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I suppose I could have titled this "How to Convert a Vintage I.C. Powered Model to Electric Power." Back around 1986 I bought a partially constructed Flair Black Magic kit from my then local model shop, having felt like building a vintage model and rather liking the looks of this particular aircraft. I finished the construction, covered the model in Antique colour Solartex, fitted an OS25 Max engine, and Futaba Challenger R/C, and flew this model occasionally over the next five years before I stopped flying due to moving out of Sussex. When I recommenced flying in 1997 I fitted the R/C and engine to another model. It was in 1998 that my varied interest in forms of R/C flying brought about a momentous decision.
I have since 1981 been interested and active in electric flight, and with the resumption of flying and my interest in electric flight and the advances in five years I was struck by the performance of a Junior 60 converted to electric power from i.c. It was seeing this that got me thinking about converting my Black Magic to electric. Having sat down and considered matters I felt that I had worked out a way forward. The overriding factor was that I wanted to prove the concept with the minimum of expense and change. These are the changes that I made:
I had determined that an 8.4V Speed 600 Motor driving a 12"x8" propellor through a Master Airscrew 3:1 gearbox powered by an 8.4V pack should be adequate, with speed controlled by a Kontronics Easy 1000 Speed Controller. It was around this package that work was undertaken to achieve my vision.
I found that I could fit the motor and gearbox to the model by drilling four holes in the wooden motor mount in the model and fixing the motor and gearbox assembly in place using cable ties. I also opened out the hole in the ply bulkhead to accommodate sliding the battery pack in via the underside cowl hatch. This was where I had my first problem - caused by the undercarriage leg. I had to remove the undercarriage and make a new undercarriage leg formed in such a way that it would no longer interfere with fitting the pack. This problem solved I then had to fit a balsa wood shelf in the cabin area to fit the receiver to, and Velcro was used to secure the receiver in place, and the speed controller behind the dummy instrument panel former. Two standard size servos were fitted for Rudder and Elevator control and the model was complete. Even the C of G was almost unchanged.
Having completed the model there was only one thing to do, and that is fly it. It was off to the field to try it. I found that unless the grass was very short a hand launch was preferable. Having given the model a good launch she gradually climbed away and performance while somewhat less sprightly than in it's i.c. life flew rather like a vintage model should - sedately. Once a reasonable height was reached the model flew quite happily on half throttle in a gradual climb. After six minutes using a 1700mAh pack it was time to land.
I have to admit that I was really pleased with my successful conversion and thus fired up spent the next year on and off refining the performance as I considered various changes. So what did I do? Well first of all I experimented with different propellors. I found that my original calculations were correct for prop size. However, prop type made quite a difference. The original APC prop was first changed to a Master Airscrew Scimitar which was both lighter thus reducing current demand, and more efficient. I subsequently fitted a Master Airscrew wooden propellor designed for electric power, and to date have found nothing superior.
The next thing I did was during the winter overhaul of my models. I decided to strip the Solartex off the model and re-covered the model in antique coloured Litespan. This gave a tremendous weight saving even after finishing with some Solarlac to provide some colour. The model was refinished identical to it's original colour scheme. No other work was undertaken to lighten the model structure, but I did fit foam wheels. These changes improved the model's performance further, and with 1900mAh cells flight times up to 15 minutes have been had, but are typically 9-10 minutes.
So did I enjoy doing the conversion and was it worthwhile? I have to say "Yes!" to both. I have learnt lessons along the way but the lazy enjoyment I get from flying the model is fantastic, and it's quiet. It is also interesting to think that this model design is of the same age as the first R/C electric powered flight in 1948. With the recent growth in electric flight in the UK, I would like to think that this article will inspire some of those new to this form of power to try and convert some of the conventional i.c. designs to electric. Certainly there are a number of vintage designs that lend themselves to conversion. Go on, dig out some of those old models, and plans and get experimenting, it beats an ARTF any day.