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

[warhawk]

Hello,

 

I have a simple question regarding exhaust pipes (both fish-tail and round), on long-nose Merlin spits (VII/VIII/IX/XVI).

Were exhaust pipes from these "Long-nose Merlins" identical to Mk.XII, Mk.XIV, or maybe even both of these Griffon variants?

 

Aleksandar

Edited December 3, 2019 by warhawk

[Graham Boak]

Logically not, as the Griffon was a larger engine so a greater mass flow was required. This would be dependent upon rpm as well. 

[gingerbob]

I believe that the distance from cylinder center-to-center was also different on the Griffon vs. the Merlin, which would certainly matter from a model point of view.

[Black Knight]

Imperfect information; the Merlin is 88 inches long, the Griffon is 81 inches

Both V12 with overhead camshafts and valves, 2 inlet and 2 exhaust per cylinder

Cylinder bore of of the Merlin is 5.4 inches, Griffon is 6 inches

Although the greater bore size of the Griffon apparently puts the centre of the pistons further apart, they would be closer together in the shorter size of the engine

Allowing that the above is only approximations; the same exhaust manifolds could be used

[Jamie @ Sovereign Hobbies]

Those dimensions are for the Merlin 60 series and upwards with 2 stage superchargers which the Griffon never had. The apparently similar size of the overall engines is because the Merlin has an externally bigger supercharger.

 

The cylinder banks and heads of the Griffon are, as logic would most strongly suggest, larger.

 

 

[Graham Boak]

Later Griffons, as in the Spitfire Mk. XIV and later, did indeed have two-stage superchargers.  There are different lengths of Merlin, and indeed Griffon, depending not only on the supercharger stages but also upon the gearbox, with one or two options.  There may also be a difference at the front, in the drive housing for the propeller - I don't know.  So which Merlin was 88 inches, and which Griffon 81?  Just what are these measurements of?    The arguments being based on them assume that they are the length of the cylinder block, which may indeed be invariant, but in that case there is an interesting discussion to be had to explain away why Griffon-engined fighters are somewhat longer than their closest Merlin equivalents.  

 

Nor does it suggest any reason why the exhausts should not be different.  If the cylinders are differently spaced, then the same manifold simply will not fit, even if it had the same flow requirements.

 

 I have found it difficult to get a measure of the additional length of these features.  The second gear add 4 inches to the Merlin XX compared to the Merlin III, but how much more for the Merlin 61?  It's of the order of 6 to 8 inches, but so far I haven't tapped the right source to say what.  Published overall lengths of variants fail to allow for differing spinner sizes, or indeed rudders.

[gingerbob]

The annoying thing is that I remember trying to establish the cylinder to cylinder spacing- I think reasonably successfully- but don't know where to now find those results!  I don't suppose it was in communication between us, Graham?

[Graham Boak]

Not that I can recall.  Feel free to prove me wrong!

[Jamie @ Sovereign Hobbies]

The 88" measurement is cited in Wikipedia as the overall length of the Merlin 60 series.

[Graham Boak]

And the 81 inches for the Griffon is also in Wiki for the Griffon 61, also a two-speed two-stage variant so the two engines should be comparable.  But there remains differences between the detail design of the gearboxes and superchargers (and intercoolers?) that possibly introduce other differences.

[warhawk]

Thanks for Your opinions.

Would it be a safer bet to use, e.g. Mk.XIV exhaust on an Mk.XII, since those are available in resin?

[stevehnz]

I would think so. It is my understanding that the XII & XIV were the same as regards the cylinder head clearance bulges so their exhausts should also be similar. I stand to be corrected though.

Steve.

[warhawk]

2 minutes ago, stevehnz said:

It is my understanding that the XII & XIV were the same as regards the cylinder head clearance bulges so their exhausts should also be similar. I stand to be corrected though.

 

There were differences in the cowling panels, and XIV also had a longer nose, which was later standardized.

XII is tricky to model, since it was a mish-mash of various Merlin spits, hence my idea that maybe the exhaust would also be the same as those versions... 

[Graham Boak]

In 1/72 scale?  I've been looking at a few photos in Spitfire The History, and suggest that you could indeed get away with using fishtail exhausts from a Mk.IX kit on a Mk.XII.  It would perhaps depend more upon the way the model manufacturer had represented the exhausts: examples in my collection show a wide range of sizes and shapes. If it looks good, do it.

 

The cylinder head bulges shouldn't differ between the Mk.XII and the Mk.XIV - the cylinder heads are the same size.  The two-stage supercharger is however providing a different air input, and so a different air output would seem to be at least possible.  

 

The Mk.XII wasn't really a mish-mash of variants: it was a development of the Mk.Vc with the single-stage Griffon engine and a fuselage that was revised structurally (smooth rivets, for a start).  Partway through production it was altered to a revised tail with the retractable tailwheel from the Mk.III and a new rudder.  (I don't recall whether the new tail was late or they wanted to use up spare Mk.Vc tails.)  This fuselage and tail was to become standard on the Mk.VIII, but it was the Mk.XII that came first, despite the mark numbers.  To be fair, most Spitfire marks can be defined as a mish-mash of other variants.

[warhawk]

10 minutes ago, Graham Boak said:

it was a development of the Mk.Vc with the single-stage Griffon engine and a fuselage that was revised structurally (smooth rivets, for a start).  Partway through production it was altered to a revised tail with the retractable tailwheel from the Mk.III and a new rudder.  

 

This is precisely what i meant by "mish-mash" - an older airframe with some improvements tried and gradually introduced as time went by (not counting the Griffon engine, of course). Not an entirely new aircraft, like VIII or XIV

Edited June 22, 2017 by warhawk

[stevehnz]

AFTER THE Spitfire Mk I, all the others could be said to be a mish mash of different types & features. With regard to the Griffon engined ones, of which the XII was the first, other than the changed length, which on the later ones took place behind the engine, ie,  between the engine & the firewall. it has long been my understanding that the nose contours were largely the same right through to the 24. Even though the XII had only a 4 bladed prop, the base plate was the same diameter as the 5 bladed ones. If I'm wrong on this, I'm happy to be put right though I've not seen anything to contradict that anytime I can recall. 

Steve.

PS, excepting for the bulge between the cylinder head fairings on the XII of course

Edited June 22, 2017 by stevehnz

[Graham Boak]

OK: most sources speak of a mix of Mk.VIII and V airframes being used, which the Mk.XIIs weren't.  I was arguing against that, an early assumption which gets repeated by lazy writers.

 

Entirely new Mk.VIII?  No such thing,  All Spitfires are variants of the original airframe with progressive developments.   You can define a Mk.VIII in a number of different ways:  a Mk.XII given a Mk.IX engine with modified fuel system and ailerons;  Just an unpressurised Mk.VII;  Another step in the Mk.I/III/Vc/XII line.  

 

The Mk.XIV is just a Mk.VIII with a 2-stage Griffon and a bodged tail.  All late Spitfire tails were "fixes" to alleviate handling faults without the break in production that the "Spiteful" tail (or an earlier equivalent) would have caused. 

Edited June 22, 2017 by Graham Boak

[stevehnz]

Pretty much my take on it too Graham. The "converted from" thing about the XIIs seems to come from the fact they were built from existing production orders that Supermarine had for Vs, the first batch with the fixed tail wheels & VIIIs, the remainder with the retractable tail wheels but they were not converted as such but took over places in the production sequence originally allocated to those other Marks & were built in their entirety as XIIs. As I understand it this is where the converted myth comes from.

Steve.

[warhawk]

3 hours ago, Graham Boak said:

Entirely new Mk.VIII?  No such thing,  All Spitfires are variants of the original airframe with progressive developments.   You can define a Mk.VIII in a number of different ways:  a Mk.XII given a Mk.IX engine with modified fuel system and ailerons;  Just an unpressurised Mk.VII;  Another step in the Mk.I/III/Vc/XII line.  

 

We seem to have a misunderstanding again.

Some IX and XII Spits were re-built earlier Vc airframes, meaning they didn't leave the factory as IX and XIIs when they were produced.

Most VIII and XIVs came out as brand new airframes with no back history.

[stevehnz]

Early IXs were certainly converted from Vs by installation of Merlin 60 series, not XIIs though AFAIK but if you can direct me to something that contradicts that I'm all ears.

Steve.

[Graham Boak]

Like Steve says.  All Mk.XIIs used "Mk.Vc standard" wings, undercarriages etc but had new fuselages.  Some had "Mk.Vc standard" tails, but for the rudder.  No such aircraft were converted from examples previously finished as Mk.Vs.  This sounds like a variation on the original myth.  It's perhaps worth adding here that in the case of the Mk.Vs to Mk.IXs, these were aircraft fresh from the assembly lines.  Their history consisted of a transfer from one factory hall to another, even at the same factory (although 48 did apparently fly as Mk.Vs to Rolls-Royce's factory.).  

 

A great many Spitfires were built under contracts originally allocated to earlier variants, altered when it became clear that better options were available.  The initial Mk.IXs were built to a contact initially issued for Mk.Is. (Fifth contract for 1,100 aircraft dated 24 October 1940: built as PR Mk.IV, Mk.Vb, Vc, VI, VII and IX).  Re Mk.XIIs. the first batch of Mk.XIIs were built to the seventh production order for 500 Mk.Vc, dated 23 Aug 1943.  Aircraft built to this contract included Mk.VC, PR Mk.IV, Mks.VI, VII, IX and XII.  The second batch was built to the tenth order for 426 Mk.Vc, built as Mk.VII,VIII,IX and XII.  So these batches included different fuselage and wing standards within the run of serials allocated to specific contracts.

[Graham Boak]

OK, something to add.  After all, the above evidence on contracts doesn't in itself prevent the Mk.XIIs having been rebuilt from earlier complete airframes.  What does prevent this is the serial.  In RAF usage, this is what identifies the individual.  Wings, engines, tails etc can all change (and often do) but the identity of the aircraft is carried with the main fuselage from from the main engine bulkhead to the break for the tail.  The Mk.XII was the first Spitfire to be flush-riveted.  I'm unsure what other fuselage structural modifications were included.  Therefore the fuselages were built that way in the first place.

 

Note that those Mk.IXs converted from Mk.Vs did not receive new serials, whereas the Hurricanes rebuilt from Mk.Is to Mk.IIs (with a longer main fuselage framework) did.

[Bonhoff]

Had a bit of a search online (search criteria: griffon bore centres) and found a pdf of a RR document about the Griffon at a site called "Spitfireperformance.com"

 

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

[Mark12]

On 6/22/2017 at 11:55 AM, Graham Boak said:

OK: most sources speak of a mix of Mk.VIII and V airframes being used, which the Mk.XIIs weren't.  I was arguing against that, an early assumption which gets repeated by lazy writers.

 

Entirely new Mk.VIII?  No such thing,  All Spitfires are variants of the original airframe with progressive developments.   You can define a Mk.VIII in a number of different ways:  a Mk.XII given a Mk.IX engine with modified fuel system and ailerons;  Just an unpressurised Mk.VII;  Another step in the Mk.I/III/Vc/XII line.  

 

The Mk.XIV is just a Mk.VIII with a 2-stage Griffon and a bodged tail.  All late Spitfire tails were "fixes" to alleviate handling faults without the break in production that the "Spiteful" tail (or an earlier equivalent) would have caused. 

 

You can define a Mk.VIII in a number of different ways:  a Mk.XII given a Mk.IX engine with modified fuel system and ailerons;  Just an unpressurised Mk.VII; 

 

The Mk XII EN serials were certainly  based on the Mk V fuselage and wing. It is possible the MB serials were different and for sure the retracting tail wheel may be an indicator.

 

PeterA

[Graham Boak]

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.