Recent activity by members of the Aeronautic Society has resulted in the production of several new aeroplanes at Morris Park, one or two of which have already been given their first trials. At the present time there are completed or under construction upon the society's grounds, a monoplane, four biplanes, and one triplane, as well as a new helicopter.
One of the novel machines now completed, and which has already undergone several tests, is the triplane of Morris Bokor. This machine is shown in one of our illustrations, Its three planes have a spread of 26 feet and a width of 61/2, feet, making a total surface of 507 square feet. A 14 x 2 1/2 foot horizontal rudder has 70 square feet additional supporting surface, while the tail, consisting of two pairs of surfaces at a sharp dihedral angle, is 14 feet long and has 72 square feet. The total weight of the machine, with water, oil, and gasoline, and with Mr. Bokor on board is 1,181 pounds, so that the usual ratio of weight to supporting surface2 pounds to the square footis closely adhered to. The upper and lower planes are 6 and 5 feet above and below the middle plane respectively. The inventor's theory as to why less space between the lower and middle planes can be used than is required between the middle and upper one is that the draft of the propellers will draw the air back below the middle plane, and thus tend to check or neutralize the interference of the lower plane. The two propellers, which are driven in opposite directions by chains from the motor, are 8 feet in diameter, with an 11-foot pitch. They are made of wood and have quite narrow blades, covered partly with cloth. The propellers make one revolution to 3 1/2 of the motor. They gave 248 pounds thrust at 500 R. P. M. with the machine held stationary. The motor used is a four-cylinder, 4 x 4-inch, A and B four-cycle automobile motor. The inventor claims 38 horse-power for it at 1,800 R. P. M., but this figure is probably somewhat high. The motor alone weighs 310 pounds, but with all accessories including a 15-pound magneto, a 30-pound Livingston radiator, 30 pounds of water, and 34 pounds of fuel and fuel tank, the weight is 419 pounds.
The main feature of the Bokor aeroplane is the use of a pendulum seat for the aviator, which is connected by cables to the ends of the lower plane at the rear. The outer rear parts of this plane are supported upon flexible trusses running along it, and which are in turn carried upon hinged rods extending back from the vertical uprights at the ends of the planes.
When the machine tips to one side or the other the aviator's seat remains horizontal and exerts a pull upon the flexible rear edges of the lower plane, thus giving it the proper inclination to cause the machine to right itself again. Another feature of this aeroplane is the tail, consisting of two large tetrahedral-like cells, which should aid in giving the machine stability. Since the photograph reproduced herewith was taken, the inventor has mounted his aeroplane upon skids. ln starting, the whole machine is placed upon a four wheeled chassis, to enable it to run along upon the ground. This chassis is left behind when the machine rises. In all probability, however, a larger engine will have to be installed before the triplane can be made to soar.
The other American aeroplane which we illustrate is that of Mr. Wilbur M. Kimball, the secretary of the Aeronautic Society. Mr. Kimball, it will be remembered, last fall built a helicopter consisting of a large number of small propellers. In constructing his biplane he has made use of eight of these propellers, and has arranged them in a ; line between the two planes, the idea being to give a propulsive effort throughout the entire width of the machine. It . has also been proven that a number of small propellers will give a greater thrust per horse-power than one or two large ones. Mr. Kimball makes use of the same motor and wire-rope drive that he employed in his helicopter; but he has improved upon this drive by installing a friction clutch between the driving drum of the motor and the driven drum carrying the wire ropes. The clutch consists of a cast-iron floating ring, and also, of a leather lining in these two drums. It allows a certain amount of slipping to occur at the start, so that the propellers are not strained and broken as before. It is also set so that it will slip with a 25 per cent overload. This improvement, according to the inventor, has made a rope drive for aeroplanes entirely practicable. The wire rope used is only 1/8 of an inch in diameter, and consists of six strands, each of which constains 19 wires. The rope has a tensile strength of 2,000 pounds, while the pull to which it is actually submitted is only 80 to 90 pounds. There are two endless cables, one for each set of four propellers . They are held under proper tension by a single idler for each one. The motor makes 1,900 revolutions per minute to 1,600 of the propeller, and the cable travels at the rate of 7,500 feet per minute, or about 86 miles an hour. The propellers have four blades each. They are 3 feet 10 inches in diameter, and have a pitch of 4 feet. The thrust obtained is about 175 pounds. The motor is a four-cylinder, two-cycle engine of an improved type, the cylinders being 4x4. It develops 50 horse-power at 2,000 R.P.M.
The main planes of the Kimball machine are 37 feet by 6 1/2 feet, and they are spaced 4 feet 2 inches apart. They have a very slight curve of about 1 in 26, and their angle of incidence is about 5 deg. The rear edges project out 18 inches beyond the main plane and are rather flexible. The machine is provided with movable wing tips, 4 by 4 feet in of size, on the ends of both planes. There is a double-surface horizontal rudder in front, 12 by 2 1/2 feet in size, the planes of which are spaced 3 feet apart. This rudder is located 9 3/4 feet in front of the main planes. It is operated by a lever convenient to the right hand of the aviator, while another lever worked by the left hand operates the two sets of four vertical rudders each, placed on the rear of the movable wing tips. This lever also operates the front wheel, in order to steer when running on the ground.
The main features of the Kimball aeroplane are the use of multiple propellers and fitting of quadruple vertical rudders close to the main planes, near their extremities. If the inventor can run his propellers at a high enough speed to obtain from 300 to 400 pounds thrust, he will probably be able to get in the air; but at the present writing he has made only one attempt, which was unsuccessful in this respect.
Originally appeared in Scientific American, 100,, June 5, 1909, p. 421f.