P-47N/M vs P-51H

[Shortround6]

The elliptical wing gave a the best performance at all altitudes. This assumed that all the different wing shapes (planforms) are the same/similar airfoils.
However the difference between an elliptical wing and some tapered wings was only a few percent. Also note that very few planes used true elliptical shapes and the Spitfire and Seversky/Republic designs were semi-elliptic. Once the aircraft designers had better wing tunnels/data the elliptical wings went away as the actual advantage wasn't worth the cost.

If the engine/propeller/fuel teams could find an extra 2-4% (40-80hp on a 2000hp engine) then the actual shape didn't matte so much any more.

 

[drgondog]

I cannot find the source (of course) but reputedly the elliptical wing was optimized for high altitude performance, which explains the Spit and P-47 configurations.
First I heard of it was from a Canadian ace who knew A LOT about A LOT. The late Rod Smith.

Hi Barrett - I doubt that the Spit wing was optimized for altitude performance as zero to a 'little' was known about compressibility in the 30's. The advantage to the threoretical elliptical wing (which did not exist in purest form) was to develop an optimized lift loading and maximum reduction to induced drag.

Both the P-47 and Spit wings were more efficient, Total Drag- wise at low to medium speed. Ditto F4U and F6F/F8F and FW 190 and Bf 109 and P-38.

The Spit advantage over Mustang (drag) at high compressibility speeds was the smaller Thichness ratio (13%) compared to Republic S-3 (14.6%) and Mustang (16%). Where the Mustang clawed back drag penalty was the fact that the design pushed the Max T/C back to 38+% (from ~28/30% for Spit and Republic wing. It had the effect of delaying formation of shock wave further aft on the wing. The Mustang also had a more even chord-wise lift distribution, which, when shock wave occurred and CL dramatically reduced aft of the shock wave - did not create the excessive pitch down forces on the airframe.

 

[drgondog]

The Thunderbolts were fast at high altitudes because of their turbochargers. They were replaced with Mustangs partially because their wings suffered more from compressibility. The Spitfires had very high critical Mach numbers because they had thin wings.

Hi Howard - the P-47D was replaced because of combat radius limitations. The P-47 wing was closer to the Spitfire airfoil - only slightly thicker. Dive speed performance of P-47D and P-51B/D were about same for limit loads, but the airfoil design of the Mustang wing both delayed drag rise as well as maintained pitch control during compressibility - unlike the P-38 and P-47 which required dive flaps.

 

[pbehn]

I cannot find the source (of course) but reputedly the elliptical wing was optimized for high altitude performance, which explains the Spit and P-47 configurations.
First I heard of it was from a Canadian ace who knew A LOT about A LOT. The late Rod Smith.

The two were from completely different eras in aircraft design. Mitchell wanted a thin wing for speed performance, the aerodynamics of the high speed low drag P-51 type wing were not known at the time. There were stipulations in the spec. about take off runs and clearing a certain height in a given distance. The Elliptical wing allowed the Spitfire to have a thin wing and have room for the undercarriage and armament in a light weight design. The U/C arrangement wasnt ideal for landing and take off but saved weight and space on a design that had to win a contract with a fixed prop that limited actual take off power to around 660HP. I doubt that the P-47 could pass the RAF requirements for take off, but that was a different era when they arrived i UK, runways were longer and made of concrete or metal matting

 

[Shortround6]

The two were from completely different eras in aircraft design. Mitchell wanted a thin wing for speed performance, the aerodynamics of the high speed low drag P-51 type wing were not known at the time. There were stipulations in the spec. about take off runs and clearing a certain height in a given distance. The Elliptical wing allowed the Spitfire to have a thin wing and have room for the undercarriage and armament in a light weight design. The U/C arrangement wasnt ideal for landing and take off but saved weight and space on a design that had to win a contract with a fixed prop that limited actual take off power to around 660HP. I doubt that the P-47 could pass the RAF requirements for take off, but that was a different era when they arrived i UK, runways were longer and made of concrete or metal matting

I think we are confusing several different things. Elliptical wing has nothing to do with the wing thickness.

You can have thick and thin elliptical wings. Early He 111s had elliptical wings.

Later ones got tapered leading edges, semi-elliptical?
As Drgondog has already stated "threoretical elliptical wing (which did not exist in purest form) was to develop an optimized lift loading and maximum reduction to induced drag."

Basic wing design for the P-47 goes back to the P-35, or earlier?

Seversky and crew were using straighter leading edges than Heinkel and Supermarine.
The wing design did give them room for things like guns and landing gear (Seversky sort of missed that one but wanted to save the plane on a wheels up landing)
The elliptical planform was supposed to give less drag than wing of the same area and thickness that used straight or parallel edges. Turned out that by carefully selecting the taper of the wing you could get close to the elliptical benefit and since nobody was actually using a pure elliptical wing anyway the benefit turned out to be very small.

P-47s problem was that it weighed over twice what the Spitfire did for only about a 33% increase in wing area which requires Divine intervention for short take-off and landing, not fancy wing tips

 

[pbehn]

I think we are confusing several different things. Elliptical wing has nothing to do with the wing thickness.
View attachment 768428
You can have thick and thin elliptical wings. Early He 111s had elliptical wings.
View attachment 768429
Later ones got tapered leading edges, semi-elliptical?
As Drgondog has already stated "threoretical elliptical wing (which did not exist in purest form) was to develop an optimized lift loading and maximum reduction to induced drag."

Basic wing design for the P-47 goes back to the P-35, or earlier?
View attachment 768430
Seversky and crew were using straighter leading edges than Heinkel and Supermarine.
The wing design did give them room for things like guns and landing gear (Seversky sort of missed that one but wanted to save the plane on a wheels up landing)
The elliptical planform was supposed to give less drag than wing of the same area and thickness that used straight or parallel edges. Turned out that by carefully selecting the taper of the wing you could get close to the elliptical benefit and since nobody was actually using a pure elliptical wing anyway the benefit turned out to be very small.

P-47s problem was that it weighed over twice what the Spitfire did for only about a 33% increase in wing area which requires Divine intervention for short take-off and landing, not fancy wing tips

The two issues are not exclusive, all designs make compromises. The Spitfire wing is a combination of elliptical shapes the leading edge is substantially straight from the wing root to the limit of the U/C folds up. In the era the Spitfire was first deployed grass airfields were the norm, just a few years later things had changed in many ways.

Edit some words from Shensone "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 an ideal shape, theoretically a perfection. There were other advantages, so far as we were concerned. To reduce drag we wanted the lowest possible wing thickness-to-chord ratio, consistent with the necessary strength. But near the root the wing had to be thick enough to accommodate the retracted undercarriage and the guns; so to achieve a good thickness-to-chord ratio we wanted the wing to have a wide chord near the root. A straight-tapered wing starts to reduce in chord from the moment it leaves the root; an elliptic wing, on the other hand, tapers only very slowly at first then progressively more rapidly towards the tip. Mitchell was an intensely practical man and he liked practical solutions to problems. I remember once discussing the wing shape with him and he commented: "! don't give a b….. whether it's elliptical or not, so long as it covers the guns!" The ellipse was simply the shape which allowed us the thinnest possible wing with sufficient room inside to carry the necessary structure and things we wanted to cram in. And it looked nice from https://www.aerosociety.com/media/4843/the-spitfire-wing-planform-a-suggestion.pdf

 

[Shortround6]

The two issues are not exclusive, all designs make compromises. The Spitfire wing is a combination of elliptical shapes the leading edge is substantially straight from the wing root to the limit of the U/C folds up. In the era the Spitfire was first deployed grass airfields were the norm, just a few years later things had changed in many ways.

The size of the Spitfire wing was result of the landing and take-off requirements, and the stupid refusal to use modern propellers. Which by chance, meant it was easier to up grade the plane with bigger engines and guns.
A lot of designs are compromises and a lot of designers are trying to make each thing/part do 2 or 3 things at once. Sometimes it works and sometimes it doesn't.
P-35 in the picture above held a huge amount of fuel for a mid 1930s fighter. They used integral fuel tanks. Simply sealed up spaces in the wing to make fuel tanks without either interrupting the structure for spaces to put tanks in or installing separate tanks with the extra weight. Turns out it wasn't so simple, the "sealant" leaked and the way they built the wing made it just about impossible to fit self sealing tanks at a later date without altering the way the wing was built.

What we do have to be careful of is not confusing cause and effect.
elliptical or semi-elliptical wings were actually pretty common in 1930s. Like Japanese A5Ms and D3As.

What else the designers tried to do with them, like spread the guns out in the Spitfire, is not the main reason they were picked. It may have contributed to it.
You will also find that some designers stuck with certain features, like wing shapes, for as long as they could. There were less surprises that way.