Elmira (oz4444)

About this Plan

Elmira. Radio Control glider for slope soaring. For 6 channel reeds or proportional.

Direct submission to Outerzone.

Update 07/05/2018: Added kit review from Radio Modeller, January 1971, thanks to RFJ.

Quote: "RM Test Report: Elmira - elegant new Keilkraft sailplane. By Dave Hughes.

It looks much nicer than it does in the adverts, was one of the most frequent comments that came to my ears, when I took my newly completed Elmira to the slope. And when it was seen soaring majestically above the 'kippers,' several of the lads made up their minds on the spot to get the kit, which was all rather gratifying.

Indeed, this is certainly an impressive model, all 9ft 8in of it, and it looks like a real sailplane in the air. It is, as we mentioned in our initial Trade News inspection of the kit (Sept '70 issue) in fact a sort of semi-scale Skylark. (The name, Elmira, incidentally, is taken from the famous American gliding centre.) Let's reverse the time-honoured procedure, and talk about the model's flight performance first.

Flying characteristics: For the first test-flight we dashed out to Colley Hill, Reigate - a half-hour's drive from the office - as soon as the wind was at 230°, the best direction for this bowl-type site. With the Dwyer wind meter reading around 18 mph I launched off, and the Elmira soared away, penetrating easily and making height very rapidly. There was no need to touch the elevator trim, which I had at neutral, with the CG at the specified position.

Response to rudder seemed quite good at first, bearing in mind that there is not over-much dihedral, and I tacked the model to and fro for several minutes, all the time gaining height, and getting the feel of its handling qualities. With a crosswind, however, I soon found that heading the model back into wind was more difficult - response was sluggish and it tended to slide sideways. The only way to get a really sharp turn was to dive quite steeply, so as to increase the airspeed, to get the rudder to 'bite.' This showed up even more on landing as, when slowed down, it was impossible to combat with rudder any rolling tendency caused through turbulence. Result - I got my new model into a tree! We got it down quite safely, though, with only a few tears in the tissue covering, thanks to springy trees.

Further flights were made at the weekend (after patching the tissue), at treeless Ivinghoe, this time in a 12-15 mph north-westerly. Again, more compliments about the model's attractive appearance and - again - the lack of rudder response in certain conditions (ie 'with the wind under one wing,' so to say, and attempting to get it facing back into wind). Several times I had to force myself to push in down-elevator to build up speed for a turn - and only just got response in time to clear the hillside.

Once aware of this characteristic, however, I began to loosen up and get a little more adventuresome. Loops were very nice and round, without having to dive all that steeply, and with no screwing out. Stall-turns were not easy to get just right but I eventually found that they were best accomplished by applying full rudder much sooner than is usually necessary, while the model is still going nice and fast.

The stall itself is quite sharp, but with no wing-dropping tendency - unless you really slow up and stall in a banked attitude (another reason to keep the speed on in turns). The model does take quite a lot of sky to recover, however, so one must beware not to stall it at low altitude, though this may sound like superfluous advice!

The most impressive manoeuvre, however, is the spin. That's a lot of wing milling around! The rotation is quite slow, and gives a very scale-like appearance. Recovery simply requires letting go the sticks, and takes a little under half-a-turn. (Actually, the first time, I thought it wasn't going to pull out, and dabbed in a precautionary pump of down-elevator to un-stall the wing, but this subsequently proved unnecessary).

Having done three consecutive loops, I discovered that the silver steel rod wing 'dowels' had bent, giving a sort of tip-dihedral effect. This looked rather quaint - but improved the rudder-response quite noticeably! Preferring the more aesthetic appearance of the original dihedral, however, I have replaced the rather soft silver steel with some piano wire I brought back from Germany. (Sold as 3 mm, it is in fact 0.1173 in diameter, the silver steel being 0.1178 in. 10swg wire will not quite fit the brass tubes, so you may like to try tempering the rods supplied if you don't want variable dihedral). I have done six consecutive loops on several occasions with the piano wire dowels and the wings still flex, but spring back again when the load is off.

For the first few landings, after my 'treeing,' I cheated and floated the Elmira backwards over the landing area, by easing in up-elevator. As long as one keeps the nose dead into wind this method works well enough. On an ordinary 'square approach' one must maintain a good fast airspeed, however, since without ailerons it's not possible to pick up a wingtip near the ground, and you need a good head of steam to keep steerage way - if you'll pardon the mixed metaphors.

All-up weight of my model is 3-1/4 lb (4 oz lighter than the prototype!) including some 5-1/2 oz of lead nose-weight needed due to not being able to get the Deacs right up into the very slim nose. With an area of approximately 711 sq in the wing loading comes out at just 10 oz/sq ft - relatively light for a slope-soarer but maybe a little on the heavy side for thermalling. (You can't really have the best of both worlds).

Constructional comments: Structually, the Elmira follows very traditional lines, the fuselage being built on a basic crutch over the plan-view, with formers and sheet sides added, then removed from the board and block top and bottom decking added, and rounded off. (I used a razor-plane for this rounding-off process, which made it relatively painless). Incidentally, I found that the rear formers were not rebated to take the 1/16 ply doublers, and this had to be done before fitting the sides..."

Supplementary file notes

Review.

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