Peter Miller Posted November 13, 2016 Share Posted November 13, 2016 An interesting point. I have just been told that the Twister, that look alike Spitfire, has less drag with the fixed U/C than with the retractable one and our local Twister is actually being converted from retracts to fixed gear. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 13, 2016 Author Share Posted November 13, 2016 Peter Apart from scale considerations it could be argued that the same conditions apply to models as full size where retractable u/c only really became an absolute necessity above 300 mph. I suspect the equivalent speed for models is also surprisingly high. After all the Miles M20 with the same engine and armament was a touch faster than the Hurricane despite its fixed u/c. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 13, 2016 Share Posted November 13, 2016 I'm pretty sure I read that a retractable tailwheel added 4mph to the top speed of a Spitfire. So I'm sure that retractable main wheels made a pretty significant difference. The M20 was generally better aerodynamically than the Hurricane, it almost certainly would have been significantly faster again with a retractable undercarriage! At model speeds it can't make much difference, but some planes don't look right with wheels hanging down. As far as the Super Marauder is concerned, Peter suggested that someone should do it and to me it looks like a 50s ground attack plane that needs retracts to bring out the best in it (I hope)! It's worth mentioning that most of the allied heavy bombers had top speeds below 300 mph and I think to suggest that a fixed undercarriage wouldn't have been a very significant handicap is stretching a point, to say the least. Designers then were pretty well informed on aerodynamics, they weren't following fashion. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 14, 2016 Author Share Posted November 14, 2016 Colin I think it is fair to say the design considerations between a light fighter and a heavy bomber are a bit different. The heavier a plane the relatively bulkier the undercarriage becomes yet the weight and space required to retract it becomes relatively smaller. The space and weight saved in the M20 allowed it to carry significantly more ammunition & fuel giving it nearly twice the range of either the Hurricane and Spitfire. On the other hand the M20 had a thick wing, 21% at the root, so even more surprising it was faster than the Hurricane but presumably it had a lower drag wing section. This probably accounted for its higher stalling speed (80 mph even with flaps down!) despite having the same wing area and weight as the Hurricane. This higher landing speed probably contributed to its end after failing to stop on a snow covered Woodley airfield. Ooops! I have not seen this picture before. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 14, 2016 Share Posted November 14, 2016 A bit different yes, but not totally different. And don't mention the Stirling! The Martin Baker MB2 also had a good turn of speed with a fixed undercarriage. It doesn't mean it was the right thing to do. I can see where the P51 would have finished up if they'd decided that a fixed undercarriage would have enabled it to carry even more fuel and ammunition! Whatever the size of the plane the fact is that a fixed u/c increases frontal area and you can fair it all you like, you will never eliminate that. I looked at the Twister web-site and the fixed u/c option is said to reduce weight and complexity. It also takes about €4,000 off the price, it certainly won't make it any faster. The main problem with the M20 according to Eric Brown was a lack of manoeuvrability. The Spitfire, Hurricane and Martlet could all turn inside it. He describes how in a turning contest with a Hurricane it stalled out of the turn at 190mph, so it doesn't sound as if it had much chance of being a good dog-fighter. He also said that the wooden construction wouldn't have been good for carrier use. I haven't seen that photo before either. The plane was clearly repairable, but as it had been rejected it wouldn't have been worth the bother. It looks like the first prototype, I don't know where the second navalised version finished up! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 14, 2016 Author Share Posted November 14, 2016 The RH aileron cutout from the wing and fully skinned with a 6 mm Depron leading edge. It has been profiled to suite a low hinge line to be a "Frise" type which limits adverse aileron yaw even with equal deflection up and down. Have to wait for the servo to be delivered before going any further. The other wing is constructionally not far behind. The 2.5" wheel built up from 4 layers of 6 mm grey Depron. Its two inner layers are cut as thin rings so the Depron "tyre" is actually hollow. The same wheel after sanding to shape on a mandrel and painted acrylic black. It weighs 2.9 g (0.1 oz). Edited By Simon Chaddock on 14/11/2016 16:29:05 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 15, 2016 Author Share Posted November 15, 2016 It appears the second prototype M20/4 was built in 1941, after the first had crashed. Initially as a private venture, possibly from the remnants of the first prototype, although later covered by Navy specification N1/41. It was scrapped in Nov 1942. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 16, 2016 Author Share Posted November 16, 2016 The barn door aileron 'pin' hinged at each end. Easier to paint it before being put in place. I had originally intended to use a conventional push rod and horn but as there is sufficient space in the wing I am tempted to use a 'direct drive servo' system as I did on the Petiterina. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 17, 2016 Author Share Posted November 17, 2016 The aileron 'direct drive' system under test. It really does give about the freest moving and least drag installation possible and as a by product there is nothing to get 'snagged' either. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 17, 2016 Share Posted November 17, 2016 It's certainly an effective method Simon. What paint are you using? I assume that you are painting straight on to the Depron again. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 18, 2016 Author Share Posted November 18, 2016 Colin Its Scola acrylic gloss, about a fiver for 500 ml. Its a water based emulsion so safe on Depron but unlike household emulsion it is completely water proof when fully dry. It needs two coats on the 'shiny' surface of standard white Depron. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 18, 2016 Share Posted November 18, 2016 Thanks Simon. I've just found an offer on Amazon for 6x150ml bottles of different colours for £10-55, so I've ordered that to mess about with. The Super Marauder is going to be covered so I don't need it for that, but there's something else I'm thinking about. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 19, 2016 Author Share Posted November 19, 2016 Still waiting for the 5 g aileron servos to complete wings so need to work out how they will be joined when they are completed. A 3 part dihedral brace. The middle fits inside the box spar and is itself a balsa/Depron/balsa sandwich. The outer balsa parts glue directly on the the outer edge the spar flanges but will be within the thickness of the 2 mm Depron wing skin. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 22, 2016 Author Share Posted November 22, 2016 Still waiting for the servos so I made a start on the tail plane. An all Depron structure with 2 mm Depron skins. To achieve a reasonable strength and stiffness it is quite thick (16 mm) at the root. The elevator halves will be joined by a glass fibre tube as in the Petiterina. Quote Link to comment Share on other sites More sharing options...
onetenor Posted November 22, 2016 Share Posted November 22, 2016 One must remember the Vampire was constructed like a Mossie. Ply balsa sandwich over male moulds so relatively light. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 23, 2016 Author Share Posted November 23, 2016 Not much to show today, just the elevator halves nearing completion. Built in practically the same way as the tail plane. All Depron, 2 mm skins and ribs with a 6 mm leading edge.. More as a test than anything else the tail plane has an upside down semi symmetrical section. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 23, 2016 Author Share Posted November 23, 2016 The tube joining the elevator halves. A thin wall glass fibre tube filled with Depron to give a greater gluing area. As before the tube also acts as a large diameter 'pin' for the centre hinge. Light and hopefully rigid enough the complete tail plane will weigh under 20 g. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 23, 2016 Share Posted November 23, 2016 Simon, do you plan to move the c of g forward a bit, with the reverse aerofoil section on the tailplane? Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted November 24, 2016 Share Posted November 24, 2016 He will pnly need to apply a fraction of down trim to make it symmetrical. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 24, 2016 Share Posted November 24, 2016 Peter, Simon always has a cunning plan and it's usually ingenious, so I'm intrigued! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 24, 2016 Author Share Posted November 24, 2016 Peter and Colin Well I don't know about a cunning plan but the Depron Ballerina looks like it is going to be seriously light with a ridiculously low wing loading which will allow controlled flight at low speeds and high angles of attack. In general I have found such a configuration tends to run out of 'up' rather than 'down' elevator hence a potential benefit from an asymmetric tail plane section. Whilst quite plausible and in part born out from experience with the Petiterina the biggest driver was it was simply easier to build a double tapered one piece structure with a predominately flat surface on one side! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 24, 2016 Share Posted November 24, 2016 Ahh! I knew there was a cunning plan. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 25, 2016 Author Share Posted November 25, 2016 The completed tailpane with hinged elevator. 17" (430 mm) span it weighs 16.3g. The 'direct drive' aileron servo installed. That really is a huge surface for a 5g servo! Just as well the Depron Ballerina is going to be seriously light. Only a guess at this stage but hopefully no more than 24 oz (650 g). Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted November 25, 2016 Share Posted November 25, 2016 First class Simon. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted November 26, 2016 Share Posted November 26, 2016 Yesss... very impressive piece of engineering, Simon. Cheers Chris Quote Link to comment Share on other sites More sharing options...
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