Wings of the Spitfire / Spiteful

[Zipper730]

I'm curious why the Supermarine Spiteful had laminar flow wings? I know in theory they often generally had higher
critical & drag-divergence mach-numbers, but the Spitfire Mk.VIII had a placard limit of Mach 0.85, carried out at least one dive to Mach 0.891, and the PR-variants achieved Mach 0.92 with a flying-tail.


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[pbehn]

By 1942, Supermarine designers had realised that the characteristics of the Spitfire's wing at high Mach numbers might become a limiting factor in increasing the aircraft's high-speed performance. The main problem was the aeroelasticity of the Spitfire's wing; at high speeds the relatively light structure behind the strong leading edge torsion box would flex, changing the airflow and limiting the maximum safe diving speed to 480 mph (772 km/h) IAS.[nb 1] If the Spitfire were to be able to fly higher and faster, a radically new wing would be needed.[1]

Joseph Smith and the design team were aware of a paper on compressibility, published by A D Young of the R.A.E, in which he described a new type of wing section; the maximum thickness and camber would be much nearer to the mid-chord than conventional airfoils and the nose section of this airfoil would be close to an ellipse.[nb 2] In November 1942, Supermarine issued Specification No 470 which (in part) stated:

A new wing has been designed for the Spitfire with the following objects: 1) To raise as much as possible the critical speed at which drag increases, due to compressibility, become serious. 2) To obtain a rate of roll faster than any existing fighter. 3) To reduce wing profile drag and thereby improve performance.

The wing area has been reduced from 242 sq ft (22.5 m2) to 210 sq ft (20 m2) and a thickness chord ratio of 13% has been used over the inner wing where the equipment is stored. Outboard the wing tapers to 8% thickness/chord at the tip.[1]

Specification 470 described how the wing had been designed with a straight taper to simplify production and to achieve a smooth and accurate contour. The wing skins were to be relatively thick, aiding torsional rigidity which was needed for good aileron control at high speeds. Although the prototype was to have a dihedral of 3° it was intended that this would be increased in subsequent aircraft.[1] To improve the ground-handling the Spitfire's narrow-track, outward-retracting undercarriage was replaced with a wider-track, inward-retracting system. (This eliminated a weakness in the original Spitfire design, giving the new plane similar, safer landing characteristics, comparable to the Hurricane, Typhoon, Tempest, Mustang, and Focke-Wulf 190.) The Air Ministry was impressed by the proposal and, in February 1943, issued Specification F.1/43 for a single-seat fighter with a laminar flow wing; there was also to be provision made for a wing folding scheme to meet possible Fleet Air Arm requirements. The new fighter was to use a fuselage based on a Spitfire VIII.[2]

The new wing was fitted to a modified Spitfire XIV NN660, in order to make a direct comparison with the earlier elliptical wing, and was first flown on 30 June 1944 by Jeffrey Quill. Although the new Spitfire's speed performance was comfortably in excess of an unmodified Spitfire XIV, the new wing displayed some undesirable behaviour at the stall which, although acceptable, did not come up to the high standards of Mitchell's earlier elliptical wing. NN660 crashed on 13 September 1944 while performing mock-combat at low altitude with a standard Spitfire, killing pilot Frank Furlong. No reason for the loss was officially established,[3] although Quill suspected that the aileron control rods had momentarily seized, the Spiteful using control rods rather than the Spitfire's cables. Quill noted that from then on a careful check was always made of the control rods at the factory, and that type of accident never re-occurred.

 

[Zipper730]

By 1942, Supermarine designers had realised that the characteristics of the Spitfire's wing at high Mach numbers might become a limiting factor in increasing the aircraft's high-speed performance. The main problem was the aeroelasticity of the Spitfire's wing

Look, I already read this... and this was fixed by the Mk.VIII, right?

The new wing was fitted to a modified Spitfire XIV NN660, in order to make a direct comparison with the earlier elliptical wing, and was first flown on 30 June 1944 by Jeffrey Quill. Although the new Spitfire's speed performance was comfortably in excess of an unmodified Spitfire XIV

Is this level flight speed, dive speed, or both?

 

[pbehn]

Look, I already read this... and this was fixed by the Mk.VIII, right?

If you read it then it is obvious that it wasn't and couldn't be because the problem was a fundamental part of the original Spitfire wing construction.

Is this level flight speed, dive speed, or both?

You read the same article as I did. Since the modified aircraft was lost in a low level mock combat with an unmodified spitfire I use my incredible powers of reasoning to conclude all aspects of performance were evaluated. The article clearly states that the Spiteful wing was better in speed performance but not as good in stall characteristics. Don't get hung up on the high mach number of the Spitfire, at those speeds the plane is at the edge of control and the propeller likely to fall off, it was drag at lower speeds that was important. This reduced drag in part meant that the Spitfire was slower than a Mustang with the same engine, there were other factors though like cooling drag.

 

[Zipper730]

If you read it then it is obvious that it wasn't and couldn't be because the problem was a fundamental part of the original Spitfire wing construction.

The earlier spitfires had torsion problems, but the VIII designs from what I was told had strengthened wings.

I remember hearing somewhere that the basic wing was good to Mach 1.3 (provided a new fuselage, tail and a jet were used): It's something that tends to make an impression on somebody when you're reading about a plane that flew in 1936

Since the modified aircraft was lost in a low level mock combat with an unmodified spitfire I use my incredible powers of reasoning to conclude all aspects of performance were evaluated. The article clearly states that the Spiteful wing was better in speed performance but not as good in stall characteristics.

So better in level flight speed...

Don't get hung up on the high mach number of the Spitfire, at those speeds the plane is at the edge of control and the propeller likely to fall off, it was drag at lower speeds that was important.

Cruise performance...

This reduced drag in part meant that the Spitfire was slower than a Mustang with the same engine, there were other factors though like cooling drag.

The windscreen was also an issue as well, if I recall correctly they would have been able to squeeze 20 mph out of the plane just by redesigning that (it wasn't a big deal because the Germans used the same bulletproof set-up early on)

 

[pbehn]

The earlier spitfires had torsion problems, but the VIII designs from what I was told had strengthened wings.

I remember hearing somewhere that the basic wing was good to Mach 1.3 (provided a new fuselage, tail and a jet were used): It's something that tends to make an impression on somebody when you're reading about a plane that flew in 1936
So better in level flight speed...
Cruise performance...
The windscreen was also an issue as well, if I recall correctly they would have been able to squeeze 20 mph out of the plane just by redesigning that (it wasn't a big deal because the Germans used the same bulletproof set-up early on)

The Spitfire was only ever acceptable in rate of roll and roll rate at high speed was one thing the Spiteful was supposed to improve.
From my limited knowledge the Spitfire would fall apart at mach 1.3.

 

[Zipper730]

The Spitfire was only ever acceptable in rate of roll and roll rate at high speed was one thing the Spiteful was supposed to improve.

I never knew that, does this apply for the LF variants?

From my limited knowledge the Spitfire would fall apart at mach 1.3.

Well in practice of course because of the fact that the fuselage, propeller and tail would never handle it: Ironically I was told the wings would, though I'm not sure at what altitude because even at 35000 feet that's like 455 knots or 523.3 mph and would be a major speed limit.

 

[pbehn]

I never knew that, does this apply for the LF variants?
Well in practice of course because of the fact that the fuselage, propeller and tail would never handle it: Ironically I was told the wings would, though I'm not sure at what altitude because even at 35000 feet that's like 455 knots or 523.3 mph and would be a major speed limit.

Roll rate varies with altitude and speed. It also varies with aircraft condition like how much ammunition and fuel is left in the wings. With some planes like the Bf109 it could even change with pilot build and strength. The Spitfire didn't have any real problem with roll rate until the FW190 turned up by which time the Spitfire had put on weight and installed cannon in the wings. The FW190 was excellent in roll rate and in this especially, it outclassed the Spitfire . The wings of the Spitfire had their tips removed "clipped" to close the gap but this was one of the issues that the "Spiteful" design addressed starting in 1942. The difference between "Spitfire" and "Spiteful" is purely commercial, it could have been named the Spitfire Mk23.

Chuck Yeager said that any WW2 pilot who believed he had broken the sound barrier was dreaming, that is good enough for me.

 

[tomo pauk]

I'm curious why the Supermarine Spiteful had laminar flow wings?

Designers expected that drag would've been lowered, and the critical Mach number would've been increased by 55 mph.

 

[Koopernic]

Look, I already read this... and this was fixed by the Mk.VIII, right?
Is this level flight speed, dive speed, or both?

When an aircraft uses its ailerons to roll it tends to twist the wing in the opposite direction which works to reduce the roll rate. It increases with speed. This is called aeroelasticity. Spitfires had their strength concentrated in a main spar at about 1/4 chord where lift is centered which formed a D section with the thick leading edge skin. Strong but it did twist a little more than twin spar design such as the Fw 190 which had the thick skin between two spars to form a box like structure.

The theoretical speed at which the wing would reverse was theoretical only and didn't happen in real life. It reduced aileron effectiveness to about 65% at 400 mph. The torsional stiffness of the wings on the mark 21, 22 & 24 was increased by 47% over previous marks, raising the theoretical aileron reversal limit from 580 to 825 mph IAS. These marks really were post war aircraft though a few did see service in 1945 but not air to air combat. The Mk XVIII didn't get a new wing but it used better materials such as a stainless steel main spar.

Some Spitfires had fabric covered ailerons which hurt roll rate. It never bothered the Corsair or 109 I believe.

The Mk 22 etc also received balance tabs or spring tabs on the ailerons. These tiny sub ailerons deflect to deflect the aileron. Hard to achieve without flutter or over driving at high speed. It allowed one man to control the B36 without power boost.

The Fw 190 actually had the opposite problem, in a high G turn the wings would twist up and reduce the 2 degree washout and this could give a sudden stall whereas in low G stall, say in landing configuration the stall was gentle. So in a way the nature of the spitfire wing torsional rigidity maintained it's well annunciated stall.

 

[pbehn]

The Mk XVIII didn't get a new wing but it used better materials such as a stainless steel main spar. .

Stainless steels generally have a higher yield strength and lower elongation values in addition to corrosion resistance.

 

[Koopernic]

Stainless steels generally have a higher yield strength and lower elongation values in addition to corrosion resistance.

The Mk XVIII "super Spitfire" was a sort of properly developed Mk XIV which itself in essence a Mk VIII with the Griffon instead of the Merlin.

It was a backup in case the Mk 22 with its new wing and control rigging ran into problems. They strengthened it in numerous ways without changing the underlying structure. Replacing some spars and stringers with stainless steel was one way. I think it was tapered rather than telescope style as well. So it would have been stiffer and more rigid.

 

[pbehn]

The Mk XVIII "super Spitfire" was a sort of properly developed Mk XIV which itself in essence a Mk VIII with the Griffon instead of the Merlin.

It was a backup in case the Mk 22 with its new wing and control rigging ran into problems. They strengthened it in numerous ways without changing the underlying structure. Replacing some spars and stringers with stainless steel was one way. I think it was tapered rather than telescope style as well. So it would have been stiffer and more rigid.

It was a great post that you made Koopernic I was just pointing out that stainless steel has different properties to plain carbon steel, generally higher (there is a huge range of stainless steels) having worked with stainless steels most people only associate it with not going rusty not that it is actually much stronger.