THE RUDY FUNK DURATION MODEL
Of the many different types of duration models that have made their appearance during the year of 1915 perhaps the model described herewith, constructed and flown by Mr. Rudolph Funk, of the Aëro Science Club, was one of the most successful. Unlike most models the propellers of this model are bent and not cut. This model made its appearance during the latter part of 1915, on several occasions having flown for over 100 seconds duration. [Diagram 15].
While retaining the important characteristics of his standard model, slight changes have been made. Instead of the usual wire for the construction of the frame of the wings, bamboo is used in its place for lightness and strength. The wing frames are single surfaced, China silk being used for covering. The “dope” which is used to render the silk airtight is made by dissolving celluloid in banana oil. This in turn is applied to the silk with a soft brush.
The camber of the main wing is ³⁄₄″ at the center, with a slight reduction towards the negative tips; it also has a dihedral angle of 2 degrees. The main beam, which is secured to the under side of the frame for rigidness, is of spruce 1″ by ⁵⁄₆₄″, tapering to ³⁄₄″ × ⁵⁄₆₄″. The ribs for the main wing and small wing or “elevator” are cut from solid pieces of bamboo ³⁄₁₆″ thick by ¹⁄₄″ wide. These pieces of bamboo are first bent to the proper camber and are then cut into strips each ¹⁄₁₆″ wide. The ribs are next tapered to a V at the bottom, toward the trailing edge, as shown in [diagram 15], and also toward the entering edge. To accommodate the entering and trailing edges of the frame, each rib is slit slightly at both ends. Both edges of the frame are then inserted in the slots at the ends of the ribs and bound around with silk thread.
Diagram 15
The frame is composed of two sticks of silver spruce 38″ in length, ⁵⁄₁₆″ × ³⁄₁₆″, tapering to ¹⁄₄″ × ⁵⁄₃₂″, held apart by a streamline bamboo cross brace in the center. An additional brace of bamboo is securely fastened across the frame toward the front. The propeller brace consists of a streamline-cut piece of bamboo 12¹⁄₂″ in length by ³⁄₈″ in width at the center, tapering to ¹⁄₄″ toward the ends. The propeller brace is inserted in slots cut in the rear ends of the frame members, then bound and glued.
The propellers are bent from birch veneer, the bending being done over an alcohol flame as illustrated in [diagram 15]. But first of all the blades are cut to shape, sandpapered and finished before they are bent. As shown in the drawing a slot is filed in the hub of each blade to enable the propeller shaft to pass through when both have been glued together. The blades are then glued and bound together, first by placing a piece of wire in the slots to insure their being centered and also to prevent their being filled with glue. After this has been done each propeller is given three coats of the same dope as is used on the wings.
The propeller bearings are turned out of ¹⁄₃₂″ bronze tubing, the length of each bearing being ¹⁄₂″. Steel washers are slipped over the propeller shaft, between the bearing and propeller to insure smooth running. The propeller shafts are made from steel hatpins which are heated at both ends, one end of which is bent into a loop to receive the rubber strands, the other end being bent around the hub of the propeller to prevent the shaft from slipping during the unwinding of the rubbers. Two strips of brass, each ¹⁄₄″ × 2″, are bent around the one-half inch bearing and soldered. The brass strips are then glued and bound onto the ends of the propeller brace as shown in [diagram 15].
Rudy Funk speed model
Schober compressed air driven monoplane. McMahon compressed air driven tractor (right)