My machine flies very well indeed, but I cannot make it start from the ground. When I add more power it swerves to one side and will not fly off. What would you advise? [Illustration: Percy Pierce launching a prize-winning model] [Illustration: Launching the sling-shot gliders] This is a common experience. Our advice is to return to the original motor and make the most of the successful flights. Your model may not be adapted to rising at all, that is, it is too light to carry the motor required to raise it from the ground. If your frame is made strong enough, it may be able to stand the increase in power, if it vibrates violently, as is probably the case with a heavier motor. What is the best time to release the propellers, just as it starts or before? Try both ways. Some model builders allow their propellers to get under way a second or so before the flight commences, and release them and push the machine forward at the same instant. One amateur secures his propellers by means of a thread which he breaks by touching it with a match, but it is rather fanciful. What is the best height for a model aeroplane to fly? In the principal model tournaments held in New York the models were seldom more than twenty feet from the ground at any time. Most model builders have this altitude in mind in designing their machines. It seems to be generally agreed that when a model rises higher than this too much power is used up in gaining altitude and there is a corresponding loss in the distance qualities. On the other hand in the remarkable 1,600 foot flight made by Cecil Peoli in July, the model rose to a height, it is believed, of more than 100 feet and gained considerable distance in gliding down. After all it is a problem which must be decided by the individual. Incidentally it is estimated that a large man-carrying aeroplane on rising to an altitude of one mile can safely soar with all power shut off for twelve miles. This means of course that an aviator has the choice of landing anywhere within a circle twenty-five miles in diameter, which gives him a rather wide choice. What is meant by "critical soaring speed?" It is claimed by some aviators that every aeroplane has a certain speed at which it flies best and beyond which it is unsafe to push it. If more power is put on, they argue, it will only tend to send the machine up in the air and will not increase its speed. This is probably true in a measure of model aeroplanes as well. When you have found the speed at which your aeroplane flies best do not change the number of rubber bands of your motor or the number of turns in winding. Do the tails of birds serve as rudders to guide them in flying?