Hydra (oz14421)

About this Plan

Hydra. Control line slow combat model. Wingspan 42 in, wing area 440 sq in, for .35 engines.

Quote: "The Hydra was designed primarily for the slow combat event which requires both a maneuverable and a strong airplane. Let's face it, although we all like to think of ourselves as great combat pilots, we know that in the heat of battle we sometimes zig when we should zag. If you have a model that stays together, this allows you to get back into the air, but a maneuverable model helps you get into the winners circle.

The Hydra evolved as an extension of my favorite slow combat model the Flite Streak (oz2652) by George Aldrich.

With the advent of Schnuerle engines and more horsepower, I decided this extra power could best be used to carry a bigger airplane. My reasoning was that a larger model with less wing loading would turn tighter, and lose less airspeed in doing so. Some may argue that a larger model would have a lower airspeed in level flight, but we know good combat matches are seldom flown with level flying. A good match is a constant series of tight maneuvers and what you need is a model that doesn't stall in tight turns.

If you look at the drawing, you'll notice a peculiar shaped object shown where the fuel tank normally goes. This is the fuel tank but it doesn't have a normal shape. It's the Cheops fuel tank which I designed about four years ago when I was having problems with the engine sputtering and missing at the top of the circle. I won't go into detail, but some high school physics and algebra told me a very thin wedge tank was enough fuel volume for a five-minute flight.

The answer was to have a square shape at the front of the tank and a thin wedge at the fuel pick-up (the back end). A friend of mine saw the prototype and remarked that it had more sides than Cheops' Pyramid - hence the name. The tank is not difficult to make if you have the pattern and can visualize the finished shape (see photograph and drawing). I've been told the Hydra will fly with a conventional wedge tank but I can't say, I've used only the Cheops tank. Even if you don't intend to build the model, you should try the tank!

Construction: The best place to begin is with the fuselage. On a piece of 1/2-inch basswood, lay out and cut the fuselage shape including the motor mount, wing, cutouts, and the notch for the stabilizer. Cut the nose doubler from 1/8 plywood. Use a slow-curing epoxy and glue the maple motor mounts and plywood doubler to the fuselage, clamp securely and set aside. When the fuselage is cured, add the canopy and shape the fuselage section as shown. Tapering the fuselage like this can remove a lot of weight where it isn't needed.

Cut the two trailing edge pieces of the wing from medium hard 3/16 x 2-inch balsa and tack them together at the center section with Hot Stuff. Cut the two trailing edge doublers from 1/32 plywood. I find the easiest way to cut 1/32 ply is with tin snips or heavy scissors. Mark the position of the trailing edge on both sides where the doublers will go. Use contact cement to glue the doublers to the trailing edge and make sure you put at least two coats of cement on the balsa and the plywood. The reason for this is the wood is absorbent, only one coat of the cement does not give a good bond. The reason for using contact cement for this trailing edge joint is because it's easier and faster than epoxy. Don't worry about strength; properly done, the contact cement bond will be plenty strong for this joint..."

Hydra, MAN, December 1983.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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