Spitfire as a diver

[Edgar Brooks]

Immagine a situation in which a Spitifre suffers an impact on the wing leading edge by a 30mm canon shell destroying everything up to but not including the spar.

We can say that the Spitfire wing has lost most of its torsional strength and the pilot would need to be very carefull to avoid high G manouvers.

If the same shell hit the leading edge of a two spar design the overall strenght and torsional rigididy would hardly be effected at all as the leading edge skinning is an insignificant component in terms of structure. I could be covered in cardboard reinforced plastic as it acts as a wind shield only.

Or, lets say that the 30mm shell missed, leaving the Spitfire pilot free to turn his aircraft, using his non-reversing ailerons, and shoot his attacker down.

 

[riacrato]

Yes Edgar, it is purely academic. If you choose to ignore the fact that the torsion box of the Spitfire wing was formed by the leading edge and the main spar because to you a torsion box is just semantics instead of being basics in wing design and layout, fine. Ignoring proven technical / scientific concepts seems to be the thing these days.

BTW: I never claimed the Spitfire suffered from aileron reversal excessively.

 

[Tante Ju]

Another contributor said that this was possible, because the Spitfire had a single spar, thereby implying that the wing, aft of that, was free to twist, which would have reversed the action of the aileron. We know that the Spitfire had a second spar (whether you call it auxiliary [which it wasn't] or rear [which it was] is academic, since it was there.) The rear spar was fixed to the fuselage, which means that it was not free to flap up and down as the wing (allegedly) flexed. If the skin (which was rigidly rivetted or screwed to the underlying ribs [not stringers] ) and spars (both of them) wrinkled by as much as 1/16" (1.5mm) the wing had to be checked, and the attachment bolts checked for bending, which must make the idea (that the wing could flex enough to reverse the aileron direction) questionable, if not completely ludicrous.

I don't think Spitfire had capacity for actual aileron reversal. However report shown show the aircraft had a very low aileron reversal speed compared to other two spar and even single spar aircraft, in order of 5-600 mph, depending on report. This suggest clear that the wing was more prone to flexing under aileron load, making the question of if it was single spar or two spar design a bit academic. Because of known twisting tendency, it was either a single spar design with load bearing more towards leading edge and so not well situated position to carry twist load (force generated far, at trail edge) - which is I believe is true - or it was an extreme poor executed two spar design which had a rear spar designed into it, but was just not working at all (since it could do little to carry twist loads). Every above suggest the 'rear spar' had no real load bearing capacity, it was what is called an auxilary spar, good to hang things on it, but cannot carry real load.

I believe Mk 21 was considerable imporved for reversal speeds, suggest new wing was better designed.

 

[stona]

Here's a picture.

That bit labelled 61. We can argue semantics and call it what we like. I'll call it what Supermarine called it...Rear Spar.

Cheers
Steve

 

[Shortround6]

There are aircraft with two spar wings that do not form a torsion box and there are aircraft with two spar wings that do use a torsion box construction and loading.

It is in the designers intention and construction. The Buffalo used a torsion box. it also used heavier than normal metal skinning between the spars to help form the torsion box. The Potez 230 used a torsion box which interested the Germans in 1940 enough to have them ship the plane back to Germany for further study.

The Hurricane had a two spar wing, I doubt it was a torsion box when fabric covered. Did it become a torsion box in the metal covered version ( there were other changes besides just replacing fabric with metal) ?

If you build a two spar wing and make it a torsion box things like landing gear bays and gun bays have to outside the "box" or have considerable reinforcement around them to carry the loads.

Just like the Spitfire had to be careful about what could be done with the leading edge.

Semantics does count but we also have to KNOW the designers intent and not GUESS from first impressions.

 

[Edgar Brooks]

If you choose to ignore the fact that the torsion box of the Spitfire wing was formed by the leading edge and the main spar because to you a torsion box is just semantics instead of being basics in wing design and layout, fine. .

And if you choose to twist my words, when I used the word "semantics" to describe the pointless debate about whether it was called a rear, or auxiliary, spar, that's fine, too. I do not call (and never have called) the leading edge a "torsion box," since it has been universally known, since WWII, as the "D" box; it would be much appreciated if you do not accuse me of saying something, which I manifestly have not.

Ignoring proven technical / scientific concepts seems to be the thing these days.

If I had a clue what you're on about, I might be able to respond.

BTW: I never claimed the Spitfire suffered from aileron reversal excessively

BTW: I never said that you did.
And this is the "torsion box," which Supermarine simply called "leading edge," and, if you look carefully, there's no true leading edge, at the nose, simply a "leading edge strap," which went from rib to rib, and to which the skins were rivetted.
lt might be some sort of "scientific concept" that the non-existent leading edge formed a "torsion box," but, according to my old eyes, there's no way that it could.

Oh, and this is the auxiliary spar, or, as you'll see how Supermarine viewed it, the rear spar:-

 

[cimmex]

This is really a funny discussion. So a one spar wing would have no rear spar, same as very early wings with no movable ailerons did and where the whole wing was twisted instead.
Regards
Cimmex

 

[stona]

So a one spar wing would have no rear spar
Regards
Cimmex

Well yes,according to the illustration drawn by that well known aircraft manufacturer "Flight Magazine" cited previously in this thread.
Incidentally their drawing of a two spar design much more closely resembles the construction of a Spitfire wing.
Cheers
Steve

 

[riacrato]

And if you choose to twist my words, when I used the word "semantics" to describe the pointless debate about whether it was called a rear, or auxiliary, spar, that's fine, too. I do not call (and never have called) the leading edge a "torsion box," since it has been universally known, since WWII, as the "D" box; it would be much appreciated if you do not accuse me of saying something, which I manifestly have not.

And what do you think the purpose of the 'D' box is?

If I had a clue what you're on about, I might be able to respond.

You obviously don't.

BTW: I never said that you did.

Then why do you even mention it in a reply to me.

lt might be some sort of "scientific concept" that the non-existent leading edge formed a "torsion box," but, according to my old eyes, there's no way that it could.

The leading edge taking the majority of torsional loads seems impossible to you? Then I surely can't help you.

 

[riacrato]

Well yes,according to the illustration drawn by that well known aircraft manufacturer "Flight Magazine" cited previously in this thread.
Incidentally their drawing of a two spar design much more closely resembles the construction of a Spitfire wing.
Cheers
Steve

From first appearance, yes. But the idea behind was to show where torsional loads are carried. And in this context the drawing for the one spar wing is more fitting.

 

[Juha]

R.J. Mitchell (the designer) called it a rear spar, not an auxiliary; not once, on any of his drawings, will you find the words "auxiliary spar," but, always "rear spar."
According to all of you, we have ribs bolted to a main spar, then bolted to a non-spar (which is rigidly bolted, by three, not a single, bolts to a fuselage former,) all covered by sheets of metal rivetted in place, and it imparts no extra strength to the overall structure. Truly we have myopia taken to a new level...

Now through the time manufactures had called parts of their products in non-standard names. So what is important is the princible behind the structure. The Flight article explain the different ways to construct wings in late 30s and a certain principle called single spar wing was utilised by Mitchell, Messerschmitt and Günther brothers in their mid 30s fighter designs. BTW the leading edge skins of Spitfire were .080". Behind the front/main spar .036". Wonder why? Would that had something to do with strenght demanded.

Juha

 

[Shortround6]

We seem to be getting into hair splitting here.

You can design a 2 spar wing in which each spar takes 50% of the load, or design wings where the load is 60/40 or 70/30 or even lower, i.e. the rear spar is just a convent place to hang the hinges for the ailerons and flaps.

How low a percentage does the rear spar have to carry before the classification changes from a two spar wing to a single spar wing?

Do any of us KNOW what percentage was carried by the rear spar of the Spitfire ( if any)?

Without access to the original calculations or intentions of the designer we are left guessing from appearances and making assumptions.

My guess/assumption is that since the spar was continuous from end to end ( unlike many false or hinge spars) and was attached to the fuselage it contributed something to the bending strength and torsional strength of the wing. I have no answer to " how much is something" or what basic category of wing construction ( and four classes means a lot of wing designs are being squashed into one category or another).

 

[Juha]

Here's a picture.

That bit labelled 61. We can argue semantics and call it what we like. I'll call it what Supermarine called it...Rear Spar.

Cheers
Steve

And what about No 71, would that by some strange reason be named as the MAIN spar?

Juha

 

[Juha]

Hello Shortround
now for ex in Morgan's and Shacklady's Spitfire bible they say that the wing was built up around the torsion box leading edge formed by the built-up spar. And all books which talked about Spitfire's wing I can recall reading since late 60s describred it as single spar wing. Clearly the rear spar carried some load but the main strenght item was the leading edge D-box.

Juha

 

[Juha]

...The Hurricane had a two spar wing, I doubt it was a torsion box when fabric covered. Did it become a torsion box in the metal covered version ( there were other changes besides just replacing fabric with metal) ?...

In the fabric covered wing there were WW like structure made by beams between the spars. The metal skinned wings were like normal 2-spar wings with ribs and stringers.

Juha

 

[Elmas]

Not bad if someone will have a look to this, in particular Part. 5:

http://www.ilb.rwth-aachen.de/KLAUSUREN/formulary.pdf

 

[stona]

And what about No 71, would that by some strange reason be named as the MAIN spar?
Juha

Yes,what's your point?
Cheers
Steve

 

[riacrato]

BTW the leading edge skins of Spitfire were .080". Behind the front/main spar .036". Wonder why? Would that had something to do with strenght demanded.

Juha

Thank you, I was just searching for those numbers. And on top of that iirc the leading edge up to the main spar was forged from single pieces.

 

[Juha]

Yes,what's your point?
Cheers
Steve

Why main spar why not front spar?

Juha

 

[Edgar Brooks]

And what do you think the purpose of the 'D' box is?.

To act as the "leading edge" of the aerofoil section, to separate the airflow, and thereby impart lift to the whole (non-twisting) wing, and, with it the rest of the aircraft.

You obviously don't.

Very helpful.

Then why do you even mention it in a reply to me.

Well, strangely enough, I consider this site to be open to all, and read by many; I do not consider it to be your sole province, so my answer was for all readers to see.

The leading edge taking the majority of torsional loads seems impossible to you? Then I surely can't help you

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.