John McMahon and his compressed air driven monoplane
Frank Schober preparing his model for flight. Gauge to determine pressure of air may be seen in photograph
The machine complete does not weigh over 7 ounces. The power plant used in connection with this model is of the two cylinder opposed engine type, with tank such as has just been described in the foregoing chapter.
The tank is mounted in the frame by drilling a ¹⁄₁₆″ hole through either end of the tank, through which a drill rod of this diameter can be inserted. About ³⁄₄ths of the drill rod should extend out on each side of the tank, to permit the fastening of the tank to the frame side members. This method of mounting the tank serves two purposes to a satisfactory degree. First, it permits secure fastening; second, as the rods are passed through the side and cap of the tank they help materially in preventing the caps from being blown off in the event of excessive pressure.
THE MCMAHON COMPRESSED AIR DRIVEN BIPLANE
In the McMahon model we find a very satisfactory type of compressed air driven model. On several occasions this model has made flights of over 200 feet with a duration of between 10 and 15 seconds, and the indications are that by the use of a more powerful engine the model can be made to fly a greater distance, with a corresponding increase of duration. The engine used in connection with the model is of the two cylinder opposed type, such as described in the foregoing paragraphs. The tank, however, is somewhat different in design from that just described, it having been made of 28 gauge sheet bronze, riveted every one-half inch. The two long bolts that hold the steel caps on either end of the tank also serve as attachments for the spars that hold the tank to the engine bed, as shown in [diagram 17]. The tank has been satisfactorily charged to a pressure of 200 lbs. per square inch, but only a pressure of 150 lbs. is necessary to operate the engine. The tank measures 10″ in length by 3″ in diameter and weighs 7 ounces.
The wings of this machine are single surfaced and covered with fiber paper. The top wing measures 42″ in span by 6″ in chord. The lower wing is 24″ by 6″. The wings have a total surface of 396 square inches and are built up of two ³⁄₁₆″ dowel sticks, flattened to streamline shape. Only two sets of uprights separate the wings, thus adding to the streamline appearance of the machine.
Both tail and rudder are double surfaced and are built entirely of bamboo for lightness, the tail being made in the form of a half circle measuring 12″ by 8″. Steel wire is used on the construction of the landing chassis, the chassis being so designed as to render it capable of withstanding the most violent shock that it may possibly receive in landing. The propeller used in connection with the model is 14″ in diameter and has an approximate pitch of 18″.