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Christchurch and District Model Flying Club |
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Electric conversion, by Martin Burr Hi folks, Following on from the Andreas build, I have converted my old plane, a Sirocco built MANY years ago (25+) from a Roy Pitts plan. The plane is a rudder elevator T tail design with all built up construction to 100” span. Over the years it has suffered from hangar rash, and a couple of unplanned landings, so I elected to not only convert to electric launch but also to strip, repair and re-cover. I had a motor and ESC combination in my parts bin which should do the job. I also decided to keep the original full size Futaba servos, they give me a grin every time I see them knowing how small some modern ones are ! The first job was to strip back the orange solarfilm on the fuz
and see what lurks underneath, this was a trip down memory lane in itself, I found various modifications that I had totally forgotten about. The original plastic canopy was pretty much only fit for the bin so something would have to be made. I wouldn’t like to put the plane through a bungee launch again, it must be 25yrs old, so no need for the hook, and I never liked the skeg under the front so that can go as well. The nose section came away from the front bulkhead without a fight and I extended the nose with plywood, cutting a hole through the inside to accommodate the outrunner. It was quite tight, and would have been easier with a narrower motor, I also made provision for the wires to route past the rotating can. I moved things around a bit in the fuz to allow space for the battery with the Rx under the trailing edge the servos under the front half of the wing and then to power battery and finally the esc and motor. After the Andreas’ slim proportions it was rather nice to be able to get my my fingers in!
The plane weighed 1135g/ 40oz ready to fly in its “pure” form, so it will be interesting to see how it finishes up after the conversion. It has a wing area of 720sq in, so the original wing loading was around 8oz per sq ft. I am expecting an increase, possibly 150g/5.3oz which will increase the wing loading to around 9oz/sq ft, we will have to see… I stripped back the wings, solarfilm as you probably know is clear, but the glue is coloured, and can leave behind a stain. I found the best method was to leave in the sun, find the original overlap, tease this back then try to pull back as much as possible in one go. I didn’t think heating it helped, it seemed to try to re-stick itself ! For the remaining stubborn bits I used a mixture of sandpaper, heat gun and thinners. In the end it wasn’t too bad a job, removing the covering left a pretty sound pair of wings, a couple of cracked ribs and a bit of surface damage, but nothing a bit of glue, filler and a light sand couldn’t sort. Without doubt the worst area was the T tailplane, this looked rather fragile, I elected to add a couple of carbon spars which has made it acceptable. At the moment I am waiting for a delivery of Oracover in red and white to give the old girl a new livery, I never liked the orange, I just thought that it would be easier to see ! The naked weight of the airframe complete with battery etc is 1065g/37.5oz, it will be interesting to see how much the film weighs. CONTINUED Well, the covering arrived, and has been applied, red fuz and white wings (which will get some decoration at some point) the covering added 140g bringing the AUW to 1205g/ 42.5oz so around 8.5oz per sq/ft (yep I know I’m mixing units, but that’s how I think !), so onto the re-maiden…. Interesting to note that the conversion to electric only added 70g to the overall weight.
Maiden (again) Chalbury 14th May 12.30 pm (ish)
After the success of the Andreas I was feeling brave enough to launch her into the sky. The last time the old girl flew must be at least 5yrs ago and probably off a slope, so this would be a new adventure for both of us. The test glide was very promising, she just flew straight and true with quite a shallow glide angle, must remember no brakes!! Ok, so I picked her up and walked a long way back up the field to give her a go with the motor, as before a gentle launch THEN apply motor progressively, this was a bit more scary than with the Andreas, anything over about half throttle causes the nose to rise severely needing large amounts of down elevator to compensate, when I had enough height I gave her full beans to see what would happen, this resulted in an unplanned sort of loop/ belly flop thing, not pretty, but high enough not to cause any trouble. I mounted the motor flat on the front bulkhead, in hindsight I should have given it some down thrust, thankfully, I can give it some down elevator compensation to help, and NOT use full throttle.The climb rate is perfectly adequate at about ¾ anyway. It was rather nice seeing it fly again, and it brought some admiring glances from those present. It was a trip down memory lane for me and the landing is much more of a challenge than the modern “mouldies” that I usually fly, the rubber band attachment of the wings always was a saviour ! Cheers, Martin
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