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#61
05-13-2011, 02:30 PM
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In other news, from the much hated wikipedia: "A similar problem affected some models of the Supermarine Spitfire. At high speeds the ailerons could apply more torque than the Spitfire's thin wings could handle, and the entire wing would twist in the opposite direction. This meant that the plane would roll in the direction opposite to that which the pilot intended, and led to a number of accidents. Earlier models weren't fast enough for this to be a problem, and so it wasn't noticed until later model Spitfires like the Mk.IX started to appear. This was mitigated by adding considerable torsional rigidity to the wings, and was wholly cured when the Mk.XIV was introduced." 
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#62
05-13-2011, 08:36 PM
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I was watching an episode of the documentary 'Spitfire Ace' today and during the interviews with veteran WW2 Spitfire pilots, some of them said that they had the chance to fly both the Spitfire and Hurricane and their opinion, the early versions of the two aircraft didn't have much between them in terms of turn rates when it came to a dogfight. At higher speeds, the Spitfire was actually slower in terms of rate of turn, as the ailerons became heavier to use and the wing loading increased. The Hurricane's higher wing aspect ratio helped turn rates at higher speeds due to the increased lift created.
Some veterans on the programme did remark that the Spitfire was a lot easier to throw around the sky, as it was designed as a thoroughbred fighter By Reginald Mitchell, unlike the Hurricane, that was derived as a monoplane version of the Hawker Fury by Sidney Camm; in fact, the Hurricane was originally called the 'Fury Monoplane' until it was renamed the Hurricane. The Spitfire was originally called the 'Shrew', until somebody at the RAF renamed it after a nickname for one of his daughters. Not the most romantic name for a classic fighter....  The veteran pilots also remarked that the Hurricane was far more robust, could suffer more damage and keep flying and was a more stable gun platform, hence the reason it was sent after the bombers, although the numerical superiority of the Hurricane compared to the available Spitfires in 1940 also had a lot to do with it. The Spitfire was left to deal with the fighter escorts on more equal terms of numbers. Here's a link to the series on Youtube, if you want to hear it for yourselves..... from people who were actually there and flew them.... Episode 1, with links to the other episodes..... Last edited by 617Squadron; 05-13-2011 at 08:44 PM.
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#63
05-13-2011, 09:37 PM
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Good post by the way - Thx 
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#64
05-13-2011, 10:03 PM
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As (I think) Viper had said previously the pilot's account have to be taken with a tiny bit of grain of salt.
The thick winks of the Hurry in itself may have produced more lift but also more drag. In fact what is interesting to know for turn rates is the angle of attack needed for the turn rate and the drag it produces and finally the engine power and weight. The engine power vs drag will overall determine the speed at which the ac will travel through air. The lift generated vs. current airspeed and weight will determine the ability to change direction = turn rate. The more engine power I have I may pull more angle of attack without loss of speed and the higher the lift will be. It is the lift that will cause my ac to turn. At the same time for same engine the less drag angle of attack produces the better I turn.
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#65
05-13-2011, 10:07 PM
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) Do you remember the Venturi effect when the air is accelerated through a narrower section ? Now take a wider look at a wing section. If you focus either on the upper or the lower surface, you will see that regarding to the free stream of air unperturbed by the airfoil, there is a section increase as the thickness of the airfoil increase and the a similar decrease after the point of inflexion. The direct effect of this (appart from the direct generation of LIFT) is that the air is accelerated and then as the section increased, expended with a rather brutal Pressure increase. Now imagine that (I am actually singing it) you are flying at a speed nearly 2/3 of the speed of sound. Due to the imaginary geometry described above, you can understand that the air is accelerated trough this partially materialized venturi. The increase in speed being directly proportional the the section decrease. Hence the more thickness the more the air flow is accelerated When the speed and the wing's thickness are high enough, the airflow ard the wing reach Mach 1, the speed of sound. As the air goes further back along the chord, the air is expended (the distance btw the free airstram and the airfoil increase) and the air is decelerated bellow Mach one trough a pressure shock. This pressure shock is what we call a shock wave. Now let say simply that due to he fact that the pressure distribution is modified because of both the shock waves above and bellow the wing, the LIFT moment is modified with a negative upward (relative to the chord) pitch down moment. What you can see is that the more the wing is thick, the earlier the air ard the airfoil section reach the critical mach number. Hence the thin airfoil series of the 50's fighters (Starfighter, F105, Mig 21 etc..). This is why the compressibility affect the wing and not so much the generally thinner tail section. Interestingly too this is what makes the Spitfire so fast in a dive. What you can see now is the sublime irony of mother nature that turned a wrong design assumption (the elliptical wing) in a wining parameter. I tell you Germany cldn't hve win !  Note : The 47 had an elliptical wing too. And it was also awfully fast in a dive! ~S! Last edited by TomcatViP; 05-13-2011 at 10:42 PM.
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#66
05-13-2011, 10:21 PM
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#67
05-13-2011, 10:23 PM
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The original design for what became the Spitfire had straight taper. The elliptical planform happened because the man from the ministry kept demanding more guns.
There wasn't enough depth to accommodate them. The two options were to increase chord outboard or to increase t/c. Mitchell was a clever man, so he opted for the former. However, the subtext of this was that he didn't anticipate a production run of 20,000+, mostly built in shadow factories. He thought that Supermarine would probably make a few hundred at most, and therefore the extra work entailed in a nightmare of compound curves was quite a neat way of making work to keep his company in business. I suspect that had he not died before his time, the Spitfire would probably have been rapidly been replaced by a more practical follow-on aeroplane with straight taper, or perhaps polytaper; though perhaps more interesting still is the possibility that fighter work might have been entirely handed to Hawker so that Supermarine could concentrate on their bomber, which was effectively a 4 engined heavy with Mosquito speed... Meanwhile the P-47 was very fast going downhill, but had quite a low tactical Mach number, and was also rather a nightmare to manage due to the extra workload and failuremodes inherent in the turbo.
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#68
05-13-2011, 10:38 PM
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 ) But the initial acceleration is imparted, you are right. By the way don't take me wrong guys... The Spitfire was a great airplane . It was only not the best one in terms of aero. Just like the 109 was one very refined design both in term of aero and structural design but a poor weapon for young conscripts with a low nbr of flying hour. Dozen hd to dye for the raise of one of the much vaunted experteen. Last edited by TomcatViP; 05-13-2011 at 11:04 PM.
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#69
05-14-2011, 07:35 AM
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That's what I meant. That is as far as I have read why the FW190 could dive away to escape as it accelerated initially sufficiently well to have gone away.
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