Wings

[GregP]

When it was said above that the Spitfire wing was "the best," that is VERY misleading. Best at what? There are certainly fighters that out-turn a Spitfire and there are certainly fighters that are faster and also fighters that can fly slower. Many can out-roll a Spitfire. So the real question of "best" is hard to answer without some narrowing of the mission.

The elliptical planform is supposed to be ideal for production of lift, but VERY little difference can be detected in efficiency between the semi-elliptical planform of the Spitfire and the tapered wing of a Seafang.

You didn't ask about "the best," and we have had enough long threads about that subject anyway (nothing ever gets settled), you asked about the shape as seen from above or below, which is called the wing planform. I have seen a discussion about planform only and a comparison of what can be expected from keeping to a single airfoil and changing the planform, but it has been several years and I can't remember just now exactly where I saw it.

I'll dig around a bit and see if I can find it.

Meanwhile, Drgondog's post above is a great start and gives you a place to start looking.

 

[GrauGeist]

...The elliptical planform is supposed to be ideal for production of lift, but VERY little difference can be detected in efficiency between the semi-elliptical planform of the Spitfire and the tapered wing of a Seafang...

Thought I'd mention that the Spitfire's wing planform was elliptical, the He280's wing planform was semi-elliptical.

 

[pbehn]

When it was said above that the Spitfire wing was "the best," that is VERY misleading. Best at what?

I think that was the ideal as far as drag was concerned as was known at the time without cold cannons. The Spit was designed for 4 rifle caliber MGs trust the Germans to go putting up armoured bombers with escorts.

 

[vikingBerserker]

Take a look at this wiki article regarding all aspects of wing types.

Not only does it cover successful types, but attempted or theoretical types as well.

Also, check out the citations and references at the bottom, you may find a good selection of books to look for, from that list.

Wing configuration - Wikipedia, the free encyclopedia

Thanks, but I really could not see where it talked about a planeform. I have bits and pieces of examples, but it would be great if there was a book that had all the major ones in it.

 

[drgondog]

Tomo - No, I haven't seen a drag analysis of a Spit but Dr. Horner presented a classic drag analysis of a 109G in his "Fluid Dynamic Drag" text in which he breaks down, component by component the effects of skin friction as a function of
1. Reynold's number (BTW the Spit deep cord adversely affects RN),
2. sheet metal gaps and surface imperfections, including rivet heads, holes, "blisters" (these parasite drag factors also important elsewhere), gaps in aileron and flap hinges, gaps beside flaps and ailerons, pitot tube, nav/landing light covers, etc
3. Surface texture such as camo paint grain size (hence the desirability of waxing and polishing) or NMF

The individual component drag elements for top and bottom surfaces are tabulated then applied against the average dynamic pressure ratio of top and bottom surfaces to arrive at the total drag area D/q. For the 109 this contribution was ~ 25% of the TOTAL drag of the 109. Having said this, a great deal of work has to be done via wind tunnel work or various table estimates as only the Reynolds Number is reduced by simple formula.

For the 109, the ratio of wing area to total wetted area was probably Smaller than a Spit indicating that the Spit's wing contribution to Total Drag may be higher than a 109. I'll have to dig it up.

Recall that a Mustang had greater wetted area even with much smaller wing area and was one hell of a lot faster with much less horsepower in the Allison.. so the conclusion that the Spit wing was a marvel of aerodynamics is not easily drawn.

 

[drgondog]

Thanks, but I really could not see where it talked about a planeform. I have bits and pieces of examples, but it would be great if there was a book that had all the major ones in it.

There are only a few basic plan form shape for wings
Elliptical (no production a/c exists including Spitfire)
Semi Elliptical (Spit and P-47 fit this broad definition)
Rectangular (Constant Chord)
Trapezoidal/Tapered (P-51, Bf 109, FW 190, A6M, etc)
Delta

Various applications of Wing Taper (wing tip chord to root chord ratio) of ~ .2 to .6 at AR=6 (close to P-51, 109, etc) provided only a 1% increase in Induced Drag over an elliptical plan form - and is one helluva lot easier to manufacture.

But CL is constant along the span for Elliptical wings. For any other plan form CL varies along the span. As taper ratio decreases (i.e. moves from 1 for rectangular wing to say .3 for a selected taper ratio) the max CL moves outboard).

This combination of higher operating CL closer to the tip and a lower actual CL of non-elliptical wing results in tip stall characteristics for low taper wing - hence introduction of twist and slats and in case of swept wings - fences.

 

[tomo pauk]

Enjoy some well-earned bacon, Bill

 

[pbehn]

Elliptical - leading and trailing edges are curved such that the chord length varies elliptically with respect to span. Theoretically the most efficient, but difficult to make. Famously used on the Supermarine Spitfire. (Note that in aerodynamics theory, the term "elliptical" describes the optimal lift distribution over a wing and not the shape).
Semi-elliptical - only the leading or trailing edge is elliptical with the other being straight, as with the elliptical trailing edges of the Seversky P-35.[11] Seen in low-aspect-ratio tailless form on the Arup S-1 and subsequent types.


This was in the linked page, was the spit eliptical or semi elliptical?

 

[Edgar Brooks]

You are perpetuating the same old myths; natural metal does not have less drag than paint (it's one of the reasons why the P-51 wings were painted,) since any panel lines and rivet divots can be filled and smoothed down before undercoating and painting. Also, a properly-camouflaged airframe is harder to spot from the air, so less likely to attract unwanted attention. Waxing and polishing gave no advantage (another myth,) but smoothness did, which is why the Air Ministry went over to synthetic paint, in 1942, which was also matte, therefore less "draggy" and less reflective. They also employed "Aircraft Finishers," from about 1942, whose job was to keep the paint as pristine as possible.
One can only ponder how much effect cannon, sticking out of the l/e, would have had on the P-51's performance, but, even pre-war, consideration had to be taken of how to deal with heavily-armoured bombers arriving over the U.K. The main purpose of the USAAF fighters was to see off other fighters, not attack bombers, hence no need for the heavier armament of cannon.
Contrary to popular belief, the Air Ministry carried out many tests, and found that (as far as bombers were concerned) the .5" offered no advantage over the .303", being heavier (so fewer per airframe,) and slower-firing (so less chance of disabling the whole bomber crew.) Leigh-Mallory did his utmost to get the .5", but that didn't happen until we started to use the gyro gunsight, in 1944, which ensured that, in a deflection shot, the pilot was more likely to hit what he aimed at.
Trials were also carried out on the front windshield of the Spitfire, including a curved front, but it was found that the curvature caused distortions, at times meaning that the enemy disappeared from view (not much help if you're trying to shoot at him.)

 

[m37b1]

OK. Great info provided. So let's see if I can narrow the question.

With all else being equal. (fuselage, weight, HP, airfoil . . . . . ) Which planform provides the best drag to lift characteristics?

 

[drgondog]

You are perpetuating the same old myths; natural metal does not have less drag than paint (it's one of the reasons why the P-51 wings were painted,)

Edgar - respectfully Edgar, nominal NMF aluminum metal surface IS less draggy than a painted surface in which the grain size exceeds one Mil. Hence the RAF and later LW exploration into smoother quality paints.

The primary reason the P-51 wings were a.) filled to normalize the flush rivet countersink/head differences, b.) sanded smooth and c.) painted - was to attempt to improve laminar flow characteristics and b.) succeed in reducing skin friction arising from joint gaps and abnormal surface imperfections. Absent any paint at all on the Spit or 109, the Mustang 'painted' wing would still have less friction drag.

Also, a properly-camouflaged airframe is harder to spot from the air, so less likely to attract unwanted attention. Waxing and polishing gave no advantage (another myth,) but smoothness did, which is why the Air Ministry went over to synthetic paint, in 1942, which was also matte, therefore less "draggy" and less reflective. They also employed "Aircraft Finishers," from about 1942, whose job was to keep the paint as pristine as possible.

In fact Edgar, waxing and polishing does give a slight reduction to skin friction drag for the reasons mentioned above.

One can only ponder how much effect cannon, sticking out of the l/e, would have had on the P-51's performance, but, even pre-war, consideration had to be taken of how to deal with heavily-armoured bombers arriving over the U.K. The main purpose of the USAAF fighters was to see off other fighters, not attack bombers, hence no need for the heavier armament of cannon.

The drag tunnel tests indicated a 12+ mph reduction in top speed between P-51 (4x20mm Extended Hispano) and P-51A (4x50 caliber flush). Not disagreeing with point of heavier firepower.


Trials were also carried out on the front windshield of the Spitfire, including a curved front, but it was found that the curvature caused distortions, at times meaning that the enemy disappeared from view (not much help if you're trying to shoot at him.)

Look to the reports I published here in the P-51 section which details the aerodynamic comparisons (pressure distributions on 3-d scale model computer simulations) between Spit IX, P-51B, P-51D and FW 190D to see the difference between the Spitfire drag caused by stagnation at the base of the Mk IX windscreen. The greater slope of the P-51D and FW 190D were significantly less drag.

 

[tomo pauk]

...
One can only ponder how much effect cannon, sticking out of the l/e, would have had on the P-51's performance, but, even pre-war, consideration had to be taken of how to deal with heavily-armoured bombers arriving over the U.K. The main purpose of the USAAF fighters was to see off other fighters, not attack bombers, hence no need for the heavier armament of cannon.
...

The main task for USAF fighter arm was to deal with perceived bomber threat. Hence Airacuda with two 37mm, while P-39 and P-38 were to carry one each. Other USAF fighters, incapable for that, were supposed to haul between 8 and 10 MGs. USAF got into an offensive mood some time in late 1942.

 

[drgondog]

Elliptical - leading and trailing edges are curved such that the chord length varies elliptically with respect to span. Theoretically the most efficient, but difficult to make. Famously used on the Supermarine Spitfire. (Note that in aerodynamics theory, the term "elliptical" describes the optimal lift distribution over a wing and not the shape).
Semi-elliptical - only the leading or trailing edge is elliptical with the other being straight, as with the elliptical trailing edges of the Seversky P-35.[11] Seen in low-aspect-ratio tailless form on the Arup S-1 and subsequent types.

The elliptical lift distribution is seemingly different from a 'mathematically elliptical wing'. Having said this, for a 'pure' elliptical wing in plan form with same airfoil section across the span and no twist, the Oswald efficiency factor is 1 and the Induced drag is at Theoretical minimum for that CL for the same AR.

Per Aerodynamic theory I would draw you to the textbooks which dive hard enough into the Derivation of Prandtl's lifting line theory differential-integral equations - for calculating the only unknown - namely Circulation (Gamma) - as a span wise distribution.

For a given CL and same AR, the achievement of a pure elliptical (function of Gamma above) span wise lift distribution - the wing plan form must also be a Pure ellipse with same airfoil section. The wing must be a mathematical ellipse - For Leading and Trailing Edge- which has been done experimentally but never in production. The Spitfire is closer with respect to trailing edge but even then not quite a mathematical ellipse. The leading edge fails by any definition of 'Ellipse'.

This may sound like quibbling but nevertheless true.

This was in the linked page, was the spit eliptical or semi elliptical?

Look to Fundamentals of Aerodynamics by Anderson, pages 243-248 page 548-554 of Karamcheti's Princoples of Ideal Fluid Aerodynamis" which was part of my grad course stack.

 

[Edgar Brooks]

Edgar - respectfully Edgar, nominal NMF aluminum metal surface IS less draggy than a painted surface in which the grain size exceeds one Mil. Hence the RAF and later LW exploration into smoother quality paints..

And, respectfully, that holds good for a perfectly smooth surface to start with; it doesn't when you have overlapping panel lines, open panel lines, and rivet dimples all interrupting the airflow. Also polishing was found to have no beneficial effect, worth more than about 1mph, but it did make the surface more reflective to sunlight, so able to give away parked aircrafts' positions.

Look to the reports I published here in the P-51 section which details the aerodynamic comparisons (pressure distributions on 3-d scale model computer simulations) between Spit IX, P-51B, P-51D and FW 190D to see the difference between the Spitfire drag caused by stagnation at the base of the Mk IX windscreen. The greater slope of the P-51D and FW 190D were significantly less drag

I've read all of those reports, which are fine, if you just want to go fast, but pilots needed to be able to see, as well, and the top line of the Spitfire's cowling (until the Griffon's downthrust angle was increased) was such that the pilot often lost sight of his enemy as he fired; deepen the angle, you have to sit the pilot lower, and make his view even worse.