I made my first trials with a soaring machine in the summer of '95, having constructed the machine during the spring.
I had seen photographs of Lilienthal's apparatus, but I purposely made mine before going to see his so that I should not copy his details. I, however, went to see him fly before I commenced to experiment myself. My first machine had 150 square feet of surface and the wing tips were considerably raised above the body. At first I had a vertical rudder only, but I soon discovered that I could do absolutely nothing without a horizontal rudder. I found that it was quite impossible to control the pitching motions of the machine, and it was not until I had put on the horizontal rudder that I was able to leave the ground at all. This point is very clearly illustrated by experiments with model gliders. It is exceedingly difficult to make a glider with one surface only which will sail properly, but with two surfaces nothing is easier.
Although a machine in which the wing tips are considerably raised would always tend to right itself when falling, it is almost impossible to use such a machine for practicing soaring out of doors, because although the machine is stable enough when the wind is right ahead, if the wind shifts and gets a little on the side it will press the weather wing up and depress the lee one so as to turn the machine over. But when I altered the shape of the wings so that they rose in the centre, but turned down again towards the tips, that is, so that the tips were scarcely higher than the middle of the machine, the machine became comparatively easy to handle, and I was able for a beginner to make some very good jumps. On one occasion when a man towed the machine by a string attached to the front of the machine I spent seventeen seconds in the air, and this is the longest time I have ever been off the ground.
During the summer I made a second machine which was straight transversely, although curved in the fore and aft direction. All the wing surface was considerably raised so that it was just above my head when I was in the machine, but with this machine I could not get along at all. When the weather became too cold I had to stop experimenting, and during the winter I built a new machine, which has 170 square feet of surface and weighs 50 pounds.
During the last summer I had to be very busy about other things, so that I have only had the machine out about ten times and have not been able to choose my days. In this machine I did away with the vertical rudder altogether. For days when there is not much wind the machine is quite manageable as it is, but for squally days I think that a vertical rudder should be added. With this machine I have twice cleared nearly 100 yards, once with a slight side wind and once in a dead calm. Most unfortunately I have never had the machine out when there has been a breeze blowing up the best hill for experimenting, or I should be able to give a much better account of its performances. Once when sailing fast I saw I was going to land in a big bush, so getting back a little in the machine I was able to rise a little and pass quite clear of the bush, although it was quite calm at the time; and I have also been able to steer sideways to a limited extent by moving the weight of my body towards the side to which I wanted the machine to turn. This is the first machine in which I have had any wheels, which are a great convenience for moving the machine about, and often save the framework from getting broken if one lands clumsily. The wheels are backed by stiff springs which can absorb a considerable blow.
A new machine is being built which will have an oil engine to drive a screw-propeller. With this machine, without the engine, I drop 50 feet in 10 seconds; that is at the rate of 300 feet per minute; taking my weight and the weight of the machine at 220 pounds the work lost per minute will be about 66,000 foot-pounds or 2-horse power. When I have been flown as a kite it seems that about 30 pounds pull will keep me floating at a speed of about 2,200 feet per minute, or 25 miles an hour. 30 X 2,200 = 66,000 foot-pounds = 2-horse power, which comes to just the same thing.
An engine is now being made which will, I hope, exert enough power to overcome the losses arising from friction and slip, and keep the new machine floating horizontally. Of course for the same wing-surface the machine will have to sail faster in order to keep afloat with the extra weight of the engine, and more power than the 2-horse power will therefore have to be used.
About 170 square feet seems to be the best area for a machine of this class for a man of average weight; if it is made larger the machine becomes heavier, and is much more difficult to handle because of its increased size and weight, and if it is smaller its sailing speed becomes unpleasantly great.
Last June I happened to be in Berlin again, and Herr Lilienthal very kindly allowed me to fly off his hill with one of his double surface machines. A light steady breeze was blowing, and after the practice I had had with my own I had no difficulty in handling his machine, but I was very much afraid that with the superposed wings high above the machine, as shown in Lilienthal's latest machine, they would prove very dangerous machines, especially in squally weather.
I hope with the new machine with the engine that I shall be able to obtain results worth reporting in your next ANNUAL, but "we shall see what we shall see."