One of the greatest needs of the present machines is an automatic balancer which shall supersede the concentrated attention which the operator is now compelled to exercise in order to keep his machine right side up. The discovery of the principle upon which such a balancer must be built is undoubtedly within the reach of the builder and flyer of models. It has been asserted by an eminent scientific experimenter in things aeronautic that “we cannot hope to make a sensitive apparatus quick enough to take advantage of the rising currents of the air,” etc. With due respect to the publicly expressed opinion of this investigator, it is well to reassure ourselves against so pessimistic an outlook by remembering that the construction of just such supersensitive apparatus is a task to which man has frequently applied his intellectual powers with signal success. Witness the photomicroscope, which records faithfully an enlarged view of objects too minute to be even visible to the human eye; the aneroid barometer, so sensitive that it will indicate the difference in level between the table and the floor; the thermostat, which regulates the temperature of the water flowing in the domestic heating system with a delicacy impossible to the most highly constituted human organism; the seismograph, detecting, recording, and almost locating earth tremors originating thousands of miles away; the automatic fire sprinkler; the safety-valve; the recording thermometer and other meteorological instruments; and last, if not of least importance, the common alarm-clock. And these are but a few of the contrivances with which man does by blind mechanism that which is impossible to his sentient determination.
Even if the nervous system could be schooled into endurance of the wear and tear of consciously balancing an aeroplane for many hours, it is still imperative that the task be not left to the exertion of human wits, but controlled by self-acting devices responding instantly to unforeseen conditions as they occur.
Diagram showing turbulent air currents produced when a flat plane is forced through the air at a large angle of incidence in the direction A-B.
Diagram showing smoothly flowing air currents caused by correctly shaped plane at proper angle of incidence.
Some of the problems of which the model-builder may find the solution are: whether large screws revolving slowly, or small screws revolving rapidly, are the more effective; how many blades a propeller should have, and their most effective shape; what is the “perfect” material for the planes (Maxim found that with a smooth wooden plane he could lift 2½ times the weight that could be lifted with the best made fabric-covered plane); whether the centre of gravity of the aeroplane should be above or below the centre of lift, or should coincide with it; new formulas for the correct expression of the lift in terms of the velocity, and angle of inclination—the former formulas having been proved erroneous by actual experience; how to take the best advantage of the “tangential force” announced by Lilienthal, and reasserted by Hargrave; and many others. And there is always the “paradox aeroplane” to be explained—and when explained it will be no longer a paradox, but will doubtless open the way to the most surprising advance in the art of flying.
It is not assumed that every reader of this chapter will become a studious experimenter, but it is unquestionably true that every model-builder, in his effort to produce winning machines, will be more than likely to discover some fact of value in the progress making toward the ultimate establishment of the commercial navigation of the air.
The tools and materials requisite for the building of model aeroplanes are few and inexpensive. For the tools—a small hammer; a small iron “block” plane; a fine-cut half-round file; a pair of round-nose pliers; three twist drills (as used for drilling metals), the largest 1/16 inch diameter, and two smaller sizes, with an adjustable brad-awl handle to hold them; a sharp pocket knife; and, if practicable, a small hand vise. The vise may be dispensed with, and common brad-awls may take the place of the drills, if necessary.
For the first-described model—the simplest—the following materials are needed: some thin whitewood, 1/16 inch thick (as prepared for fret-sawing); some spruce sticks, ¼ inch square (sky-rocket sticks are good); a sheet of heavy glazed paper; a bottle of liquid glue; some of the smallest (in diameter) brass screws, ¼ to ½ inch long; some brass wire, 1/20 inch in diameter; 100 inches of square rubber (elastic) “cord,” such as is used on return-balls, but 1/16 inch square; and a few strips of draughtsman’s tracing cloth.