Chris Walby Posted January 10, 2021 Share Posted January 10, 2021 Well folks as the club mass Ohmen build edged towards completion last year a couple of us thought about the next build. If you don’t know already then it will soon become apparent that I have a preference for ic twins and although this build will be electric it is at least a twin. There are already a few build logs here for ic versions (as per the original design) and electric plus scaled up with retracts and flaps, but for me it will be a straight as possible standard build. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 10, 2021 Author Share Posted January 10, 2021 Boring for the experienced builders out there although I would like it to be helpful to those like me who don’t have decades of building under their belt and want a proven good flyer Cheat 1 – Kit purchased from Sarik last year Cheat 2 – Electrical bits purchased from 4-Max last year Cheat 3 – Read through all of the build logs here to gleam any information I could For those that aren’t familiar with Peter Miller’s Grumpy Tiger Cub its vital statistics are: Wingspan: 53in (2125 mm) Weight: 4 lb 11 oz( 2.126 Kg), Wing area: 500sqin( dm2) Wing loading: 21oz/sq ft ( g/dm2) Servos: 4max 2x 10g and 2x 45g) Retracts: Fixed Motor: 4-Max 3035 870Kv ESC: 30A x 2 + 5A UBEC Prop: 9x6 tractor and pusher Battery: 4 S 3700mAh (I have 4S3300 so will use those) Calculated thrust (4max) 4.6 lbs (weighs 4.68 lbs) 2068g Calculated speed 62 mph Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 10, 2021 Author Share Posted January 10, 2021 Lets start the build and hope I can keep the building work with the pace of posting updates Things to consider pre-build Canopy from Steve at Vortex, big thanks as there was so waiting due to COVID 19 but no rush and good job Modification of the cowls/nacelles to suit the electric set up Modification to the fuselage for the battery access Nothing major and looking at the drawings it has Peter's signature design/construction style throughout which is reassuring from the experience gained from the Ohmen build and limited overall experience. I will be using the plasterboard and plastic sheet method of bas board and dusting down the SLEC board for the fuselage once I have cleared enough bench space. I thought I would get clever and attach the drawings on both sides of the plaster board which does limit the “I just need a peek to check that” if there is balsa and pins stuck in. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 10, 2021 Share Posted January 10, 2021 Posted by Chris Walby on 10/01/2021 07:55:01: Wingspan: 53in (2125 mm) Hey Chris, ... it seems that the inches are quite a bit larger in the UK than they are on the Continent... ... but then that's probably the reason why I'm still an apprentice modeller... Cheers & keep the faith Chris Quote Link to comment Share on other sites More sharing options...
Piers Bowlan Posted January 11, 2021 Share Posted January 11, 2021 Chris, You say you 'purchased the kit from Sarik last year'. I can't find it on their website only the plan, was it a one off? Nice looking model, following with interest. Quote Link to comment Share on other sites More sharing options...
Levanter Posted January 11, 2021 Share Posted January 11, 2021 Posted by McG 6969 on 10/01/2021 09:42:50: Posted by Chris Walby on 10/01/2021 07:55:01: Wingspan: 53in (2125 mm) Hey Chris, ... it seems that the inches are quite a bit larger in the UK than they are on the Continent... ... but then that's probably the reason why I'm still an apprentice modeller... Cheers & keep the faith Chris Hi Chris (The one from Belgium) You forget that since 1st January 2021 we can make our inches as big as we like Levanter Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 11, 2021 Author Share Posted January 11, 2021 Thanks for the feedback and having checked it would appear that the incorrect conversion (Trump) factor was used resulting in a wildly inaccurate wingspan, the correct size should be 1346 mm. Piers, I have PM'ed you regarding your question. The build continues with assembly of the nacelles and the wings. Only mod to the nacelle was a large hole cut in N2 to allow the ESC control wire through as the power cables will traverse via the unused aileron pushrod/bell crank rib holes. I'll be using in wing aileron servos just in case I fancy a bit of flaperon or differential later on. Oh and I made the motor stand-off on my 1940's Myford lathe. Nothing to report on the wing build, all standard assembly with just the wings to join and nacelles to fix later on. Edited By Chris Walby on 11/01/2021 11:40:18 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 14, 2021 Author Share Posted January 14, 2021 On with the build and having moved more static useful items (rubbish, parts, materials for other projects and tools) from the end work surface I set the SLEC building board for the fuselage assembly to start. This has the benefit of allowing work on the wings and nacelles all to be progressed at the same time! Fuselage would be easy except as this will be electric it will need a battery hatch in the nose. I want the flexibility to move the lipo between F1 all the way back to under the LE of the C of G even to the point moving the rubber/elevator servos by a bit (deal with that later). The plan is to make F1 and F2 out of ply and open F3 out to allow the lipo to pass through in either orientation. Then build the fuselage with the intension to cut the top off F2 to form a hatch from F1 to F3 as I need the length to feed the lipo in and then move it about to achieve C of G I’ll add a photo of the fuselage shortly once I get back in the workshop. Edited By Chris Walby on 14/01/2021 07:09:49 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 14, 2021 Author Share Posted January 14, 2021 On to wing joining and this went without issue, the drawing says dihedral of ½ inch under each tip although I was told that in previous thread discussions it should be an inch under each tip. I went with the drawing and the supplied brace on the basis that it was easier and generally more dihedral make it more stable right way up and less when inverted! Off topic but I have loads of fun with my foamboard Nutball (flying disk) with massive dihedral trying to fly inverted with rudder and elevator only controls! Look at supports for the aileron servos mounting plates (more of that later). PS - Nacelles dry fitted as I was still working on the first LE strip, but more on that later. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 16, 2021 Author Share Posted January 16, 2021 Had to have a bit of a chuckle as I finished of the last of the motor stand off’s as it was a bit of touch and go with the ali stock (leftover included). Dad would be proud with the lack of waste and no option of making a mistake. . Talking about the nacelles I was having a think about making them removable and added a ply plate against N1 then screwed it from the back. Okay it will be fiddly when all assembled, but at least won’t mean breaking the cowl to remove it. Nacelles have proved a little more interesting as I was intending on to strap the ESC to the stand offs, but when it came to the cowl construction its was obvious that's not going to work. The ESC's can go where the tank has vacated and that brings me on to the cooling requirements. Perhaps a small chin scoop on the cowl and another scoop where ESC will live. The back of the nacelle underside is sloped and a larger exit scoop should work ok Balsa glued to get the general shape and I'll add a more for the shape/scoop. ….Order the covering film.... Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 22, 2021 Author Share Posted January 22, 2021 Sort of decision time as the covering arrived after a couple of days in the post. Peter’s was yellow, but then I thought tigers are orange and then that go me thinking that bight be hard to ss and the stripes won’t show up. Then I thought it could not be any worse than the Extra Slim Twin that is translucent yellow and appears to change orientation depending on the sun shining through the covering and open structure wing. The votes are open Traditional yellow Tiger orange Along the same theme I contacted one of my fellow club members who has a film cutter and likes a challenge (not sure if that’s me or the decals). Anyway he has come up trumps with these which look spot on to me. And now back to the build Nacelles trimmed to fit the wings Fuselage battery hatch build (planked, now that’s an interesting technique that needs to be practiced once retired as it’s a bit time consuming Fit snakes Fuselage turtle deck formed (balsa sheet dampened and masking taped to formers, once dry then same again on the other side. When both are dry, cut and glue in place Glue and sand motor cowls I’ll attach some more photos on the next post. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 23, 2021 Author Share Posted January 23, 2021 And a bit of wiring for good measure before sheeting. Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 23, 2021 Share Posted January 23, 2021 You are doing a great job. I know that it is a bit cramped for electric power really. You have done a really neat job on the planking. There is just enough to get some experience of planking which is a really useful technique. Then you can try my Destiny Only joking Edited By Peter Miller on 23/01/2021 08:38:00 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 23, 2021 Author Share Posted January 23, 2021 Hi Peter, No real issues with the electrics as the motors are small volume compared with IC, no tank so the ESC has loads of space, battery in the fuselage. There are other ways, but George's (4-Max) seems the most elegant although at some point it will light a fire of controversy. Only real mod is the hatch for the battery as the wires go down the aileron rod hole in the ribs + plenty of room for the servo cables down their paper tube. The big question will be to leave the Elevator/Rudder as plan or move them back for more flexible location of the battery. My gut feeling is it will need the battery as far forward as possible and if that's the case the servo can go in as plan. I can't quite see where the nacelles go on the Destiny (only build twins ) and the planking looks nice. Is it any lighter than rolling sheet or just better and complex curves? Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 23, 2021 Share Posted January 23, 2021 Hi Chris I agree that George always has the best answer. I never worked out an electric conversion for Grumpy Tigercub. I think another electric conversion was dione but can't remember it. I hate to say it but once a model has been and gone I usually don't remember a lot about it. I have even looked at a picture and thought "That is a nice little model!" and then realised that it was one of mine. With a fully compound curve shape such as Destiny planking is the only way I can think of doing the job but then, back when I started building models planking was the only way to do the job unless you wanted to hollow out vast lumps of balsa. (Jim Walkers Fireball was a classic example of that!!!!) Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted January 23, 2021 Share Posted January 23, 2021 Peter, you could be thinking of Tim's excellent build: Here PS Peggy Sue 2 build coming along nicely and it will be electric! Edited By Ron Gray on 23/01/2021 21:51:22 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 24, 2021 Share Posted January 24, 2021 Of Course!!! Tim did a sensational job with the retracts etc. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted January 24, 2021 Share Posted January 24, 2021 Peter, Not sure about sensational but I certainly enjoyed myself messing around with your Grumpy Tigercub . After all my mods I refer to it as the Grumpy Tigercat ! Managed a few outings with it last year despite the lockdowns, really great fun to fly. Fun watching other folks build logs of the same basic model so I have been following this build , thanks Chris. Tim Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted January 24, 2021 Share Posted January 24, 2021 My ‘oversized’ build keeps getting put back but I will get round to it! Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted January 24, 2021 Share Posted January 24, 2021 Only slightly off topic, sorry Chris (But it is about another twin). Ron , did you get your Laser powered ESM Tigercat sorted to your satisfaction. I seem to remember some engine tuning issues last I saw. Tim Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 24, 2021 Author Share Posted January 24, 2021 The point of this build thread is so that if a newbie were to decide to build an electric twin (as close to the original design) without resizing or adding bits like flaps or retracts they could with the minimum of off topic departures. Sorry but its one on by bug bears where a thread heads off topic (some for pages) and it makes the read very disjointed. Tim's runs to 18 pages and while useful it heads in all kinds of IMHO unhelpful directions. Ron's thread is here **LINK** Building continues with sheeting the upper and lower wing surfaces, only departure is to a fully sheeted wing. Sue's Ohmen was a bit of a nightmare with the semi sheeted wing and applying the decals with positioning and possible puncher of the covering. Glued the nacelles in at the same time and the (found in the bits box) pre made LE strip. Grumpy's mate thinks he will need to go on a diet to fit Edited By Chris Walby on 24/01/2021 16:52:46 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 24, 2021 Share Posted January 24, 2021 Yes,I have noticed that some threads do tend to be hijacked. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 28, 2021 Author Share Posted January 28, 2021 With the top sheeting completed I moved on to adding the aileron hinge blocks, a replacement balsa block where the central aileron servo would go (using servos in the wings) and the TE blocks. After that it was a case of gluing the nacelles in and sheeting the underside. Moved on to the nose and laminating the wingtips prior to shaping Minor clash with the wing bolts to snakes and no issue, will just have to remember if I ever change a wing bolt to cut it down to the right length. Question for the modellers out there? As its electric it was supplied with a standard and pusher prop, but which goes where? Hope you know your cats before answering? And will it make a difference on the GTC? Quote Link to comment Share on other sites More sharing options...
chris larkins Posted January 28, 2021 Share Posted January 28, 2021 On a full size the props spin with the blade going down next to the fuselage, there is a reason for this but without resorting to google I can't remember why. So looking from the nose of the model the left motor would be clockwise and the right motor anti-clockwise Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted January 28, 2021 Author Share Posted January 28, 2021 Hi Chris.....It was a trick question as Tiger cats have them the other way around to resolve a pitch stability issue IIRC. And part 2 of the question....would it make a difference to the GTC (especially as peter designed it for IC) to have them either way? Quote Link to comment Share on other sites More sharing options...
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