Model Aeroplanes and Their Engines: A Practical Book for Beginners

by George Anthony Cavanagh

THE COOK NO. 42 WORLD RECORD MODEL

(TWIN PROPELLER HYDROAËROPLANE, 100.6 SECONDS RISING FROM WATER)

During the National Model Aëroplane Competition of 1915 held under the auspices of the Aëro Club of America, a number of new world records were established, one of which was for twin propeller hydroaëroplanes. The credit for this record is due Mr. Ellis C. Cook of the Illinois Model Aëro Club, who succeeded in getting his model hydroaëroplane—which by the way is a rather difficult type of model to operate—to rise from the water and remain in the air for a duration of 100.6 seconds. This model is of the common A frame design with the floats or pontoons arranged in the familiar fashion, two forward and one aft. The model is fairly light, weighing, when complete, 3.33 ounces, ¹⁄₂ ounce of which is made up in rubber strands for motive power. [Diagram 14].

The frame is made of two sticks of white pine for side members, each member measuring 38¹⁄₄″ in length, ⁵⁄₁₆″ in depth, by ¹⁄₈″ in width. These are cut to taper toward the ends where they are only ¹⁄₈″ in width by ³⁄₁₆″ in depth in the front and rear respectively. Three “X” strips of streamlined bamboo measuring ³⁄₁₆″ in width by ³⁄₆₄ths of an inch in depth, are used for bracing the frame between the front and rear and are arranged as shown in [diagram 14]. The propeller bearings are of small streamlined forgings of light weight, and are bound to the rear end of each side member first by gluing, then binding around with thread. The front hook is made of No. 16 piano wire and is bound to the frame as shown in [diagram 14]. The chassis which holds the floats or pontoons is made of ³⁄₃₂″ bamboo bent to shape and bound to the frame members. By the use of rubber strands the floats are attached to the chassis; the forward ones being attached so that angle may be adjusted.

The main wing has a span of 36″ and a chord of 5″ and is constructed of two white pine beams each 39″ long, with bamboo wing tips. The ribs, seven in number, are also made of bamboo and are spaced along the edges of the wing at a distance of 4¹⁄₂″ apart. The “elevator” or front wing has a span of 14″ and a chord of 3¹⁄₄″, the framework of which is made entirely of bamboo. The entering edge of this wing is given a slightly greater dihedral so that the angle of incidence at the tips is greater than at the center. By this method the added incidence in the front wing is obtained. By the use of rubber bands both wings are attached to the frame.

Diagram 14

The two forward floats are spaced eight inches apart and are of the stepped type, the step being 3¹⁄₂″ from the front and has a depth of ¹⁄₈″. These two floats are separated by two bamboo strips as shown in the [diagram], which are tied to the rounded portion of the under carriage by small rubber bands. By the sliding of these strips back and forth the necessary angle of the floats may be obtained to suit conditions. The floats are built up with two thin pieces of white pine for sides, separated by small pieces of wood about one-half the size of a match in cross section. Chiffon veiling which is used for the covering of the wings, is also used for the covering of the floats, after which it is covered with a special preparation to render both the wings and the floats air and water-tight.

The two ten-inch propellers with which the model is fitted have a theoretical pitch of twelve and one-half inches. The propellers are carved from blanks one-half inch thick, the blades of the completed propellers having a maximum width of one inch at a radius of three inches. The propeller shafts are made from No. 16 piano wire and have small washers for bearings. Each propeller is driven by three strands of ¹⁄₄″ strip elastic. The rubber is given 1700 to 1750 turns and revolves the propellers at 1150–1200 r.p.m., when the model is in flight.

The model usually runs over the surface of the water for a distance of from two to three feet before it rises, after which it climbs at a very steep angle to the necessary altitude. The model seems, when in flight, to be slightly overpowered but this is misleading. The rubbers usually unwind in from 85 to 90 seconds. On four out of six flights this model has made a duration of between 98 and 100 seconds which is rather unusual for a model of this type.