Spit aieleron reversal

[TheCrazyOrange]

So while playing today, there were a few guys on vox complaining about how the spitfires aileron's would reverse at high speeds in real life, and that they don't do so in AH (they said "like 450mph+).

Is there any truth to this; I've never heard a thing about it. If so, what is the physical mechanism by which this oddity of aerodynamics occurs? Is it universal to all ailerons (and I suppose all control surfaces, given that they're all just altering the flow over the airfoils), or is it a quirk particular to the Spitfires? Or does the spitfire's design just happen to have a particularly low speed at which this occurs, similar to the 109's compression? Is it modeled in AH? I've never had this happen to me.

[Skyyr]

So while playing today, there were a few guys on vox complaining about how the spitfires aileron's would reverse at high speeds in real life, and that they don't do so in AH (they said "like 450mph+).

Is there any truth to this; I've never heard a thing about it. If so, what is the physical mechanism by which this oddity of aerodynamics occurs? Is it universal to all ailerons (and I suppose all control surfaces, given that they're all just altering the flow over the airfoils), or is it a quirk particular to the Spitfires? Or does the spitfire's design just happen to have a particularly low speed at which this occurs, similar to the 109's compression? Is it modeled in AH? I've never had this happen to me.

Wing-twist due to large amounts of lift at high speed is usually the culprit. And no, AH's flight model doesn't actually calculate physics at the level needed for it to occur naturally ingame.

[TheCrazyOrange]

Just so I'm clear;

The forces generated by the control surface are such that the wing would physically deform so as to keep the aileron at "neutral" relative to the flight vector? Wouldn't forces acting on the entire wing be greater than those acting on just the ailerons, resulting in "heavy controls", thereby preventing this from happening?


It just seems odd to me that even though the forces are sufficient to significantly deform the shape of the wing, the ailerons are apparently unaffected by the forces.

[BaldEagl]

It is caused by a twisting of the wing itself making the rolling motion mushy at best and particularly noticeable at higher speeds, even in the game. Its most evident in the Spit I, VIII and XIV. I'm not sure why the full span V and IX don't suffer from this as well.  I suspect it's mostly the I with the VIII and XIV being more affected by higher output engine torque effects.

Regardless, the twisting of the wings in the I was a well documented occurrence.

[Skyyr]

Just so I'm clear;

The forces generated by the control surface are such that the wing would physically deform so as to keep the aileron at "neutral" relative to the flight vector? Wouldn't forces acting on the entire wing be greater than those acting on just the ailerons, resulting in "heavy controls", thereby preventing this from happening?


It just seems odd to me that even though the forces are sufficient to significantly deform the shape of the wing, the ailerons are apparently unaffected by the forces.

An aileron rolls the aircraft by effectively changing the camber of the wing. This, in turn, creates more lift on the wing where the aileron is deflected downward and less lift on the wing where the aileron is deflected upward.

At very, very high speed on aircraft that have low wing loading (i.e. they have wings that produce lots of lift) and low torsional wing stiffness, the aerodynamic forces can cause the wing to bend/warp. This warping causes the wing, overall, to deflect the relative wind opposite the direction it normally would, causing a roll in the oppositely-expected direction. For example, an aircraft usually rolls towards the wing with the upward-deflected aileron, as that wing is producing less lift. However, at high enough speeds, that upward-deflected aileron can generate enough drag that it "twists" the wing down, therefore causing the wing to deflect the relative wind downward. This causes the aircraft to roll away from that wing, instead of towards it.

[danny76]

There is also a fair amount of evidence that the Jug suffered a reversal of elevator control in very high speed turns which also appears not to be mapped in game. (Smell of Kerosene)

[FLS]

We don't have aileron reversal because our wings don't flex under load.

[TheCrazyOrange]

Was this permanently damaging to the aircraft? Like if a new pilot panicked and continued to try to roll, instead of cutting throttle, and trying to pull out of the dive, would the spitfire need to be overhauled when it got on the ground?

[Skyyr]

Was this permanently damaging to the aircraft? Like if a new pilot panicked and continued to try to roll, instead of cutting throttle, and trying to pull out of the dive, would the spitfire need to be overhauled when it got on the ground?

You have Vno and Vne speeds in aircraft. I'm not sure what they were in Spitfires, but as long as Vne airspeed wasn't exceeded, no overhaul or inspection should have been necessary. That said, I would suspect that aileron reversal happened close to or past Vne.

[Charge]

"Was this permanently damaging to the aircraft?"

AFAIK there was never permanent damage to Spittys caused by aileron reversal. Usually the damage to wings (in any plane) was done in high speed pull-ups where the upper skinning of the wing would wrinkle and the wing would more or less permanently deform.

-C+

[GScholz]

At high speed the force of the airflow hitting the aileron twists the whole wing creating a net lift opposite of what was commanded. Aileron reversal can also happen near the stall if the downward deflecting aileron increases the effective angle of attack beyond stall. The outer wing stalls and the aircraft rolls in the opposite direction of what was commanded. I have not experienced any type of control reversal in AH.

http://en.wikipedia.org/wiki/Control_reversal

[Cthulhu]

There is also a fair amount of evidence that the Jug suffered a reversal of elevator control in very high speed turns which also appears not to be mapped in game. (Smell of Kerosene)

Yes, aileron reversal was definitely an issue with the Jug. Like you guys have been saying, the local pitching moment created by the deflected aileron would be severe enough at high speed to produce enough wing twist to change the effective angle of attack at the wingtips. This twist could be severe enough to negate the ailerons and in some cases even roll the airplane in the opposite direction. Thin wings, because of their low torsional stiffness, can have a real issue with this.

The coupling of aerodynamic forces and structural stiffness can also produce destructive aeroelastic behavior like flutter, which can rip a plane to  pieces in short order.

[Karnak]

The shorter span ailerons on the Mk VIII and Mk XIV were intended to address, or reduce, aileron reversal.  If you look at those two Spitfires in AH you can see that their ailerons don't extend as far out towards the wing tip as the ailerons on the Mk I, V, IX, XVI and Seafire Mk II.

In AH this seems to not be modeled and the shorter span ailerons simply produce a poorer roll rate.

[Cthulhu]

The shorter span ailerons on the Mk VIII and Mk XIV were intended to address, or reduce, aileron reversal.  If you look at those two Spitfires in AH you can see that their ailerons don't extend as far out towards the wing tip as the ailerons on the Mk I, V, IX, XVI and Seafire Mk II.

In AH this seems to not be modeled and the shorter span ailerons simply produce a poorer roll rate.

Which is weird because the lower rotation inertia and stiffer wing structure of low aspect ratio wings usually give them pretty nasty roll rates. Consider the roll rates of low AR planes like the F-104 or T-38. Those things will crack your head on the canopy!

[danny76]

Yes, aileron reversal was definitely an issue with the Jug. Like you guys have been saying, the local pitching moment created by the deflected aileron would be severe enough at high speed to produce enough wing twist to change the effective angle of attack at the wingtips. This twist could be severe enough to negate the ailerons and in some cases even roll the airplane in the opposite direction. Thin wings, because of their low torsional stiffness, can have a real issue with this.

The coupling of aerodynamic forces and structural stiffness can also produce destructive aeroelastic behavior like flutter, which can rip a plane to  pieces in short order.

This was referenced specifically as elevator reversal, assuming that similar forces were at work here. The test pilot describes a scenario whereby a Jug pilot was in a Lufberry with an Fw190 at very high speed and was forced to reverse his control input to stay in the turn