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Smoke Trail

Nick Cripps

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Just a small update on progress this time. The picture may not appear to show anything different from some previous ones but Smoke Trail has now been fuelproofed and is getting closer to being flight-ready.


I used black Solarlac for the engine bay and then Clearcoat on the remainder of the fuselage and the flying surfaces; a single coat, brushed on. It's a pity that the picture doesn't do it justice as the colour has washed out somewhat. The red flying surfaces are much brighter in reality and the Clearcoat has given the whole model a good shine.


Anyway, I'll leave it to dry for a few days before installing the rudder (hinged with thin aluminium) and attaching the undercarriage again. Then it's another job I'm not looking forward to: the dreaded windscreen ?



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  • 3 weeks later...

Three weeks later and I think I can now say that Smoke Trail is finally completed ?


I had originally intended to do the windscreen in 3 pieces; both sides and the front section separately but realised that the front former edges were just too thin to allow a join so went with the one-piece option instead. It took a couple of paper templates to get the shape right before transferring the pattern onto some thin plastic salvaged from an Easter egg carton. A few bits of final trimming and then the screen was glued into place with RC Modeller's glue.


The engine (Boddo Mills 0.5) with Kavan 7x4 prop was installed with a washer under each rear bolt to give some downthrust and the undercarriage refitted. My local postlady very generously provided a bag of assorted rubber bands to hold the wings and tailplane in place, ready for the photo session:








Note that I've tweaked the colour balance on these 3 photos to get a more accurate representation of how the model looks to the naked eye.


Smoke Trail weighs in at 189g (6.7oz) and balances about 1.5 inches back from the leading edge, just ahead of the spar. This would be an ideal position for an r/c model but is probably too far forward for free-flight (the plan shows it should be 1/2" further back) as the tailplane has a lifting section. Interestingly, we had a talk from FF scale guru, Andy Hewitt, at our club meeting last week (he's one of our members) and he said that he always balances his models in the 25-30% chord range and simply adjusts the glide with elevator trim. Comments welcome but I think I will try out a few test glides as is and only adjust the cg if I feel it is necessary. Of course, I've first got to find the mandatory long grass and a calm day for test glides, as it states in the Keil Kraft instructions...


The other task is to track down some diesel fuel. I've got a tin of D2000 somewhere but as it's about 15 years old I suspect the ether is long gone. I called into Model Shop Leeds a couple of weeks ago and they were asking £25 for a litre of D1000 - a bit steep, I thought! I was hoping to pick some up at Old Warden at the weekend but was surprised to find none on any of the stalls. There's no rush, so it might be later in the year before I get chance to pick some fuel up at one of the shows (Southern Modelcraft list sport diesel fuel at a much more reasonable £10/litre).


Anyway, all done now, and I'm happy with the result, even if it has taken 3 months to build a simple free-flight model ?.


Next update when Smoke Trail finally takes to the skies!

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Nice job Nick.

The Smoke Trail is very similar in size to my Poppet (a Vic Smeed design).  Although I have rudder and throttle controls fitted they're only used to keep it out of the wood by our club field, so it's really just flown as a free flight model.  I've got the C of G at about 38% back from the LE, which seems fine.

Just be careful how much fuel you put in on the first flights though. These little diesels seem to run forever on tiny amounts.


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Yes, Poppet looks very much like Smoke Trail but I guess there's only so many ways you can design a high-wing cabin free-flighter! Nice model you have there, I bet it's great on those calm summer evenings.


Thanks for the tip about fuel quantity. I need to get a small syringe for fuelling up.

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  • 3 weeks later...

After today's rain cleared, it left a lovely evening with not a breath of wind - ideal conditions for doing some test glides. I attached the wings and tailplane to the fuselage, picked up a few scraps of 1/32" plywood and some cardboard and nipped out to the park next door.


As mentioned earlier, Smoke Trail balances about 1/2" ahead of the plan position (nose-heavy, that must be a first) so, on the 1st test glide, she headed rapidly towards the ground. I progressively added 2 pieces of plywood and thin card at the tailplane LE but still failed to get a reasonable glide. Back to the house, I picked up some Blu-tac and added a noggin to the tailskid. This brought the cg back about 1/4" and improved the glide, but still not enough, so another piece was added to get closer to the plan. Further glides showed slightly "stally" behaviour so I was able to remove some of the packing and get a reasonable(ish) glide.


Back home again, I removed the Blu-tac and weighed it: 7g. The plan now is to glue some lead into the back of the fuselage to get the cg to the plan position and to trim a bit of the tailplane seat to decrease the tailplane incidence. Once that's done I'll probably have to wait another few weeks for a calm evening for the next attempt...

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  • 2 months later...

Well, it was quite a few weeks but Smoke Trail has finally flown!


The mods mentioned above have been incorporated and the calm weather forecasted for yesterday prompted me to pack the model and a can of diesel fuel along with my RC models for the regular Tuesday morning trip to the field.


I was fortunate that scale free-flight guru Andy Hewitt was also there and he helped me greatly to re-trim Smoke Trail (more negative incidence on the tail) with some test glides over the long grass in the outfield. It must be 15 years since I last ran a diesel engine and it took me quite a while to get the Boddo Mills running sweetly but I got there in the end.


With just a sniff of fuel in the clear tank, and the engine pop-popping away, Smoke Trail was launched into the lightest of winds and climbed up to around 20ft before the engine cut and it headed back to earth. Big cheer from the crowd in the pits and a big grin on my face!


I had a couple of further flights with the same engine setting then leaned it out a bit for more power. This time the climb was more positive and, with a lot more fuel in the tank (too much!), Smoke Trail climbed to around 60ft or so and did several circuits before the engine cut and it drifted down just inside the field boundary. Phew, no tree climbing today.


Overall I'm really happy with how Smoke Trail turned and I'm looking forward to the next outing. I've just got to get rid of the smell of diesel fuel from my clothes now!



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