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Hurricanes again - wing centre section


ClaudioN

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Hello BMers,

 

time to raise a new question about the Hurricane. I opted for a new thread rather than hijack the Canadian Hurricanes one, although this still partly relates to it.

I hope collective knowledge here on Britmodeller may help.

On 7/6/2019 at 10:22 PM, Graham Boak said:

There is at least one other (fortunately non-visible) feature to consider.  The early Mk.IIA ser.i used the centre-section from the Mk.I.  The Mk.IIA ser.ii had a strengthened centre-section (and fuselage frames?) designed to permit the carriage of the 12-gun wing but retained the 8-gun wing.  I am not sure whether or not there was later another redesign for the 10-gun fighter-bomber wing with jettisonable tanks, but apparently these were initially referred to as Mk.IIE, then later as Mk.IIBB (or CB) but these designations were never officially adopted.  How this fuselage/centre-section strengthening was carried over to Canadian production I don't know, but presumably it was.

This is the most detailed explanation I have ever found, thanks to Graham.

Out of curiosity, I searched for photos of the Hurricane centre wing structure, comparing a Mark I like this to a Mark II/XII like this. It turns out Graham made no understatement when he said the feature is non-visible. To me, there seems to be no visible structural difference at all.

 

So my question is:

is it comfirmed that the Series 2 wing centre section was strengthened and, if so, how? Perhaps thicker gauge metal?

 

Another possibility would be that modifications only referred to the wiring and accessories needed to operate different types of gun and jettison the drop tanks. Admittedly, wing loads from the Mark IIB onwards could be higher and strengthening would appear more logical. On the other hand, Mark Is were flown by Hawkers as cannon-armed prototypes, although they might not have been subjected to the stress of combat manoeuvres.

 

Cheers

 

Claudio

 

 

 

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To answer the last point first, two (both?) of the cannon armed prototypes were flown in combat.  Whether they had any strengthening appears unlikely, and I suspect that the version with underslung cannon possibly wouldn't have needed any.  The 4-gun wing would be heavier, but perhaps less so than 10 guns plus 2x250lb bombs and carriers.  A slightly weaker wing would be acceptable for such one-offs.

 

The phrase I've seen definitely said "strengthened", which as you say would be logical.  I suspect (as Claudio says)  this was a slightly thicker gauge on the frames and a stronger spar rather than any extra parts, but have not seen any description.  I have seen a fairly wide range of descriptions of the differences between the early and later Mk.IIs, even after excluding the impossible, but the one above seems to make the most sense.  Even so it still leaves open the matter of the IIB fighter and the IIB fighter-bomber.  It would be easy to assume that early Mk.IIBs were built "for but not with" carriers, wiring etc, but if so that could have been said somewhere, and why would there have been any suggestion of a new variant suffix?

 

One minor point: no different types of gun unless you assume that the strengthening was carried out with the forthcoming Mk.IIC in mind.  Much heavier guns, yes.  I don't think bombs were thought of in conjunction with the Mk.IIC at this stage, as it was intended as a bomber interceptor for BoB2(1941).

 

Looking again, I don't think that there's enough information in those photographs to distinguish anything more than gross changes, which probably didn't exist.  Plus there's the comment about using parts from a Russian source (Mk.II) on a Mk.I restoration.  Not good evidence, I fear.

Edited by Graham Boak
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5 hours ago, Graham Boak said:

Even so it still leaves open the matter of the IIB fighter and the IIB fighter-bomber.  It would be easy to assume that early Mk.IIBs were built "for but not with" carriers, wiring etc, but if so that could have been said somewhere, and why would there have been any suggestion of a new variant suffix?

Thank you Graham,

to summarise, here again Mason gives clues but he is not entirely clear, possibly because things did overlap:

  • from what I understand from Mason's book, deliveries of Mark IIA Series 1 began on 4 September 1940
  • "Hurricane IIA Series 2s continued to be produced intermittently from October 1940 until about September 1942, almost all with eight-gun wings"
  • "unless fitted with the 12-gun wings, (the Mark II Series 2) was almost indistiguishable from the Series 1 - Note: no suffix here
  • "Authority to go ahead with production of 12-gun wings was received at Canbury Park Road on 2 November, 1940"

Mason says "the Air Ministry asked Hawker to modify the armament wiring on all Mark IIs to permit the fitting of bomb racks" in early 1941, then adds:

  • "In February 1941 the first Hurricane IIBs (without bombing modifications) were delivered to" Nos. 56, 242, 249 Squadrons
  • "The first Mark IIB bombers reached the squadrons in May, and thereafter working teams from the maintenance units toured the fighter stations to carry out the electrical alterations to enable the earlier Hurricane IIs to carry a pair of 250 lb GP bombs.

This seems to agree with what you are suggesting.

 

The very simple conclusion appears to be that the indication Series 1 and Series 2 refers to the wing centre section and, independently, suffixes A, B, C and D to armament, with Series 1 enabling A only, whereas Series 2 can be fitted with any wing armament. This makes the sentence above "almost all with eight-gun wings" a little suspect for Mark IIA Series 2, but it may just be a minor fault of the writer. I take it to mean that, with the Series 2 wing centre section becoming standard, only the armament suffixes remained relevant.

 

Claudio

 

 

Edited by ClaudioN
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Unfortunately, that's only one version that Mason offers in his various writings on the subject.  I suspect that a lot of what he says is OK, but which bits?  Better to ignore him completely on this branch of the subject, as on Sea Hurricanes.

 

Some of this is because he was writing first, of course, and without access to everything we have now.  But it seems clear that he did have access to much Hawker stuff, including Hurricanes, but for whatever reason failed to integrate it all properly.  It would be wonderful to wave a magic wand over his combined works that wiped out the dross - I'm sure there'd be most left.  But not this particular corner in its current forms.

 

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On 8/5/2019 at 8:11 PM, Graham Boak said:

Unfortunately, that's only one version that Mason offers in his various writings on the subject.

You are right. Here's the one from the Kookaburra technical manual, written by Mason in 1971:

 

"Subsequently an additional fuselage bay was included forward of the cockpit, and the tolerances on the wing attachment point dimensions were relaxed in order to accommodate more easily the attachment of wings with alternative armament. This version was known as the Mark IIA Series 2 (...)"

 

Mason corrected the first part of the sentence in his new edition: "The Hawker Hurricane - The Royal Air Force Museum Edition", published in 1987 and 1990.

He expressly stated that the additional fuselage nose bay was only fitted to the first few "tropically-equipped Mark IIA Series 2" produced by Austin Motors, and added: "This has always been understood to indicate that all (author's emphasis) Series 2 aircraft possessed a greater overall length, but it is now known that only the first dozen or so aircraft included the enlarged header tank (...)"

 

Mason ended the Author's Note to the 1990 edition with this sentences:

"In the course of continuing research down the years I have, however, become aware of the earlier errors of omission and misplaced emphasis. I can only hope that the present work makes amends."

 

Putting all this together, what I may understand is:

  1. all (my emphasis) Mark IIs needed an additional 4 inches to fit the Merlin XX - this was never clearly stated by Mason but has been positively proven (by photos, countless posts, discussions, etc.);
  2. the sentence from the Kookaburra publication I reported above is the only reference I found so far in Mason to the nature of the Series 2 versus Series 1 modification: the tolerances on the wing attachment point dimensions were relaxed in order to accommodate more easily the attachment of wings with alternative armament. This sounds almost as a non-modification for any Mark I turned into a Mark II. Also, the seeming lack of visual differences between Mark I and Mark II centre wing sections is easily understood, as well as the use of a Mark II centre section on a Mark I restoration. On the other hand, there is no mention of a "strengthened" design;
  3. this said, we might perhaps think that "strenthening" referred instead to the outer wing sections and their heavier armament?
  4. as a minor issue, it is still unclear whether on the "dozen or so" Austin-built "tropically-equipped Mark IIA Series 2" the additional fuselage bay was 6 1/2 inches long in addition to the standard Mark II 4-inch extension, or if it was just 6 1/2 inches instead of 4.

As you say, it's hard to decide which bits are OK, but perhaps something is beginning to surface.

 

All the best

 

Claudio

 

Edited by ClaudioN
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1. Yes.

2. I don't think that relaxing tolerances on the wing attachment points would result in anything but poorly fitting wings.

3. It might, but additional loads on the outer wing have to be carried into the inner structure.

4.  I disbelieve this story and will continue to do so until I see evidence for it appearing in individually researched material. It is however a very peculiar item to appear from nowhere.

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24 minutes ago, Graham Boak said:

2. I don't think that relaxing tolerances on the wing attachment points would result in anything but poorly fitting wings.

I understand your point and have no precise idea. The design of the joint to the outer wing sections (this is a photo of a Mark II) looks simple and robust. It doesn't look too critical about tolerances, but I'm no expert.

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24 minutes ago, Graham Boak said:

3. It might, but additional loads on the outer wing have to be carried into the inner structure.

Agreed. The inner structure may already be strong enough, or need reinforcement.

 

24 minutes ago, Graham Boak said:

4.  I disbelieve this story and will continue to do so until I see evidence for it appearing in individually researched material. It is however a very peculiar item to appear from nowhere.

I have doubts as well. Given the experimental nature of the "tropical" modification, some picture should have been taken.

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Don;t be fooled into the notion that because the wing skins are not a butt fit, that you can entertain any slop or imprecision in attaching the outer wings. Each of the end joints for the spar booms is a highly critical joint. If there were any slop then the outer wing would be able to shift in flight, and if the alignments were wrong then in most cases you wouldn't be able to fit the wing at all, or if you forced it you would most introduce unplanned stresses into the structure and/or aerodynamic rigging errors.

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