Teeny Trainer (oz6689)

About this Plan

Teeny Trainer. Radio control trainer. All-sheet design.

Quote: "A basic, inexpensive 37in wingspan trainer for .75 - 1.5cc diesel engines and 2 channel radio gear. Ideal for beginners."

Direct submission to Outerzone.

Quote: "If your idea of the ideal trainer is something powered by a .40 hauling 4-1/2 lbs of model around whilst waggling the sticks of a very expensive four-channel R/C set, turn past this article! If that is your ideal but you can't afford such a beast then perhaps this will be of interest to you after all.

This model is designed to be cheap to build and run, powered by anything from an .049 to a 1.5 cc diesel and cheap two-channel radio gear. Mind you, a 1.5 cc puts it past the raw beginner. The original model has had all these sizes of moinr at one time or another! The cheapest option is probably to use .75 cc diesel (no glow battery or clip to buy or worry about) as the fuel costs will be very low despite the apparently high cost of diesel fuel, because so little of it will be used per flight. I used two-channel 27 Mhz gear because it's cheap and I have never experienced any interference despite the abundance of other users of the frequency. The wing and tail are all sheet for cheapness and simplicity and, all told, the model needs barely more than six sheets of wood! Not using wheels saves weight, drag and expense as well as giving one less item to break when the thing hits the ground!

Let's get carving! Construction could hardly be simpler. The sheets for the wings need to he fairly springy medium weight to avoid being either for heavy or too weak. Make sure that they will butt together nicely without gaps, then tape the join on one side. Turn the pieces over and open the gap using the tape as a hinge, put a bead of glue along the join and leave it tape side down with some weight on top to set. It's advisable to use a bit of scrap 1/4 in wood to do the anti-warp tips though you might get away without them.

The same procedure is used to glue the tips in place. When all this is set the tips are shaped, the front of the wing is rounded off and the back of it can be taken down to a fairly thin edge, no thinner than 1/16 in or it will be too weak. Find the middle of the wing and mark it accurately square with a try square, cut the wing in half along the line and sand the edges with a block and grasspaper to give a slight bevel to the edge, this is to approximate the dihedral angle and give a stronger join. Pin one wing to the board over a sheet of polythene and glue the other half to it, chocking it up with something to give the dihedral angle. When set, the join will be reinforced with either very thin glass and resin or glue soaked bandage. Cover the wing with film to finish the job.

Tail bits: The tail and fin are also cut from sheet. Shape them as you did for the wings before cutting the elevator and rudder free. Sand the leading edge of the rudder to give a 'V' shape to enable you to centre hinge it. The elevator can also be sanded to this shape or simply chamfered on the lower edge to give a top hinge with mylar by cutting a slot with the knife blade into the centre of the surfaces, insert the piece of mylar and put a drop of superglue in the gap. Add the control horns in the position shown and put them to one side.

Fuselage: The final job is the fuselage. The sides can either be cut from two near identical pieces of 3 in wide wood or, with a hit of juggling, from one piece of 4 in wide wood. I'm mean and used the latter! The wood used can be quite hard as there is very little bend in the sides, just so long as both sides are the same. The piece of ply reinforcement I used was 1/64 thick, glued in place with Evo-Stick impact adhesive. 1/32 would be OK but I think that 1/16 in would be a bit over the top. Some sort of extra strength in the nose is a must as this is a highly stressed area.

Dependent on the motor used is the method of mounting it to the nose. Some small motors can be bolted directly to a ply former using the backplate screws, others need to have beams to bolt the motor to. The latter will have to be used if a 1.5 cc motor is chosen, for rigidity. The position of the motor mount (F1) will also vary according to the motor. If a Cox .049 is to be used, then (F2) and a separate fuel tank can be omitted as this motor has a buitt-in tank (except for the .049 which is a bit pricey). The tank I used was home made but a commercial control line tank ui about 10-15ce capacity should be easily obtainable.

As drawn on the plan the fuselage is quite narrow so that the top and bottom sheeting can come from a single sheet of 4 in wide wood cut down the centre. This might be being just a bit too mean and it may be better in add a little to the width of the formers to give more room for access to the gear and buy an extra sheet of 1/16 in wood. Once all the parts are cut out the reinforcements are glued in place as stated earlier and the main four formers are glued in place. Superglue is a lot quicker than anything else here, though not cheap.

When one side is set the other side is glued in place checking that everything is square - putting the tailplane in place temporarily can be an aid here. The tail can then be pulled in and the other formers added. Do check to make sure that the fuselage is straight. The servo bearers can be almost anything that is hard enough to take a woudscrew and are added next, along with the servos. Pin the tail in place and make up the pushrods checking that everything moves in the correct direction - unless your set has reversing switches. When happy with it remove the tail and sheet the fuselage top arid bottom. I prefer to have the grain running along the fuselage length for strength but some prefer it across for some reason.

The part in front of the wing, top and bottom, is sheeted grain across in order to get the wood to bend; it can either be 1/8 or two layers of 1/16 laminated. My tank was boxed in by the top sheeting just leaving the pipes sticking out - don't forgot to fuelproof the nose area. Add the side cheek doublers if your motor installation allows it, then sand everything smooth and cover it with film. Cut away just enough film from the tail and tin to allow a wood- to-wood join and glue them in place. Note that the fin is glued to the trip of the tail as well as to the lop sheeting. The dowel band retainers can now be glued into their pre-drilled holes and painted. Try to make very sure that everything is square during gluing.

You should now have a nearly ready to fly model. Check the balance point. You might need to move the battery around to get the balance right. I used white styrene blocks to stop the battery shifting around. Try to put the switch on the side opposite to the exhaust, though I realise that this is impossible with the radial exhaust of most small motors. Don't exceed the movements shown on the plan, you really don't want too much control unless you want the plane to be a mini-aerobatic job, not a trainer.

Off we go: Now to the flying. If this is your first model then it is advisable to get someone with experience to try it out for you just to make sure that there is nothing drastically wrong with it. He should be able to trim it for you so that it will fly steady and straight. When powered by the smaller motors the performance is not exactly staggering and climb out is slow, rather like a powered glider. Too much up at this stage will cause the model to wallow around and perhaps stall - it will almost certainly lose altitude rather than gain it. A balance has to be achieved between forward speed and climb. Naturally the bigger the motor the hotter the climb but you don't want a pylon racer either!"

Supplementary file notes

Article, thanks to RMC.

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