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Thinking aloud about Spits...

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Colin Leighfield14/09/2019 22:02:59
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To say that any version of the Spitfire isn’t really a Spitfire is a bit odd, everyone of them was a Spitfire and the strain ran right through every version from first to last with absolute continuity. To me it is the most aesthetically attractive aeroplane ever built, built in so many different and progressively improved versions yet still thought of as “the Spitfire”! The photo is of the Seafire FR47, truly the last Spitfire and it looks absolutely stunning. All versions from start to finish have this rare quality that is so often captured in photographs.

Adding wash-out makes no difference whatsoever to the wing area or lifting capability. If a designer chooses an angle of incidence of 1.25 degrees it makes no difference if he does it with a wing having no wash-out and constant incidence from root to tip, or with a root incidence of +2 degrees and tip of -0.5. The average is still 1.25 degrees. The lifting ability will be identical. In theory it can increase drag slightly, but in practice the progressive wash-out from root to tip will have some co-incidence with the natural span-wise air flow that occurs across a wing and help to control it, with a corresponding effect on the drag-inducing tip vortex. There is no question at all that the Spitfire wing was proven to have remarkably low drag at high speed and a limiting Mach no. beyond that recorded for any piston engined aeroplane. The combination of shape, thin wing section and wash-out was better in this respect than any of the later “laminar-flow” wings that followed and were supposed to be superior.

Compared with the 109 and later 190, the Spitfire with 240 square feet of wing area against these both with only about 70% of that area achieved similar level speeds with less horse power. The 109E had 100 more hp than the Spitfire 1, the 190A had 200 more hp than the Spitfire IX. That is a very good measure of superior aerodynamics. To combine this with benign low speed handling and no tip-stall was remarkable, the flaps and undercarriage down stalling speed of some versions was only 58 mph. Additionally the high speed stall in a tight turn was at much higher speeds, a recent article in Aeroplane describes that in a sustained high speed turn the 109 would eventually flick out into the opposite direction while the Spitfire sustained the rate of turn without difficulty. Where the 109 and 190 had the advantage was more rapid initial acceleration in a dive because of their heavier wing loading, although if sustained for long enough the Spitfire would eventually wear down that advantage.

It wasn’t perfect by any means and fortunes varied as its opponents were also improved, but it was capable of continuous improvement beyond probably any other fighter ever built. We shouldn’t forget that from 1941 it was intended to be replaced by Hawker Typhoons and Tornados and Supermarine were expected then to build Beaufighters. A good job for us that when Hawker failed to come up with the goods that we had the Spitfire and it was so capable, otherwise we would have been in very serious trouble. 78e2031b-b5e9-4434-9ffe-b66d219d7f0c.jpeg

leccyflyer14/09/2019 22:10:46
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Posted by mrwood on 14/09/2019 21:09:08:

Leccyflyer, I'm pleased to recognize that you and I share the same bias in favoring the aesthetic virtues of the MK1a. As you say, a matter of taste for which there is no accounting.

Yes indeedy.

Here's a few of mine.

2891 spit on close pass e.jpg 5944 brians spit & moon e.jpg1737 ripmax spit side on e.jpgThey all fly beautifully, but it's the Mk1a which captures the true Spitfire essence IMO

leccyflyer14/09/2019 22:16:25
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Posted by Colin Leighfield on 14/09/2019 22:02:59:

. To me it is the most aesthetically attractive aeroplane ever built,

Me too - provided that it's a Mk1a - maybe a MkV or IX at a push, buit no clipped wings or bubble canopies, thanks all the same.

Colin Leighfield14/09/2019 22:34:46
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Well, the Mk1a doesn’t really look any different from a MkII or even a MkVa. It doesn’t really matter though does it? It would be a sad old world if we all saw things the same way.

Tom Sharp 214/09/2019 22:42:48
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Simples really, each mark of Spitfire was a child of it's times so it is impossible to make comparisons.

leccyflyer14/09/2019 23:45:10
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Posted by Colin Leighfield on 14/09/2019 22:34:46:

Well, the Mk1a doesn’t really look any different from a MkII or even a MkVa. It doesn’t really matter though does it? It would be a sad old world if we all saw things the same way.

They all look very different to a clipped wing MkXIV or bubble canopy, pointy tailed Mk 24 though, which is what I specified.

As for whether it really matters, the thread title is Thinking Aloud About Spits (sic).

That's what this is,

PatMc15/09/2019 00:47:09
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Posted by Peter Christy on 14/09/2019 08:58:01:

PatMc: I don't think anyone is suggesting raising the ailerons as a substitute for built in wash-out. However, presented with a finished wing that exhibits tip-stalling, the options are either 1) build another wing or 2) find an alternative solution.

One alternative is raising both ailerons slightly (doesn't work with strip ailerons, though!). This is simple, and often surprisingly effective.

Aerodynamics - like my own speciality, electronics - can be something of a black art, especially at model sizes.

Sometimes effective solutions are weirdly counter-intuitive. And at the end of the day, even if it doesn't work on a specific model, you are no worse off for trying it!

wink

--

Pete

Peter, it was once explained to me (by a retired aerodynamicist) that the main purpose of washout (in full size aircraft) was to maintain aileron authority at low airspeeds, tip stalling being a secondary consideration.
Also that raising the ailerons as a fix for lack of washout would help to maintain some aileron effectiveness near the stall. The downgoing aileron would still help raise the wing, the upgoing one would do nothing behind the separation point but because of the overall excess drag being produced by both wings there would be little if any adverse yaw. Overall result would be sluggish & limited but positive aileron control albeit still prone to provoking a spin.

A simple. if agricultural,retro substitute for washout is to progressively blunt the LE for the final 1/3 - 1/4 span to the tips. By blunt I mean still round. Because of the bluntness when the wings AoA is increased the point on the LE that the airflow splits moves down effectively retarding the increase at the tips compared to the root.
I've helped with this mod on models of newcomers to glider comps on a couple of occasions. Used as on field cures to thermal gliders that couldn't be adequately controlled during fast towline launches. Both models were R.E. only, had polyhedral with no washout & had the outer panels LE blunted. A strip of cover film was first removed from the affected LE's. then when blunted by sanding covered as a temp measure with adhesive tape.
I've also seen this method used on aerobatic slope soarers. I see no reason it can't be effective on power models, Rarely an acceptable fix for a scale model but fine for many sports models.

Peter Jenkins15/09/2019 01:02:05
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Leccyflier, I rather think that if you asked any Spitfire pilot during WW2 if he preferred the Mk1 to a later mark that he was then flying you might have got a rather dusty answer. These were fighters and if you were trusting your life to it you would want the fastest most heavily armed version to ensure at the very least parity and at best superiority over the enemy aircraft. Whilst you might think the aesthetics of the Mk1 are the best, I suspect that most would go for the Mk IX as being the point beyond which the Spitfire started to lose some of it's earlier flying characteristics. When the Spit entered service it grossed 3 tons while by the end of the war it grossed 8 tons. Of course, the fuselage was lengthened and wings either clipped or extended to suit the role for which that Mark of Spitfire was designed.

You might think that the Mk1 was the only true Spitfire but as Colin Leighfield points out, if the Spitfire hadn't been developed to match the opposition, this conversation would be in German!

You could say the same of almost any aircraft that has a long life span and takes on many roles. Just look at the Boeing 707 that is still flying as an AWACS. It's nothing like the original 707 but does a completely different job. Instantly recognisable though as were all Spitfires!

By all means say that you prefer the Mk1 but don't say that later marks of the Spitfire are not really in the spirit of the original. We are talking about the development of a fighter in a life or death struggle not about aesthetics - pilots would have been disgusted if your views had held sway at the expense of their lives.

leccyflyer15/09/2019 07:42:04
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We were actually talking about the aesthetics of the various Marks of Spitfires, as it happens - and as has been explained several times now.

Colin Leighfield15/09/2019 08:19:22
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PatMc makes an interesting point. When Supermarine produced the type 371 Spiteful using an aerodynamic design developed by the National Physical Laboratory, the assumption was that the theoretical lower drag of the “laminar flow” wing section would enable it to be slightly thicker and also that wash-out wouldn’t be necessary in the interests of minimising drag by every means. When they flew the protype Spiteful NN660, which was actually a Spitfire XIV with the new wing, it was about 30 mph faster than the Spitfire in level flight with good high speed handling and roll rate, but at landing speeds demonstrated wing dropping and aileron snatching. Sadly NN660 was destroyed in a few weeks killing Frank Furlong, initially thought to have been caused by this tendency in a tight turn although later believed to be due to aileron binding through the rod controlled system. (The Spitfire wing used cables). The full prototype NN664 and the “production” planes used for testing from RB515 onwards were developed to resolve this problem and one of the changes was to reduce the sharpness of the wing section leading edge. However in so doing the level speed advantage was reduced to about 20 mph.

When the Seafang variant of the Spiteful was being evaluated by the Navy, one of the reasons for rejection was that in return for this comparatively small difference of about 4.5%, the landing speed was 30 mph faster. Consequently they chose the Seafire 47 instead and when the Sea Fury was sorted out, that became the main fleet fighter. The handling problems must have been reasonably resolved because otherwise the Attacker (originally Jet Spiteful) with the 371 wing would never have got into service, although that took so many years it was past its sell-by date by then. As mentioned in an earlier thread, Jeffrey Quill told Joe Smith that the Attacker would have been a “b****y sight better aeroplane with a Spitfire wing”. He was no doubt right and also it could have been in service much earlier.

All of this begs the question, why then was the Spiteful/Seafang faster than the equivalent Spitfire in level flight when it was proven to actually have a lower limiting Mach number of around 0.82, similar to the P51? Almost certainly the answer lies in the much lower drag of the cooling system, which was extensively tested with the wing in the NPL high speed wind tunnel. In other words, the same reason why the P51 was about 30 mph faster than the equivalent Spitfire in level flight, nothing to do with its “laminar flow” wing which was later found not to achieve laminar flow, but because of the low drag of the cooling system.

Another interesting event was the idea to improve the laminar flow characteristics of the Spitfire wing by raising the leading edge profile, this thickening the leading edge and moving the point of maximum thickness further back. Such a wing was built and tested and would have been used in a version called the Spitfire 23. However it was found in testing to make no worthwhile difference to performance and introduced some handling problems, so it was dropped and they focused on the 371 wing instead.

As Leccyflyer says, the thread is all about “thinking aloud about Spits”, So I hope this is of some interest in that vein.

Edited By Colin Leighfield on 15/09/2019 08:35:13

Edited By Colin Leighfield on 15/09/2019 08:35:39

Edited By Colin Leighfield on 15/09/2019 08:37:25

Edited By Colin Leighfield on 15/09/2019 08:38:48

Erfolg15/09/2019 15:41:12
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The link that Patmac found, sheds a lot of light on the development of the Spitfire, particularly the wing, and also draws some useful comparisons with other aircraft.

The virtues of elliptical wings is not at the low end of the speed range, particularly at the stall. Although many of the gliders in the 30s incorporated the plan form. I understand, again with washout, although not certain, having thrown out the magazines that dealt with them.

From the Patmac paper the NPL wind tunnel was producing erronasiously results, particularly with regard, T/C ratios and effects of camber. Apparently Mitchell and his team did not believe the data, and choose to ignore it, whereas Hawkers did believe the data and built a thicker wing.

The whole paper is full of nuggets of information with respect both the Spitfire and some other aircraft. Much is down to detail. The attention to detail in the design and manufacture resulted in an expensive aircraft to produce. Whereas the 109 right from the start, featured compromises designed to contain costs, apparently fixes to improve performance were kept in the back pocket, to be able to pull a rabbit out of a hat, when needed.

The issue of turning circle is dealt with with respect the 109, which comes down to wing loading. As observed by another pilot, if turning circle that is all that matters, then the CR 32 would take a Spitfire every time.

We need to bare in mind that the flight evaluations were undertaken primarily to obtain data. The data was used both to evolve tactics with the current opposing aircraft and feed information into the aircraft industry. From a pilots perspective, knowing for instance, that initially that trying to follow another aircraft into a dive may not be productive, if it is known your aircraft will be slower, even that in theory eventually you would catch up with it. The reason being that the opposing aircraft in most cases has done something else, before the catch. The other issue that the reports are a snap shot on a time line, which probably used more to inform pilots of what not to do, with the hope that the adversary does not know his own aircrafts weak points.

The plan form is quite interesting that the use of elliptical plan forms is pretty much avoided these days. Even Heinkel a prolific elliptical wing builder compromised to aid production with the 100, becoming a pseudo elliptical form, being a double type taper, which produced possibly a generally better aircraft than the 109. More often these days straight taper is used, again for a variety of reasons. There is the odd glider with 1/4 ellipse type wing tip, although most go for pseudo form (probably ease of production).

In some ways I am surprised that many WW2 aircraft such as the Mustang and FW 190 (variants) had radiator and carb inlets set outside of the boundary layer, yet many early side inlet jets did not incorporate splitter plates, some even took air in from the boundary layer (with poor results).

At the end of the day the Spit was an exceptional design, where the truth may not be glamorous as the PR but every bit as interesting.

Martin McIntosh15/09/2019 17:34:31
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My original TN 72" was built as Mk1A AR213 with 1/4" washout. After a serious crash due to gear failure the undamaged wing core was simply re skinned as it was without the washout packing. Cannot really see any difference when landing.

I do not recall adding washout on my new lighter version of the above. I still seem to get one arrival for every greaser and just put it down to dumb thumbs at the time. Judging the landing in the case of a model is down to the wind conditions on the day. Do you use full flap/half/ none at all? Throttle use to touch down is quite different in each case and makes or breaks it (no pun intended).

Colin Leighfield15/09/2019 17:36:21
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The reason for the intake on the P51 being outside the boundary layer was because it was found that early problems with buffeting etc. were resolved by moving the ventral intake outside of It, very noticeable on the P51D. It was the solution to the problem. It would probably have been the answer to the similar difficulties with the Hawker Tornado prototype, but Hawker solved it, also for the Typhoon, by moving the radiator etc under the nose, where the problem doesn’t arise behind the propeller. Almost certainly Kurt Tank had identified the issue as well.

Erfolg15/09/2019 17:51:33
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Colin

What surprises me that in WW2 many designers realised that boundary layer was not the best place for an inlet, come the Jet age, for engine intakes it seemed to have been forgotten. Or perhaps they thought different criteria applied to jet engine intakes.

As Patmacs link indicates, by the time you get passed the nose on a propellor aircraft, the air is seriously turbulent. May be they thought without a propellor, everything would be laminar with a nice velocity gradient?

Colin Leighfield15/09/2019 21:47:30
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You could be right Erfolg!

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