Jumping Gemini (oz7529)


Jumping Gemini (oz7529) by Dave Tafler 1963 - plan thumbnail

About this Plan

Jumping Gemini. Radio control sport model. For single channel and .049 power.

Quote: "WE were watching the lads practicing for the followings day's contest at the British National Championships 1962. The voice that we had heard a number of times that afternoon came over the loudspeaker again - Next on please - suddenly I was shoved out on to the runway - It's your turn Dave - The Orbit 10 Tx which I was holding seemed a little out of place, for it had just that second been pushed into my hand and the surrounding crowd were laughing their heads off, their reason, in my other hand was a Keil Kraft Gemini, a 22 in span rubber model, converted to free flight with a Cox TD .010. The impish grins on the faces of Ray Brown and Roy Norris, even made me see the funny side of it.

The two days I spent at the Nationals, set me thinking, why was it not possible to R/C a model of similar dimensions to the KK Gemini? So in the following weeks I got to work sorting through many magazines to find a miniature radio unit that would be constantly reliable. This I found in the Otarion O-21 which was ideal, being only 1 x 14 x 5/8 in and 1/2 oz in weight and needing only 3 volts to operate. Then came the actuator, and on the advice given by Otarion themselves the Elmic Range were ideally suited to the receiver, being that all the Elmic line have 12 ohm coils, I chose the Conquest, being the most compact of them all. Then came my first 'Jumping Gemini', a 24 in span weirdly! The first flights of which were absolute disaster, after flying erratically around our flying field it did a perfect spiral dive from about 150 ft from which, unfortunately, it never ever recovered. This put paid to my Otarion Rx for a while, I had broken off one of the condensers (well, no one told me that it was really necessary to wrap the Rx in sponge rubber, I guess I always learn the hard way!)

After this experience I got down to some more serious designing. My second Jumping Gemini started to look a little more like the model I wanted, being slightly larger, at 27 in wing span, all sheet fuselage, sheet tail plane and a balsa and ply laminated fin. Not being fond of slow flying models I decided to step up the power from 0.02 to 0.049.

The Otarion was returned from the USA after exceptionally quick service, the model was now completed and ready to fly and after a few satisfactory glide tests the motor was started, the radio checked, then 'All systems go'. I think in the few seconds that followed all Hell was let loose!

That afternoon I put the model on my workbench and looked at it, where had I gone wrong, why wasn't it constant? On the other hand, what was I looking for? In the back of my mind was a cross between Chris Olsen's Uproar (oz2220), Johnny Dumble's 'Sixgun' and Ken Willard's Schoolboy(oz1030) - condensed! Whereas, at the moment, I had a missile with characteristics not unlike 'Skybolt', on reflection I jotted these down as follows:

Weight: 20 oz.
Flight characteristics: uncontrollable.
Maneuverability: virtually nonexistent.
Glide attitude: fast and vertical.

I would start designing all over again, taking into consideration what I had learned with the two previous models. Obviously the 6 per cent wing section I had used was insufficient so I decided to try 17 per cent, also a lighter construction using a 'D' box section and 1/16 in sheet balsa throughout, no leading edge just a lap over. Now, for the fuselage. In the previous model I had used 1/8 in sheet balsa throughout and a knock-off nose block, containing the fuel tank and the motor, but I had not found this satisfactory. I now use 3/32 in sheet for the fuselage sides and keep the 1/8 in for top and bottom using only one ply former to take the nose-wheel. The length of the fuselage is now increased by 2 in, giving a slightly longer tail moment. I felt the tail plane area should be increased to help the glide stability, so I added 2-1/2 sq in, laminating two pieces of 3/32 sheet to prevent warping.

The model was duly completed, weighing 4 oz less than its predecessor and looked a lot cleaner in design. On the day of flying, the first launch was again tragic! As the model left my hand it just went nose in (too much down thrust). This was adjusted and to my delight it soared away a real treat, its air speed greatly reduced by the drag caused by the considerably thicker wing section and it handled very well. After flying this model consistently for many weeks I decided to build another for proportional control, which..."

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