Elliptic 40 (oz9816)

About this Plan

Elliptic 40. Radio control sport model. Wingspan 58in, wing area 653 sq in. For .40 to .51 2-cycle, or .60 4-cycle engine, and 4 channels.

Quote: "DOES AN airplane have to be ugly to fly well? My friend Paul Wood and I have been pondering this question for some time now. Most of the acrobatic airplanes I've seen have been designed with the emphasis on functional aerodynamics and ease of construction, with the aesthetics of the ship somewhat of an afterthought. Could an aircraft be designed with good flight characteristics and pleasing lines? Could we achieve this goal using standard construction techniques? These questions brought us to the design of the Elliptic.

The version presented here is the .40-size of our design, a size popular with most sport fliers. The .40-size ship offers the best compromise between fuel economy and flight performance; big enough to see the flight attitude in the air during maneuvers, yet small enough for easy storage and transport. The key to any good flying aircraft is to keep the weight down, which reduces the wing loading and gives better vertical performance. This size aircraft coupled with a hot .40-A5 two-cycle engine will give you plenty of performance and meet the light weight requirements desired. Adding a pipe only increases the effect. If you are a four-cycle fan, a .60 four-cycle will give greater torque at a lower rpm and swing a larger prop. Some modification to the fuselage will have to be made to accommodate the added weight of this engine to get the CO in the right place.

The obvious starting point of any design is the wing and what better way to get away from the straight-style wings than with the ellipse. This shape is pleasing to the eye and offers some real advantage in terms of aerodynamics. The elliptical wing produces a constant downwash at all speeds and near perfect load distribution over the entire surface area, something not easily achieved by any other platform shape. The effective angle of attack is the same along the entire span. There is a simultaneous stall over the entire surface with no.tip,stalling tendencies. This reduces induced drag and the tip vortex effect. An 18% airfoil section was chosen to give a high lift coefficient and a constant airspeed through maneuvers.

The problem was how to build this desirable shape with simple construction techniques. An all-balsa wing was chosen to have the lightest weight possible, without sacrificing the strength requirements of an aerobatic aircraft. It uses the standard open-frame with ribs and partial sheeting used on most model aircraft today. Since most of the curve in the ellipse is at the tip, the tip block does most of the shaping. The leading edge is deceiving in that there is only one break to achieve the curve. The rear of the wing gets most of its curve on the trailing edge of the aileron, which is made of an easy-to-shape thin pine strip. One servo in each wing panel drives each aileron individually, which gives precise control with no slop in the linkages and is easier to install than torque tubes. This cuts down the chances of flutter on the control surface. The two servos are connected with a Y-chord and run off of the aileron channel of the receiver. The weight difference between two servos versus one and the savings of not using the torque tubes comes out about even.

The fuselage uses the standard box-type construction rather than the built-up type to achieve the curved contours. The trick is to use thick top and bottom sheeting with large corner triangles. This allows you to sand the contour you want and retains the mass necessary to dampen the engine vibrations. The rounded contour makes the fuselage clean aerodynamically and produces low parasitic drag figures. This method builds strong and light - and allows you the freedom to make it as round as you like - while keeping the construction simple. The tailfeathers are sheet balsa with ply plates for the control horns. Long nose and tail moments give the aircraft a smooth feel through maneuvers instead of the twitchy feel you get with a short-coupled plane..."

Elliptic 40, MAN, March 1986.

Direct submission to Outerzone.

Supplementary file notes

Article, thanks to RFJ.

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