Martin Harris - Moderator Posted March 21, 2021 Author Share Posted March 21, 2021 Thanks Nick. I certainly realised that the tests weren’t a test of torsional strength but empirically, I think that diagonals will impart a lot of resistance to twisting for a small weight penalty- the difference was quite noticeable after adding the lightweight ones to the tailplane. The trusses are the full height of the ribs so provide resistance to twisting. As you infer, this isn’t intended to be thrown around like an extra and it’s “raison d’etre” is to emulate single channel, blip throttle operation as per the old MacGregor outfit. I can always build a D box based aileron wing with scale dihedral later if I feel the need! I have to keep reminding myself that this isn’t a pukka scale build! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 21, 2021 Author Share Posted March 21, 2021 17 hours ago, Danny Fenton said: I have also heard that tissue over laminating film adds more tension. I am sceptical but have not tried it. I believe the issue is the bond with the surface, dope soaks into the surface, and its true the structure is much stronger than using conventional iron on films. There have been a few suggestions for this method - one that I did consider but with similar reservations. I know that we used to use tissue paste for initial adhesion - I still have an unopened tube from "back in the day" - but I think this was more to do with applying the damp tissue and like you, I suspect the real adhesion is in the doping. This would be born out my experience with recovering the ruddervators of a full sized SHK glider that I had a share in back in my transitional period from models to full size where I volunteered to re-cover them in my model "workshop" (you might call it a bedroom!) after the original fabric failed a C of A inspection. They looked just like a pair of large model wings but did the opposite of most models which seem to shrink when you get them to the field - they seemed enormous as I took them upstairs! I still lived at home then and my mother was complaining about the aroma of dope for days afterwards! The directions from our inspector about fixing the Dacron (not much different to the nylon covering I'd used on models) were to pre-dope the structure and then apply the fabric, brushing dope onto it over the wood, which would re-activate the dope which would be thoroughly impregnated into the wood. The glider is still in regular use over 40 years later (whether or not it's been recovered since, I can't say) so the dope was certainly up to the job. The SHK shortly after re-covering the tails but before repainting. No point going to the bother if it didn't work! ? 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 22, 2021 Author Share Posted March 22, 2021 A lovely flying day - so I’ve moved out to my workshop to start on the wings... ‘er indoors has been exceptionally accommodating over the last couple of weeks but the full size building board on the kitchen table might be a step too far! I’m just giving the aliphatic time to dry after framing the port wing - although I’ve used cyano for the balsa/balsa joints. Assembly before adding gussets and half a bottle of cyano! After reading several reports that these models have a reputation for wing failures at the centre section joint, I’ve elected for a spruce main spar which as well as providing additional bending strength should go a little way towards improving resistance to the aerodynamic twist that I’ve been a little concerned with. It’s adding about 20g to the AUW but I think it’s worth it. Like other aspects of this build from what may be untested templates, a fair amount of fettling of components and dry assembly was required but it seems to be coming together reasonably well now. 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 22, 2021 Author Share Posted March 22, 2021 How does the old song go? “One wing on my (Sky)wagon”... One done and the other is pinned to the building board. I did notice that (presumably) some distortion has crept into the original wing plans during the copying or printing process and the wingtips were misaligned by half an inch so once the port wing was off the board, I turned the plan over and anointed it with diesel (between cling film) to bring through an exact mirror image - something that worked really well with my Airsail Chipmunk build some years ago when I followed the instruction to use paraffin. I'm quite pleased with the way the spars and braces fit and interlock - despite the numerous little niggles in the cutting patterns this area worked beautifully and everything aligns perfectly - its not glued to the centre section yet.. Having assessed the (uncovered) flexibility, I’ll turn my attention to some diagonal bracing tomorrow. I’ve just remembered that the song goes on to mention Cherokees (and Pioneers). 2 Quote Link to comment Share on other sites More sharing options...
Nick Cripps Posted March 23, 2021 Share Posted March 23, 2021 Flaming spears, Around my ears... 1 Quote Link to comment Share on other sites More sharing options...
Eric Robson Posted March 23, 2021 Share Posted March 23, 2021 (edited) As long as you keep on rolling along. I have covered wings like that with solar film and they have been OK I was banned from doping aeroplanes when we lived in a terraced house with out a garden and shed. As with doping beware of wing warps. Edited March 23, 2021 by Eric Robson Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 23, 2021 Author Share Posted March 23, 2021 There wouldn’t be much option! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 24, 2021 Author Share Posted March 24, 2021 After yesterday’s musical interlude I spent some time today adding diagonal bracing to the wings and it's made a real improvement to the torsional rigidity. Don't you just love it when a plan comes together... I diverted to the tail end and dry hinged the elevator to give me a break from wings Back to the wings a bit later and time to join them. Luckily I had plenty of dihedral in stock... ? While it destroys any pretence of scale, at least it should make it turn... Go on - admit it, we all like to do a trial assembly! I suspect I'll be doing a lot of sanding tomorrow although I do have some more work to do on the rear end. The excuse for the trial assembly was to give me some idea of the likely C of G. With just the engine in place, the fin/rudder balanced on the tailplane, and a couple of pound coins on the elevator hinge line it balances less than an inch from the leading edge so with the plan's very specific "about a third chord" guidance, I'm looking at a fairly comfortable radio installation even after covering the tail end, with the servos tucked away at the rear of the cabin and no added nose weight. 2 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 24, 2021 Share Posted March 24, 2021 Dry fits should be mandatory ? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 25, 2021 Author Share Posted March 25, 2021 Returning to the dodgy musical references, remember this line - or something very similar - from a popular song in the mid-seventies when I first encountered the 180...“Mercy sakes alive, looks like we’ve got us a Cessna” ? The dry fits, with the exception of the yet to be covered control surfaces, have been replaced with glue and the basic structure is complete, including locating the wing fixing bolt and making the dummy wing struts - I’ve updated the fixing method from the original dressmakers snap fasteners to modern neodymium magnets. While on the subject of modern materials, I have to say that life is so much easier than when I first built the Cessna - particularly with CA taking the place of balsa cement (which was specified for every part of the original structure) and judicious use of aliphatic and epoxy. Permagrit tools make shaping and adjusting fits so much easier too. My 1/8” spar slotter has been invaluable. Next on the agenda should be the radio fit and once I’ve finished making holes, final preparation for covering. 1 Quote Link to comment Share on other sites More sharing options...
Nick Cripps Posted March 25, 2021 Share Posted March 25, 2021 Looking good, Rubber Duck! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 25, 2021 Author Share Posted March 25, 2021 ? “Ain’t she a beautiful sight?” ...unlike the engine, which although to the best of my recollection was running perfectly the last time I used it, was as rough as a badger’s armpit when I tried turning it after removing the plug and dropping a little oil into it. The carburettor barrel was stuck fast and needed a good boil to get it loose. I thought this was a good time to address that as I've just started on the throttle linkage and servo installation but not having attempted to turn it until now, the engine came as a surprise. New bearings are on order. There's no significant rust in the bearings so I can only assume that it’s old castor that was in the engine from its previous life and has hardened during storage - both bearings are gritty but the front one is worse. The bore and piston are in excellent order and I've run the parts through my ultrasonic cleaner to dislodge any remaining flakes of castor. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 25, 2021 Author Share Posted March 25, 2021 Not much to report tonight. I’ve started the radio fit which I find usually involves a lot more thinking than action. This may not be the case for everyone - I remember a conversation at the club where someone claimed it didn’t take him more than an hour to do the job. Oddly, his models often suffered from unexplained crashes... On a model of this size and weight, I have no qualms about using snakes so have opted for their convenience. This end will have Z bends - simple, light and reliable. I'm trying to keep the installation at low level in case I decide to add some internal detailing. Not too long before I start covering... 1 Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted March 26, 2021 Share Posted March 26, 2021 Nice and neat Martin. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 27, 2021 Author Share Posted March 27, 2021 I was busy most of the day fitting the control linkages, magnets for the top cowling retention and a myriad of little odds and ends, rubbing down etc. but having removed all the extremities in preparation for covering it looks like I’ve gone backwards! The only unusual thing to report is that having used light balsa I felt that the fin and rudder were a little on the flexible side so after some thought, I added what I’d call a cricket bat handle reinforcement of thin carbon fibre strip in the fin after slitting it carefully with a razor saw and some additional support on the fuselage - a little messy but a lot less messy than having it fail in flight! The result feels a lot stiffer. I’ve given it a light sanding - you can see the carbon dust where it just touched. I might run a second piece up the trailing edge as well if I can make successful slits for the hinges to pass through - there’s a small overlap area available under the tail cone to locate it. I very nearly had a rather nasty encounter during this exercise when I was looking for some appropriate carbon fibre - I keep oddments in an old cardboard postal tube and some are shorter than it’s depth so I was gently tipping it to extract the short bits, when something silver caught my eye. I’d found one of my missing scalpels which must have fallen off the bench many months ago and it was lurking blade first, waiting patiently to pounce! Thank goodness I was tipping it carefully... 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 28, 2021 Author Share Posted March 28, 2021 The bit I dread...covering. (Close examination will reveal that I did manage to Dremel hinge slots in a piece of carbon fibre to add to the trailing edge of the fin) Anyway, I persevered and now have a covered fuselage and tail feathers. In the slightly misquoted words of Free, “?It’s all white now” - well it is a Cessna... There are some wrinkles to go over but I’ve had enough for today. I’m planning to use a colour scheme I came across on the ‘net - simple but to my mind, attractive. Wings next - a little more preparation before the covering goes on though. 2 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 29, 2021 Author Share Posted March 29, 2021 Not much to report from today - spent some time with the missus... Just a little trimming detail done...remember it isn’t a proper scale model and the colour isn’t a proper match. Annoyingly, I’ve just noticed that the letters slope the wrong way on the port side - they are correct on the other side. I should have checked the photo above before cutting them out from the same pattern! As they are cut out from the blue film they will have to stay that way! Nobody will notice it if I keep quiet... ...but I did finish a job I started 46 years ago on the model - I de-rusted, drilled, countersunk, mounted and painted the metal cowl. 4 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 29, 2021 Author Share Posted March 29, 2021 A few words of explanation regarding the lettering... The way I did them was to select a side view photograph and resize it to full size to the model. I printed it out, stuck it together then cut out the blue area and the letters within it to make a cutting template. This was then taped to the backing film and cut round. The most difficult part wasn't cutting out the letters, it was removing the backing from the HK polyester film around them, which if you've used it, you'll know sticks like the proverbial! Other than the tricky to remove backing I find it every bit as good as Profilm at a fraction of the price. Once applied, the underlying white covering shows through as lettering and has the advantage that short of losing the whole piece of covering, the letters can't lift. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 29, 2021 Author Share Posted March 29, 2021 Limited progress today as family matters took priority with a garden visit from my daughter. I did manage a little more covering though - and the bearings for the engine arrived in the post. 5 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 30, 2021 Author Share Posted March 30, 2021 Airframe completed - just needs fitting out and (a little) I need to track down some acetate for the glazing. I might have a bit somewhere if I can find it - otherwise I may have to search the socially distanced Pound Shop for something suitable. Any good ideas for tinting the windshield green? 2 Quote Link to comment Share on other sites More sharing options...
Nigel Sharp Posted March 30, 2021 Share Posted March 30, 2021 You could buy a 1 1/2 litre "7up" bottle they are green. Should be able to flatten it after being stuck to the frame with a little heat from a hairdryer. Might be worth a try. 1 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 30, 2021 Author Share Posted March 30, 2021 Thanks Nigel, I had wondered about green plastic bottles but thought they were usually the smaller ones. A 1 1/2 litre one might well provide enough uncorrugated material. Ideally it needs to be quite a subtle tint. The side window material is sorted though - 'er indoors had a presentation box of cakes the other week with a clear lid which I've snaffled! 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 30, 2021 Share Posted March 30, 2021 Rit do a dye for plastic, i bought some red and green with the intention of trying it and writing about my adventure never got around to it. Supposedly works well. https://www.amazon.co.uk/dp/B00U2IXIWW/ref=cm_sw_r_cp_apa_fabc_664F3PDSMA9TQYQABHTW 1 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 30, 2021 Author Share Posted March 30, 2021 Thanks Danny - I might give this a try if the green bottle idea doesn't work. 1 Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted March 31, 2021 Share Posted March 31, 2021 Tamiya do a clear green spray - could try that on the inside...... GG 1 Quote Link to comment Share on other sites More sharing options...
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