Rob Ashley Posted January 30, 2018 Author Share Posted January 30, 2018 True Tim - I'm sure there are better rants on here - I guess I have had time to process it all so my rants have faded out. However - the positive is I am building models again. I have even cajoled my 12 year old into making a flat plate delta design for a bit of fun. You must be nearing the maiden flight for your GTC? Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted January 30, 2018 Share Posted January 30, 2018 Rob , posted 4 times; that’s nearly a rant 😉 Still got some covering and trim to do yet. Then it’s a matter of weather and plucking up courage at the same time ! Took my skywriter for a couple of flights today just to prove I can still fly. Tim Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted January 30, 2018 Author Share Posted January 30, 2018 Wow - Not sure how I managed that? Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 4, 2018 Author Share Posted February 4, 2018 I managed some progress this week. After putting the wings aside whilst giving the propulsion problem a stern head scratching I cracked on with the fuselage. The CNC'd formers fitted perfectly and were a pleasure to build with, just needing cyano for the balsa ones and epoxy for the 2 ply ones that take the stresses of holding the wing in. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 4, 2018 Author Share Posted February 4, 2018 A few evenings later I managed to put the remainder of the bulkheads in got a little further. Then it was onto planking. Now I'm not really a great fan of it but I do agree with Peter Miller that it can be therapeutic - but for me that's only when it goes well. I'm reasonably content with the result so far - just needs some sanding. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted February 4, 2018 Share Posted February 4, 2018 That is looking very nice. Try planking Destiny!! Very tedious but extremely satisfying when complete Edited By Peter Miller on 04/02/2018 18:08:16 Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 4, 2018 Author Share Posted February 4, 2018 Hey - thanks Peter, Destiny is on my to build list. Quite far down at the moment but it is on there. Is there anyone who can check my calculations/guesstimations for an electric conversion? Please? My GTC version is 68" span with tgt weight of 6 1/2lbs. I was going to put in 2 x OS 32s (until one of them blew a cylinder liner) and OS claim the output is 1.2hp (!) at 18000rpm and props from 9x6 to 11x6. A good starting point of 1492 Watts or 229 watts per pound!?. Seems excessive. Going another way and using 120 watts per lb for sport aerobatics gives me 6.5x120 = 780 Watts. A little more than half I would have had from the IC engines. As this is a twin I can divide the power between 2 motors and plumb for 400 watts of power. If I buy 2 motors that can deliver a max of 665 Watts each and a max of 46 Amps (from the manufacturers specs) but that would be 60 Amps on a 3S. But that watts would be determined by the prop and voltage of the battery wouldn't it? I am thinking of buying two motors that have 1250kv which would drive a 10x6 prop on a 3S battery (13,750 rpm) or alternatively a 790kv motor that would turn a 12x12 prop at 8690 rpm. Any thoughts or suggestions gratefully received - I'm getting bogged down in the choice available to me. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 4, 2018 Author Share Posted February 4, 2018 I guess my next question is when the manufacturer quotes a max amps for the motor that means that is the max the motor can draw safely? Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted February 5, 2018 Share Posted February 5, 2018 Based on my very limited experience of buying good electric motors and ESCs a couple of SC 32s would be cheaper!!! When I bought the motors and ESC for Easter Eagle Sr my reaction was "Ye Gods!!!! I could buy a good used four stroke for that!!" Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 5, 2018 Author Share Posted February 5, 2018 Very true Peter - my forays into electric so far have shown that electric is more expensive to start with. I guess my thoughts to change were based on frustration with loosing a really nice IC engine. I have bought 2 motors and ESCs with plenty of capacity in the ESCs to upgrade the motors if I need some more thrust from a larger prop. Although I am tempted to buy some SC engines I think I will stick to electric for this model - it was always intended as a very nice test bed for my in progress BT Mosquito. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 5, 2018 Author Share Posted February 5, 2018 Right - Canopy time. I made a plug from some pine I had lying around and cut the outline shape on the bandsaw. A quick tickle with the belt sander and some hand sanding produced this. I tried the plastic bottle method and spent ages trying to shrink it with an old hair dryer. Realising this wasn't cutting the mustard I let rip with a paint stripper. MUCH better. I melted the very end of the plastic on my first run but will have another go tonight. Couldn't resist a dry fit of components. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted February 5, 2018 Share Posted February 5, 2018 Rob, Let me say I am no expert on electric power and although I have a few electric models I have only actually sized the motors for 2 of them myself. First one was last year’s skywriter build. I went with a 700 W motor in a 5.25 lb model giving 133 W/lb. It was dam near ballistic and you had to be very careful how you fed the power in or you could generate most unwanted Aeros. I suppose I am a bit of a wimp but having reduced the power by 70% by altering the Throttle curve it became altogether more pleasant and still loops from level flight with ease. Second one will be this years GTC . So this time I was aiming at 90 -100 W/lb. I also checked the static thrust of my setup with the motor supplier and a total of 6lb seemed reasonable since I was aiming at coming in @ the 6lb mark. I have yet to weigh the final result but having got a little carried away with cowls and all I am now expecting 6.25lb. That means the max figure will be more like 85-90 W/lb . I am a little nervous I have gone too far the other way . I may see what it is like on 2 blade props for the first flight or if it feels wrong on a fast taxi I may even re- engine before the maiden. We will see. Doubt any of that helps you much but there you go. Tim Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted February 5, 2018 Share Posted February 5, 2018 Well, although Grumpy is amazing on one engine electric will take away any worries on that count. THat pattern looks nice. I use a hand held power plane and sanding discs in a power drill and I really do not enjoy it. The old Solarfilm heat guns worked but I now have a proper stripper which works well. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 5, 2018 Author Share Posted February 5, 2018 Hi Tim, That really does help - thanks. It gives me a little more confidence in what I am doing. I bought 2 x 430 Watt motors and assuming a 7lb model will give me 122.8 Watts / lb. So theoretically there is a little spare power if the weight comes out a little higher. This may also be slightly overpowered which should mean lower throttle and longer flight times. Only flight testing will see. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 5, 2018 Author Share Posted February 5, 2018 Peter, I'm feeling a little more confident about the power train I have picked - I 'spose I can always add a bigger motor if needed, but to know she will fly on 1 engine well is comforting. I must admit the belt sander made a huge difference to the proceedings, as did the bench disc sander when I could keep my knuckles away from it... takes off skin quite quickly, so it appears. I think I would loose my fingers if I used a power planer..... Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted February 18, 2018 Author Share Posted February 18, 2018 Well not much progress for a couple of weeks. I have bitten the bullet and changed to electric motors after much deliberation. Problem was my firewalls were cut for IC motor mounts so looked like this: Still complete with hole for needle valve. After a little thought, and as I had the holes and F1 already drawn in CAD, I re-drew another F1 to accept the X shaped electric motor mount. Next problem was the standoffs. I had to wait a while for the 70mm M3 screws to arrive and source some alu tube of the right inside diameter. End result was this: I can now bolt this to the original firewall using the IC T nuts and holes which should allow access/servicing. The standoffs were cut on the bandsaw, with careful sanding and electronic Vernier gauge I could get them to within 0.05 mm of each other. Took some time but I am happy with the results. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted February 19, 2018 Share Posted February 19, 2018 Good you are on track again Rob. Looks like a professional job on the standoff. Makes me think I must have cheated by buying mine ! Tim Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 10, 2018 Author Share Posted April 10, 2018 OK so it's been a while since any work was done on my GTC, but I have completed some projects in the house, made some retracts for a HE111 and designed & started to build a delta with my son...Oh and replaced an engine in a mates model too. I have finally made some progress with the nacelles - for some reason it was one of those jobs that I just didn't want to face - don't know why. I guess because of the late stage change from IC to elec and the alterations needed to fit the battery, ESC and motor into where the fuel tank and engine were originally. It was simple really and as I say I don't know why I didn't want to do it. They look a little square and need some TLC with the sanding block but at least the project is moving forward. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 10, 2018 Author Share Posted April 10, 2018 I guess I felt guilty that Levanter was catching up rapidly and needed the motivation...? Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted April 10, 2018 Share Posted April 10, 2018 Nice work Rob. What prompted the late change from IC to electric and which motors are you using, or are they 'under wraps?!' Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 10, 2018 Author Share Posted April 10, 2018 Hi Piers, I swapped to electric because the engines I was using (OS 32 SXs) stripped their chrome cylinder linings. Alas they are not available anymore so I used that as an excuse to change this plane to electric. I fully admit I know nothing about electric, so after some research and a lot of head scratching I bought some Turnigy D3536/8 1000kv motors and 60Amp ESCs. I calculated that with my anticipated AUM (plus a little) these would provide 120 watts per lb which should be more than enough power. I know Tim Ballinger's GTC flies very nicely on less watts/lb so I think/hope I have got it right. Best, Rob Quote Link to comment Share on other sites More sharing options...
Levanter Posted April 10, 2018 Share Posted April 10, 2018 Hi Rob. With all those projects you have hardly been sitting on your hands! You have a lovely GTC coming along and what with Tim's larger version as well, mine is feeling a bit more like a Grumpy Tiger Kitten. I know exactly what you mean about the nacelles. I think part of the problem is having to do two. One is fine because it doesn't have to match anything but as soon as a sibling comes along everything changes. Bit like real life I suppose. What diameter is your wing dowel? It looks thin but that might just be the photo. It seems like we might start covering at roughly the same time but at the moment I am really short of ideas. What are you going for? Inspiration much needed. Levanter Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 11, 2018 Author Share Posted April 11, 2018 Levanter, True - but I CNC'd the frames of my nacelles so it was really the task of taking off the ply nose ring and adjusting to suit the elec motors, then filling in the side where the engine would have been and placing a hatch underneath for access to the elec motor. I am also going to add a scoop on top with the air flowing through the nacelle, over the motor, ESC and battery then exiting through the rear of the nacelle. Looking at the photo it does look like the dowel is small. It is an 8mm hardwood dowel. I tested a few different sizes a year or two back and with this I can pull 80 kg before it deforms but couldn't snap it. Oddly my tests showed I can use a single 1/4 in size dowel on this model and with my anticipated AUM it will shear at approx. 25G - way more than the wing will stand - hopefully one would only record this high level of G during a crash.... Rob Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 11, 2018 Author Share Posted April 11, 2018 Ok so no model stuff today but as it wasn't raining for the first time in 11 days I thought I crack on with the workshop extension. A wasted 5.5ft x 12 ft at the back of the current building seemed, well - a waste so floor down and with some help from the kids framing too. A full day of work and the floor and framework is almost complete. I need to add a window and then clad with shiplap. If the weather holds - it is the UK and spring right so it's likely to rain - I will complete tomorrow so I can get back to the GTC. Quote Link to comment Share on other sites More sharing options...
Rob Ashley Posted April 11, 2018 Author Share Posted April 11, 2018 Levanter, Sorry missed the last part of your post about covering. I have bought some bright yellow and navy blue Oracover so I was going to emulate Peter's original with top of wings in yellow but with blue underneath then have yellow triangles on the underneath LE of main wing and tail with the opposite in navy blue on top LEs . I think I have just confused myself. Basically copying Peter's but with the 'teeth' on the LE on top and bottom on main wing and tail. As for size - I'm sure yours will have as much growl as the larger versions. Rob Quote Link to comment Share on other sites More sharing options...
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