Slingsby Eagle 3. (aka Mini Eagle). Scale glider for radio control.
Quote: "This mini scale Slingsby Eagle came into being as a result of chatting to your editor on the phone. He was asking for models that would fit RM roll out plans, but was looking for something a little different to the usual run. So it gave me an excuse to try an idea that had been in my mind for some time - a mini scale series of Slingsbys. They must be easier to transport, cheaper and quicker to build than the 1/4 scale variety.
If the flying was still reasonable then it would be super, so out with the drawing board and arrive at a suitable size to fit the paper. Around 66 in span seemed about right which must make this Eagle about 1/8 scale or thereabouts. I was lucky in having one of Slingsby's own rigging drawings so the model outline is pretty true to scale and so are the tail areas and control surfaces. The construction is, however, not scale since I reasoned at this size it wasn't worth making such a fiddly constructional exercise.
The wing section is a Gottingen 398 which is in keeping with the full-size Gottingen 535 - I think! I designed the model to accept the average radio pack, but I must confess it would be easier to use a mini servo on the ailerons. I used Futaba Challenger and 148 servos on my model and the flying weight is around 24 ounces all up. The model is finished in a colour scheme supplied by John Watkins who built a 1/4 scale Eagle a few years ago and says it was the best model he ever had.
The flying is superb and not in the least jumpy. It will slow down to a scale speed or go like a bat out of hell if needed. It loops, rolls, stall turns and spins - which I bet the full-size couldn't manage - but will also fly around in a most sedate and stable manner, if you are looking for scale effect. At height you can't tell whether it is a mini scale or a 1/4 scale at a higher ceiling. She is happier in a force four but will scratch in much lighter winds. So, all in all, the Eagle has proved to be very successful.
Now I don't see much point in giving blow by blow constructional notes, it really is easy. However, a few warnings of possible awkward areas could be useful. I think the wingtip panels are the worst bits. The spars are 1/4 x 1/8in spruce tapered with a razor plane to 1/4 x 1/16 in and the tip ribs are small. Do note the 1/8 in washout; this is also carved into the, sheet ailerons ie, the aileron is slightly twisted in its length.
The wing root canopy area on my model is faked using silver dope; you could glaze it as per full-size but this could make it a bit weak at a strategic position - you are on your own over that one! The fin and rudder are cut from 1/4 in sheet outlines, shaped with a razor plane and sanded then cut out and ribbed with blanks. This is optional but my model did carry a couple of ounces nose weight.
The cockpit canopy was a near commercial type fixed to a hoop mould and pushed to a final correct profile using a male former and an electric fire. This made a perfect canopy whereas my first efforts using a flat sheet of celluloid were a complete failure. I got the correct shape but it was too thin and split on the sides.
The nose block is hollowed out to accept the nicad; get the weight as far forward as possible and give the receiver room in the cockpit. The forward wing dowel is a bit tricky to line up; do use a good quality 1/Sin ply for the dowel wing mount brace. The 3/4 in dowel is designed to break in a heavy arrival but you don't want it to part company before that so do make a good job of it. Take a bit of time over the ply brace, don't split out the hole but make a clean drill hole and epoxy the dowel into position and form a 3/8 sheet block of fair and reinforce the dowel into the upper surface of the wing centre section.
The control movements are as follows, measured at the trailing edge of the appropriate surface: Aileron up 3/8 in; down 1/4 in. Rudder left/right 3/8 in; Elevator up 3/8 in; down 1/4 in. The rudder and aileron are coupled together with a 'Y' lead - I don't know that it is necessary but I haven't tried them uncoupled. So it's up to the individual builder; if you can mix both controls with either hands then have a go. I think it would be OK.
Of course if you have an electronic mixing transmitter, then you can start off with coupled aileron/rudder and try it at a safe height. The CG is at 25% which seems a good safe compromise position. I covered my own model with Solartex and sprayed the fuselage with Ford Olympic Blue car cellulose which I think looks pretty and is a very simple scheme. Thanks again John for the colours; I couldn't find a scheme, so yours works well.
Finally, I would like to say that mini Eagle would, I think, be a good model for anyone who fancies a scale glider without too much financial worry or five months hard labour! Have a go, you could well be pleasantly surprised. Good flying and happy landings."
Update 23/05/2016: article pages, text & pics added, thanks to RFJ.
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