why the spit turns most effectively at the limit edge and the 109 doesnt

[Rumcajs]

Originally Posted by Kurfürst

I'd love to see some lift distribution graphs to support that.

There are plenty of resources on the internet. Not sure if one can find exactly the spitfire's lift distribution, but generally there are many sources for elliptical and other shaped wings.

Originally Posted by Kurfürst

If wing shape would have been such a factor, planes like the Curtiss Hawk, Zero or Hawker Hurricane wouldn't run circles around the Spitfire, but they did.

Size, shape, weight, airfoil .... many variables go into the equation. No need to make simplifications like this.

Originally Posted by Kurfürst

Simply because the British Air Ministry specified an 8-gun armament, and Supermarine could not find space in the wings to house them without enlarging the original trapezoid wing of the Spitfire (which was meant for a four gun armament). The design team was simply practical about it.

http://en.wikipedia.org/wiki/Supermarine_Spitfire
In 1934, Mitchell and the design staff decided to use a semi-elliptical wing shape to solve two conflicting requirements; the wing needed to be thin, to avoid creating too much drag, while still able to house a retractable undercarriage, plus armament and ammunition. Beverly Shenstone, the aerodynamicist on Mitchell's team, explained why that form was chosen:
The elliptical wing was decided upon quite early on. Aerodynamically it was the best for our purpose because the induced drag, that caused in producing lift, was lowest when this shape was used: the ellipse was ... theoretically a perfection ... To reduce drag we wanted the lowest possible thickness-to-chord, consistent with the necessary strength. But near the root the wing had to be thick enough to accommodate the retracted undercarriages and the guns ... Mitchell was an intensely practical man... The ellipse was simply the shape that allowed us the thinnest possible wing with room inside to carry the necessary structure and the things we wanted to cram in. And it looked nice.

So again, you are doing a simplification here.

[ATAG_Colander]

My 2 cents...

Lift is related to the wing foil used and the surface area of the wing.
An elliptical wing is not needed to increase the surface area or change the wing foil. However....

One of the big culprits of drag in a wing are the wing tips. The elliptical wing is very good at not creating a vortex in the wing tips thus reducing drag.


See http://en.wikipedia.org/wiki/Wing_tip

[Kurfürst]

Originally Posted by Rumcajs

There are plenty of resources on the internet. Not sure if one can find exactly the spitfire's lift distribution, but generally there are many sources for elliptical and other shaped wings.

Again the problem is that the Spitfire does not have an elliptical wing from the aerodynamic POV as explained above, so the theoretical lift distribution properties of a aerodynamic wing do not apply to the Spitfire.

What I have pointed out that you have made a very specific claim about the relative lift distribution on the 109 and Spitfire, based on generalisations. I wonder if even Supermarine or Messerschmitt were aware of how it looked like back in the 1940s...

Size, shape, weight, airfoil .... many variables go into the equation. No need to make simplifications like this.

It's a simplification but its ultimately giving the right results as can be cross-checked by practical examples. I am quite certain that the airfoil shape has next to non-measurable effect on the Spitfire turning characteristics and it shows no special qualities - fighters with low wingloading tend to turn well, nothing new in that.

Whatever increased efficiency they may or may not have gained by using the shape they lost it as they sacrificed the aspect ratio in return. Elliptical wings seemed to be a nice idea in 1930s, and the theory was that they would offer some advantage, but as it turned out it simply did not, and everybody dropped them quickly, including Supermarine when it first got a chance (Mark 2x series Spitfires).

I have to agree with Kur this time.

The elliptical form in itself had aerodynamically only most minimal to vanishing advantages above a trapezoid wing with rounded wingtips but had some advantageous side effects such as increased wing aera and reduced relative chord thickness due to the long chord lengths. That is why supermarine chose elliptical wings above trapezoid wings because these side effects provided advantages with respect to the specifications issued by the ministry.

It came at the cost of a wing very difficult to produce and it was commonly abandoned by all air forces.

If the elliptical form would have been so advantageous why did so few other air forces not adopt them? Supermarine was neither the inventor nor the patent holder of the elliptical wing.

[ACE-OF-ACES]

Originally Posted by 41Sqn_Stormcrow

If the elliptical form would have been so advantageous why did so few other air forces not adopt them? Supermarine was neither the inventor nor the patent holder of the elliptical wing.

I think you answered your own question when you noted

Originally Posted by 41Sqn_Stormcrow

It came at the cost of a wing very difficult to produce and it was commonly abandoned by all air forces.

War espically WWII was more about logistics and economics.. Along those same lines is one of the reason they went with the P51 over the P38.. economics

[Rumcajs]

Just found this article, really nice to read.
http://thoughtality.com/the-spitfire-wing
It looks like the decision was really influenced by the need to accommodate 8 guns.

A trapezoid wing with rounded wingtips comes close to the "ideal" elliptical wing.

And as Kurfurst mentioned, the advantages of truly elliptical wing are more theoretical than practical. Just in 1934 when the wing was designed it all looked a bit different than during WWII. Average performance of fighter planes was much lower and they probably saw the need for good low speed handling and efficiency. As performance and speed increased these aspects were less important. Also the 8 guns in wings design became obsolete with introduction of more powerful canons.

Back to the original question. I believe the 109 performs worse than the spit at very low speeds, because when it has to deploy slats, the wing is already working far behind its optimum. The spit can achieve similar lift without slats and with lower angle of attack. So yes, the induced drag would be lower. (I don't want to dig into boundary layer separation and stall questions)

At the same time Kurfurst is right, that this aspect became obsolete during WWII.

[NZtyphoon]

Originally Posted by 41Sqn_Stormcrow

I have to agree with Kur this time.

The elliptical form in itself had aerodynamically only most minimal to vanishing advantages above a trapezoid wing with rounded wingtips but had some advantageous side effects such as increased wing aera and reduced relative chord thickness due to the long chord lengths. That is why supermarine chose elliptical wings above trapezoid wings because these side effects provided advantages with respect to the specifications issued by the ministry.

It came at the cost of a wing very difficult to produce and it was commonly abandoned by all air forces.

If the elliptical form would have been so advantageous why did so few other air forces not adopt them? Supermarine was neither the inventor nor the patent holder of the elliptical wing.

Partly it was a Mitchell design signature, because Mitchell believed the ellipse presented the best aerodynamic compromise available. He also designed a heavy bomber (the B.12/36) and a flying boat with thin, elliptical wings; on some later projects, such as a two-seat, carrier borne version of the Spitfire, he compromised and used wings with straight leading and trailing edges.
A really interesting book to get a hold of is British Secret Projects 3 Fighters and Bombers 1935-1950

Quite similar to Heinkel whose chief designers the brothers Günther had some strange fancy for elliptical wings.

But as I said the elliptical planform in itself brought minor to none primary aerodynamical advantages over trapezoid wings with rounded wing tipps. Only secondary advantages because of higher wing surface allowing to reduce AoA for same lift and a small relative chord thickness. He may as well have achieved the same advantage with a large trapezoid wing with rounded wing tipps like in his seaplanes that he used for winning the snyder trophy.

[NZtyphoon]

Originally Posted by 41Sqn_Stormcrow

Quite similar to Heinkel whose chief designers the brothers Günther had some strange fancy for elliptical wings.

But as I said the elliptical planform in itself brought minor to none primary aerodynamical advantages over trapezoid wings with rounded wing tipps. Only secondary advantages because of higher wing surface allowing to reduce AoA for same lift and a small relative chord thickness. He may as well have achieved the same advantage with a large trapezoid wing with rounded wing tipps like in his seaplanes that he used for winning the snyder trophy.

Had Mitchell lived longer he may well have decided the same thing; as I mentioned some of his late design projects used different wing shapes. The carrier borne and two seat Spitfire derivatives are described more fully in Morgan and Shacklady's book and I'll dig out my copy of Secret Projects.