An aeroplane twenty times the length of this model, however strongly it may be made, if dropped the same distance, would be crushed, and probably broken into fragments.
If the large machine is twenty times the dimensions of the small one, it would be forty feet in length, and, proportionally, would have only seven square feet of sustaining surface. But an operative machine of that size, to be at all rigid, would require more than twenty times the material in weight to be equal in strength.
It would weigh about 800 pounds, that is, 4800 times the weight of the model, and instead of having twenty times the plane surface would require one thousand times the spread.
It is this peculiarity between models and the actual flyers that for years made the question of flying a problem which, on the basis of pure calculation alone, seemed to offer a negative; and many scientific men declared that practical flying was an impossibility.
LESSONS FROM MODELS.—Men, and boys, too, can learn a useful lesson from the model aeroplanes in other directions, however, and the principal thing is the one of stability.
When everything is considered the form or shape of a flying model will serve to make a large flyer. The manner of balancing one will be a good criterion for the other in practice, and experimenting with these small devices is, therefore, most instructive.
The difference between gliders and model aeroplanes is, that gliders must be made much lighter because they are designed to be projected through the air by a kick of some kind.
FLYING MODEL AEROPLANES.—Model aeroplanes contain their own power and propellers which, while they may run for a few seconds only, serve the purpose of indicating how the propeller will act, and in what respect the sustaining surfaces are efficient and properly arranged.
It is not our purpose to give a treatise on this subject but to confine this chapter to an exposition of a few of the gliders and model forms which are found to be most efficient for experimental work.
AN EFFICIENT GLIDER.—Probably the simplest and most efficient glider, and one which can be made in a few moments, is to make a copy of the deltoid kite, previously referred to.