Skydelta (oz6414)

About this Plan

Skydelta. Radio control sport model. Delta for .074 - .09 power.

Direct submission to Outerzone.

Update 7/10/2022: Added article, thanks to RFJ.

Quote: "More than two years in development stage, this delta can also be flown as free flight sport. Skydelta, by Donald Broggini.

The delta shape has established itself in the aviation world. Now here is a radio-controlled delta with a rakish, modern, realistic look to it. The craft, powered with an .075 to an .099 cubic inch motor, weighs 24 ounces with all radio equipment ready to fly. A good .065 will also prove satisfactory. If it is desired to be tried as a free flight without radio, any .049 motor will provide ample power.

Skydelta is exceptionally rugged and warp resistant (the delta shape is ideal in this respect); it has plenty of room for radio equipment. Leading edge, spars, and ribs unite in a strong geodetic-type structure, further lending exceptional strength and warp resistance. The plane has cartwheeled, spun into a road, hit a pile of rocks and taken other assorted hard knocks with only superficial damage. The photos, incidentally, were all taken after these adventures.

Skydelta is the result of a development of a series of deltas. First a number of small balsa gliders were made from which a few lessons were learned, and later substantiated in the full-size model. Then came Jetex-powered deltas followed by a 2 ft Infant-powered free flight of various configurations; our 3 ft radio job was next.

The craft has a number of interesting features. It is just about impossible to stall the ship. The airfoil is essentially symmetrical to prevent adverse center of pressure travel and to insure good longitudinal stability. The slightly raised elevons give both reflex effect to the airfoil for stability, and since each increases in chord towards the wing tip, they also give a washout effect to delay tip stall. These desirable results are obtained without having to build or twist reflex into the structure of the wing. The plane has no dihedral since sweepback accomplishes the same thing; it is ideal for sustained inverted flight since the dihedral effect continues although the model is upside down.

The movable rudder is under the wing to insure effectiveness at extremely high angles of attack when the wing tends to blanket out part of the upper rudder. Quite maneuverable, Skydelta does not drop its nose in a relatively tight turn.

For those interested in one of the more technical aspects of the development of the plane, it might be mentioned that the initial R/C job exhibited some lateral stability deficiencies. These were corrected but under certain extreme conditions of high lift coefficients (generally with a rearward CG) there was a snaking tendency (similar to a Dutch roll) so characteristic of the highly swept wing. Full-size planes use a complicated system called a yaw damper to stop the yaw almost the moment it starts. Other remedies are to limit the angle of attack at which the plane flies, increase the fin area, or move the CG forward.

While the snaking was small and did not affect flying qualities in any way, we wanted to eliminate it. The CG was changed and the rudder area was varied by large amounts; various combinations of a rudder under the wing, one, two, and three rudders on top of the wing made little difference. Then the present fin configuration was developed. The plane was modified, adding the long dorsal fin above and below the wing, retaining the highly effective lower fin and reshaping the upper fin. Rudder area was actually decreased by a large amount over that on some of the previous configurations. This did the trick, proving very effective, and also improved the plane's characteristics in a turn.

It is very important to select three hard pieces of very straight wood; the two leading edge pieces of 1/4 in square and the 1/4 x 1 in trailing edge piece. Construction can be in the conventional manner of pinning down the structure to a flat surface if both the wing ribs and spars are first split lengthwise. The upper half of the wing is built and when dry it is removed from the working surface and then the lower part of the spars and ribs are g;lued to the structure..."

Supplementary file notes

Article.

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