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Author Topic: Spitfire aileron reversal  (Read 11394 times)
NZTyphoon
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« on: January 27, 2009, 06:45:07 AM »

Now here's a topic which seems to have generated a popular myth viz; the Spitfire's thin wing meant that at high speeds aileron reversal, due to flexing of the wings, was a real problem. But was it?

This is a topic which seems to generate some heat on certain forums, to the point where people say definitively that the Spitfire's wings flexed so much that aileron reversal was guarenteed eg; this little beauty. http://www.ww2aircraft.net/forum/polls/bf-109-vs-spitfire-3406-5.html...

and this unreferenced paragraph in Wikipedia
"One flaw in the thin-wing design of the Spitfire manifested itself when the aircraft was brought up to very high speeds. When the pilot attempted to roll the aircraft at these speeds, the aerodynamic forces on the ailerons were enough to twist the entire wingtip in the direction opposite to the aileron deflection (much like the way in which an aileron trim tab will deflect the aileron itself). This so-called 'aileron reversal' resulted in the Spitfire rolling in the opposite direction to the control column input and occurred at much lower airspeeds than on other contemporary designs. In March 1943, R.A.E. noted that at 400 mph I.A.S., roughly 65% of aileron power was lost due to wing twist.(Morgan, M.B. ''R.A.E. Technical Note No. Aero 1106'', March 1943.)

Tech note 1106 says nothing about aileron reversal. The paragraph doesn't say what the very high speeds were, and the passage implies that the Spitfire was (somehow) more dangerous to fly than contemporary fighters. It should be noted that the Spitfire article is the only one which raises the bogy of aileron reversal afflicting the aircraft. The problem is that this article has been used in its entirety in numerous other websites on the Spitfire. No doubt, because of the way it has been edited and reedited by one or two people, the article leaves many with the impression that the Spitfire was a dangerous and unreliable aircraft to fly! This was one paragraph which was introduced by the same contributer.

If the stick was pulled back too far on the Spitfire in a tight turn, the aircraft could stall rather violently, flick over on to its back, and spin. Knowledge of this undoubtedly deterred Spitfire pilots from tightening their turns when being chased, particularly if they were inexperienced. Source: Morgan and Morris 1940 - this was the RAE report on the captured Bf 109...

The pilot's task was not made easier by the fact that the elevator was exceedingly sensitive; during tight turns or loops in bumpy conditions, movements to the pilot's body due to bumps were liable to cause movement of the controls and large and sudden fluctuations in g-load.

This used as it's scource something purported to be "General Flying". ''Spitfire II Pilot's notes'' (AP 1565B), July 1940. I have a copy of AP1565B and so far I've had no luck finding this information. It must be buried deep in an undecipherable code. Then came this wonderful sentence;

The very effective elevator, coupled with the instability in pitch of the Spitfire made it very easy for the pilot to greatly exceed the 10 g limit imposed on the airframe and the wings would certainly fail if this occurred. Supposedly from "Diving". ''Spitfire II Pilot's notes'' (AP 1565B), July 1940...can anyone else confirm that AP1565B says this? (not strictly about aileron reversal, but  illustrative of the lengths some people will go to in a bid to "add balance" lest the article praises the Spitfire too much!..)

I have since replaced these two paragraphs with far more reliable and properly sourced information.

Some facts. One useful source of information is chief test pilot Jeffrey Quill, who wrote about how aileron reversal affected the Spitfire;
"...had we, in 1941, been able to produce a design of aileron capable of allowing much greater control displacements at very high speed we should soon have been in serious trouble with what was known as 'aileron reversal' arising from lack of torsional stiffness of the wing. In other words the load applied to the wings by more powerful ailerons would have caused the wings to twist, thereby nullifying or reversing the effect of the ailerons and, incidentally, causing damage to the structure itself (Quill; Spitfire: a Test Pilot's Story; 1983 pp.272-273)

Note that he quite definitely states that the problem would have manifested itself had the ailerons been capable of greater control displacements ie: aileron reversal was not a big problem, although the Spitfire was "teetering on the edge" of suffering from aileron reversal. Quill goes on to say that the theoretical speed at which reversal would have occurred was 580 mph - still well above normal combat speeds and one only likely to have been exceeded in a prolonged and steep dive. To be fair this speed was a great deal lower than many contemporary designs, and it was quite possible that Spitfires were lost when the pilot attempted an aileron turn at these speeds.

Quill goes on to describe the redesigned wings for the Mk 21 on, which were stiffened by 47% and had a theoretical aileron reversal speed of 825 mph, meaning that aileron reversal would only have occurrred as the rest of the airframe was dismantling itself.

I haven't had much time to research this issue, and I could well be proven wrong on many points. In particular it would be interesting to have a good look at the official RAE reports which have sometimes been quoted in the likes of Wikipedia.
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« Reply #1 on: January 30, 2009, 06:25:30 PM »

My, very uneducated, understanding of the aileron reversal story is that:

- It hasn't been much of the problem with fabric-covered ailerons, mostly because their movement in high speed was very limited due to the ballooning effect.

- Once fabric ailerons were replaced with metal ones, pilots were able to execute effective high-speed rolls and this is only then that the reversal problem had become a noticeable issue.

- Quill might be referring to the issue of disparity between the Spitfire and Fw 190 in the roll plane. As is widely known, the latter excelled in the roll plane, the capability which give the Luftwaffe pilots a substantial advantage (easy escape) in dogfight situations.

- This undoubtedly put pressure on Supermarine to increase the roll performance of the Spitfire. One way of doing this would be to enlarge the ailerons, but this would lead to increased torsional loads on the wing and therefore put aileron reversal problem from very tolerable to untolerable scale. This is my understanding of Quill's statement above.

- In the end, all Supermarine could do without substantial strengthening of the wing was clipping the wing tips, but the entire issue seem to have remained on the drawing table. The new wing which solved the problem on Mk. 2* Spitfires was actually designed mid-war, but due to other prioritties only found its way to production at the end of the conflict.

Best regards,
/Martin

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