Probably not, unless we take seriously the suggestion of a writer on aerial warfare, who believes they will some day be so perfected that they may be used to drop bombs or high explosives over forts or besieged cities. His suggestion is that hundreds of model aeroplanes equipped with miniature engines might be released in a swarm, each carrying a deadly explosive which would be dropped automatically at a certain time. It would be impossible, he argues, for gunners to bring down an entire fleet of these swiftly moving machines, and so while many of them might fall short enough would succeed in dropping their missiles to make them an exceedingly dangerous weapon. The writer points out that the expense of such a mosquito fleet would be trifling compared with the cost of the ordinary engines of warfare and might be operated without risking any lives. [Illustration: A tractor with large plane forward built by F. W. Curtis] [Illustration: Model built by William Robinson] How large may a model aeroplane be made with good results? None of the successful strand motor models at present exceed five feet in length. This would seem to be the practical limit at which a model may be carried with this motive power. Flights of more than 1,500 feet have been made with models but two feet in length. When regular engines are installed there is of course no limit to the size of models. When was the first model aeroplane constructed? Crude machines propelled through the air by twisted rubber strands were used as playthings more than a century ago. The model built and flown by Langeley in 1887, was probably the first machine to appear on the lines now generally followed by aeronauts. Successful model aeroplanes have been used as toys for less than five years. Their development in this period has been remarkable. Are the equations for calculating the thrust of propeller in terms of wing area and skin friction and general proportions useful in designing model aeroplanes? Only in a general way. When the dimensions are very small these complicated equations are misleading. They are for the most part extremely complicated and for this reason we have avoided them entirely in the present volume. Much better results may be obtained by proceeding merely by the rule of thumb, and testing out the proportions of your aeroplane by actual practice. What is the American indoor record for model aeroplanes? A flight of 265 feet was made at a New York tournament by Stewart Easter, the model rising from the ground under its own power. This was made diagonally across the hall as far as it could go. Many flights have been made at the New York meets in which models have flown the entire length of the hall and struck the further wall with their motors far from run down. In other words, model aeroplanes have reached a state of development where they have outgrown the largest indoor enclosures available for flying. CHAPTER XIV AMONG THE MODEL BUILDERS