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MY FORAY INTO ELECTRIC CONTROL LINE by Brian Waterland Over the years I had often thought about the possibilities of Electric powered Control Line flying. Having once used Laystrate as a substitute for nichrome wire in foam wing cutting I dismissed "power down the lines" as a non starter. If the lines had that much resistance it was plainly an unsuitable choice for all but the simplest of models flying on very short lines. The alternative solution of "on board batteries" had been impressively demonstrated by our Belgian friend Jan Odyn on his regular visits to the Peterborough Cabbage Patch Nats. Back then Jan used special lightweight models and brushed motors with Nicad cells located within the wings At one August Nationals a group of us discussed the possibilities of using the, then fairly new, Outrunner motors and Lipo cells. Ian Lever (current SAM35 Chairman) promised to build one and bring it to the Flying Aces meeting the next week! He achieved this with a model incorporating an RC Receiver. The Control Line pilot had a transmitter attached to his belt thus allowing him to vary the power throughout the flight and, perhaps more importantly, switch off the power at the end. The model and system worked well (right up to the point where the pod parted company with the boom!) but somehow I didn't like the use of RC. In my eyes it was a "hybrid" and not a "pure" control liner. No,to me the answer was a self contained aircraft using a brushless outrunner and Lipo cells. As you will no doubt understand, at that time this presented a major problem. The brushless ESC (Electronic Speed Controller) needs a square wave input signal of between 1 and 2 milliseconds simply to operate. The ESC normally gets this signal from the radio receiver (throttle channel) - but I didn't want to use radio! Obviously I needed a device that would mimic that signal, limit the time of the motor run and, if possible, give some warning that the motor was about to quit (akin to the motor blip from an empty fuel tank). I wrote a simple specification and a club member kindly made up an electronic device. Unfortunately both this, and the subsequent commercial units I purchased from abroad, all gave problems. In part this may have been caused by the fact that ESCs do not have a common "architecture" What works with one ESC will not necessarily work with another. Convinced that the ESC problem would be solved I had gone ahead anyway and built an Electric CL model. I was tempted to follow Jan Odyn and build an ultra lightweight model (after all there is very little vibration) but, in the end, I settled on building a Peacemaker! Having flown an Oliver Tiger powered Peacemaker in competitions for many years I thought it would be interesting to see how the different power sources affected the flying characteristics. I was reluctant to tie wrap the cells to the side of the standard fuselage and instead opted to change the fuselage from a profile to a rectangular box with 1/8" sheet sides spaced just wide enough apart to fit the Battery pack between. Moving the batteries forward and incorporating a cooling duct for the cells and the ESC gave the model a somewhat bulbous nose so I turned it into a sort of jet Chance Vought Corsair complete with U.S. Navy type grey colour scheme. In homage to its famous forebear I named it "Buntline Special" and adorned the wing with a silhouette of that gun. The wings, tail and fin are all very close to the original model, just squared off a little bit, and the mono-wheel undercarriage is retained. The top of the cooling duct is quickly detachable (by removing two bamboo dowels) and retains the battery pack throughout the sharpest of manoeuvres. The overall weight is about I oz more than my i.c.version which probably makes it about the same if fuel is included I recalled that a standard Oliver Tiger develops around 1/3 HP so I chose an Outrunner motor of 250 Watts and 1000 KV.The battery is a Loong Max 3 cell 2250 mAh pack (11.1V) - both from GiantcodRC. The prop is, currently, a 10 X 6 Master Airscrew. This setup draws around 24 Amps (260Watts) It should however be remembered that the shaft power will be lower than this due to the inefficiencies within the ESC and motor. The GWS ESC is rated at 35 Amps (generally speaking the less sophisticated the ESC the more chance of success you will have in this application!). BUT the widget that made it all work and solved all the problems associated with the ESC is an Horizon Hobbies E-flite "Motor Timer" (ref EFLA172) costing £9.99. This lacks the super sophistication of some units but gives a motor duration of between 1 and 7 minutes in one minute steps, a blip 10 seconds before motor shutdown, has adjustable max rpm and connections and signals for an undercarriage retract/lower servo. So, how does the Buntline Special fly? Very well, but not, at the moment, as well as the Oliver powered version. It is however fully aerobatic and will fly the complete Vintage Schedule. It is not as good at the "square" manoeuvres and this may be helped by moving the CG back (by re-locating the battery pack).On the other hand this may cause it to "fishtail" coming out of the manoeuvres or "rock" on the lines! To date I have only flown it on 52 ft lines and feel it needs a bit more power. This could probably be improved by further propeller experiments. Experimentation with electric powered models is inherently more protracted -unless you have an infinite supply of ready charged battery packs to hand! When time permits, I intend to change the motor for an Overlander C3536 (1000kV) unit. It is very easy to forget the dangers inherent in handling a motor of 1/3HP and to make the battery connection from the front, over the propeller, or to carry the model back from a flight under your arm. This SHOULD be safe, but we are relying totally on the integrity of a bunch of surface mount components on a cheap PC board. Unlike ic engines electric motors don't stall, they just keep hitting you! Fitting a switch capable of handling 24 amps is impractical so I am now considering fitting an "arming device" made from a modified Deans plug. Removing the plug would kill all power to the ESC and motor. In flight the model is quiet (most of the noise comes from the propeller) and it is strange having a conversation with someone on the outside of the circle without shouting! I will not fly it without a helper to ensure that a member of the public, unaware of the danger, doesn't wander into the circle. As with other electric models, it is nice to fly in your Sunday best (that's the trousers without the patches) and not going home oily and smelly. All in all there is, I feel, a great future for electric CL. We already have Electric models in F3B and RC Pylon Racing, when are we going to see CL Electric Speed as a Nats class? Brian Waterland |