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Spit VII/VIII/IX/XVI vs XII vs XIV exhaust


warhawk

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On 22/06/2017 at 11:17 PM, Bonhoff said:

It quotes the bore centres of a Griffon to be 6.9 inches.

 

Well, the best I could manage was a dimensioned drawing of the Merlin II.  No dimension for the cylinder spacing, but scaling from given dimensions results in 5 7/8" (Edit: or, on a second attempt, 6") for the Merlin.

Edited by gingerbob
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3 hours ago, gingerbob said:

 

Well, the best I could manage was a dimensioned drawing of the Merlin II.  No dimension for the cylinder spacing, but scaling from given dimensions results in 5 7/8" (Edit: or, on a second attempt, 6") for the Merlin.

 

Which means on a 1/72 scale Spit, a difference in pitch of 0.3mm between cylinders on a Merlin and a Griffon.

 

Or put another way. A Merlin exhaust bank would be 1.5mm shorter than a Griffon

 

Would that be noticeable?

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I'm not convinced that's necessarily the right set of numbers, but if so then that's round about 1/6th of the total length of the manifold.  That kind of difference should be visible (it's equivalent to one missing cylinder.).  It is a fair match for the difference between a Hurricane Mk.I nose and that of a Mk.II, and that is visible.  it's easy to be led astray by mistaking a small number for a small proportion.

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I'm not sure I could find them if I had them but are there any decent Spitfire drawings showing both Merlin (Mk IX?) & Griffon (MK XIV/XIX) exhaust banks & measure them. I see references to Mountford (?) drawings on here but not sure if they cover the later marks, are there any that do?

Steve.

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On 23/06/2017 at 3:58 PM, Graham Boak said:

I would normally take your voice as authority, but counter your "certainly" with the following quote.  Spitfire the History p.405 states  "The new Mk,.XII was the first of the Spitfires to have a flush-riveted fuselage and EN221 was closely examined in order to assess external finish."  This would not have happened had it a Mk.V fuselage.  There's no dispute about the wing - all Mk.XII aircraft had Mk.Vc-standard wings.  This was one point that led me to question the established account: if the MB batch were based on Mk.VIIIs then why didn't they have a Mk.VIII wing?  It was the Polish Spitfire researcher Wojtek Matusiak who told about the Mk.XII having a revised fuselage: whether this implies more than the flush-rivetting I don't know.

 

'Spitfire the History' would not normally be my first port of call on technical matters.

 

Certainly, this is the official notification of the major changes to the Mk Vc up to the Mk XII

 

12-EN224%20tech%20details%20001a_zpsclxs

 

Note on my own MK XII EN224 that the four bolts on the lower spar are all the same diameter as Mk V and the parallel Mk IX. 

 

On Mk VIII's with the stronger new wing the two centre bolts on the lower spar are of significantly increased diameter. Also the fuselage spars are set wide by two times 16SWG to accommodate the reinforced Spar booms on the wing.

 

12-EN224-07-001a_zpsz3sf7ilf.jpg

 

PeterA

 

 

Edited by Mark12
typo
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Whilst agreeing that STH is not without its flaws, when it is talking about an individual aircraft going to A&AEE for specific purposes, giving specific dates and describing details from the results, then it can't be dismissed out of hand.   As for the wing, I appreciate seeing the interesting detail about the differences in wing design, but don't suggest that any of the Mk.XII had anything other than the Mk.Vc wing.  The difference between us is whether the main fuselage of the first batch retained the Mk.V structure or that of the Mk.VIII.  (Assuming for the moment that those are the only two options, rather than something intermediate.)

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32 minutes ago, Graham Boak said:

 The difference between us is whether the main fuselage of the first batch retained the Mk.V structure or that of the Mk.VIII.  (Assuming for the moment that those are the only two options, rather than something intermediate.)

 

Read the words on the diagram. The Mk XII has a strengthened Mk Vc fuselage.

 

The fuselages are not interchangeable, the very visible differences being the engine mount forgings and the firewall bracketry for the auxiliary gear box for the Griffon.

 

PeterA

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I fear we are arguing the same point but using different words to describe it.  I don't think that you are saying that there was any structural difference between the two batches of the Mk.XII.  The table tells me that the Mk.XII did not have a Mk.V fuselage (aside from the modifications needed for the Griffon).   The Mk.Vc was the then-standard production fuselage, so saying the Mk.XII has a strengthened Mk.Vc fuselage is simply saying that it has a strengthened Spitfire fuselage.  The Mk.VIII also had a strengthened Spitfire fuselage:  Other those differences driven by the engine, did the Mk.VIII simply use the flush-rivetted Mk.XII design?  Or were there other structural differences?  Six months does give a fair bit of space for further development.

 

I think that this is confirming that the Mk.XII had its own fuselage and the stories that half were built from Mk.Vs and the other half from Mk.VIIIs is wrong.  (Which is where this started.)  Not least because the Mk.VIII production came later.  The only difference between the two batches of Mk.XIIs is the tail section, and that was "Mk.V production standard" vs "Mk.VIII production standard" (but earlier.)    If there were any additional differences between the Mk.XII fuselage and the Mk.VIII fuselage, and these differences appeared in the second batch of Mk.XIIs, then the original story has more credence.

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You are forgetting the Mk.VII, which came into (small) production about the same time that the XII did.

 

Mk.XIIs were built as Mk.XIIs, though obviously using quite a few common parts.  People are thrown off by the serial blocks (which I might have to have another look at) and the introduction of the retractable tailwheel.  Note that a few very early PR.XIs also had fixed tailwheels, and it seems clear to me (which is to say that I'm applying reason, not documentary evidence) that this was just a change of production standard at Supermarine, as the basic tooling shifted to the VII/VIII airframe.  That can be interpreted as saying the same thing as "fixed tailwheel until the new stern-end was available in sufficient numbers".

 

All this talk of "conversions" in Spitfire production is, with extremely rare exceptions, misinterpretation and/or over-simplification.  (I mean general talk, not pointing the finger at anyone in particular.)

 

bob

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The new and unique Mk XII Spitfire fuselage was designed to mate with  the basic Mk Vc wing.

 

The new  Mk VIII Spitfire fuselage was designed to mate with the new and awaited stronger Mk VIII wing.

 

The new Mk XIV Spitfire fuselage was also designed to fit the stronger wing.

 

The Mk XII Spitfire is on the same branch of the family tree as the MK Vc.

 

The Mks VIII and XIV Spitfires are on another branch.

 

PeterA

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Thanks for the clarification.

 

Can I try your patience a little more?  When I asked about structural differences between the Mk.VIII (vs Mk.XII) other than that required to take the new engine, I should have added the changes to take the new wing which you'd mentioned above.   It (now) occurs to me that the Mk.VIII also has a larger main fuel tank, so presumably there are changes in that area too.  My thoughts at the time were whether the term "a stronger fuselage" could possibly mean a general strengthening of the rear fuselage - heavier longerons or skins?

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Just to try to return this topic to its original course, 

I have done some comparing of plans drawn by Y. Temma, and the exhaust opening on Seafire Mk.XV (a short-nose Griffon, just like Spit XII) is visibly longer than on Mk.VIII/IX.

 

One more question, was the Mk.XII prop actually the same as used on Mk.VIII/IX?

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5 minutes ago, warhawk said:

One more question, was the Mk.XII prop actually the same as used on Mk.VIII/IX?

No.  The Griffon rotated in the opposite direction from the Merlin. 

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28 minutes ago, Greenshirt said:

No.  The Griffon rotated in the opposite direction from the Merlin. 

 

The blades look identical in shape, so were they essentially just "mirrored"? 

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39 minutes ago, warhawk said:

 

The blades look identical in shape, so were they essentially just "mirrored"? 

Nope. The XII has a lower thrustline and the prop diameter is smaller than than of the IX to maintain ground clearance with the tail up.

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11 hours ago, Graham Boak said:

Thanks for the clarification.

 

Can I try your patience a little more?  When I asked about structural differences between the Mk.VIII (vs Mk.XII) other than that required to take the new engine, I should have added the changes to take the new wing which you'd mentioned above.   It (now) occurs to me that the Mk.VIII also has a larger main fuel tank, so presumably there are changes in that area too.  My thoughts at the time were whether the term "a stronger fuselage" could possibly mean a general strengthening of the rear fuselage - heavier longerons or skins?

 

The early main fuel tank was in simple terms two flat ends with a single curvature wrap. The later and larger main fuel tank was achieved by constructing it out of welded pressings that could explore every available space in the tank bay to gain precious volume. This was assisted by a redesign on the non structural aluminium diaphragm that separates the fuel tank from the pilot below the datum longeron.

 

On the Mk VIII it was time to sort out the streamline of the semi armoured  top fuel tank cover which was an early modification to Mk I's sitting on or proud of the external lofting line.  The Mk VIII utilised a new flush fitting top tank cover that physically held the top fuel tank in position when fully screwed/locked down as opposed to the four 'pit-pins' on the earlier marks. 

 

Mk VIII..a stronger fuselage? In what respect? Torsional stiffness? Bending moment? The firewall carry through spar area was 'beefed' up. The wonderful engineering thing about the Spitfire was its ability for the design to be continuously modified  by gauge changes, doublers in high stress areas, transitions from upgraded aluminium through to stainless steel as the loadings increased. Somewhere in the AP for the Mk VIII will be a diagram of the various gauges of skin material used for comparison with the Mk V. I do not have a copy.

 

PeterA

 

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8 hours ago, warhawk said:

 

The blades look identical in shape, so were they essentially just "mirrored"? 

 

I used the wooden blades and hub from a Seafire Mk XV on my XII project. The hub, bearings and metal parts are carry over Mk IX

 

Looking  at photographs of Mk XII's on the ground, and there aren't that many, the rounded profile of the prop tip would suggest to me the the prop blades may have been made of aluminium.

 

PeterA

 

 

 

.

Edited by Mark12
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While I was checking the second group of Mk.XII serials, I noticed a note to myself that the first 6 XIIs had 'dural' props, with the rest being 'wood'.  I don't, however, have a high degree of confidence in the accuracy of that statement, without looking for corroboration.

 

That second batch, by the way, were ordered as Vc (the production standard of the time), but with a caveat that some would probably be required to be fitted with Merlin 61s (thus becoming IXs).  The orders (with serial blocks assigned) were frequently just "adding to the total on order", with particular groups of serials being divvied up between variants as plans evolved.  Interestingly, I found a comment that the requested 100 Mk.XIIs were offset from Seafire IIc orders, which were reduced by 100 (at Supermarine, at least).  This is not to suggest that Spitfire XIIs were "conversions" of Seafire IIcs!

 

One interesting exception to the "common pool" ordering process, is that Supermarine (or rather Vickers) insisted that the Mk.VIII orders should be under a new contract, not just further orders under the existing contract.  The VIII airframe was considered that fundamental a change to the production line.  Of course, some muddling ended up happening, so it turns out not to be as cut-and-dry as was intended...

 

Jeffrey Quill talks about the Griffon aircraft having (I think) stainless steel longerons, but whether that's true of the Mk.XII I don't know.  I have no idea what is really different about the VIII fuselage (aside from the wing mount) compared to previous, nor do I understand how similar or different the VII structure is from the VIII- they are always associated in memory, but that may be another over-simplification!

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6 hours ago, gingerbob said:

While I was checking the second group of Mk.XII serials, I noticed a note to myself that the first 6 XIIs had 'dural' props, with the rest being 'wood'.  I don't, however, have a high degree of confidence in the accuracy of that statement, without looking for corroboration.

 

Bob,

 

I concur. Images of my own EN224 (4th production Mk XII) show the prop tip profile typical of an aluminium blade whereas this shot from the famous 41 Squadron photo-shoot, all MB serials, shows a profile typical of the Mk IX wooden blades with brass leading edge sheath as per the second shot of a blade from MK923, currently sitting on my desk. The previous owner had exposed the sheath, that is of course usually painted over.

 

12-%20MB8xx%20prop%20Peter%20Arnold%20Co

 

9-MK923%20prop%20blade%20Peter%20Arnold%

 

PeterA 

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6 hours ago, gingerbob said:

Jeffrey Quill talks about the Griffon aircraft having (I think) stainless steel longerons, but whether that's true of the Mk.XII I don't know.  I have no idea what is really different about the VIII fuselage (aside from the wing mount) compared to previous, nor do I understand how similar or different the VII structure is from the VIII- they are always associated in memory, but that may be another over-simplification!

 

Mk XII and XIV Spitfires have aluminium datum upper longerons.

 

Seafire 46 / Spitfire 22 have stainless steel datum upper longerons

 

All Spitfires have aluminium lower longerons, latterly reinforced locally with stainless steel doublers at high stress points as more power was introduced.

 

PeterA

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