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

[ATAG_Colander]

From http://en.wikipedia.org/wiki/Stall_%28flight%29

Dynamic stall is a non-linear unsteady aerodynamic effect that occurs when airfoils rapidly change the angle of attack. The rapid change can cause a strong vortex to be shed from the leading edge of the aerofoil, and travel backwards above the wing. The vortex, containing high-velocity airflows, briefly increases the lift produced by the wing. As soon as it passes behind the trailing edge, however, the lift reduces dramatically, and the wing is in normal stall

[Kurfürst]

There she blows!

[Kurfürst]

Originally Posted by Kwiatek

Generally slats cause more drag and effect also higher energy bleeding but other hand allows to get higher angle of attack - good for deflection shoting.

Slats do not cause more drag - higher angles of attack permitted by slats do.

Spit other hand has elipitical wing desing which reduced induced drag which is important at slow speed and high angle of attack and with lower wings loading it casue less energy bleeding in turns then 109.

1, The Spitfire doesn't have elliptical wings, from the aerodynamic POV. Otherwise stall would be awful - a true elliptical wing stall as a whole. That's why most planes have a washout/twist built in the wing to 'ruin' the even lift distribution and make the outer wing area stall later than the inner.
2, Lower induced drag on the Spit doesn't have anything to do with wing shape, its simple that its a huge wing, and needs less angle of attack to provide the same lift. Less angle of attack - less drag.

[Rumcajs]

Originally Posted by Kurfürst

2, Lower induced drag on the Spit doesn't have anything to do with wing shape, its simple that its a huge wing, and needs less angle of attack to provide the same lift. Less angle of attack - less drag.

The wing is elliptical. Lift distribution is modified to a certain degree that's true, but it still has lift more evenly distributed than the wing of a 109. And the elliptical shape is responsible for that. Your claim is not exactly true, because induced drag simply has something to do with the shape and lift distribution. You are right that the wing of a spit is large and that's why lower angle of attack ... ok. But the shape contributes too.
BTW if the elliptical shape didn't bring advantages, why would the Brits bother to manufacture them?

[Kurfürst]

Originally Posted by Rumcajs

The wing is elliptical. Lift distribution is modified to a certain degree that's true, but it still has lift more evenly distributed than the wing of a 109. And the elliptical shape is responsible for that.

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

Your claim is not exactly true, because induced drag simply has something to do with the shape and lift distribution. You are right that the wing of a spit is large and that's why lower angle of attack ... ok. But the shape contributes too.

Certainly shape is a factor, but I do not think it's a major or measurable factor compared to sheer wing size. The Spitfire had a very large wing for a very small airframe, much larger than any other with the possible exception of the Zero.

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.

BTW if the elliptical shape didn't bring advantages, why would the Brits bother to manufacture them?

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.

[palker4]

Spit has a negatively twisted wing that means that angle of attack will be always lower on the wingtip + wingtip probably uses different airfoil than root with different lift characteristic so that it will never stall first. That means spit can have eliptical wing without dangerous stall characteristics.

[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 palker4

Spit has a negatively twisted wing that means that angle of attack will be always lower on the wingtip + wingtip probably uses different airfoil than root with different lift characteristic so that it will never stall first. That means spit can have eliptical wing without dangerous stall characteristics.

That's simply called washout and is found on the vast majority of WW2 fighters. There's nothing magic or uncommon in it.

Elliptic planform theoretically means even lift distribution. Even lift distribution means the whole wing stalls all at once. With a twisted wing you no longer have an even lift distribution, no reduced induced drag, and no dangerous stall charateristics.

Simply to put from the aerodynamic POV, it's not an elliptic wing.

[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).