starting at 30° she took 5s to get to 20°, another 10s (15 total) to 10° and didn't quite reach upright before the minute. Heading change not obsserved (L bank)

At 15.000ft and M0.8 (~400KIAS) at 90° bank, she took 8s to get back to 60°, rolled through 30° at about 18s and never reached less than 10° of bank before I had to jank her out of the dive that had developed. The nose went through about 40 degrees of heading change. (L bank)

Power = iso, same for all trims.

Interesting.With any significant bank angle I would have expected an observable heading change since the lift vector is now tilted to one side in the direction of roll and now has a sideways component, which is what normally produces heading changes.

Edited January 3 by Snappy

[Bremspropeller]

Not observed is meant to mean "I didn't look for it".

There's a 40° heading-change in the 90° bank test.

[Snappy]

On 1/3/2024 at 6:17 PM, Bremspropeller said:

Not observed is meant to mean "I didn't look for it".

There's a 40° heading-change in the 90° bank test.

Ah ok, got it! Thanks for your clarification!

[Cgjunk2]

On 12/20/2023 at 12:48 PM, Dragon1-1 said:

Actually, for most part, a stable aircraft will stay where it is, in roll. A jet aircraft that is stable in roll will maintain the roll rate commanded by the stick, and when that rate is zero, it'll stay where it is. Anything that doesn't have prop torque effects will behave the same at smaller bank angles.

This is my understanding as well.   From a purely aerodynamic perspective (meaning no artificial FCS intervention), my understanding is that as dihedral increases, a plane will show increasing tendency to roll back to level when roll input is nulled.   So a basic trainer or ultralight plane with high angles of dihedral (wing tips higher than wing roots), will naturally want to return to level when rolling input pressure is relieved.  

Conversely, when a wing is built with anhedral (wingtips lower than wing roots) it’s the opposite…it will have less tendency to stay where you put it.   It will also require less aileron input to roll, as a side benefit, if that’s what you are looking for in the basic aerodynamic traits of the design.    

First time I flew the F1, I thought it was odd that it wanted to roll level, especially since it has an anhedral wing.   I figured maybe the FCS commanded that as an auto-level type thing.  But that didnt make sense to me because requiring constant roll input pressure to hold a bank angle means it has to drag a wing spoiler out in the breeze the whole time it’s banked in a turn, which will induce a bunch of drag,  and just generally mess up how it cuts through a turn.  

Anyone that has built paper airplanes, you had to put dihedral into the wings to make it stay level.  But if you folded the wing tips lower than the root, it tended to fall off in either direction very easily, leading to a very short flight.

Edit: a quick perusal of wiki regarding dihedral effect and roll stability revealed the fact that high mounted wings by themselves produce lots of dihedral effect due to pendulum effect, and anhedral is added to tone down the self leveling to more neutral levels.  
It also revealed that the self-leveling tendency of dihedral angle result as an effect from sideslip.  In other words, even a plane with a high dihedral angle wing, if flown coordinated, will not self level.    So if the Mirage F1 FCS keeps the plane coordinated in bank, it would have even less reason to show self-leveling effects on the roll axis
 

 

 

 

Edited January 12 by Cgjunk2

[Bremspropeller]

10 hours ago, Cgjunk2 said:

It also revealed that the self-leveling tendency of dihedral angle result as an effect from sideslip.  In other words, even a plane with a high dihedral angle wing, if flown coordinated, will not self level.    So if the Mirage F1 FCS keeps the plane coordinated in bank, it would have even less reason to show self-leveling effects on the roll axis

I'm not sure I can follow you, but the dihedral effect in terms of sideslip needs to be understood in the correct context.

Dihedral effect in sideslip is the same effect, but in yaw and it affects swept wing aircraft to the same degree as dihedral - just in a different axis (roll through yaw). It's not directly related to the dihedral angle, but it may superimpose and fight the dihedral angle, if a roll and a skid persist into the same direction. By the same token, an anhedral wing will have roll and skid add to each other. This might be an issue, as I think the rudder should create a little more rolling-tendency at high AoA.

Not sure how much the "anti slip" AFCS-function is trying to footwrestle us there, though.

PS: The F1 is more or less mechanical-direct in roll. It's only analogue FBW in pitch and yaw, with a FBW-function in roll (differential stabilizer) with the autopilot engaged. That's just +/-3° of authority, though - basicly a beefed-up wing-levelling function.

 

 

[Dragon1-1]

11 hours ago, Bremspropeller said:

Dihedral effect in sideslip is the same effect, but in yaw and it affects swept wing aircraft to the same degree as dihedral - just in a different axis (roll through yaw). It's not directly related to the dihedral angle, but it may superimpose and fight the dihedral angle, if a roll and a skid persist into the same direction. By the same token, an anhedral wing will have roll and skid add to each other. This might be an issue, as I think the rudder should create a little more rolling-tendency at high AoA.

The point was different, and related to what I said earlier. A jet will, in general, stay where it is in roll, as long as its flown coordinated. Self-leveling effects come from a sideslip angle which is induced when the aircraft is rolled on the side. This will create a righting force which will tend to return the aircraft to level flight, and regain the equilibrium state it was trimmed for.

Yaw dampers are pretty universal in jets, so in practice, the result will be what I said: when you roll the jet and let go of the stick, it'll maintain the roll angle. This is how you can trim an aircraft to hold a steady turn (without a yaw damper, it'd require trimming the rudder a bit, too). 

[Bremspropeller]

I don't think the yaw damper plays a significant role there. For several reasons:

1) The aircraft exibits natural directional stability, so sideslips will righten themselves out quickly. Especially with a low aspect ratio swept wing. This would be oscillatory with a dampening coefficient, so additional stabilty (actually dampening) is provided by the YD through yaw-attenuation.

2) Yaw dampers are mostly used to counter dutch roll, which is caused by a high spiral stability in relation to the directional stability. Their authority is limited, otherwise we'd have no adverse yaw issues when using ailerons at higher aoa. That's also why additional ARI is used on some jets in some circumstances. Yaw dampers don't really control sideslip per sé, but rather yaw-rate. Some turn coordination functions may exist, though, depending on the system's architecture. Most of that is by cancelling adverse yaw on the turn-entry.

3) The only trim required in a steady turn is pitch trim, if the turn entry was flown coordinated. If you need anything on top, it's mostly a matter of spiral stability and the associated dihedral effect through bank angle. This would be a pretty sh1tty design though, requiring aileron into the turn, meaning additional drag on the outboard wing (adverse yaw out of the turn). Hence most aircraft have a reasonable, but not excessive spiral stability. It's more for letting go of the stick for a minute and not doing a JFK Jr., rather than crossing the Atlantic stick-free.

 

Think about it another way: If you're using the sideslip technique for crosswind approaches, you'll find yourself crosscontrolling (aileron banking into the wind, opposite rudder to hold the heading). And that's without YDs. In fact, YDs are normally off during the landing, or you'd run into trouble during the flare...

____

The more I'm thinking about it, the more I think the current spiral stability on the F1 is way excessive. I guess its a leftover from the last "asymmetric loads" fix and I'm positive we'll see another iteration.

 

Edit: I did some more testing. The uprighting moment seems to be reasonable, when tested under several sideslip conditions with YD in Anti-Slip, YD and off. There's a defiante connection between a sideslip indicated by the ball and a resulting roll movement. Certainly in qualitative terms.

Roll by rudder seems a little slow at slow speeds, though, and you need a good deal of AoA for her to do more than just a lackluster roll. Still won't do much with some alpha on. She'll do a quite nice rudder induced roll, however, at 500 KIAS

Edited January 13 by Bremspropeller