Smoke Trail

[Nick Cripps]

I thought I'd join in this initiative started by John Stones as it will help give me motivation to build something I've been planning to do for years but other things have always seemed to get in the way. A bit of background to start...

 

For many years, when work schedules permitted, August bank holiday weekends have been spent at Barkston Heath, home of the BMFA Nationals, one of the highlights of the modelling year for me. Every year I spend the evenings ducking and dodging models at the free flight mayhem and, every year, I solemnly promise myself to "build one next year" which, of course, never happens. This time, however, having made the commitment in print, there's no escape!

 

The model I have chosen is Smoke Trail, a 32" cabin model for .5cc diesels designed by some bloke called Chris Foss - you may have heard of him? It was first published in the July 1964 Aeromodeller and revisited in the same magazine in December 2019 where I first discovered it while browsing the magazine racks in WH Smith (supposedly Christmas shopping). Described as suitable for free flight or radio control, the plan shows options for single channel operation using a rubber-wound escapement and also optional skis for those occasional snowy days.

 

 

Smoke Trail has typical sport FF wing and tail construction with an all-sheet fuselage so should make for a straightforward build. I plan to try out the tissue-over-mylar covering method on this model to make it more robust and also to learn the technique which I will document here.

 

Off we go...

 

 

[Wilco Wingco]

The first R/C model I ever built. DC Merlin power, Terrytone receiver, rubber powered bang bang actuator. I was 14 at the time and loved every minute of building the model and the receiver. Flew like a FF with a little nudge now and then to keep it in the park. .  Ah those were the days ?

[Nick Cripps]

I've spent a little bit of time today gathering together some of the things needed for this model while trying hard not to get drawn into it full-time as I have other things that really need to be done first. Others could, I'm sure, knock together this simple model in a week of evenings but for me doing a bit here and there will eventually see it finished - there's no rush!

 

Below is a view of the plan as it appeared, spread over 2 double pages, in the December 2019 Aeromodeller magazine. I've made a few photocopies to cut up where necessary and use as templates for cutting the various components. 

 

 

Incidentally, it's also available for download from the outerzone.co.uk

 

Handily, the plan also shows a list of the materials required to build the basic airframe, most of which I already have in stock, collected over many years of hoarding.

 

 

The other important item is a suitable engine, in my case a CS "Boddo" Mills 0.5cc. It has never been used and hopefully won't suffer the same fate as Engine Doctor's similar engine. I also have a DC Dart in reserve, just in case, but it will obviously require a separate tank.

 

 

That's all so far. I'm off to have a rummage in the balsa box to see what, if anything, I need to order.

[EarlyBird]

Impressive! Nick you are getting into the spirit and I like the vintage diesel theme you have chosen. 

[Nick Cripps]

I've had a root around in the balsa box and think I've got all the materials I need to get started on the build. Interesting that the list didn't mention trailing edge stock but I guess that the hard men of free flight eschew such frippery and carve their own (as Whittaker might say) ?. Being a lesser mortal, I found some 1" x 1/4" TE stock which I can strip down to the sizes needed for the wing and tailplane.

 

Not having beech bearer in the required size of 1/4" x 5/16", I set up my bandsaw to rip some 1/2" beech down for two 4" lengths. The cut edge is a little rough but can be cleaned up a bit with sandpaper and the rough sides hidden from prying eyes.

 

Next job was to cut up some of the plan copies to make patterns for marking out the more complex shapes such as the wing and tailplane ribs. The rib patterns were stuck to some scraps of thin ply ready for rib production.

 

 

I also christened the model with some of my own blood when I caught the sharp end of a scalpel while digging around in the tool box!

 

Hmm, now what did I say about not spending too much time on this ?

[Engine Doctor]

On 31/01/2022 at 16:38, Nick Cripps said:

 

 

 

 

The other important item is a suitable engine, in my case a CS "Boddo" Mills 0.5cc. It has never been used and hopefully won't suffer the same fate as Engine Doctor's similar engine. I also have a DC Dart in reserve, just in case, but it will obviously require a separate tank.

 

 

That's all so far. I'm off to have a rummage in the balsa box to see what, if anything, I need to order.

Hi Nick . Your CS Mills is the CS miniaturised version of the proper Mills and is probably / hopefully a far better engine. It's totally different the the Boddo Mills I have. It's now  been resurrected from the scrap box as I have made a new crank case.

[Nick Cripps]

Thanks, ED, I hope you're right.

 

But at least I know where to order a new crankcase ?

[Nick Cripps]

23 hours ago, john stones 1 - Moderator said:

It'll be the Mini Super....20 for me then, I'll not be starting yet though, wasn't expecting the quick starts.

Come on, John, try and keep up ?

 

More prep work today using Patricia (Chris de Burgh reference) to make the spars and leading edge sections from sheet stock. I also cut out tailplane and wing rib blanks and made a couple of jigs to help make accurate spar slots and cut out the rib shapes themselves. The first one is just a piece of 1/16" ply with appropriately-sized slots glued to a length of 1/4" square hardwood which acts as a depth stop. The rib blank is placed behind the plywood and a razor saw used to cut a perpendicular slot:

 

The blank is then turned over and set on the 2nd jig which locates the rib template, ensuring it doesn't move while the rib is cut out:

 

Overkill? Perhaps, but I now have all the ribs ready for assembling the flying surfaces:

 

The observant amongst you may have noticed from the rib shape that I have changed the spar design from that shown on the plan, which calls for a single 1/8" square spruce spar on the upper surface only. I couldn't understand the logic behind this so I had a look through a few free-flight designs on Outerzone for some inspiration. Some models had a similar design with just a single spar (either top or bottom), others had 2 spars (but no shear webs) and others had multi-spar arrangements (usually 2 lower and 1 upper). I decided that pretty much anything goes so chose a full depth 1/8" balsa spar with ribs slotted in from the top.

 

More tomorrow...

[EarlyBird]

Good stuff which has got me thinking as I am sure I will use the jigs on future builds. ? 

[Nigel R]

13 hours ago, Nick Cripps said:

the logic behind this

 

At a guess;

 

The spar on top is for compressive strength at the top surface. A period type covering e.g. doped nylon on the underside gives tensile strength.

 

The whole ensemble is stronger for positive G type loads, but might not be up to much for negative G.

 

 

[Nick Cripps]

I understand the forces, Nigel, but surprised that tissue is considered sufficient to take the tensile load, especially after it has aged a bit and is susceptible to puncturing. I suspect one benefit of a continuous upper spar is to help maintain the aerofoil section by minimising covering sag between the ribs.

 

I didn't have any 1/8" square spruce, only 1/8" x 1/4", which I felt would be difficult to strip down but I guess could have been used as-is for little weight penalty. I'm comfortable with my decision though, it maintains the full section depth and has a continuous section along the bottom surface to take the tensile loads.  OK, the compressive loads are taken across the grain of the ribs but I think there is sufficient strength overall.

 

I'm hoping the loads are always positive but the there's usually a lot of rough and tumble at the evening free-flight sessions!

[Nigel R]

Not much loads of any sort involved in something this big, I'd hazard...

[Nick Cripps]

Too true, it should come in at around 9oz.

[Nick Cripps]

Just a short update, not much time spent on Smoke Trail today.

 

The spar sections for the wing were cut slightly overlength then aligned at the root and taped back-to-back for the rib slots to be cut with a Permagrit needle file. The spars were then separated and taped to the leading and trailing edge sections to guide cutting of matching notches. A similar process was followed for the tailplane strip stock and all parts put aside ready for assembly, hopefully tomorrow:

 

 

PS - sorry about the photo quality, they were taken on my phone using flash. I'll try and do the next ones in daylight.

[Nick Cripps]

The glue bottle has been uncorked and the proper work has begun. I usually start with the tail surfaces to ease me into a build gently before tackling the wings and finally the fuselage. I find I can put the flying surfaces together fairly accurately but always struggle a bit with the fuselage. Despite measuring several times before cutting, using a jig, and other good strategies, when it comes to pulling in the fuselage sides at the tail, I always seem to end up with the tailplane seat not quite parallel to the wing and a few wonky formers somewhere along the line. Ah well, better practise a bit more.

 

I use a piece of an old wardrobe door cut down to 48" by 12" and faced with cork tiles for my building. It's big enough to do wing panels on the size of model I usually build and more than enough for Smoke Trail, enabling me to assemble the wing panels and tailplane at the same time. The plans were placed on the board, covered with solartex backing and then the structures were loosely assembled and placed on the board. The tailplane was pinned down and built over the plan but for the wing I placed a ruler along the whole length of the rear edge before pinning down the left-hand trailing edge piece with the root end aligned with the centre. This enabled me to use a square placed against the ruler to make sure that the spar and leading edge pieces were all in line at the root. Once that was all pinned down and secure, I butted up the leading and trailing edge sections and the main spar for the right-hand panel and looked along the span to check for straightness. Once happy with the alignment, I ran a thin bead of Superphatic glue along each join line, allowing it to wick into place, then left the whole thing to dry overnight. I left out the 2 centre ribs as these will be fitted later when the panels are joined with the dihedral braces.

 

 

 

And, oh yes, Smoke Trail has claimed more of my blood. I now have a hole in my left index finger to match the one on the right ?

[john stones 1 - Moderator]

You'll have it built for the morning. ?

[Nick Cripps]

Not quite, John, too many distractions today (parkrun, FA Cup and 6 Nations) but I have added the lower centre section sheeting and tips to the wing panels and tailplane.

 

 

Gotta keep up with the pace set by EB, he starts earlier in the morning than I do...

[EarlyBird]

17 minutes ago, Nick Cripps said:

Gotta keep up with the pace set by EB, he starts earlier in the morning than I do...

04:00 this morning so a bit earlier than my normal 05:00-06:00 but then it takes me a couple of hours to get moving. ?

BTW you were first to hit the bottle (glue) so I felt compelled to follow suit. You beat me there?

It's not a race apart from competing to have the most fun.

Bed time now!

 

[dave windymiller]

Looking good Nick.  It looks a robust model so every gram you can shave off eg holes in bulkheads etc will help!

 

Roll on the Nats!

[Nick Cripps]

Still plodding along. Next job was to add the centre section sheeting to the top surface of the tailplane, which was then put to one side to dry before shaping. 

 

 

I mentioned earlier that I cut down some 1" x 1/4" TE stock for the trailing edge of the tailplane (1/4" x 1/8") and wing panels (3/4" x 3/16") which left me with some offcuts which were repurposed for the leading edge sections (with a bit of trimming in the case of the wing). This helped a bit as the resulting sections were tapered rather than square. The first task was to chamfer the root ends of the wing panels. I did this by propping up the tip to the right height and then making use of the square section of a Permagrit sanding block to achieve a vertical centre:

 

 

I decided that it would be easier to shape the wing panels before joining them so a fresh blade was put into Plastic Bertrand (another musical reference ?) and I set to it. I ran some masking tape along the front rib bays first to protect the ribs during shaping, finishing off with a long sanding bar:

 

 

 

Happy with that, just a tickle with some fine sandpaper later will have that ready for covering.

 

Dihedral braces were cut from 1/16" ply and trial-fitted with each panel blocked up to the required dihedral angle. I put a thin bead of aliphatic along the root end of one panel and pushed it up against the other. The dihedral braces were then given a thin smear of epoxy and clamped into place:

 

 

Once this is all set I'll finish off the wing construction by adding the upper centre section sheeting then it will be onto the fuselage - yay!

 

 

 

[john stones 1 - Moderator]

I like making wings.

Your work area is disgracefully tidy, you have a cleaner come in ? ?

[Nick Cripps]

I've got 2 workbenches, you should see the other one ?

[Nick Cripps]

Here you go, John, here's the other end of the bench:

 

 

And this is the other bench:

 

 

No exciting piccies from today's efforts, I'm afraid, all I did was to glue in the centre ribs and the wing centre section sheeting and then finish off shaping the tailplane. These are both done now ready for covering which I'll start when the fuselage is complete and all the doping can be done together.

 

That's all for now as I'm off to the Lake District for a few days, hopefully doing a bit of walking if the weather cooperates.

[Nick Cripps]

Back home and a start was made on the fuselage. There are 3 formers cut from 1/16" ply with the remainder being 1/8" balsa. Former F3 will be glued between 2 spruce uprights against the rear face of F2 and then the small, v-shaped, piece glued across the top which will support the leading edge of the wing.

 

For the fuselage sides, I first "finish" sanded 2 sheets of 1/16" balsa then taped them together by the edges with the sanded faces on the outside. I use the time-honoured method of pricking a pin through the plan onto the balsa beneath and joining the dots with a biro before cutting the parts out with a scalpel.

 

 

Oops, just realised I'm missing former F1A. I'll get that cut out and start the assembly tomorrow.

[EarlyBird]

On 13/02/2022 at 21:03, Nick Cripps said:

For the fuselage sides, I first "finish" sanded 2 sheets of 1/16" balsa then taped them together by the edges with the sanded faces on the outside. I use the time-honoured method of pricking a pin through the plan onto the balsa beneath and joining the dots with a biro before cutting the parts out with a scalpel.

Good tip that will come in handy for the Team MiniMax, I assumed tracing off the plan cutting out the paper template sticking to wood was how it was done. Finish sand and tape together I like that. ?