Bijou (oz14650)

About this Plan

Bijou. Radio control aerobatic slope soarer model. Wingspan 40 in.

Quote: "Build from our full-size plans! Bijou. Build Len Whalley's 40 in aerobatic sloper.

Quick to build lightweight, convenient. All the information you need is on the plan so what shall we talk about? There are always some things we can add.

Development: Similar in size and proportions to the built-up Laser of the early '80s (an American design from the San Fernando Valley Silent Flyers) which has been reproduced in many guises, a number of radical changes have been made to produce this aerobatic design. The fairly long nose and tail moments, and light loading have been retained and are still desirable, but it was felt that the model should be slimmer, demountable and a modern aerofoil (S-6061 @ 1-13) was chosen with the aileron servo set into the depth of the blue foam wing.

All these changes have worked well and with only one slight exception, the present design has hardly varied from the earliest concept. That change has come about from a desire to further reduce all-up-weight.

It was found that since the modern standard receiver fits (just) above the wing, the elevator servo can be placed in front of the wing, and allows further reduction of the nose-weight. The slimmer fuselage will not accept a square 500mah or 700 pack and so the four cells need to be arranged as a 'three and one'. If you are careful, this can be done without breaking the tags on a standard flat four, but do remember to cover over any now-exposed wires with insulating tape.

Probably the single most essential improvement from the earlier design is in the tip construction and shape. This is a bit of a hobby-horse of mine that we can talk about another time. Having experienced the vagaries of sharp edged wing tips and the flip-flopping nuisance of square ended wings which need to be kept above critical flying speed to avoid tip-stall, the tips shown, if carefully formed can produce a much more carefree style of flying. You still need to put the wings level from time to time but you can happily lean back a bit on the elevator stick in light lift without the risk of throwing a tip earthwards thus extending the lower end of the flyable wind speed range.

Don't pick up the idea that this model is of any use for first experience on ailerons, no more than any other flat low-winged design. There is, as usual with this type, no self-stability in roll and very little in pitch, so you need to know what to expect and have a good sense of orientation (or be a fast learner) if you wanted to move to this type from Rudder- Elevator.

Obviously the Bijou is not a serious aerobatic competition type so just what is it? Well, on days when the wind is between 20 and 40 Mph and the lift is strong, you can fill the valley within visible range with inside-outside-upright-inverted manoeuvres to your heart's content. This is what it is all about, isn't it? On the chilliest exposed edge of a craggy escarpment with an inane grin on your face as you fight the good flight. Why else do we do it? Then for all those days when the wind is less than 6 knots or more than 50, you can happily use the Bijou to test out the conditions without too much concern about cost or consequences.

Construction: The fuselage is a 1/8 balsa box with ply doublers leaving a minimum width necessary to take a standard sized servo but for the same old reasons of weight reduction, a smaller servo is better. The side view of the fuselage has been drooped over the wing to keep the CG low and the tailplane is held in place with bands. The fin has a ply platform base held onto the tailplane with waterproof adhesive tape of the type we use for all our hinges (clear Sylglas or similar).

Construction is extremely simple. The 1/16 ply doublers are fitted to the fuselage sides and then these are aligned by eye onto F2 and F4. The rear ends are pulled together, pegged with 1/4 in between, ensuring that the fuselage box is not twisted, and the top and bottom sheeting is scribed and cut to size. Likewise the front end onto F1, then the sheeting can be completed. The small amount of nose weight now needed to bring the CG onto the marked position can be located by drilling into the underside of the nose block itself and inserting a small lead slug. The dowels must be left long enough and if they are a tight fit in the ply of doublers they need not be glued. This will aid any future replacement.

Wing: First attach the leading edge and drag spar (false TE) then fit the ply full-depth spar and the tip blocks. The curved snakes and linkages to the ailerons are let into the underside with the minimum of disturbance to the surfaces as they exit to the top horn locations. The recess for the aileron servo can be simply cut into the foam so that the servo is a fairly tight fit, flush with the top surface. The two ball links are on either end of one 8 BA bolt, one over and one under the servo arm..."

Bijou plan/article from Silent Flight, April/May 1995.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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