Back to the photosUpdate. The motor has been upgraded with an 18 turn double wound "Leisure 05", and a timed motor switch has replaced the radio system. The motor draws 40 amps from a 7 cell pack. The propeller is a 10 x 7 spinning at the same speeds expected from a 35 to 40 size IC motor. The Super Zilch now flies with authority on 60 foot lines.
The title may appear to be an oxymoron, but it accurately represents some experimentation I have been doing recently. The concept was to build and fly an electric control line model, but the idea was subsequently extended to use radio to provide throttle control so the motor could be started and stopped at will. You may be wondering why someone would experiment with such a concept, but radio control becomes boring after while. I also wanted to try out something that does not appear to have been done before, and possibly create a new branch of our hobby.
I began to think about the idea, and how it could be achieved, towards the end of last year. I did not want to spend a lot of money just in case the concept was a failure, so therefore I would use as much existing equipment as possible. This fixed the propulsion system as a Graupner Speed 600 BB coupled to an Olympus belt drive unit and being powered by seven 1700 mAH cells. I know from previous experience this configuration works quite well and manages to throw an 11 x 8 propeller. For the amount of power available, the all up weight of the model should not exceed 1500 grams.
Other considerations centred on the speed controller and radio gear. The speed controller could be a standard high frequency unit with BEC to power the receiver. The radio gear needed to be a custom design as I did not fancy trying to operate a standard transmitter while hanging onto the handle! I envisaged a clip on belt mounted low power transmitter with a single channel. Some time earlier, I had been given a couple of unwanted 29MHz two channel AM receivers, so this solved the problem of a receiver.
Building the electronics required was fairly easy. The speed controller is a design off the Internet, with a few modifications to suit the application. While the resulting controller is large and ugly compared to commercial units, it only cost me $4, and that was for the servo lead! I won't bore you with the transmitter details, other than it provides a single channel from a potentiometer, and works on the 29MHz band.
With the electronics completed, I now needed a model. Sorting through the control line plans turned up two contenders with enough wing area to carry the expected weight. The decision fell to a 1947 design called Super Zilch. I felt this was the best design as far as wing area and lightweight construction were concerned. Other factors were that the Super Zilch, with an Ohlsson 60 or Super Cyclone 10cc spark ignition motor, weighed around 3 pounds, or 1363 grams. If the model flew at this weight, then it should fly with electric power.
Building the Super Zilch was an easy enough, though time consuming, affair. The only changes from original were to replace the folded metal hinges on the elevator with pinned nylon types, and lowering the wing position by 10mm to give easier access to the battery pack. Even the covering was original, using a single layer of lightweight tissue on the fuselage and a double layer on the wings. For the price of tissue and dope, why would anyone consider using that horribly expensive and heavy plastic film stuff?
The model was finished off by installing a pilot in the cockpit with mock voltage and current meters on the instrument panel. Labels were added to indicate the motor is an Ohlsson 600 BB and it is being flown by Oberleutnant Wolfgang Graupner. Hopefully you can tell I am not taking it all too seriously!
The completed model without radio gear and electric's weighed in at 550 grams, much lighter than I had expected. With everything installed, the weight came in at a quite respectable 1325 grams.
With all of the usual checks completed, it was off to Yokine Reserve for a test flight. Being a WA Radio Soarers member is handy as the field is only a few minutes away and any sort of electric power is allowed. It was weird to have to put a frequency key in the keyboard to fly a control line model! The Zilch was hooked up to a U-Reely handle and the lines set to around fifty feet. The motor was started up and the model slowly trundled away. The Zilch did not accelerate in the first quarter of a lap. I was thinking it was underpowered and would never go, but then it suddenly picked up. Another quarter of a lap and the model was in the air and seemed to be quite stable, so I must have set the CG correctly. After a few laps, I tried throttling back, but the motor kept going. Another couple of laps later the motor did stop and the Zilch glided in for a good landing.
The radio gear was put on the bench for testing, and I discovered the transmitter did not seem to be radiating the signal efficiently. Some experimentation later saw the hanging wire antenna replaced with a whip antenna and the addition of a hanging ground wire. This made sense as transmitters are held in the hand, and it is the pilot's body that provides a ground connection.
A month went by before the weather was suitable for flying. The motor was started up and the Zilch lifted into the air after a short run. On a full charge with maximum throttle, the Zilch was pulling heavily on the lines, so I reduced the throttle until it was comfortable. After six or eight laps, I began to feel a little dizzy so I landed. A few minutes rest and the Zilch was off again. This time I was used to spinning around. The Zilch completed forty to fifty laps before the battery showed signs of discharge, and was brought in for a landing.
The flying tests showed the idea of electric control line was successful, provided consideration was given to the type of model, motor, and weight. I am sure that others will take up the challenge of converting IC designs to electric power, using better motors and lighter batteries to obtain aerobatic performance. With increasing restrictions on noise, electric power is the way of the future, unless you enjoy the long drive to a site where the only potential complainants are a herd of cows!
© 2001 Lex Cunningham