Say 'model airplane' and most people think about somebody with a transmitter in his/her hands. Less known, but still alive, are free flight and control line airplanes, without R/C. Most youngsters don't know about this "pre digital" hobby. A model aircraft flying in circles on a line around the pilot, who has a handle in the hand to control the up/down movement. This project wants to inspire people, to build a balsa wood airplane from a drawing. Special for this project is that the motor of the aircraft is powered over the control lines. The on/off switch is on the control handle and the battery is carried on the person.
Watch the VIDEO of the project here:
With a control line aircraft you can fly 'feelingly', this is an advantage with respect to R/C. The line between the handle and the model let you feel force feedback; acceleration power, motor vibrations and air pressure on the flaps like the control stick in a 'real' airplane. Success!!!
Step 1: What do you need ?
The best start is a beginners C/L model with a full size plan. My choice was the Scoot by Ron Warring. You are free to choose any other C/L model of the same wingspan. The Scoot full size plan and the parts list, you can download below as PDF files, for print out. Most of the stuff you can buy in the local hobby shop or over internet. For the Scoot you buy balsawood; 3mm or 0.12inch for elevator and rudder, 6mm or 0.23inch for the wing, and 10mm or 0.4inch for the fuselage. Plywood from 2mm or 0.08inch for nose, tumbler and line guide. For the handle, plywood from 6mm or 0.23inch thick. The balsa I bought was enough for 2 models.
Step 2: Cutting and sanding balsawood.
First you cut out the outline of the model parts. They are full size when you print on A4 paper. Draw the outline on to the balsa wood by pen or with carbon paper. Cut out the parts with a hand bow saw or a Stanley knive. Take care; take time to do it right! Be careful with the wing and elevator cutout in the fuselage. The sanding is done with two grades sanding sponges; 60 and 180. Follow the shape of the section when sanding the wing, elevator and rudder.
Step 3: Landing gear and motor
The landing gear is made out of a rod spring wire. It's hard to cut and to bow. As you can see; it can be done! The wheels are fixed on the axis by a wire terminal connector. Now it's time to attach the landing gear to the fuselage. I placed an extra dowel to block the landing gear to slide to the front. The 2 brackets for the motor attachment are made of alluminium strip 2mm or 0.08inch thick and 2cm or 0.8inch wide.
Step 4: Painting and attachment wing and elevator
Before attaching the wing, elevator and rudder to the fuselage you can paint the model with acrylic transparant varnisch, as primer. Paint it in thin layers and more times. Line out and correct the wing, elevator and rudder related to the fuselage before putting the pegs in. For the hinges of the elevator I used very thin fiber pieces. Use always the best glue for the job.
Step 5: Attachment line guide, tumbler, rod, handle
Now it is time to build the elevator control system. We need a triangle shape tumbler, a thin rod and an elevator lever piece. The tumbler is made from thin ply, the lever piece I bought in the shop. The steel rod is 30cm or 1foot long. It has been made exactly to keep the neutral position. For the line guide I choose alluminium square profile of 1cm or 0.4inch and 1mm or 0.04inch thick. Use rings on the 3mm or 0.12inch bolt and nut, this to connect the tumbler with the wing.
Step 6: The finishing touch
All is coming together in the last step. Testing is a important part of prototyping. For example: I had to calculate the (copper wire) line for diameter and strenght. I wanted to use soft cable, but the isolation made it to heavy for use. It worked out that enamel winding copper wire was the best option. Other example: Was their enough power left for the motor after cable losses? From a 12V battery was 5.2V left for the motor by a current of 5.4A. So a motor power of 28W (can be 37W). Don't forget to balance the plane. First the motor has to be directed 5 degree to the right, to pull the lines. Second; taking the plane at 1/3 from the wingtip it needs to be horizontal. Else, use lead to counter weight. I used 20gr or 0.7ounce lead around the fuselage. Roll always the line (copper wire) to a cable drum, else the wire can easily damage.
Step 7: Conclusion
Flying the Scoot for the first time was a surprise. All my calculations; motorpower, line losses, battery, etc. made that the model was flying and reacting sufficient to my control. The switch on the control handle is a godsend; I can solely start de airplane from a flat surface and decide when to stop. It is even possible to do some power on/off tricks during flight. I am shure that this concept can be enhanced. I was carrying a sealed battery of 3 Kg or 6 Pound in a strong bag (thanks Kaspar!). The goal of this project, building and testing an easy and cheap way of C/L flight, has been reached. The fun, making from a plan a model airplane, was great; even bigger the fun to fly. I hope that this instructable let people choose for the old craftsmanship; working with balsawood and a simple electric circuit.