Spitfire, elliptical wings --- Why?

[zetland76]

The Spitfire is probably my favourite aircraft and I have made several flying models but I wonder, why were it's wings so designed?
From what I can gather the wings were a pain for the production department. In the Battle of Britain they fought on equal terms with the Bf109 which had straight edged tapered wings. Arguably the best fighter of WW II was the Mustang, which again had straight edged wings.

Thanks

Mike

 

[claidemore]

Arguably the best fighter of WW II was the Mustang

The key word there is "arguably". The Mustangs #1 advantage over other fighters was range, #2 would be speed but there were other late war fighters that were comparable in speed. In other areas of performance, climb, roll rate, turn, armament, toughness, there were other designs which held the edge.

I know others will be able to better explain the advantages of the elliptical wing (or in the case of the Spitfire a semi-elliptical wing) but my understanding is that the elliptical design gave the Spit a lower wingloading, which gave it an excellent climb rate (+4000 ft/min in late models) and lower stall speed,hence good turn performance.

There were some benifits with regards to drag as well, which I'm sure is about to be explained by others more learned on the subject of aerodynamics.

Note that Sydney Camm eventually put an elliptical wing on his Hawker fighters, namely the Tempest and Sea Fury.

 

[timshatz]

Wing area, I would guess. Think Mitchell who had a guy who did nothing but work on the design of the wing.

 

[Shortround6]

You have to remember that in the 1930s there were a lot of theories floating around and not a lot of practical experience.
Metal monoplanes were just a few years old when the Spitfire was designed and most of them used different airfoils making direct comparisons difficult.
Wind tunnels were few and far between and most of them were either small (under 10-12ft wide) or low speed or both. Most wind tunnel work was done with models and needed scaling up with "correction" factors to be used. Without the practical experience the accuracy of the "correction" factors was a little doubtful.
You also had rather low powered engines. In the early 30s a 750hp engine was pretty hot stuff. If you needed a fast plane or one with a good speed/payload combination the elliptical wing had the reputation as being the one to use for best efficiency. The semi-elliptic was considered next best.
With more experience both real world and wind tunnel work) it was realized that a straight taper of the PROPER proportions would come close to the elliptical and with engine power increasing all the time the difference of a few percent could be covered by the next engine improvement.

Planes that used the elliptical were the Heinkel He 70 Blitz (which was built to beat the Lockheed Orion), and the Heinkel He 111, 112 and 116 among others.

 

[zetland76]

Thanks shortround.A good explanation, much appreciated.

Mike

 

[Capt. Vick]

Aerodynamically an elliptical wing has an even lift distribution over it span - a desirable feature for reasons I don't remember. However, production wise it is more labor intensive to produce than a say a regular tapered wing (all things being equal).

 

[drgondog]

Simple explanation - a true elliptical wing planform generated the least possible Induced drag when compared to rectangular or trapezoidal planforms.

That being said, wing twist to achieve wing tip control near stall (washout) negated some of the advantages. The Spit designed wing twist into the wing for just that pupose.

Rectangular wings with a good tip to root chord ratio and twist had a spanwise lift distribution 'close' to that of an Elliptical wing planform.

 

[Wurger]

As memo serves R.J. Mitchell chose the eliptical shaped wing because of a compromise between the aerodynamc features of the planform and the possibility of mounting of armament. You should remember that the first variant of Spitfire was armed with 12 MGs in both wings. Thanks to that the front part of the Spitfire fuselage was clear of unwanted intakes or holes that might have reduced the speed of the aircraft. The RR Merlin engine was fitted to the cowling very tight. As a result there wasn't too much room for armament and an interrupter gear that undoubtedly , would be needed for it there.In that way Mitchell achieved the limitation to the fuselage surface in the cross-section at the area. It gave a possibility of getting higher speed by Spitfire contrary to the blunt-nose Bf109.

 

[zetland76]

This is becoming an interesting debate. Suggesting Mitchell would have been happy with a "straight" wing but had to "broaden" the wing to accommodate the armament. There appears to be no other advantages to the eliptical wing once more powerful engines were introduced. (see shortround6 above).
It would be interesting to know how the Tempest and Sea Fury made out as mentioned by claidemore.

 

[BikerBabe]

From Gordon Mitchell's book about his father R.J.Mitchell: "Schooldays to Spitfire":

In 1930, the Air Ministry, inspired by Dowding, issued Specification F.7/30, in which they asked for a day and night fighter to replace existing outdated fighters then in service with the RAF.

The essential requirements were:

1. Low landing speed and short landing run.
2. Maximum speed of 250 mph.
3. Steep initial climb rate for interception.
4. High maneuverability.
5. Good all-round view.

No specific shape of airframe was called for, but the fighter was to be armed with four Vickers machine guns.

Because Britain was in the middle of a slump, orders were very difficult to obtain, and there was keen competition between aircraft companies to win the F.7/30 competition.
Sir Robert MacLean wanted Supermarine to compete, and Mitchell was thus given the chance to start creating the fighter he had in his mind for some time; the operative word here is "start".

It has been suggested that Mitchell felt the requirement of a speed of 250 mph would be "dead easy" when his S.6B had achieved over 400 mph.
Certainly, certain aspects of the resulting Type 224, as it was known in Supermarine, suggested a degree of general over-confidence by Mitchell and his team.
At the same time, the F.7/30 Specification was constricting and tied Mitchell down severely.

- - - - -

To create the new fighter, Mitchell made several important revolutionary changes to the F.7/30 design.
After several straight-winged designs and after detailed discussions with Beverley Shenstone, his aerodynamicist, the wing shape was changed to the now famous, and almost unique, elliptical configuration.

The wing, which had a single main spar, was also made as thin as possible consistent with strength, but towards the root it had to be thick enough to accommodate the retractable undercarriage and the machine guns.
This concept was completely opposite to the aerodynamic thinking at the time, which was for high-lift, thick wings. It also had a unique induced twist built into it.

The wing, like the fuselage, was of stressed skin construction, while the fin was integral with the tail end of the fuselage, which was detachable.
A good wing, its is said, makes a good aeroplane, and there is no doubt that Mitchell's final decision for the wing design of the Spitfire was a feature of major importance in relation to its success.
That it was so complicated and advanced was to be shown later when it proved initially to be so difficult to mass produce.

It is interesting that for the hand-built prototype, the skin on the wing surfaces aft of the D nose leading-edge configuration was fixed in long. narrow overlapping strips, after the fashion of a clinker-built boat. This method was never again used on any of the production Spitfires.

Mitchell replaced the "trousered" wheels with a retractable undercarriage, and the cockpit was given a sliding canopy which improved streamlining while allowing the pilot a good all-round view in the air.
All these changes reduced the drag which had impaired the performance of the Type 224. [First Spitfire prototype]
Joe Smith, as chief draughtsman, was responsible for the whole of the detail design of the new aeroplane.

Supermarine prototype K5054.

- - - - -

 

[Wurger]

Excellent Maria.

 

[cocky pilot]

The Spitfire is probably my favourite aircraft and I have made several flying models but I wonder, why were it's wings so designed?
From what I can gather the wings were a pain for the production department. In the Battle of Britain they fought on equal terms with the Bf109 which had straight edged tapered wings. Arguably the best fighter of WW II was the Mustang, which again had straight edged wings.

Thanks

Mike

There were many things about the spitfire wing which were problematic, Supermarine was basically an aviation company with a racing shop and so the spitfire was designed like a racer with little thought for mass production, the Hurricane was completely the opposite. The "eliptical" wings were one problem so was the washout, so was the undercarriage (I believe it needed special tyres) The wing was so thin it needed to mount the guns along it laid horizontally which meant with wing twist in a curve it fired like a pepperpot. However one of the biggest problems for mass production was the wing spar which performed very well but was hard to produce "en mass"


If you look at the following link you may get an idea of the problem for the spars, sort of concentric square sections progressively thiner from the inside out with a bend for the dihedral. In 1938-40 very few people had experience of producing such a "THING"
Spitfire wing

edit .... some of the other graphics on the links are so beautiful they go beyond engineering into art like this one

http://spitfire3d.com/wingloft3.png

 

[BikerBabe]

Excellent Maria.

Thanks Wurger. Anything (- almost!) for my fave plane-nutty boys and girls.
...just a stray thought about the name of the plane: What a fitting and appropriate name for that small but efficient fighter!

 

[cocky pilot]

Thanks Wurger. Anything (- almost!) for my fave plane-nutty boys and girls.
...just a stray thought about the name of the plane: What a fitting and appropriate name for that small but efficient fighter!

I believe that the proposed name was supermarine "shrew" and when Spitfire was proposed Mitchell said "that is the sort of stupid name they would give it"

 

[Wurger]

I thought the name of the aircarft was becuse of its initial armament and the fire power.

 

[cocky pilot]

I thought the name of the aircarft was becuse of its initial armament and the fire power.

It had to be something starting with an "S" and government departments dont have much imagination but do have an idea of public appeal.

Supermarine Spitfire
Hawker Hurricane
Westland Whirlwind

Then they lost imagintion

Spitfire ....seafire

Hurricane Typhoon Tempest

Whirlwind ....Welkin Wyvern wessex (they went on to helicopters) Aeroplane orders were stopped around 1940 because the names were rubbish.

 

[BikerBabe]

-cut-
Aeroplane orders were stopped around 1940 because the names were rubbish.

Because of a name???
I find that hard to believe when we're talking millions of punds worth of orders from the various airforces.

More likely, the factories didn't live up to the expectations of their customers and clients, new designs may have been scrapped because of details that didn't work out properly, and plane types became outdated. I guess it was time to move on to better and more recent models.

 

[Maximowitz]

... actually Mitchell allegedly was less than impressed with the name "Spitfire."

 

[drgondog]

There were many things about the spitfire wing which were problematic, Supermarine was basically an aviation company with a racing shop and so the spitfire was designed like a racer with little thought for mass production, the Hurricane was completely the opposite. The "eliptical" wings were one problem so was the washout, so was the undercarriage (I believe it needed special tyres) The wing was so thin it needed to mount the guns along it laid horizontally which meant with wing twist in a curve it fired like a pepperpot.

While the wing t/c ratio was in the 10% range (13% root/6% tip ratio)where the Hispano's were mounted, it wasn't an issue of the Hispano being too large to mount upright.

IIRC they were side mounted to accomodate the 20mm ammo drums. There was plenty of room, per se, with such a huge chord that 9-10% thickness was around the same depth as the P-51..IIRC the P-51-1 had vertically mounted 20mm w/belt feed of 125 rounds each. All the .5 and .3 were mounted vertically in the Spit wing well outboard with no issues.

However one of the biggest problems for mass production was the wing spar which performed very well but was hard to produce "en mass".

If you look at the following link you may get an idea of the problem for the spars, sort of concentric square sections progressively thiner from the inside out with a bend for the dihedral. In 1938-40 very few people had experience of producing such a "THING"

It (main spar) was a very innovative, and as you say hard to mass produce. My recollection was rather than decrease the square tube wall thickness going outboard, they instead 'nested' sequentially smaller square tubes to accommodate the large root to tip decrease in t/c ratio? maybe this is a language thing?

 

[cocky pilot]

It (main spar) was a very innovative, and as you say hard to mass produce. My recollection was rather than decrease the square tube wall thickness going outboard, they instead 'nested' sequentially smaller square tubes to accommodate the large root to tip decrease in t/c ratio? maybe this is a language thing?

Its a language thing, if you look at the link it shows a 3D computer graphic which is better than a thousand words I could come up with.

Regarding the guns I was talking about the 8 brownings not the hispano cannon which also as you say had problems. I have just looked at a picture of spitfire wing design and I think the guns were upright but they couldnt loop a feed over the top so they were spread along its length.
http://spitfiresite.com/2010/04/concise-guide-to-spitfire-wing-types.html