neilfergylee Posted July 21, 2022 Share Posted July 21, 2022 Over on the Ready for Inspection part of the forum, I recently submitted a post for a Spitfire XIVc conversion and mentioned that one component (the fuel tank) was going to be reused on a Spitfire Mk.III conversion and @Troy Smith suggested I post the build here. Background I'm not sure about the rest of you but when I was growing up and starting to develop an interest in aviation (and trains - that's another story), I was intrigued by the gaps in the mark numbering. Like many of my age, my first Spitfire kit was a Mk.IX. Naturally I saw also a Mk.I and Revell made a Mk.II. Then I learned about the Mk.V and when I saw the FROG Mk.XIV and then learned about the Mk.24 in the RAF Museum, my head was spinning! I then acquired a copy of this book and it was a revelation as it filled-in so many gaps. From then on, a small part of me was forever intrigued by the Mks. III and IV. I have built the Mk.IV prototype in its Mk.XX guise (that mark number is another story) which I have reproduced below but the Mk.III is far more enigmatic as it was even less well-documented than the Mk.IV.. The Spitfire Mk.III The Mk.III was the first major design change to the Spitfire. First flying in 1940, the Mk.III involved a series of enhancements, namely: Merlin XX engine Clipped wings Retractable tailwheel Modified windshield. The tailwheel was to find its way into a number of later marks from the VII onwards (with notable gaps, e.g. the Mk.IX), while the armoured windshield was an attempt to improve on the basic windshield of the Mk.I which was 'lashed-up' with the addition of an external armoured windshield. The engine and wings were radical. The engine was the Merlin XX. This was a single stage, two speed Merlin and it warrants some extra description. Now, your eyes may glaze over at this point because in the spreadsheet I put together documenting Merlin variants has 117 rows and I don't think for a minute it's definitive. However, Merlins came in three basic types which all involved supercharging. Single stage, single speed. A single supercharger impeller, geared directly to the engine crankshaft. Single stage, two speed. A single supercharger impeller attached through speed gearbox which allowed the supercharger impeller to speed-up at high altitude by means of a barostat. Two stage, two speed. One supercharger impeller feeding a second to provide a higher level of compression and possessing the two speed barostatic speed change. Because the compressed gas was heated significantly by the two-stage compression, it required an intercooler (a heat exchanger). These changes necessitated the extended nose in later Spitfire models and also the symmetrical radiators under the wings which formed the other part of the intercooler circuit. The Merlin XX was the second model of the two-speed Merlin, the first being the Merlin X. The Merlin XX involved an aerodynamically superior supercharger impeller courtesy of Stanley Hooker, who was very much 'Doctor Supercharger' at Rolls Royce and, ultimately at Bristol where the Olympus and Pegasus were developed under his leadership. The slipped wings weren't the usual clipped wing either. The normal wing had a span of 36' 10", the usual clipped wing had a span of 32' 7" and the long span wing was 40' 2". The span of the Mk.III was a mere 30' 6" thus noticeably stubbier: although using the same planform, they looked very different and the ailerons were much shorter too. Neither the engine nor the wings ever found themselves in production. The Merlin XX was a complicated engine to build and with limited resources, the Air Ministry decided that production should be allocated to bomber aircraft plus the Hurrricane where the additional performance helped stave off obsolescence. Cutting to the chase, the improved impellor of the Merlin XX was used in the single-stage Merlin 45 which formed the basis of the next version of the Spitfire to go into production, the Spitfire V. The wings were not a success. The story goes that Lord Dowding didn't like them as they looked too much like those of the Me 109 and, certainly their stubby appearance looked that way but the reduced size meant a smaller wing area leading to a hight wing loading and less manoeuvrability. It also led to an extended landing run that was described as 'dangerous'. A second Mk.III was completed in 1941, which is curious because by then the Mk.V was firmly in production. Certainly by 1941 the Mk.III was out of the running and the two prototypes found themselves used for a variety of experimental uses but perhaps the most notable was the first installation of the two-stage Merlin 60 engine which led to the Mk. VII, VIII and - most significantly - the Mk. IX. Modelling the Spitfire III If you're going to model the Mk.III, you really need to say "I'm modelling the Spitfire Mk.III on this date..." because the aircraft changed considerably over its life. For example, the clipped wings were replaced by a regular wing and a later version of the second prototype was fitted with the 'C' wing. In turn the windscreen changed design from the streamlined version to a more conventional version and the camouflage and markings also developed. Ultimately, fitting the Merlin 60 engine resulted in something that looked very close to a Mk.IX. The Model I chose the Airfix Mk.I kit as the basis. Whilst later Airfix Spitfires have been just lovely, the Mk.I is what I would call 'conversion quality': you wouldn't sacrifice an Eduard of Tamiya Mk.I for this job! Here is a picture of present WIP and I shall provide more updates in the next couple of days. Best wishes, Neil 19 Link to comment Share on other sites More sharing options...
cngaero Posted July 21, 2022 Share Posted July 21, 2022 I'll be following this with interest Neil, as I to have a great interest in the gap numbered aircraft. I see what you mean about the stubby wing form. Good luck with this project. 1 Link to comment Share on other sites More sharing options...
mark.au Posted July 22, 2022 Share Posted July 22, 2022 Interesting and informative description of the engine variants, I've not understood that very well before. I'm curious as to what the extra deep wing clipping was trying to achieve if the result was so poor, and even to me somewhat predictably so. 1 1 Link to comment Share on other sites More sharing options...
Troy Smith Posted July 22, 2022 Share Posted July 22, 2022 10 hours ago, neilfergylee said: I chose the Airfix Mk.I kit as the basis. That is the old tool Mk.I from what I can see? It's really clunky. Note, years ago John Adams had posted a photo showing what need to to be reduced to make it less so, if you have already glued the wing, then you won't be able to thing it, but the thickness of the fin is clear in the above. A really easy improvement is to replace the rudder and elevators, you can use the early style ones that come as options in the Edaurd or ICM VIII/IX kit for this. Worth looking at other leftover bits as well, wheels, hubs, exhausts, canopies Also, the nose, the thrust line is too high, making the nose ring too big. .main point this means the kit spinners are wrong, but plenty of spare of the right size are in other kits,(new tool Airfix, Eduard MkI/II) given the cowl top looks more bulges around the cylinder heads above the exhausts, you might want to cut the upper cowl off, and move the side panels in slighly, to match the new fuel tank cover width, and the sand/ blend upepr cowl. One other point, as the Spitfire III has a unique nose, so the side panel lower cowl line is at a different angle from what I can see, in this shot, as the paint line is now the lower cowl edge, while this is Vb, the nose panels are essentially the same, as it was able to squeeze the merlin 45 into the same engine bay as the Mk.I Hmm, looking at these, it look the the angle maybe the same, and the break point is slightly lower on the Mk.III nose. Hope this is of some use, I'm interested to see how you tackle the new front canopy. I suspect the easiest maybe to make a plug and smash mould it. I'll @gingerbob @Greenshirt (Tim did this in 72nd) @Peter Roberts @Magpie22 @lasermonkey as Spitfire aficionados who may find this interesting. cheers T 6 Link to comment Share on other sites More sharing options...
Graham Boak Posted July 22, 2022 Share Posted July 22, 2022 Visible in the photos but not so far mentioned (I think) is the larger/deeper radiator. The reason for going for the Merlin XX was the search for superior performance at altitude. This was a dominant theme in the Air Ministry's demands for improvements. The reason for the reduced wingspan was to increase speed, though it would also have improved roll rate. Sadly the speed gain was not as great as hoped for, and the reduced wing area (and lower aspect ratio) gave a significant deterioration at altitude. Not what the Ministry wanted. Apparently the matter was greatly improved when a conventional wing was fitted, but by then the Merlin 45 was providing most of the performance benefit requested and the decision had been made. Given that the Mk.III required considerable retooling of the airframe, there seems to be no reason to be critical. One point to bear in mind is that the Merlin XX was the long-awaited mass production version of the Merlin, to be poured out in huge numbers by Ford. I find the comment supposedly credited to Dowding rather odd, to say the least. There would be little to no chance of confusing the longer thinner (high aspect ratio) wing of the Bf.109 with the shorter wider one of the original Mk.III. 3 1 Link to comment Share on other sites More sharing options...
HAMP man Posted July 22, 2022 Share Posted July 22, 2022 I love it when the Spiteratti start chewing the fat Looking forward to more discussion and plastic bothering. Box on Strickers 2 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 22, 2022 Author Share Posted July 22, 2022 Fuselage Thank you all for your comments. My starting point was this pair of drawings in the Morgan & Shaklady Bible. I have broken all the rules about scaling from drawings etc. but this comparison provides a good illustration of where the small difference in length (nowhere as big as for the two-stage Merlin) came from. The starting point is the angled firewall in front of the fuel tank. This was the only implementation of this feature in a Merlin engined Spitfire although it was standard for all two stage Griffon variants. You will see that this is the source of the longer nose, providing a few extra inches and it would appear to be to accommodate the marginally longer Merlin XX engine. In the image below, I have crudely placed a Merlin III above a Merlin XX and you can see there is slightly more 'gubbins' at the back end of the Merlin XX to accommodate the gear change mechanism. To model this, I tacked-together the Airfix fuselage. I removed the fuel tank section and replaced it with the Mk.XIV tank and then filed-away a the (by now detattched) engine cowling assembly. Being a Spitfire, I did have to build the cockpit section, improving it with some PE and using a spare Mk.XIX seat and frame assembly. I then built it up and after several goes, managed to align the components. Below is the intermediate result. You will see that this provided a 3mm gap that equates to 3.7" which is more or less the extension of the Mk.III over earlier marks. @Troy Smith, I am not totally convinced that the cowling around the exhausts was dramatically differnt to other marks. The Merlin XX was no wider than other versions and this view shows that although it was possibly slightly more angular, it was not really any wider. As I write this the fuselage as been filled and tomorrow I hope to provide pictures of how it looks. As for the canopy, that's another story! Cheers, Neil 6 Link to comment Share on other sites More sharing options...
Peter Roberts Posted July 22, 2022 Share Posted July 22, 2022 (edited) Wow, interesting project. Looks good so far. Canopy - early flat sided sliding canopy (Mk I) with a Mk Vc windscreen? Radiator - modified Mk XIV/XIX?? Is this the Spitfire III version you are making (as per photo in the last post)? Interesting to see the anti-fouling mechanism on the fin and additions to the u/c doors. That bulge above the exhausts does look a bit different, a little angular (?) - may be an optical illusion. And a Vb style spinner? Unusual prop. Any Aussies fly this? Hope not or I'll have to add it to the collection! Edited July 22, 2022 by Peter Roberts 2 Link to comment Share on other sites More sharing options...
Dunny Posted July 22, 2022 Share Posted July 22, 2022 Neil, An unusual project - I shall follow along with interest! Cheers, Roger 1 Link to comment Share on other sites More sharing options...
Troy Smith Posted July 22, 2022 Share Posted July 22, 2022 54 minutes ago, neilfergylee said: This was the only implementation of this feature in a Merlin engined Spitfire Not the only one see https://www.britmodeller.com/forums/index.php?/topic/235071928-spitfire-vii-prototype-ab540-colours-stated-pru-blue-over-deep-sky/ 54 minutes ago, neilfergylee said: You will see that this provided a 3mm gap that equates to 3.7" which is more or less the extension of the Mk.III over earlier marks. The Merlin XX is 4 inches longer, or, a Hurricane Mk.II is 4 inches longer than Hurricane Mk.I 3.7 inch is not 3 mm, 1 inch = 25.4 mm, x3.7 = 93.9848 /48 = 1.95 crudely 1mm = 2inch in 1/48 4 inches in 1/48th is also exactly 1/12th inch. One possible problem, you seem to have angled the upper cowling down, but this maybe just a trick of the photo. Does make me have an itch to get the razor saw out though. In the case of Hurricane I vs II, I have a stalled conversion, which I used 2 mm strip, https://www.britmodeller.com/forums/index.php?/topic/235077619-airfix-hurricane-iia-in-148th-gaffa-tape-here-we-come/#elControls_3774132_menu with some observations as to why and how which maybe of use, and would be the basis for my proposal of a Spitfire III My suspicions is you have made work by incorporating the new fuel tank cover, rather than using it to make a scribing guide, which is my theory, but you are actually doing it, and how you do the conversion is irrelevant, if it get you the result you want at the end. Great to see a WIP for this, and look forward to the next instalment 54 minutes ago, neilfergylee said: I am not totally convinced that the cowling around the exhausts was dramatically differnt to other marks. The Merlin XX was no wider than other versions and this view shows that although it was possibly slightly more angular, it was not really any wider. I don't think the upper cowl is wider, but the panel below is in closer, causing the apparent 'bulge' .... I'm mostly worried this is going to cause me to chop up a Spitfire and put my money where my mouth is ... cheers T 10 minutes ago, Peter Roberts said: Canopy - early flat sided sliding canopy (Mk I) with a Mk Vc windscreen? Radiator - modified Mk XIV/XIX?? Is this the Spitfire III version you are making (as per photo in the last post)? Interesting to see the anti-fouling mechanism on the fin and additions to the u/c doors. That bulge above the exhausts does look a bit different, a little angular (?) - may be an optical illusion. And a Vb style spinner? Unusual prop. read the link, 10 minutes ago, Peter Roberts said: Any Aussies fly this? Hope not or I'll have to add it to the collection! Ah... now that is an interesting questions... were the any in various test programs? 1 Link to comment Share on other sites More sharing options...
Peter Roberts Posted July 22, 2022 Share Posted July 22, 2022 2 minutes ago, Troy Smith said: Ah... now that is an interesting questions... were the any in various test programs? Hmm, think there was at least one at Farnborough at one stage - bit sketchy on that and haven't looked too closely. Too many other subjects to do. Sorry for the stray off topic - back to our usual programming.. 2 Link to comment Share on other sites More sharing options...
bigbadbadge Posted July 23, 2022 Share Posted July 23, 2022 Now this looks interesting, I was ignorant of tge info you posted in your initial post re the engines too. Look forward to seeing this progress . Great start Chris 1 Link to comment Share on other sites More sharing options...
Biggles87 Posted July 23, 2022 Share Posted July 23, 2022 A different Spitfire! I’ll follow if I may. John. 🇺🇦 1 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 23, 2022 Author Share Posted July 23, 2022 @Troy Smith Not the only one. You've got me there! OK, I'll modify my statement: production Merlin powered ones didn't have the angled firewall. 😁 Dimensions: you're quite right. I think I've added about 2mm. One possible problem, you seem to have angled the upper cowling down, but this maybe just a trick of the photo. Oh crud, you're right. Worse still, the nose is now attached with a quite frightening rigidity. I don't think the upper cowl is wider, but the panel below is in closer, causing the apparent 'bulge' .... I'm mostly worried this is going to cause me to chop up a Spitfire and put my money where my mouth is ... I think we're going to have to do some more research about that blessed cowling! Cheers, Neil 3 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 23, 2022 Author Share Posted July 23, 2022 23 hours ago, Peter Roberts said: Wow, interesting project. Looks good so far. Canopy - early flat sided sliding canopy (Mk I) with a Mk Vc windscreen? Radiator - modified Mk XIV/XIX?? Is this the Spitfire III version you are making (as per photo in the last post)? Interesting to see the anti-fouling mechanism on the fin and additions to the u/c doors. That bulge above the exhausts does look a bit different, a little angular (?) - may be an optical illusion. And a Vb style spinner? Unusual prop. Any Aussies fly this? Hope not or I'll have to add it to the collection! Thank you! It seems always to have had the flat-sided canopy but the exact version I produce is going to be a function of whether I can come up with a sufficiently accurate first-pass windshield. If I can't then it'll be the slightly later version with the more traditional windshield. Similarly, the Vb-style spinner is an interesting option, so at the moment, all options are open. I don't know who flew the Mk.III but you I don't think it left the UK's shores. Neil 1 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 23, 2022 Author Share Posted July 23, 2022 13 hours ago, bigbadbadge said: Now this looks interesting, I was ignorant of tge info you posted in your initial post re the engines too. Look forward to seeing this progress . Great start Chris I have to confess that I did have to do a lot of reading to get my head around all the versions but I'm glad you found it useful! 1 Link to comment Share on other sites More sharing options...
Troy Smith Posted July 23, 2022 Share Posted July 23, 2022 4 minutes ago, neilfergylee said: I think we're going to have to do some more research about that blessed cowling! Bear in mind this was a one off prototype, and the cowlings were hand made, as nothing else would fit. This would explain possible quirks like the upper cowl bulge. Probably best not to worry too much as it's it a minor aspect. I did have a look at the same kit, and had a ponder. If i feel inspired I may have a go at carving a canopy mould, as it does look very slab sided, and this was always the sticking point for me. If work great, if not, try again. Looking at the kit it maybe possible to add new triangular side panels to an existing flat front screen, but moulding a new bit maybe easier than trying to do the joins in clear sheet, and does not mess up the kit in the process.... cheers T Link to comment Share on other sites More sharing options...
neilfergylee Posted July 23, 2022 Author Share Posted July 23, 2022 10 minutes ago, Troy Smith said: Bear in mind this was a one off prototype, and the cowlings were hand made, as nothing else would fit. This would explain possible quirks like the upper cowl bulge. Probably best not to worry too much as it's it a minor aspect. I did have a look at the same kit, and had a ponder. If i feel inspired I may have a go at carving a canopy mould, as it does look very slab sided, and this was always the sticking point for me. If work great, if not, try again. Looking at the kit it maybe possible to add new triangular side panels to an existing flat front screen, but moulding a new bit maybe easier than trying to do the joins in clear sheet, and does not mess up the kit in the process.... cheers T Interesting you say that! I've just put this together to illustrate the different versions of the windshield and I do wonder if they went for the more conventional design for reasons of manufacturing simplicity: it would have involved fewer changes to the fuselage and the windshield mounting. P.S. the bottom image has been flipped to permit the comparison: the clear vision panel was not fitted on the starboard side! Tomorrow, I intend to explore the alternatives. Cheers, Neil 4 Link to comment Share on other sites More sharing options...
Peter Roberts Posted July 24, 2022 Share Posted July 24, 2022 Note the armoured panel is now located towards the inside of the windscreen, and not prominently on the outside. Good clear photo on the bottom, you can even see the bolts securing the armoured panel. 1 Link to comment Share on other sites More sharing options...
stevehnz Posted July 24, 2022 Share Posted July 24, 2022 9 hours ago, Troy Smith said: Bear in mind this was a one off prototype, and the cowlings were hand made, Fwiw, I can't help but think the cowl was a one off, made to a different design, for reasons possibly lost to history, but obviously to try stuff out. It is obvious when looking at the Hispano Buchon cowl, there is plenty of room under a standard Merlin Spitfire cowl to make it this way, though I imagine it was found to be simpler to produce it with a flattish top & vision & performance advantages were insufficient to warrant changing the design for something involving a more complex production process. Steve. 2 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 25, 2022 Author Share Posted July 25, 2022 START AGAIN Looking at the cowling line on the windshield photos, it was very clear that mine was way too high. Therefore, I'm dismantling the fuselage and starting again. 2 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 25, 2022 Author Share Posted July 25, 2022 It hurt, especially as I'd get the filling pretty much smoothed-down but it was clear that the nose was going badly wrong with the high windshield line plus the slope as noticed by @Troy Smith. I've tried again and here is a comparison: 4 Link to comment Share on other sites More sharing options...
neilfergylee Posted July 26, 2022 Author Share Posted July 26, 2022 This looks a little better: The orange Dymo tape is there to help align the base of the windshield. Cheers, Neil 6 Link to comment Share on other sites More sharing options...
Learstang Posted July 26, 2022 Share Posted July 26, 2022 (edited) Nice work on the Mk.III! I've long had the desire to build every mark (marque?) in the Spitfire range (in 1/72nd scale), and this one is just about the most obscure. It looks like it's going to take a little more work than I had anticipated. To me, the Mk.III just looked like a Mk.I or Mk.II with the Mk.VII retractable tailwheel, clipped wings, and later the Mk.Vb propeller (and spinner). As always, things are more complicated than they first appear. Keep up the good work! Regards, Jason Edited July 26, 2022 by Learstang 1 Link to comment Share on other sites More sharing options...
Rob G Posted July 26, 2022 Share Posted July 26, 2022 26 minutes ago, Learstang said: every mark (marque?) Mark. 'Marque' is just a 2 dollar word for 'brand'. 3 Link to comment Share on other sites More sharing options...
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