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Early cannon-armed Spitfires


Welkin
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I am hoping to build the Spitfire Ib and IIb in 1:48 scale by changing the wings from Tamiya's Vb with those on their Spitfire I, plus switching the fabric-covered and metal ailerons, removing the spurious humps over the wheel wells, and using a spare rotol propeller for the IIb. I can also get a Spitfire Va by going the other way.

I am assuming that the lumps, bumps and bulges associated with the canon were the same on the Ib and IIb as they were on the Vb.

Am I correct?

Also, would the Va have had the early round exhausts, or the later fishtail type?

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Also, would the Va have had the early round exhausts, or the later fishtail type?

Round exhausts were used on many early Vbs and the few pictures I've seen of Vas show these.

Re. the other questions, the large bulges associated with the gun (above and below the wing) were the same, I'm not sure if there was any other small difference.

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Actually, there IS some difference in 'b bulges', though I haven't done proper investigation to understand it myself. As I recall Hasegawa and Tamiya render them (the underside?) somewhat differently, and it is possible one represents "early" while the other represents "late". No idea where the dividing line falls.

Not sure what you mean by "spurious humps"- the 'a' and 'b' DID have a very shallow 'hump' over the wheel well, which went away with the 'c' wing.

Most (all?) photos I've seen of IIbs actually have DH props, rather than Rotol. It seems they had a shortage of Rotols 'round about then, and they were needed more for the Mk.V than for the Mk.II.

Metal ailerons are a maybe/maybe not thing during spring '41, so it may depend on the subject and time that you are choosing. The Va, by the way, would have a DH prop also, and almost certainly the "external glass" style windscreen.

bob

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Thanks for the info guys.

I have Xtradecals X48059 which has Spitfire Mk.IIb (which they have wrongly captioned as Mk.IIa) P8522 RF-W of 303 Squadron, and this was the one I was hoping to make.

IMHO the bulges over the wheels on the Tamiya kit are way too pronounced, but I would agree that it's quite a subtle thing to render correctly.

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This is the drawing, for the underside bulge, and it's dated October, 1940, so seems likely to have been fitted to the IIb & Vb, at least. The legend, in the top l/h corner gives its application as mod 260, which applied to the cannon to be fitted to the Mk.I.

As well as the bulges, top and bottom, there was an extra control fitted on the starboard wall of the cockpit; this consisted of a square box, with pipes running up to, and down from, it, with a turnkey on its face. This enabled the pilot to cock the cannon while in flight.

33108SHT667668HMagFairing-Copy.jpg

Edgar

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I am hoping to build the Spitfire Ib and IIb in 1:48 scale by changing the wings from Tamiya's Vb with those on their Spitfire I, plus switching the fabric-covered and metal ailerons, removing the spurious humps over the wheel wells, and using a spare rotol propeller for the IIb. I can also get a Spitfire Va by going the other way.

your making work.

No need to swap fuselages, externally they are the same, as some clever replumbing of the Merlin 45 left the engine compartment the same externally [which is why the Airfix kit is builds a I/II/Va]

regarding wing bulges, Edgar mentioned no kit gets them right, representing them as 'teardrops' .... whose posted as I type

HTH

T

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I have Xtradecals X48059 which has Spitfire Mk.IIb (which they have wrongly captioned as Mk.IIa) P8522 RF-W of 303 Squadron...

IMHO the bulges over the wheels on the Tamiya kit are way too pronounced, but I would agree that it's quite a subtle thing to render correctly.

I agree P8522 is a IIb. It was with 303 from 19 June only to around 13 July, when they moved to Speke and went back to Mk.Is (and maybe even some Hurris!) It probably was built with fabric ailerons, and Vs got priority for the metal ones (unless you were Douglas Bader or somebody!), so may not have gotten metal ones until later, if at all.

Agreed on the wheel bulge- in reality it is so subtle that it often disappears in photos.

Sort of re Troy's comments: the Mk.V (Merlin 45) had a subtly different carb intake- position and fairing (opening myself up for Edgar's corrections!) but I don't remember whether the kits actually reflect that.

Edited by gingerbob
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The Merlin 45 was longer than the Merlin III, because the air/fuel mixture's entry into the compressor stage was taken into the centre of the rotor, via an elbowed duct, rather than into its edge.

Rolls-Royce, and Supermarine got round this by rotating the carburettor controls 180degrees, and hiding them under the crankcase. The only visible effect (and then only just) was that the carburettor intake moved back about 2" (with a consequently shortened fairing) to compensate.

Edgar

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The Merlin 45 was longer than the Merlin III, because the air/fuel mixture's entry into the compressor stage was taken into the centre of the rotor, via an elbowed duct, rather than into its edge.

Rolls-Royce, and Supermarine got round this by rotating the carburettor controls 180degrees, and hiding them under the crankcase. The only visible effect (and then only just) was that the carburettor intake moved back about 2" (with a consequently shortened fairing) to compensate.

Edgar

For the layman, Edgar's explanation is no doubt perfectly acceptable, but as an engineer I'd like to clarify a couple of technicalities.

Firstly, the supercharger on all Merlins was a centrifugal compressor, and for this to work at all, the inlet has to be axially into the centre of the rotor (and the discharge is radially from the edge of the rotor).

On early Merlins, mk III included, the (updraught) carburettor is mounted slightly aft of, and below, the compressor discharge volute. The air/fuel mixture is routed upwards and slightly aft before turning through approx 110 degrees (rough eyeball measurement for illustration purposes only!) to enter the compressor inlet flowing forwards parallel with the engine centreline.

On later Merlins, mk 45 included, the (updraught) carburettor is mounted further aft, and the air/fuel mixture is routed vertically and turns through 90 degrees to enter the compressor as before. The radius of this bend would appear to be larger than the earlier tighter bend, no doubt all done to improve gas flow, compressor efficiency and ultimately engine power output.

Secondly, the carburettor "controls" ie float chambers & jets etc are indeed on the aft side of the carburettor of the Merlin III and the forward side of the Merlin 45, (and under the supercharger compressor, not the crankcase, which ends further forward); but the drawings and photo's I've looked at seem to indicate it's a different model of carburettor, not the same one turned through 180 degrees.

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Didn't the Spit Ibs also not have the .303s fitted while the IIbs did? I may have gotten that transposed, but I recall reading somewhere that one of the two variants didn't have the Brownings and the other did.

As I recall, the Tamiya Vb kit has metal Ailerons, so yes those need to be replaced with fabric ones. The oil cooler also needs replacing as well I believe. Airfix got it a little wrong there as for their I/Ia/IIa kit, they show a V style oil cooler for the later Spits and the early oil cooler is also a little too tall. I had to chop that item down last night to improve its appearance on my early Mk I. It wasn't hard to do mind you, but it was a slight hassle as in my haste I had already glued the part on before I had to pop it off to modify it (which is what I get for not checking references as close as I should and only relying on the kit to get it right).

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Didn't the Spit Ibs also not have the .303s fitted while the IIbs did? I may have gotten that transposed, but I recall reading somewhere that one of the two variants didn't have the Brownings and the other did.

Quite right, that was one of the complaints made by pilots of the cannon armed MkI's, if stoppages occured , which they often did the aircraft was effectively unarmed. At least with the later Mk's the mg's were still availible. The Mk I's were simply known as cannon armed MkI's since they didn't carry any mg's , the B wing carried a 2x20mm and 4x .303 and appeared on the Mk II Spitfire.

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NOT quite right- initially they (or at least most) had only cannon, but the outer 4 mgs were re-installed subsequently, and the surviving "cannon Mk.Is" went on to become the very first Mk.Vs by having Merlin 45s installed by Rolls Royce.

bob

Edited by gingerbob
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NOT quite right- initially they (or at least most) had only cannon, but the outer 4 mgs were re-installed subsequently, and the surviving "cannon Mk.Is" went on to become the very first Mk.Vs by having Merlin 45s installed by Rolls Royce.

bob

Okay, that is important to know as at least it shows that while the outer gun bays on the cannon armed Mk Is didn't have Brownings in them, at least they still were present in the wing. Granted I wasn't expecting the bays to be removed since that is kind of silly when the production line was tooled to make them. But it does at least say that the wing still had the MG firing ports (but likely wouldn't have any red cloth/tape patches since there were no armed guns fitted).

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Canon armed Spitfires? I don't recall seeing one with a priest strapped to each wing, though perhaps Edgar can help. Now if it was cannon armed Spitfires, that's a different thing......

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spitfire-wing.jpg

I scaled the underwing bulges using Edgar's drawing, and the dimensions seem to be about right, even if they haven't quite caught the correct shape.

Mea culpa - you are of course right about cannons rather than canons.

:oops:

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Your wing photo reminds me of a few points:

You'll need to add the gun heat exit vents for your Va- they left them off the Mk.I kit (underside near the wingtip). Also, you'll want to get rid of the stiffening rails on the 'b' wing- they weren't fitted until sometime in early (?) '42. One of the kits, I think the Mk.I, has a mis-located aileron hinge on one side, I think the top surface. Compare the two and you'll spot it.

bob

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Concerning the cannon mounts in the wings themselves, were the cannons oriented a little differently inside the Ib wing compared to the later marks? I recall reading a reference that the jam problems were primarily due to how the cannons were oriented inside the wings (horizontally oriented instead of vertical). Reason I ask is just in case the Ib wing maybe didn't have all the bulges found on the IIb and Vb wings (or perhaps smaller bulges). The reference I read could be all wet anyway, which is why I am asking.

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It wasn't the position of the cannon that changed (not enough to be significant, anyway,) it was the method of ejection of the empties. Initially a right-angled (though curved) guide was set next to the ejection slot in the cannon, with the empties supposed to drop out of the wing, just as with the .303", but the different movement of the cannon, in relationship to the guide/wing, meant that the empty shells were continually jamming between the gun and the guide; eventually, this was cured by cutting a hole in the inner wingrib, beside the cannon, allowing the empties to pass through, then drop out of a hole beside the wheel well, hence the triangular hole, by the wheel wells, that you see in kits like the Hasegawa 1/32 Vb.

This is the original cannon installation, which differed little from the later airframes, apart from the curved guide, for empty shells, which disappeared, later:-

1B-cannon-4-1.jpg

Vertical orientation of the cannon didn't occur until the advent of the universal wing/Vc.

Edgar

Edited by Edgar
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Thanks - I had picked up on that, which was one of the reasons for the wing-swap. Plus the rear-seat armour plating in the Va, on the assumption that the Ib wouldn't have had that installed, althought I will need to scratch-build it for the IIb, which would have had it.
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I imagine the cannon Is also had rear armor- it was standard by that time.

Just to clarify the cannon question, essentially a 'b' wing is a 'b' wing, though as Edgar pointed out they had to do some serious fiddling to get the cannon to actually work, partly because they were mounted on their sides in order to better fit the ammunition drum into the wing.

With the 'c'/Universal wing, which was belt-fed, the cannon could be mounted upright, which they were most definitely designed for. They were also mounted with a slight up angle compared to the longitudinal axis of the aircraft (I want to say one degree, but can't remember for certain), whereas the 'b' was parallel to it.

bob

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I was going to do R6776, QV-H, 19 Squadron, Flt/Sgt George Unwin, August 1940 (two 20mm cannons, no .303 machine guns) - I guess that it's a reasonable assumption that when the cannon were being fitted they would probably have fitted the armour protection as well (if it wasn't already installed).

Edited by Welkin
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