It requires a comparatively powerful motor to raise a model from the ground, whereas a lighter motor would be sufficient to propel it through the air. Many models, capable of flights of several hundred feet when thrown will refuse to rise, while, on the other hand, some models which rise well enough have poor distance qualities. It should be borne in mind that the length of the motor, speaking broadly, controls the distance qualities, and its diameter the speed of the model aeroplane. A long slender motor, capable of from five hundred to one thousand turns which will revolve the propellers for thirty seconds or more, should insure a flight of several hundred feet. As you increase the number of strands of rubber, building up the diameter of the motor, you cut down the number of turns and therefore its duration, although you increase its speed. A motor capable of one thousand turns must be about forty inches in length and consist of but six, or at most eight, of these strands. A model which may be driven by this motor, it will be found, must be very light. A model aeroplane weighing upwards of one pound, on the other hand, will require motors composed of fourteen strands or more to raise it from the ground. It is a very simple matter, of course, to add strands of rubber until your motor develops sufficient energy for the work it is expected to do. The length and diameter of your motor, again, has a direct influence on the height of the flight. Too much power tends to raise the aeroplane higher than necessary above the ground. Since it requires more energy to drive a model aeroplane upward than along a horizontal direction, this is obviously a waste of energy. If it is desired to fly the model as far as possible, it must be kept close to the ground. In the case of weight-lifting contests, the problem of altitude is, of course, entirely different. Overwinding is even worse than underwinding, since it shortens the life of the motor. Try out your aeroplane with ten strands on each motor and increase them later. The motor, as previously explained, is formed by looping the rubber strands loosely between the hooks, just as zephyr is wound on a skein. Keep the strands very loose and fasten them to the hooks by tying with a strand of rubber. In winding, do not turn the propeller after the rubber has a double row of knots for its entire length. Such a motor should take up from three hundred to five hundred turns, perhaps more. Do not keep the elastic wound up too long before starting your flight. The strain is great and it quickly wears out. [Illustration: A Metal Motor Anchorage]