Scorpion (oz13634)

About this Plan

Scorpion. Control line combat model.

Quote: "A 127 mph lightweight combat ship, with simple but well-thought-out construction. Scorpion, by Tom Biebuhr.

Let's settle one thing once and for all. I am a Stunt flier! Now if this statement hasn't scared everyone away, I guess an explanation is in order.

For years I was the lone Stunt flier in a Combat club in the New York City area. This group not only managed to win most contests entered, but with the help of Richard McIntyre did development work in 1959 with the first pacifier fuel tanks. So the problems and demands of the competitive Combat flier have been thoroughly squeezed into the old pea-sized brain.

The Scorpion is not a hastily thrown together aircraft. With the help of Ralph Supinski (Cleveland, Ohio), who was a fellow student at Parks College of Aeronautical Technology, over 20 changes, large and small, have been incorporated into the Scorpion over the last five years. Let's look at what has been considered in the design envelope of the Scorpion:

(1) Maneuverability
(2) High Speed
(3) Light Weight
(4) High Strength
(5) Ease of Construction
(6) Low Cost
(7) Safety

The first three items listed dictate the outcome of the final product. The high aspect ratio wing, longer than usual tail moment arm, balanced stabilator, and airfoil selection coupled with fight wing loading, result in the desired maneuverability and speed,

The lightweight construction used deserves some discussion, since this concerns the last five items on our list of design considerations.

Liberal use of sheeting and heavy balsa members does little to assure a strong model. It is a shame that many people have been scared away by some early lightweight designs that had the tendency to crumple badly when contacting old mother earth, or even worse, when the outboard wing failed in a high-speed turn. The key is to follow the philosophy used in full-sized aircraft design. Beef up only the areas that require beefing up!

Unfortunately there will never be a design that will survive 100% of the contacts with the ground. We feel, however, that when properly built the Scorpion will actually take more of a beating than most of the ironclad Combat ships flying, by absorbing the major impact forces that a more rigid wing could not withstand.

The outboard wing failures have been eliminated on the Scorpion by the use of two separate items - spruce spars and the gusset shaped center section sheeting. Remember that the gussets are not for appearance. When made as a one-piece integral part of the center section sheeting, the gussets distribute all flight loads properly. To summarize: The gussets are mandatory!

Perhaps the most neglected part of a Combat model when considering strength and flight characteristics is the finish applied. A poorly finished model with only two or three coats of clear dope not only will not fly well due to porousness, but will be subject to more wing flex and will not withstand the punishment required of a Combat model. All Scorpions constructed to date have a minimum of ten coats of 20% thinned clear dope over silk, sanding between coats with 400 and 600 grit wet sandpaper. This results in an extremely strong and efficient stress skinned wing.

Construction of the Scorpion is straightforward, so we will only make some suggestions. We cannot say enough about quality of construction. Remember, a poorly built aircraft will fly poor-ly.

The 1/16 trailing edge should be made from hard balsa, however, if only a medium grade balsa is available, we recommend installing a 1/16 vertical web at the forward edge of the trailing edge, between each rib.

All edges of ribs and spars that come in contact with the covering material should be sanded round. For maximum strength one coat of clear dope on all ribs before assembly is recommended.

The engine pod can be constructed from 1/2 in balsa or by laminating 1/4 in balsa. it may be necessary to hollow out the pod slightly to clear the engine crankcase. It is a good idea to install two 3/16 dowels through the engine mounts and engine mount support. Use fiberglass resin and cloth to reinforce the engine pod.

An excellent safety idea required by WAM rules is a safety cable from the bellcrank mounting bolt to the engine backplate. This can be fabricated from a length of heavy flexible leadout cable and electrical terminal ends.

Note that the stabilator is not hinged at the leading edge. The stabilator bearing is installed by cutting a notch into the stabilator deep enough to install the brass tubing at the hinge point. Install the brass tubing and tail booms and fill in the remaining notch with scrap balsa. This area should be reinforced with fiberglass resin and cloth as shown on the drawings.

Although the drawings show a fuel pod for use with a pacifier type fuel tank, the spars are spaced to accept a standard pressure fuel tank if desired. Any tank protrusion above the airfoil can be faired in using the same method as in constructing the fuel pod shown or the plans.

Scorpions have been flown with Fox and Supertigre engines turning 9-7 propellers and obtaining speeds up to 127 mph. So take it from there!"

Direct submission to Outerzone.

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