Slim Jim (oz1183)

About this Plan

Slim Jim. Free flight contest gas model. Streamlined and with retracting gear.

Quote: "We don't claim that this model will do everything, but it does have a lot of ideas and theories incorporated into it - ideas and theories that have been proven by those who know the thrill of modeling - designing your own ship.

The fuselage is long and slender like a pencil bomber but for the sake of appearance it is a little larger in diameter than a true pencil bomber. It is equipped with a spinner, retracting landing gear, and a narrow pylon giving a fast sleek look to the ship. We are using a Glo-Torp which eliminates the necessity of trap doors for batteries and the inconvenience of coils, wire or protruding timer arms. The Glo-Torp is very easy to start with the proper fuel, and shows a good output of power. Any glow plug engine of comparable displacement may be used, such as Ohlsson .29, McCoy .29 Sportsman, OK .29 and the like.

The wing has an aspect ratio of 8.4 to. 1 with 500 square inches of wing area. A taper was used to obtain greater strength and more efficient performance. The square tips make construction simple. The airfoil is a hybrid of the Davis foil used on a number of ships by the author. The high point is located about 33% back and has a maximum thickness of a little over 15%. This percentage thickness runs from the center to the start of the polyhedral, from there to the tip it decreases to a thickness of 11% of the chord length. This decrease in thickness of the tip gives the same effect as an elliptical tip with much simpler construction. The author has done a great deal of experimenting with various airfoils and has found the thick foil the most satisfactory. The thicker foils give a definite increase in stability besides making room for deeper spars.

The stabilizer has an area equal to about 30% of the wing and uses a Clark-Y airfoil. The twin rudders give a distinctive look to the model and result in improved performance especially in a quick recovery from a very fast climb. The area of the rudders is 11.5% of the wing and there is no indication that they are too large. Of course, with twin rudders an increase in area of about 25 to 30 percent over a single rudder is necessary because of loss of efficiency due to tip vortices. On previous models using these airfoils it was discovered that rudder area must be about 9% for good stable flight so allowing for the proper increase for twin rudders, the 111/2 % area was used on Slim Jim. The original (lost on an 8-second engine test hop at the Nationals) certainly proved that the design will give top contest per-formance. The second one confirmed all our hopes.

The model is not difficult to build and even the novice should have no trouble with its construction. The fuselage is built by the crutch method with the bottom half being built first. The four front bulkheads may be assembled whole on the hardwood engine mounts and then allowed to protrude over the end of the board where the crutch for the rest of the fuselage is being built. Be sure that the engine mounts are drilled and the hold-down plates are in place before all the planking..."

Supplementary file notes

Article pages, thanks to Donjamin.

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