Triplet (oz12324)

About this Plan

Triplet. Radio control muti-purpose model for use as a sailplane, motorised sailplane, or floatplane. For single channel, with .3 to .8 cc engines.

Direct submission to Outerzone.

Update 02/03/2021: Added article, thanks to RFJ.

Quote: "A 42 inch span single channel model for slope soaring, powered soaring, or over water operation from Finland. Triplet, by Tom Prukner.

IN the summer three years ago, my work as a concert pianist took me to a beautiful island off the west coast of Norway. No real R/C modeller goes anywhere for any length of time without a model, and I had my R/C aircraft with me. However, this was no place to fly a normal land model, for the island was densely forested. In the first days after my arrival I searched for an open space but none was to be found. I began fishing and while watching the seagulls, evolved the idea of a motorised slope soarer that could be landed in the water.

For this purpose the fuselage of the model had to be buoyant but at the same time of aerodynamically sleek shape. To simplify things a little, the model would not necessarily have to take off from water.

Two or three days later the model was finished and I took it out to fly along the coast with the seagulls. From the very beginning the model performed in excellent style, but it took longer than I had envisaged to master the technique of soaring over the coastal cliffs, and over the trees, and to hold the model into the lift over the cliff edge without losing it among the trees a short distance further inland.

Certainly it is easy to fly Triplet when the motor is running and to maintain altitude for thermal soaring, but the most exciting flying was in maintaining 100 to 150 feet altitude, soaring on the lift along the coast line. After the three month summer, I knew this little island better than the seagulls that were born there.

On many occasions I would observe the seagulls soaring along the cliff edge on lift insufficient to sustain my model. The exceptional soaring performances of the gulls I attributed to their ability to flex their wings as necessary. However, to create a rigid wing machine that would respond quickly to all commands was an achievement in itself.

During this summer we had many British tourists in the hotel, who became very interested in my model flying activities, and many good manoeuvres were accompanied by applause. The island is a very quiet and peaceful place and in consequence the little Cox Pee Wee engine sounded very noisy, demanding a home constructed silencer. What the tourists really appreciated were the long gliding flights, especially if they were prolonged over the slope.

Another flying technique which I evolved, was to control the model from a boat in the water, from which I would bring the model in for a water landing. The boat was very handy for retrieving purposes, since to swim in the cold waters of these northern latitudes was not very pleasant.

Construction: Begin by selecting the best balsa wood, warp free and lightweight. Dope all sheets before cutting, with thin dope and sand smooth. To shorten the work time, cut all parts accurately from the plan so that you end up with a complete set of parts as if you were building the model from a kit.

Wings are of all sheet construction for simplicity. The bottom sheet is layed on the work bench and ribs, trailing edge, leading edge and spars are cemented to it. Be sure that the cement is dry before removing the wing from the work bench. Sand carefully over the ribs to achieve a good airfoil section and then sheet the top sheet in place. Do not soak the sheets in water to achieve the top surface camber because in drying, the sheet will shrink and deform the wing. It is much better to curve the sheet carefully over the work bench edge using finger pressure.

The model was originally designed to use the Webra Picco pulse proportional system but should be capable of accepting many other single channel installations. If not, the fuselage will require some enlarging. If the model is likely to be rather heavy, then I suggest you increase the wing chord to 4-3/4 in. The same goes for the engine nacelle, if you intend to install a .5 to 8 c.c. motor instead of the Cox Pee Wee, you will have to enlarge the cell to suit. Actually, I feel that most modellers tend to modify specific designs to suit their own radio and power plant systems as they desire. Complete with Cox Pee Wee motor, my model weighs 8 oz. ready to fly, 2.8 oz. of which is accounted by the Webra Picco installation. My Picco incidentally is three years old.

Waterproofing is, of course, of immense importance, since my model was operated from salt water, a little sea water that penetrated the radio installation compartment did some damage to the equipment and after two seasons of this type of flying my receiver ceased to work and had to be overhauled due to the corrosive effect of salt water. It is therefore a good idea to put items such as receiver in nylon bags sealed with tape. From 1 mm celuloid you can make a very good all-enclosing waterproof case, which also offers good crash protection for your R/C equipment. At the same time it provides a very compact installation unit which can be switched from model to model as desired. Commence fuselage construction by cementing together the water hull. The basic hull is designed to provide the necessary buoyancy for the model and consequently must be constructed accurately to be absolutely waterproof, it is also very strong.

The tail boom also has to be buoyant so that it will not sink into the water when the model lands and consequently must also be waterproof. The tail float and wing tip floats are provided and should be added to the model when flown in windy conditions. These are easily and quickly fitted by the use of rubber band retainers. The wings are held down to the fuselage by rubber bands also, and the wing seat should also be waterproofed with a foam rubber cushion. Obviously there must be holes in the fuselage for the receiver aerial and wire torque rod to the rudder. But if you reduce hole size to the minimum acceptable, you will get little water inside the fuselage.

Flying: Check the angles of wing, tailplane and engine thrust line, and be sure that the model is balanced correctly. After three seasons of flying, repair work and extra colour tissue decoration has increased the total weight of the original to 12-1/4 oz. The little Pee Wee motor provides plenty of power for fast flight, a good climb rate and stunting ability. On the slope, the model performs really well. if the wind is very strong, ballast the model to 17-1/2 oz all up weight. Thus loaded, the model should be very fast but still has an excellent glide ratio.

Altogether, you have here a perfect model for slope soaring, power flying, stunts, hand launch over land operation (add wheels if you wish) or over water flying.

I can really recommend this model to all single channel enthusiasts, beginner or expert. Try one and enjoy R/C flying more."

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