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Smoke Trail


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There are several ways to transfer the plan shapes onto wood, I just used one that I've used many times in the past. Cutting out the plan and gluing with a Pritt stick works well, or you can lay a photocopy of the plan face down on the wood and use a hot iron to transfer the pattern. I'm sure there are other ways too.

 

I'm sure this tip is well known, but when using thin sheet over a structure such as sheeted leading edges or, as in this case, fuselage sides, it is better to sand the outer surfaces to a good finish before assembly. The reason being that if you try to do it afterwards, the sheeting bows under the pressure of the sanding block and you risk sanding too much off the areas supported by the underlying structure.

 

Thinking about it, I should have put the sanded faces together and leave the unfinished faces to the outside. I could than have more easily transferred the former positions onto the inside face.

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Now for the part I always dread doing: assembling the fuselage. I decided to try a different approach this time by tacking the 3 main formers (all the same width) to the right-hand fuselage side with cyano. After the firewall was tacked in place, the hardwood bearers were fed through to help with the location of F2 and then given a squirt of medium cyano. The rear former was held square and cyano run along the rear joint line and Superphatic along the front:

 

IMG_20220215_140820657.thumb.jpg.62d0f3b6ee0f33065e9d32141df11a0e.jpg

 

I then laid the left-hand fuselage on the building board and placed the other side, complete with formers, over the top. After checking in several locations that all was square, cyano was run along each join to hold it all in place with the help of some suitable weights:

 

IMG_20220215_143257818.thumb.jpg.2ad54c8cd7137f760ff0935beead8e7a.jpg

 

After leaving it to dry for a while, the fuselage was removed from the board and the tail drawn together to check alignment. Hmm, not perfect but acceptable - perhaps it's not such a difficult job after all ?

 

Next task is to run some epoxy to form fillets along the join lines of the plywood formers and the hardwood bearers but that will have to wait until after I'm back from visiting my dear old Mum on her 90th birthday tomorrow ?

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Thanks, John, she did have a good day with various family members visiting or calling via Zoom.

 

Anyway, the build. It isn't going too well but I'm soldiering on regardless. As I mentioned, I always seem to struggle with fuselages and the "small" misalignment was worse than I thought. When I drew the sides together at the tail there was a mismatch of over 1mm which meant that I had to hold the sternpost vertical and accept that the sides were not at the same level horizontally. I toyed with scrapping the fuselage and starting again but thought I'd try and rescue it first. It's not my best work but I have now joined the sides and added the remaining formers, after which I planed and sanded down the sides to match and spent some time recutting the tailplane mount so it was parallel to the wing.

 

I decided that I would change the undercarriage arrangement to piano wire rather than the plan design which uses a banded-on, 20swg dural undercarriage, mainly due to the sheer effort involved in hacksawing, filing and bending up the dural. Often, free-flight power models like this have a one-piece wire undercarriage sewn and glued to a suitable fuselage former but this gets in the way when sheeting and sanding the underside of the fuselage. I've chosen to use two 14swg piano wire legs which locate in vertical slots behind former F3 (at the leading edge) in the style typically seen on Peter Miller's designs. To do this, I made up some ply "pockets" to hold the top of the legs vertically up against the rear of the former and will then clamp the legs to the underside of the fuselage once all the covering has been completed.

 

Not much to show from these efforts, I'll take a few pics tomorrow when I hope to progress onto sheeting the fuselage top and bottom.

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Feeling a little more upbeat about the fuselage now and have made progress by gluing the top sheeting to the rear of the fuselage and adding the side cheeks to infill between the engine bearers and the fuselage sides at the nose. Here it is weighted down while the glue dries:

 

IMG_20220219_141517556.thumb.jpg.e1aec2740cb37bec564753acfeb0c8ca.jpg

 

You can also probably just make out the ply pockets to hold the undercarriage torque arms and the scraps of liteply which will be under the lower sheet to take the u/c screws.

 

And here are the aforesaid undercarriage legs, obviously overlength at this stage:

IMG_20220219_145629181.thumb.jpg.32dc6c41857a8b09dc879aafffe2ddca.jpg

 

I also shaped the front deck ahead of the cabin from 1/16" sheet which was wetted and wrapped around a suitable former:

 

IMG_20220219_141926208.thumb.jpg.37a8822af96327f16c1c7fa0dc0038dd.jpg

 

I'll finish off the lower fuselage sheeting later today, leaving just the front deck and leading edge support piece to complete the basic fuselage assembly. Then it will be onto final sanding ready for covering but that will have to wait until later in the week as I am away again for a few days.

 

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Even though it's only a small model, it's amazing how many little jobs there are to do and how much time it consumes, even when I thought I had finished the basic assembly.

 

The upper and lower sheeting had plenty of time to dry so was trimmed and then sanded to shape, with just a little rounding of the corners. Next up, I cut out the fin, sanded it to shape and cut a slot in the upper sheeting to locate it. That meant I could loosely put the model together for the obligatory, morale-building, photo:

 

IMG_20220223_185058360.thumb.jpg.05003a8ac985496a4a9f9e78658fe87e.jpg

 

And it even looks reasonably straight:

 

IMG_20220223_185219857.thumb.jpg.1fe3d7f6689c2e281ba7887949136bbd.jpg

 

Final shaping of the nose to do and it still needs the cabin roof to be added to the fuselage ahead of the leading edge. Then it will be time for covering, honest...

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All the woodwork has been completed with the fitting of the cabin roof and shaping of the nose. Also another small milestone has been achieved: first fitting of the engine. I knew that 8BA box spanner I bought 40-odd years ago would come in handy again:

 

IMG_20220225_120426692_HDR.thumb.jpg.b080ae9420665628d8a900fe4067a68a.jpg

 

We're now ready for the first coats of dope to be applied...

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With the smell of cellulose dope pervading the workshop, I got my selection of lightweight tissue out to decide what colours to use. I'm going for the traditional coloured wings with black fuselage but I now have something of a dilemma over the wing covering itself. What I thought was a roll of thin mylar bought from SAMs some years ago turned out to be something else, a lot thicker and slightly opaque in colour. It looks similar to laminating pouch material (ie, adhesive-coated) but tests on a scrap framework showed it had little resistance to temperature and wrinkled easily, while still staying opaque.

 

Not having anything else suitable as a base to tissue over, I now have to either order some mylar from Mike Woodhouse or change to a one-shot covering such as Solarfilm Litespan (which I already have in stock). Either way, I will need to find a suitable adhesive to stick the covering down as my jar of Balsaloc is just a solid lump!

 

The obvious alternative is Deluxe Materials Cover Grip but have you seen the price? ?

 

Some research shows that thinned PVA can be used (but my experiments so far with Poundland glue have been unsuccessful) or contact adhesive thinned with cellulose thinners. I will give that a try but if anyone has any other suggestions/experience, please let me know.

 

So, back to the workshop, and some thinking to be done while I get high on dope fumes ?

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Thanks EB and Andy for your suggestions.

 

I'll have to experiment with clingfilm but my initial thoughts are that it is thicker (hence heavier) than mylar and I'm not convinced that it has the same puncture resistance. I'll give it a try and see how it goes, it may be ok in conjunction with doped tissue.

 

I didn't think 5-star/Starloc adhesives were still in business, Andy? Good thought, though, I think I may have some tissue paste somewhere. If I'm going to stick the covering down with wet paste then PVA should be just as good?

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I've put a couple of test pieces onto my scrap framework, both with the Poundland PVA used wet (no tissue paste). I have not thinned the PVA as it already has a very watery consistency straight from the bottle, much thinner than you would typically get in diy shop PVA. One panel is covered in Litespan and the other is covered with clingfilm, with the tissue to be added later. With both panels, I'm going to let the PVA dry before the next stage.

 

Apparently, clingfilm is made from PVC or polyethylene and is typically around 10 micron thick and therefore thicker than the mylar I was planning to use (although still acceptable). The particular brand I have is stated as "non-PVC" so will be polyethylene which, as you know, stretches very easily - it will be interesting to see how it behaves with the tissue over it.

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After letting the test panels dry for a few hours, I moved onto the next stage: heat-shrinking to tighten the covering. Using a heat gun on the clingfilm and gently warming it as described in the video above, I found that the edges pulled away rather easily and clearly weren't really stuck down at all well.

 

I decided that method wasn't for me so looked at the Litespan panel instead. I shrunk that with a covering iron turned up to about 125 deg C and this seemed to work well, with the covering still appearing to be attached firmly to the framework - success!

 

I'd only covered one side of the panel and, holding it up to the light, the covering appeared to show some pinholes. Gently blowing through the surface confirmed it was not completely airtight, despite the instructions claiming so. I've now given it a coat of 50:50 non-shrink dope to seal the surface and, I hope, help to ensure the covering stays firmly stuck to the framework. I'll give it another coat tomorrow and see what it's like. With luck, the dope will not only seal the surface but also make it look even more like the tissue finish on the fuselage.

 

A shame I won't get to try out the tissue over mylar method on this model. I'll give it a go another time but, for now, I need to get Smoke Trail finished so I can get back to the other model I've been working on, ready for the summer season.

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Nick, would you like to try tissue over laminating film ? I have a roll of 30cm wide (12") x 38 micron film, if you estimate how much you'd need then  PM me your address I'll send it to you by letter post. I would reckon a couple of yards should do it but check if the tailplane can be done from that as well.

 

BTW I don't think the weight would be an issue, I have a thread showing me using the same film plus tissue as a test exercise on a glider tailplane & another thread using it on an all surfaces of a Graupner Amigo2 vintage glider. I also intend re-covering a Veron Deacon & a KK Chief in the near future. 

 

 

Edited by PatMc
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That's a very kind offer, Pat, thank you. I'm going to use the Litespan on this model but there's a set of parts for a Tomboy somewhere in a cupboard which I may build later in the year and could try it out on that. I'll measure it up tomorrow and send you a PM.

 

Thanks also for the links to your threads, I'll have a good read of them.

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Hi Pat,

I've looked at the Tomboy plan today and realised it is much bigger than Smoke Trail and, with a built-up fuselage as well, would probably need at least 3m (possibly a bit more to allow for wastage). If you have that quantity available, please let me know the cost including postage and the easiest way to pay you.

Regards,

Nick

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Hi Nick, sorry I haven't replied sooner but I've been quite busy & I haven't looked in on this thread for a while.

Re the laminating film - I'm sure I've enough to spare. I'm not looking for any reimbursement, if you would like to make an estimate of what you need then send me a PM with your address we can sort out the rest. If the model is the standard Tomboy I think it will need around 4 mtrs.

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I've had a bit of a break from Smoke Trail to do other things, including actually going flying for the first time in about 4 weeks! And, to be honest, the cancellation of the Nats at Barkston has knocked the wind out of my sails a bit as well so little progress was made last week.

 

Anyway, back to it now, and tissue covering the fuselage was the next job on the agenda. I'm using some tissue which I obtained from a friend who was giving up the hobby and it came in a roll along with about 20 or so other assorted colours. I suspect it is intended more for gift wrapping as its wet strength is low and the dye comes out when you brush thinners through it but it went on reasonably well with just the odd wrinkle - fewer than I've got! You can see some of the dye on the wing seat which I've left uncovered. There's more on my fingertips from rolling the tissue round the edges. The tissue is also quite thick and will probably take quite a few coats of dope to seal.

 

IMG_20220310_142050662.thumb.jpg.a39f8e0c3f552f872006db06565082ca.jpg

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I'm normally more of a night owl than an early bird but I wanted to do a quick update on Smoke Trail before going off-grid again for a few days.

 

In between doping the fuselage, I've covered the tailplane and made a start on the wing. The Litespan was stuck onto the tailplane lower surface using the cheap PVA (used wet) and, once dry, trimmed along the edges. I had to apply some extra PVA where I wrapped them around the edges and found that it did in fact adhere quite well with the use of the covering iron on the dried glue. My earlier tests with this method weren't successful and I suspect this was due to having doped the framework first (as recommended by George Stringwell). More PVA was brushed onto the upper framework and the Litespan laid on top, leaving the tips unglued at this time. The leading and trailing edges were trimmed once dry and more PVA was applied to stick the tip covering down. This was a bit tricky using the one piece and resulted in some wrinkling. Thinking laterally I tried brushing on some shrinking dope which has reduced the wrinkles a bit but I think I'm going to have to cut the tip covering away and do it again using separate pieces of Litespan.

 

IMG_20220315_154123339.thumb.jpg.bd3d9010efc4bdb40e0a7b103088d355.jpg

 

With that experience, and despite having previously baulked at the price of Cover Grip, I decided to bite the bullet and order a bottle as I wanted to be sure that the wing covering was as secure as possible. I have to say that it has worked well so far on the one panel I have covered using it.

 

IMG_20220315_154225264_HDR.thumb.jpg.8ba46d133f53792ae8a9697c15cfa4b8.jpg

 

And here's a view from the other side:

 

IMG_20220315_154303729.thumb.jpg.92482fca9901fd7c5152643cd3c15dfd.jpg

 

Back in a few days to finish off the wing covering.

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  • 2 weeks later...

With 3 family birthdays in 2 weeks and (finally) some decent flying weather, albeit for a short period, plus numerous other jobs to do, poor little Smoke Trail has been pushed firmly down the pecking order of late.

 

The odd few minutes to spare saw the covering completed on the wing which went well using Cover Grip as the adhesive. I found this much better than using wet PVA as I was able to use the heat of the covering iron to ease the Litespan around the edges, reducing wrinkles. I covered each panel underside first then each top surface from centre to tip rib. The actual tip sections were covered in a separate piece as described in the instructions which I found easy to do. When covering the tailplane, I had tried to do the top surface and tips in one piece but couldn't remove the resulting wrinkles with either heat or shrinking dope. These were cut away and new tip covering was added. There's a bit of colour change where the 2 pieces of covering overlap but it's not too obvious.

 

The final job completed today was gluing the fin in place. For this I used good old balsa cement and, once positioned, I ran a brush loaded with cellulose thinners along the join line to smooth it out and form a small fillet.

 

Here's what it looks like now:

 

IMG_20220330_180213205_HDR.thumb.jpg.dfda76124ee098d0f55f09ee2033a89a.jpg

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Just a few more little jobs to do before fuelproofing and getting Smoke Trail ready for flying. The first of these was to give the little lady some legs.

I picked up a couple of small wheels at a swapmeet last weekend which look like they previously did duty on the noseleg of an EDF but have been pressed into service on Smoke Trail. They are not ideal for this model and I would prefer some of those old plastic Keikraft wheels if I can find them but will do for now.

The undercarriage legs were made up from 14swg piano wire earlier in the build so the next stage was to solder some 2mm washers in place to locate the wheels. The wheels have plastic hubs and I was worried about the amount of heat used to solder the washers so made up some retainers from a length of copper wire twisted around the axle. These soldered better and I was able to fix them in place without damage to the hubs.

 

IMG_20220331_140915222.thumb.jpg.443c934c4541dea54c6789e935ddf590.jpg

 

The upper ends of the legs locate in torque boxes built into the fuselage and are held in place with a couple of small clamps made from a strip of 1/4" x 0.025 brass strip. To make these, I first annealed the brass by heating with a blow torch then used a drill press to fold the strip around 2 spare lengths of the piano wire.

 

IMG_20220331_141702270_HDR.thumb.jpg.7e65570085003c4be30d1942ac348c0a.jpg

 

IMG_20220331_142022113.thumb.jpg.ea0ffccce2d48f60ad9af832fff27a71.jpg

 

The clamps were cut to length, cleaned up with a file and drilled for self-tapping screws. Should have centre-punched before drilling ?

 

IMG_20220331_184612458_HDR.thumb.jpg.56b0b9e543e117b96856cdc85feaf9d0.jpg

 

And here she is, standing on her own 2 legs for the first time.

 

IMG_20220331_185048098_BURST000_COVER.thumb.jpg.2daf7ff4c96832d43e3b9352ac790990.jpg

 

IMG_20220331_185151587_HDR.thumb.jpg.d5a345b7f1822a59957a130016085277.jpg

 

And, just when I thought I'd finished the airframe, that last photo reminded me that I'd forgotten to make the small fuselage fairing to fit under the tailplane. Out with the scalpel and sanding block again...

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That didn't take too long to cut out from 1/4" balsa, taper with a razor plane and sand off the corners. It was then glued in place with balsa cement, with the glue fillet smoothed in the corners with a brushload of thinners, as per the fin, earlier.

 

IMG_20220404_180628474_HDR.thumb.jpg.e53b015fd82fb078474d79721567d659.jpg

 

A quick splash of dope then it was covered with tissue to match the fuselage.

 

IMG_20220404_185640758.thumb.jpg.6b590508f84197301d2dc3e8dc5bf672.jpg

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