Stormhawk (oz14709)

About this Plan

Stormhawk. Rubber sport model.

Quote: "Proof positive that a sport rubber job can have both good looks and good performance. Stormhawk, by John Morrill.

A green field, a blue sky, warm buoyant air, 800 turns and Stormhawk is away for a beautiful two-minute flight. High above your head, now and then a glint of sun off the canopy. This is sport flying at its best, A throwback to those good old days - what the old timer movement is all about.

I didn't want to build an old airplane, but I did want to see what I could design that would have a 1938 flavor; see if I could rediscover the magic of the Golden Era.

Stormhawk is performance limited. It has fixed landing gear, a free-wheeling propeller, a fuselage cross-section, and weight. It follows the 1941 AMA rules quite closely, It was designed to be a good, stable flier, combining good duration model proportions with a full-scale look. Under minimum power, the model makes a fine ball-park flier. Full power turns the model into a high performance airplane.

If you are a novice builder or new to stick-and-tissue construction and are saying to yourself I would like to build that model, but it is too complicated, take another look at the plan. Stormhawk is intentionally laid out in all staight lines; there are no compound curves. It thus becomes quite easy to sheet the nose, lay out the stringers, and most important, to tissue cover the model. If you feel the sliced rib construction on the wing and stab is too difficult, by all means substitute solid ribs. The canopy and wheel pants are not as difficult as they first appear, and I will cover their construction later on.

Construction: Before we start actual construction, I would like to mention our structural aims. Stormhawk should weigh in at 90 grams, or 3 ounces, ready to fly; any heavier and the glide suffers. My model weighs 68 grams, finished, without the motor. I am using 4 strands of 1/4-inch rubber, braided. The motor weighs 20 grams.

The fuselage main frame is a truss construction for light weight and good torsional strength. Sheet balsa sides could be substituted for ease of construction. If you elect to do that, you will be adding weight and destroying the light, airy look that is the aesthetic hallmark of the tissue-covered model.

I feel that Stormhawk would fly better with a little more wing area. I would therefore suggest the wing span be increased 2 inches (to 28 inches). This is easy enough to do, since the wing ribs are on 1-inch centers. The stab need not be changed; it will work fine as it is. If the model dutch-rolls with the additional wingspan, a slight amount of additional rudder area will cure that tendency.

FUSELAGE: The fuselage side frames are built with the second one on top of the first one to assure symmetry. Assemble the basic frame upside down over the top view of the plan. Add the top crosspieces and then the bottom. The bottom is narrower than the top and is indicated by the shading on the plan. A small triangular template will help you get the angle the same on both sides. Diagonals are added between the bottom crosspieces. Formers are next added, being erected perpendicular to the top longerons.

The wing saddles, through which the wing must slide freely, are cut from 1/32 plywood. Use a brand new No.11 Uber Skiver blade. Cut the inside airfoil shape first, then the outside contour. The 1/32 plywood is very easy to cut using a sharp blade. Add the rear stringers; they butt against 'J' and lie on top of 'K'. Place the center stringer first, then the ones on either side, The spacing is shown on former K. They are again spaced evenly across where they end at the fuselage rear. The lineup on the intermediate formers should be automatic.

Finish the rear fuselage with 1/32 sheet, grain running crosswise, The nose sheeting may now be put on. I use white glue for sheeting, As it ages, it doesn't pull the wood down around the formers, adding an unintentional scalloped effect. I use Ambroid for all the rest of the frame construction. I feel it is still the best wood cement for stick construction.

The top sheeting is put on first. Cut the piece extra long by a couple of inches. Butt it along the top longeron of one side. Let the glue dry. Now bend it over the farmers. Use rubber bands to hold it in place. The wood will now be at all sorts of cockeyed angles to the other longeron and end formers. Make sure it covers everywhere it needs to. When the glue is dry enough to hold the wood in place, cut it flush with the top of the other longeron and glue it into place.

Trim the overhang from the formers at each end. The cowl pieces are now added. Bevel one edge at an acute angle and cement it on the longeron side. A little effort here will produce a perfect joint to the top sheeting. Use two pieces, one on each side. Wet the wood, bend it around and overlap the two pieces on the bottom. Hold in place with rubber bands until the wood has dried. Make one cut longitudinally along the bottom center with a good sharp blade. This will give you a perfect butt joint. Glue the wood to the farmers and hold in place with rubber bands..."

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