§ 9. When launching a twin-screw model the model should be held by each propeller, or to speak more correctly, the two brackets holding the bearings in which the propeller shafts run should be held one in each hand in such a way, of course, as to prevent the propellers from revolving. Hold the machine vertically downwards, or, if too large for this, allow the nose to rest slightly on the ground; raise (or swing) the machine up into the air until a little more than horizontal position is attained, and boldly push the machine into the air (moving forward if necessary) and release both brackets and screws simultaneously.[46]
§ 10. In launching a model some prefer to allow the propellers to revolve for a few moments (a second, say) before actually launching, contending that this gives a steadier initial flight. This is undoubtedly the case, see note on page 111.
§ 11. In any case, unless trying for a height prize, do not point the nose of the machine right up into the air with the idea that you will thereby obtain a better flight.
Launch it horizontally, or at a very small angle of inclination. When requiring a model to run along a field or a lawn and rise therefrom this is much facilitated by using a little strip of smooth oilcloth on which it can run. Remember that swift flying wooden and metal models require a high initial velocity, particularly if of large size and weight. If thrown steadily and at the proper angle they can scarcely be overthrown.
CHAPTER XI.
HELICOPTER MODELS.
§ 1. There is no difficulty whatever about making successful model helicopters, whatever there may be about full-sized machines.
§ 2. The earliest flying models were helicopters. As early as 1796 Sir George Cayley constructed a perfectly successful helicopter model (see ch. iii.); it should be noticed the screws were superimposed and rotated in opposite directions.