Supermarine Spitfire F Mk 21 – Build

Photographic Observations:

While doing some research on the F.21 (internet trawling mostly) a few things come to light… (by the way, if I’ve got something wrong here, please let me know)…

• In order to improve the C.of G. position, the radio equipment seems to have been moved further back in the fuselage. The normal rear radio hatch on the port side is omitted in favour of one further back on the starboard side – one fuselage frame further back even than starboard camera hatch on the Mk XIX.
• Some F.21s appear to have the Mk XVIII-style rudder; a slightly modified shorter fin with a taller and broader rudder. This modified rudder also has a kinked and notched trim tab similar to that of the Mk 22/24. All my photographs of contra-prop airframes show a ‘Mk XVIII’ fin/rudder while the five-bladed versions seem to have a standard Mk XIV rudder.
• There seems to be a mix of 3- and 4-spoke wheel rims in use on the F.21. The mod to change them must have been issued sometime in the operational life span of the F.21.
• The radiator tubs are wider with a more curved plan view, and slightly different in profile, than those provided in the Mk XIX kit.
• Some 3-view artwork shows extended span horizontal tailplanes, similar to the Mk 22/24 airframe (which had the so called full ‘Spiteful’ tail – which included larger horizontal tail, fin and rudder). I could find no photographic evidence that the F.21 had the larger horizontal tail. As far as my photos show, where they do show, the horizontal tailplane looks standard. To my understanding, tail modifications employed to cure handling and stability issues with early 21s took the form of configuration changes to rudder and elevator control mechanisms and changes in elevator balancing.
• Exhaust studs appear to be horizontal and tubular. Early war-time machines appear to have ‘fish-tail’ type stubs – notably the prototype. At least one photo shows a contra-prop machine, with XVIII-style rudder, having downward angled 6-stub tube exhausts (wearing squadron codes ‘GO-G’).
• Recognition/signal lamps; the second production machine seems lacking in any lamp (either the old-style single central fuselage lamp, the later Mk XIV single more rearward lamp, the Mk XIV wing-mounted lamps or the later bank of three down the fuselage). But the F.21 machine that was hanging in the museum in Glasgow clearly shows the later style bank of three.
• Gun camera port; on the Glasgow machine this appears in the starboard wing root (same as the F.24 at Hendon).
• Fitting of hooks for attachment of long-range belly tanks; I only have one photo, head on, that shows anything that remotely looks like these hooks – and it is difficult to see. I have no photos showing a long range tank fitted (odd since I have plenty of F.22 photos with hooks only or hooks with tank fitted).
• Beam approach aerial; not seen in any photos of the F.21. This seems to disappear with the F.21. (F.22 prototype PK312 being an exception).
• Undercarriage geometry; my understanding is that the main gear oleo was lengthen around 2.4mm at 1/48 scale. Yet the F.21s don’t appear to sit nose high. The prop diameter was increased to 11 feet on 21s from 10 foot 5 inches on XVIIIs and XIXs. This is an increase of 3 inches on the radius – about 1.5mm at scale. That is, ground clearance was reduced by 3 inches. In my view, the reason the 21 doesn’t look like it’s nose is in the air with their longer legs is due to the change in undercarriage geometry. Looking head-on at the airframe the main gear looks far more ‘splayed’ out from the centre than previous marks. Splaying out the gear, or widening the wheel track helps stability but will also lose some height through simple trigonometry. Despite this angle change, the wheels still retain that classic slightly positive camber angle. Here’s a series of photos comparing the XIX and 21 from the front. You can see the relative angles between oleo, leading edge and radiator tub walls.

Getting on with the job:

On first look, offering up wings and fuselage, one can see the fit isn’t perfect. Viewed from above, the wide, flat and on-its-side ‘V’ shape of the wing root joints are not the same between the two kits. The apex of the ‘V’, and what might be the position of the main spar, is not in the same place. In addition, the fuselage’s wing joint is wider by about 1.5mm and there is a difference in length of about the same amount. The bigger issue is that the ’46 wing lower piece is two camera ports short of closing the XIX’s fuselage. Filler will be required!

One big surprise is that the XIX’s fuselage appears to be narrow. I had planned to use a very nice and spare windscreen (correctly moulded with the armour on the inside) from a Tamiya kit, but proved to be 1.5mm too wide to be of any use. I offered up the ’46’s cockpit windscreen to the XIX fuselage. Interestingly, this too is a bit big but with some fitting will be made to work.
So overall, the job looks fairly simple, right?
From these pics you can see I’ve already made some effort to change panel lines for the fuselage hatches and lopped off the crude triangle lumps from the top surfaces of the ’46 wings – they are supposed to be open flap mechanisms. Hmm.

Parts from donor Seafire 46/47 kit:

• Mk 46 wings; 3 pieces, two tops and the lower full span piece.
• Main flaps, items 60 and 61. Use the Mk XIX ‘down’ optional items for the smaller inboard flaps.
• Undercarriage doors and legs. Using these would leave the Seafire 47 airframe incomplete. This is unacceptable to me so I intend to clone them using my own casting methods (silicone rubber and 2-part resin; more details later).
• The long barrel 20mm cannon covers (or buy new ones).
• Seafire 46 windscreen.
• (With hindsight…) One might use the carburetor intake parts too.

Parts from elsewhere:

Required, from other sources other than the two kits:

• A gyro gunsight and mount. Mine will be scratch built.
• New decals, or I might make my own – undecided yet.
• New fuselage rear cockpit framing to replace the Mk XIX’s rear pressure bulkhead. Mine was scratch built.
• Whip aerial made from stretched sprue (or whatever you normally use).
• IFF di-pole aerial from stretched sprue.
• Wingtip navigation lights. Made from scrap clear sprue.

Optional (and obviously there are more possibilities here, such as some PE, for your own improvements):

• Since I like displaying my Spitfires with the cockpit door open I scavenged the spares box for a replacement standard Spitfire cockpit door suitable for and unpressurized airframe (from an ICM kit I think – a MkVII!).
• The XIX’s 5-bladed prop and spinner are good looking, more so than that of the 46’s, and would be the item of choice to use here. The ’46’s has a spinner about 0.5mm in diameter too big for the XIX fuselage and the blades have a very strong twist. The real Mk XIX prop measured 10 ft 4.5 in in diameter. The F.21 used an 11ft prop so I bought a new scaled 11ft diameter resin item to use instead of either XIX or ’46 kit parts (Barracuda Studios BCR48026).
• New long-barrel 20mm cannon covers from Quickboost (by Aires) QB48064. I could have made do with the kit items, leaving the short-barrel versions for the Seafire 47, but these replacements look better.

Fuselage skin modifications:

• Panel changes on fuselage; mainly filling camera-related doors. Both the port and standard camera doors on the XIX are to be filled, including the small D shaped door forward of the starboard camera hatch. A new access door was needed one door’s width aft and slightly below that filled on the starboard side. The pressurisation intake on the nose under the port engine exhaust and the exhaust outlet just behind the cockpit on the fuselage spine both need removing and filling too. In the photos below the red rings show where I am filling (including some sink holes around the cockpit and some mould marks just behind the cylinder head covers). The blue ring shows the rough position of the new hatch to be.

• Cockpit door. This is a mod since the late version Mk XIX kitted by Airfix has no side door panel lines moulded. It was easy to see where the door should be by taking note of the inner cockpit framing structure. Removing was a simply a matter of scoring and cutting. In the photo below the replacement ICM door was used to make sure the whole size was correct.

Wing skin modifications:

Just a couple of tweaks here.

• Under wing cannon blisters. On the wing under-surface of each wing (on the kit ’46 wings), just aft of the shell case ejection chutes, is a blister shaped like a rounded rectangle. According to my limited references, these blisters should be slender and more pointed and tear-drop in shape. I removed the originals and added my own, shaped and sanded, from more plastic card.

• As mentioned in an earlier post above, there are two small triangular wedges on the both upper wing surfaces toward the rear and close in to the fuselage. There are the crudest representations of the flap mechanism which opens up proud of the wing surface when the flaps on the real machine are deployed. These had to go.

Moulding Replacement Items:

And this is ‘the big one’. If I couldn’t do this there was going to be no F.21 (there still might not be, but this was something I needed to prove out before I went any further).

As mentioned already, a number of the Airfix Seafire 46/47 parts are needed to complete the build. Since there are two sets of wings in the kit, a complete Seafire 47 is still possible but the F.21 needs a number of parts that are not duplicated, notably the undercarriage components. In order to provide these items for my F.21 I have moulded my own parts direct from the Seafire items.

Here’s how I did it.

Creating The Mould:

1. The first task is to mount the required part in a new ‘sprue’ to make a mouldable pattern (see pic of the oleo leg below, as an example). The part may be big enough not to need this, but I have found that doing this helps resin flow and air bubble reduction. My intent is to make a mould that is essentially a long slit that can be squeezed at the ends to open it up to allow the resin to fill it completely. And squeezing it flat will help push out trapped air pockets. To make a ‘slit’ I add flat plastic card to the sides of the part being moulded. Some thought is needed however. You need to think about which way up the part needs to be when pouring the resin; typically the bigger/thicker end needs to be at the top. As well as attaching the flat card I also build up some ridges that will become wider pour tubes in the mould. Here’s the trick; the plastic card is carved to closely follow the side contour of the part – a millimetre or less is ideal. I leave two ‘legs’ touching the part by which the flat card can be glued. When dry, the gap around the edge is filled with a dab of Kristal Klear which, due to capillary action, runs around the gap. Leave to dry and there’ll be a very thin film filling the gap. It’s important that there are no holes through the whole pattern otherwise it won’t come out of the mould.
2. Once the pattern is dry it is mounted on some modelling clay which is smoothed and blended with the pattern. The clay will form the top of the mould and the clay volume will be the resin mounting block from which the part will be cut.
3. A plastic card ‘dam’ is built to fit around the pattern (see pics below).
4. Before mixing and pouring, the inside of the dam and any modelling clay should be smoothed over with light gel-type grease (a branded product called ‘Vaseline’ is usually part of most women’s makeup kit! There are others). Cover the parts completely but keep the coat light.
5. Before the dam is installed around the pattern, the silicone moulding compound is mixed. I then use an old brush to dab the silicone into the holes and detail of the pattern. This will help prevent air bubbles in the mould (which will create spheric lumps on the finished part).
6. While still wet, the dam is installed around the pattern, and modelling clay seal is formed around the outside bottom edge of the dam.
7. The silicone is poured carefully and slowly into the mould away from the pattern. The silicone should be allowed to flow around the pattern in its own time. The pattern should be covered completely by a good few millimetres of silicone.
8. When dry, the solid silicone mould can be eased out of the dam, then the pattern can be eased out of the resultant mould.
9. Once the pattern has been extracted the original part can be freed from the card – just like cutting it from an original sprue, The Kristal Klear should peel off. The part may need a little clear up before use, and a wash, but that’s a small price to pay.
10. The mould then needs cleaning out i.e. make sure there’s no modelling clay left in.
11. The fresh silicone has a tendency to gather and hold dust. Keep it away from your work bench – I store mine in little sealable plastic bags until ready for use.

Casting The Parts:

1. With the silicone mould ready for use, the 2-part resin can be mixed according to the manufacture’s instructions. I use a very runny equal parts fast drying resin so I need to work quickly.
2. Once well mixed I pour the mixture into the mould to about half or two-thirds full and then squeeze the mould repeatedly from both ends and sides. This squeezing seems to help the resin fluid around the walls of the mould and reduce air bubbles being trapped in the detailed cavities.
3. The mould is then topped up with more mixture and set aside to dry – about half an hour or so. As an additional step with the F.21’s new oleo legs, I inserted a thin metal rod down the main leg void into the liquid resin. When dry this provided additional strength to the part – like making reenforced concrete.
4. Making sure that the resin has hardened, peel back the mould from the part and gently prize it out.
5. The new part, like the original and commercial resin parts, will require some clean up. You may find you need to make a couple before you get a good one. And you may find that your best one needs a bit of filler to fill in a couple of air bubble pockets.
6. Wash the part before using it on the model.

Here’s what I got for my efforts… (by the way, it took two attempts to get a good result with each oleo).

The light coloured parts are mine, the darker ones are the kit’s. The outer doors are also done.

(one of the legs needs a bit of repair due to my own inability to handle a sharp knife!)

Moulding Supplies:

There are plenty of moulding and casting suppliers out there. I used to following supplier and products:

MB Fibreglass:

• Polytek EasyFlo 60 Polyurethane Liquid Plastic Casting Resin
• Polycraft Food Grade Addition Cure Silicone Moulding Making Rubber

With hindsight I would use a slower drying resin next time.

Cockpit mods:

• The XIX kit comes equipped with cameras and fuselage structure to mount them. All this was omitted from the normal fuselage build, all the cameras and the three gas bottles right behind the seat – all added to the spares box ready for the Mk XI future build. However, I used the kit’s pressure bulkhead as a pattern for a non-pressurised version of fuselage framing. The picture below shows, on the right, my creation from plastic card:

• As well as the bulkhead replacement I also removed the camera switch and control box from the cockpit instrument panel – it’s mounted where the gun sight should be. After clean up of the area I then added brackets for the gun sight (yet to be made) from more plastic card.

I’m not one for detailed scratch building of every detail in the cockpit. There are other builds that detail the addition of plumbing and other pipe work – I’ll leave that up to you. For me, I painted the available moulded detail and followed the XIX kit instructions for the rest of the cockpit build.

More on the cockpit later.

Markings:

Nothing like drooling over a nice clean fresh decal sheet to keep up the motivation through the boring build phase…

At the moment I am undecided; ocean grey/dark green or high speed silver with a polished metal cowling? At the moment I think it’s going to be Ocean Grey/Dark Green.

Here’s the front runner:

I just love Freightdog Model’s decals!

(Interesting that on this line art they have drawn in the beam approach aerial. I can’t find any photo evidence for this, yet)

Mating the Wings in Detail:

• I am glad to have confirmation that the horizontal tail is pretty much standard rather than a ‘Spiteful’ size as some 3-views would indicate. Obviously, this would of made a big difference to the look.
• On the wing-fuselage mating; here’s a couple more shots from a different angle, see below. Having just spent a few more minutes playing with this, I am still of the view that lining up the leading edge is the way to go. If I do this I think a make things much easier; around the carburettor intake and under nose panel, and at the trailing edge and rear wing root intersection. The only chore will be the main wing root joint – and I’ve seen kits with worse issues than this. Also, at the very rear, surprisingly, the very back edge of the ’46 lower wing part, where it joins to the fuselage (where the camera ports should be) does line up with the XIX panel lines. There is still the camera port gap to fill, but obviously that was always going to be a job to do anyway. (In the images, I’ve dropped the fuselage down into position without any side-to-side trimming. This means that more of the underside fillet is visible than will actually be there for trimming – i.e. the whole fuselage, in the images, has yet to be moved about 1mm to starboard. The narrowness of the XIX is a factor still in that the ’46 rear section mating under the fueslage is a tad wider.)

Here’s the photos…Blue shows the gap to be filled due to the loss of camera ports. Red is general wing alignment. The Green and ‘Apex Issues’ shows the ‘miss-alignment’ of panel lines associated with the main spar – although who knows if the panel lines equate to spar front edge or rear edge or centre line, or is this inaccuracies in the kits. Regardless, at the moment, I plan to live with it (or I may just fill and re-scribe the panel line on the fuselage, under the upper green arrow).

All good fun!

Undercarriage Doors:

Just had a look at undercart doors… Bob, you are right, there are differences. From my photos it looks like 21s had a set of doors with less of an angle on the leading side – more likely to foul an arrestor wire I guess. Seafire 46s and 47s seem to have a steep leading angle on the main U/C door. But… I have a couple of pics of 21s with the same 46/47 type door (notably LA139). But there’s another ‘but’… the kit parts from the 46/47 seem to reflect the angles on the majority of 21s! Go figure! Was there are mod retrofitted back onto some 21 after the improvement for Seafires? Not looked at the Seafire 45 yet. I have pics of Mk 22s with the same steep angle as the Seafire. Here’s a pic to show the extent of the difference:

• First pic is a Seafire 46. One can see the steep leading angle on the main wheel door.
• The second pic shows, not very well (I have better photos in a book) a Spitfire 21.
• The third pic shows another Seafire and overlaid is a scrap of the outer kit door. It is real clear to see that the kit door follows the F21 angles! I have a photo of an F21 underside onto which I can physically lay the kit parts. This backs up the fact that the kit parts are better shaped for a F.21 than they are for a Seafire!

The more one looks, the more one sees. Looking again I see other photos of 22s and 24s with a mix of different UC door types. There’s a photo of 24s under construction at South Marston with the non-Seafire type doors, yet there are photos of late 24s with the Seafire-type fitted (VN324 for example). I’ve now seen 24s with the Royal Hong Kong AF with both types fitted – in the same squadron (VN318 and VN485).

I assume Airfix must have kitted up their Spitfire 22/24 first and just reused components for the Seafire 46/47, not noticing that the UC doors on the earlier 22s and 24s are different to Seafires. And these Seafire doors must be a dead swap (in matched sets) for the earlier type and retro fitted at MUs or on squadron, or something like.

Looks like I should just use the Seafire 46/47 undercart parts for my F.21 and think about building some correctly shaped parts from scratch for my Seafire 47 later! That moulding my own replacements to save the 47 was a waste of time.

Seems like we need some resin improved replacements for the 46/47 kit.

Researching is the best bit about modelling, well, almost!

Radiator Tubs:

Again, it’s my plan to leave the Seafire 46/47 kit with a completely buildable Mk 47. To this end I plan to use the radiator tubs from the Mk XIX. But these are a different shape to those of the Mk 21, and they join to the under-wing surfaces with a slightly different joint line.

Here’s a pic of the Mk XIX and Seafire wings, viewing the underside centre section:

The Mk XIX kit is the better thought out. The joins for the rad tubs fall on the panel line, while those of the Seafire do not – part of the rad tub edge is moulded onto the wing underside.

This means that adjusting the Mk XIX rad tubs to fit required 3 stages.

1. The first stage is to trim the edges of the rad tub until they fit into the curved slots of the Seafire wing.
2. Second stage is to build up the edges of the rad tubs as those of the F.21 look wider/fatter than those provided with the Mk XIX kit.
3. The last stage is to trim back the rear profile – cutting an angle in from the bottom of the tub up to the wing under surface.

Here’s a few pics of what’s going on:

This picture is Spitfire F Mk 21 underside showing the shape of radiator tubs; right.

Diagram [1] below shows the contours of both Mk XIX and F.21. The Red lines are those of the Mk XIX kit – the outer set are the join lines into the wing slots, the inner lines are the contours of the tub wall. The Green lines show the new contour needed to fit the Seafire undersides – which is fatter and rounder than those of the XIX.

Diagram [2] shows what material was removed.

Diagram [3] shows what material (filler) was added then sanded back in order to create the right shape.

And lastly,  the picture below shows the ‘before’ and ‘after’.

This image also shows the area on each side that I chopped off in order to get the correct looking profile, and to fit the Seafire wing slots (shown by the little red triangle).The final picture shows a good close-up shot of LA188. You can see the shape of the radiator tub rear in this:

While I was at it, I also closed the radiator shutters, just for something different. The finished item on the right has a coat of primer (to spot issues with the filler) and panel lines re-scribed.

Both are sides are done and ready to attach. When the time comes, I will be using the XIX kit parts for the internals – the radiators.

References:

Following on with the F.21 undercart doors observations here’s the main references I’m using:

Books:

A – The Spitfire Story, by Alfred Price

B – Spitfire, A Complete Fighting History, by Alfred Price

C – Camouflage & Markings No1 RAF Fighters 1945-1950 UK Based (Scale Aircraft Monographs) by Paul Lucas.

D – Camouflage & Markings No5 RAF Fighters 1945-1950 Overseas Based (Scale Aircraft Monographs) by Paul Lucas.

The internet:

Here’s a list of some of the photo evidence I’ve seen on this subject (obviously this is a limited list since it’s only photos where the doors can be seen):

Mk 21s, 22s and 24s with ‘Spitfire’ doors:

• LA187 (B, page 243). I can’t confirm the serial from the photo however. If it is LA187 the she was repaired and upgraded, see below.
• LA188 (B, page 247) (A, page228)
• DP851 and PP139 prototypes (B, page 242)
• 21s under construction at South Marston (B, page 244/5)
• LA217 with contra-prop (Internet)
• LA255(?) (couple of photos; colour photo: Internet)
• In service 91 squadron machines, DL-F and DL-Y (A, page 230)
• LA218 (A, page 231)
• LA232 (couple of photos in different paint schemes: Internet)
• LA256 painted in silver with post war bright red/white/blue markings. (Internet)
• LA331 also painted in silver with post war bright red/white/blue markings. (Internet)
• LA228 painted siliver, polished cowel, RAuxAF (C, page 51)
• LA308 RAuxAF (C, page 26)
• LA275 RAuxAF (C, page 26)
• LA223 RAuxAF (C, page 22)
• LA315 41 Sqdn (C, page 10)
• LA276 1 Sqdn (C, page 3)
• Mk 22 PK683 (Internet)
• Mk 22 PK605 (C, page 79)
• Mk 22 PK437 (C, page 79)
• Mk 22 PK562 (C, page 53)
• Mk 22 PK430 (C, page 31)
• Mk 22 PK569 (C, page 69)
• Mk 22 PK481 (Internet)
• Mk 22 PK431 (Internet)
• Mk 22 PK542 painted in silver with post war bright red/white/blue markings. (Internet)
• Mk 22 PK599 (Airliners.net: Internet)
• Mk 24 VN485 (Internet)
• Mk 24 PK724 as she is in Hendon. Difficult to count museum airframes as they may have been cobbled together from parts that fit. (My own photo collection)
• Mk 24 PK713 (Internet)
• Mk 22 prototype PK312 (Internet and A, page 232)
• Mk 22 PK547 (Internet)
• Mk 24 or 22(?) PK684, or it might be 664 or 634, contra-prop (Internet)
• Mk 24 VN318 80 Sqdn (D, page 83)
• MK 22 PK690 74 Sqdn (D, page 35)

Spitfires with ‘Seafire’ doors:

• F.21 LA187 as photographed by Air Service Training, a repair organisation. The photo is entitled ‘Last of the many’ and implies the subject is the last repaired airframe dated Dec 1946. She clearly has ‘Seafire’ doors at this point. (Internet)
• F.21 LA198 shown in post war bright red/white/blue markings (b/w photo). A little difficult to see, but looks like Seafire doors. (Internet: Air Britain Photographic Images Collection). And F.21 LA198 as she is hanging in the museum in Glasgow (assuming it’s the same airframe).
• VN324. Billed as “a late production Mark 24” (A, page 237)
• VN318 ‘E’ RHKAuxAF, ex- 80 Squadron airframe I think. (A, page 238), And on the opposite page is VN485 with ‘Spitfire’ doors – and these two pictures are implied taken at the same time for the same event in 1955 and thus imply mixed use on squadron.
• F.21 LA269 LO-(?) with guns removed. Photo looks late, post ops. (Internet)
• F.21 LA139 painted silver with post war bright red/white/blue markings and guns removed. (Internet) […Bad info, I miss read the serial on a poor black and white photo of LA198. There is no LA139! Sorry.]
• Mk 24 VN496 TN- (Internet)
• Mk 22 PK481 modern photo of a museum airframe so it’s difficult to count this one. (RAAFA Museum: Internet)
• Mk 22 in Egyptian service in several photos (Internet)
• Mk 24 VN318 with Seafire-like bullet/torpedo shaped centre line drop tank and wing mounted bombs. (Internet)
• Mk 24 VN317 with 80 Sqdn (D, page 16)

All the pictures I have seen of Seafires, including some of Mks XV and XVII, all show ‘Seafire’ style doors. The Airfix 1/48 Seafire XVII has correctly shaped doors.

I have pictures of TM379, the Seafire 45 prototype, and she’s clearly booted with ‘Seafire’ type doors for sure – and looks very different from the clear photo of LA139 looking very obviously a 21 without a hook.

My conclusion from all this:

• F.21s with the ‘Seafire’ doors seem to be very late, or even post operational career, and are fewer in number judging only by the proportional split on the photos I’ve seen – and where the doors are visible. Most F.21s have the ‘Spitfire’ doors, with limited arrestor wire clearance. This seems true for Mks 22 and 24, although more care is needed since there’s a greater chance Seafire-type doors might have been fitted.
• The doors, as moulded for the 46/47 by Airfix, with the low leading angle forward of the wheel axle, are not correct for the 46 or 47 airframes. They are, however, correct for a percentage of Mks 21, 22 and 24 airframes – but due to some retro fit or late production mod, one should try and check 22s and 24s with direct photo evidence.

I plan to use my cloned Airfix doors, unaltered, for my F.21. My Seafire 47, when I get to it, will need a change of doors, somehow.

This all means that when building a Spitfire F.21 from the two Airfix kits (the whole point here), depending on how accurate you want your remaining Seafire to be, you could go ahead and just use the doors on the F.21 – without all the trouble of cloning (like wot I did) – and accept that you will need to source better ones for the 47 from elsewhere.