Spitfire as a diver

[Edgar Brooks]

Why main spar why not front spar?

Because it was more important than the rear spar, perhaps?
Sorry to rain on the parade, but, as you'll see, it was also known as the front spar:-

I realise the quality isn't the best, but the original is, at least, 70 years old.

 

[Elmas]

It's just as well that I'm not asking for your help, just clarification, then. As far as I'm concerned, the mainspar (to which the leading edge components are attached) takes the majority of the torsional loads, with the front half-ribs going along for the ride.

Good Lord........
Have you ever heard of the Bredt formula?

 

[riacrato]

It's just as well that I'm not asking for your help, just clarification, then. As far as I'm concerned, the mainspar (to which the leading edge components are attached) takes the majority of the torsional loads, with the front half-ribs going along for the ride.

The skinning on the leading edge is much thicker than that of the rest of the wing. The "C" portion was forged from a single piece for additional strength. Together with the spar they formed a stiff D-box taking the majority of torsional loads.

Your own quoted article: "The leading edge of the wing is covered with 14 gauge, forming with the main spar, a torsion box."

 

[Elmas]

 

[Edgar Brooks]

Good Lord........
Have you ever heard of the Bredt formula?

No, and R.J.Mitchell probably hadn't, either.

 

[Elmas]

No, and R.J.Mitchell probably hadn't, either.

That you don't know the Bredt formula is quite evident from your posts.
Not so sure about the same ignorance about the Bredt formula by R.J. Mitchell and his team even if, in the early '30s, the stressed skin wing and fuselage construction was in its infancy.

 

[Edgar Brooks]

Put quite simply, you can twist and turn, throw in as many red herrings as you like, even do handstands, but the fact remains that the Spitfire had a mainspar, which was also known as the "front spar," by Supermarine, and a rear spar, as noted on Supermarine's drawings.

 

[Elmas]

It is not my intention to be rude but to establish a study of the Spitfire wing on a scientific basis and not on completely wrong "feelings".
Fortunately the Boeings, Airbuses, etc. etc. on which from time to time I don't know you, but myself for sure and many other people travel every day are designed by some Gentlemen that perfectly know the Bredt formula.....

 

[Juha]

Because it was more important than the rear spar, perhaps?
Sorry to rain on the parade, but, as you'll see, it was also known as the front spar:-
I realise the quality isn't the best, but the original is, at least, 70 years old.

Hello Edgar
Firstly thanks for the photos on original drawings, I probably have seen some before but not all, very interesting indeed.
And you didn't spoil my day. As I wrote I have read several books/articles on Spit and in all they describe the wing as single spar construction with the heavy gauge leading edge and the main spar forming a torsion box. In fact that and the structure of the main spar, built up of square section booms and joined by a channel section web and stiffeners together with the thinness of the wing were IMHO the most interesting elements of the design. And of course that thinness of the wing was the main reason for the very high critical Mach number for Spit and same time the thinness and the single spar structure were reasons why wing twist and the following diminishing of aileron effectiveness was bigger problem to Spit than to many other WWII fighters, most of which were later designs.

So as a diver Spit had very high critical Mach number and because it had light elevators it could also be pulled out from dive fairly easily. On the other hand some Spit Vs were lost because too much Gs were pulled during the pull-outs (the main reason for that was wrong loading of planes in front-line sqns which produced too aft CG) which was at first corrected with bob weights in control circus and later with small modifications in elevators so they could drop the bob weights and Spit also suffered poorer initial acceleration in dive than more "tightly packed" 109 and 190 and had some lateral control issues at high speeds, 109 had more but 190 less.

Juha

 

[tomo pauk]

All in all the discussion is bound to produce a nice overview of both construction and capability of Spitfire's wing. Please keep it clean

 

[stona]

Edgar,Mitchell's quote was given by Jeffrey Quill.

"At that time I was only 23 and had not trained as an engineer,so I had something of an inferiority complex when it came to dealing with the aerodynamics and structures experts at Woolston with slide rules sticking out of their pockets. But Mitchell put me right about this one day,in his usual very direct way.
He said.

'Look,I'll give you a bit of advice Jeffrey. If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it,take it from me it's all balls.
I have never forgotten what he said,and in fact it's absolutely true'

I'll take that from the man who designed one of the best and most important fighter aircraft in history.

Cheers
Steve

 

[Edgar Brooks]

Firstly thanks for the photos on original drawings, I probably have seen some before but not all, very interesting indeed.
And you didn't spoil my day. As I wrote I have read several books/articles on Spit and in all they describe the wing as single spar construction with the heavy gauge leading edge and the main spar forming a torsion box. In fact that and the structure of the main spar, built up of square section booms and joined by a channel section web and stiffeners together with the thinness of the wing were IMHO the most interesting elements of the design. And of course that thinness of the wing was the main reason for the very high critical Mach number for Spit and same time the thinness and the single spar structure were reasons why wing twist and the following diminishing of aileron effectiveness was bigger problem to Spit than to many other WWII fighters, most of which were later designs.

Thanks for calming things down; I tend to get a touch irritated when I see red herrings dragged across what should be a fairly simple discussion. People seem to forget that Mitchell's original design was supposed to meet a criterion of a speed of "not less than 310mph at 15,000ft." I do wonder if that Bredt formula (which only seems to show shapes with a completely wrap-round leading edge) takes account of an item in which two sheets of duralumin come together at the apex, and are rivetted to an underlying strap of metal. I would expect the strength of the (usually aluminium or magnesium) rivets to have some sort of effect, but I'm a researcher, not an engineer.

So as a diver Spit had very high critical Mach number and because it had light elevators it could also be pulled out from dive fairly easily. On the other hand some Spit Vs were lost because too much Gs were pulled during the pull-outs (the main reason for that was wrong loading of planes in front-line sqns which produced too aft CG) which was at first corrected with bob weights in control circus and later with small modifications in elevators so they could drop the bob weights and Spit also suffered poorer initial acceleration in dive than more "tightly packed" 109 and 190 and had some lateral control issues at high speeds, 109 had more but 190 less.

Well, I don't think that the Mach No. was that high, since the IX was limited to 450mph, by the constraints of the engine (I don't know about the XIV, etc., with the Griffon.) Talking to a friend, yesterday, he reminded me of an incident, reported by Pierre Clostermann, when diving a Spitfire VI, in which he said that the controls locked solid, and he was only able to pull out by use of the elevator trim. I don't know, for sure, if he tried the ailerons (though saying that the controls locked solid implies that he did,) but, if he did, they didn't work, neither did the wing flex (which is what this thread is, or was, all about.)
As well as the bobweights (which were decidedly unpopular with many pilots, when they were asked to test them,) other items were tried, to do away with the tail-heaviness, like removal of the IFF, and one of the oxygen cylinders once an efficient regulator had been fitted. The weights got as heavy as 6.5lbs, but the Air Ministry tried to get them back to 3.5lbs; they were installed on the bellcarank, in the elevator system, behind the pilot's seat. Later, heavier, weights were installed in Seafires, and were attached directly to the joystick; in his book "Up In Harm's Way" Mike Crosley says that it wasn't realised that this was probably a death warrant to many pilots. As he says, none got back to tell the tale; to abandon the Spitfire/Seafire it was recommended that the pilot should turn it on its back, and drop out, but this caused the bobweight to reverse its action, and throw the elevators to full "up," dropping the airframe straight into the sea.

 

[Edgar Brooks]

It is not my intention to be rude but to establish a study of the Spitfire wing on a scientific basis and not on completely wrong "feelings".

I do not go by "feelings," but by research. As far as possible I try to correlate facts, to gain a consensus, before coming up with a conclusion.

 

[Edgar Brooks]

The skinning on the leading edge is much thicker than that of the rest of the wing. ]

True

The "C" portion was forged from a single piece for additional strength.

No, it wasn't; it was formed by two pieces of 14swg duralumin, laid over, and rivetted to, short ribs, then brought together at the apex, and rivetted to an underlying (not very wide) piece of aluminium. The underside piece also had many removable inspection plates. As well as the gun tubes, the l/e box was also used for items like heating tubes, carrying warm air out to the nos 3 4 guns.

 

[Elmas]

"Sapiens nihil affirmat quod non probet", ( A wise man do not affirm things without demonstrating them) Ancient Romans used to say.
And if you are not able do demonstate your ideas in a scientific, and thus a mathematical way, they can be only considered feelings.
Some time ago, by request of a Friend of mine who owns an aeromodeling magazine, I did write some articles about the design of the wings were the Bredt formula ( and others) are explained for persons with not much, if any, mathematical background.
But unfortunately the articles are in Italian.....
"Et de hoc satis" (and for me thats enough") the Romans used to say: if you are of the idea that in that masterpiece of structural engineering that is the Spitfire wing "the mainspar takes the majority of the torsional loads", well, you can have it.
Ciao

btw, I'm perfectly aware of those Mitchell's phrases

 

[riacrato]

True

No, it wasn't; it was formed by two pieces of 14swg duralumin, laid over, and rivetted to, short ribs, then brought together at the apex, and rivetted to an underlying (not very wide) piece of aluminium. The underside piece also had many removable inspection plates. As well as the gun tubes, the l/e box was also used for items like heating tubes, carrying warm air out to the nos 3 4 guns.

Like I mentioned above, it was just what i read, i wasn't sure about it. It would've give the D-box = torsion box argument more weight, but I think even if it's not true, the evidence is enough.

I found the source in the meantime, but it's just an internet site, so not reliable. I'm posting it just for the interested, not as proof:http://spitfiresite.com/2011/07/guided-tour-of-the-spitfire-pr-mk-xix-the-bowser-wing.html/dsc06603

 

[Juha]

Spitfires supposedly could experience control reversal though I would like confirmation of that. Either way the relatively thin wing and essentially single spar design meant the early wings could twist opposit to aileron direction thus reducing roll rate...

Hello Siegfried
accidentally I came across a test report from April 1941 according to which Spit aileron reverse speed was 477mph IAS that means 477mph TAS at SL, 555mph at 10000ft TAS and 654mph TAS at 20000ft. That was calculated from test data, earlier based on conventional theory was appr. 550mph IAS, so not much a danger to Mk I-V and from Mk Vc onwards the stronger C-wing became the standard wing before late in the war it was replaced with E-wing. But according to the same report at 400mph IAS aileron lose 65% of its effectiveness due to wing twist.

And The RAE 1231 (DSIR 23/12865) gives reversal speed 580 mph EAS for the Spitfire V with standard wings and that value is calculated from flight test results.

Juha

 

[Juha]

...Well, I don't think that the Mach No. was that high, since the IX was limited to 450mph, by the constraints of the engine (I don't know about the XIV, etc., with the Griffon.) Talking to a friend, yesterday, he reminded me of an incident, reported by Pierre Clostermann, when diving a Spitfire VI, in which he said that the controls locked solid, and he was only able to pull out by use of the elevator trim. I don't know, for sure, if he tried the ailerons (though saying that the controls locked solid implies that he did,) but, if he did, they didn't work, neither did the wing flex (which is what this thread is, or was, all about.)
As well as the bobweights (which were decidedly unpopular with many pilots, when they were asked to test them,) other items were tried, to do away with the tail-heaviness, like removal of the IFF, and one of the oxygen cylinders once an efficient regulator had been fitted. The weights got as heavy as 6.5lbs, but the Air Ministry tried to get them back to 3.5lbs; they were installed on the bellcarank, in the elevator system, behind the pilot's seat. Later, heavier, weights were installed in Seafires, and were attached directly to the joystick; in his book "Up In Harm's Way" Mike Crosley says that it wasn't realised that this was probably a death warrant to many pilots. As he says, none got back to tell the tale; to abandon the Spitfire/Seafire it was recommended that the pilot should turn it on its back, and drop out, but this caused the bobweight to reverse its action, and throw the elevators to full "up," dropping the airframe straight into the sea.

The limit was according to Mk IX, XI and XVI Pilot's Notes Mach .85 and the 450mph was IAS speed and in force up to 20'000 ft, between 20'000 and 25´000 it was 430 mph IAS etc. Already at 10'000 ft 450 mph IAS means 524 mph TAS. I'd be a little careful with Closterman's statements, his books are great reads but IMHO he puts a bit too much "colour" in some of his stories. But it is true that the controls of Mk VIs and VIIs were heavier than those of other marks because of their pressure cabins, control runs when running out from cabins had to went through glands, it that is a right technical term, which added friction and so made controls heavier.

Juha

 

[Shortround6]

Like I mentioned above, it was just what i read, i wasn't sure about it. It would've give the D-box = torsion box argument more weight, but I think even if it's not true, the evidence is enough.

I found the source in the meantime, but it's just an internet site, so not reliable. I'm posting it just for the interested, not as proof:http://spitfiresite.com/2011/07/guided-tour-of-the-spitfire-pr-mk-xix-the-bowser-wing.html/dsc06603

There may be some translation difficulties. Forged and formed are not the same thing and even extrusions are not forged. Even stamped is not the same as forged. Sheet aluminium is rolled, not forged and even if stamped or other wise bent, folded, or twisted into a particular shape it is still not forged.
Forged in one piece would also show no seams, welded, riveted or otherwise.

 

[stona]

Like I mentioned above, it was just what i read, i wasn't sure about it. It would've give the D-box = torsion box argument more weight, but I think even if it's not true, the evidence is enough.

I found the source in the meantime, but it's just an internet site, so not reliable. I'm posting it just for the interested, not as proof:http://spitfiresite.com/2011/07/guided-tour-of-the-spitfire-pr-mk-xix-the-bowser-wing.html/dsc06603

Don't believe everything on the internet. You could refer to drawings already posted or even take a look at this original document,one of the many that Edgar has made available over the years.

Paragraph 5 confirms the joint running along the wing's leading edge.

I have a photograph which I can't seem to find of a Spitfire in American service in North Africa. It is in shabby condition and the paint of the leading edge has worn,clearly revealing the filler in this butt joint.

Cheers
Steve