[1] See U. S. Letters Pat. No. 376937.
Now, in order to travel long distances in the air it is only necessary to improve the dirigibility of the aeroplane so that the angle of descent can be brought to a minimum.
How can this be done? By making repeated experiments with very simple and inexpensive mechanical contrivances called soaring machines, these to be dropped from a height.
In [Fig. 2] it will be noticed that the course marked B indicates a speed of twenty-five miles per hour, that marked C a speed of one hundred miles per hour.
What speed may we expect of an improved soaring-machine? and upon how gentle a decline can we hope to see it maintain its initial velocity? First, note the fact that with a dirigible aeroplane or soaring machine the rate of speed is practically a matter of choice and depends at the start upon the length of the first swoop. The limit of speed will probably be decided by the strength of the machine and the breathing requirements of the aerial pilot. Let us consider a railroad train. Man has safely travelled at a rate of one hundred and twelve miles per hour. On May 11, 1893, the Empire State express on the N.Y.C. R.R. reached that speed in a mile run in thirty-two seconds, one mile westward from Crittenden. So we know that man can safely breathe when travelling at over one hundred miles per hour; yet for this, of course, he needs the same protection which a cab gives to the locomotive engineer.
We will answer as well as we may the second question, Upon how gentle a decline may we hope to see an aerial machine maintain its initial velocity? When a railway car is at rest upon a smooth steel track having a down grade of one and twenty-three one-hundredths feet in every one hundred feet, it will remain at rest if undisturbed; but let it be once started downward by ever so slight an impulse and it will run down the track, gaining velocity to the end of the grade. It encounters the head resistance of the air and the friction of the track, but an aerial machine would encounter only air-resistance; is it not, therefore, reasonable to suppose that a dirigible aeroplane would in a calm, maintain its initial velocity while running upon a down grade of air of one foot in every one hundred feet? If so, an altitude of ten or twelve hundred feet would send a soaring machine eighteen or twenty miles, and greater altitudes would give longer flights, if, as may be supposed, the rarefaction of the air can be offset by an increase of velocity. These are surmises, but the way to learn is to experiment with soaring machines.
It is above all things important that a soaring machine should, when desired, automatically keep itself in a horizontal or slightly descending course. I have this winter begun a series of experiments with soaring machines, and when these are finished the full details will be reported.
In November, 1893, I launched several of these machines from the balcony of the tower of Boston Light, and more recently I have experimented from the top of the cliffs at Manomet. The former place is an ideal one for the purpose of experiment, being as it is, one hundred and eleven feet above the sea with a straight drop of seventy or eighty feet. Unfortunately, a gale of wind was blowing when I visited the light, and two out of the three machines were total failures, being badly bent by the wind before they were launched. The third machine righted itself before reaching the ground, but the pendulum, which will presently be described, was too light to do efficient work.
The experiments from the cliffs at Manomet were even less successful, owing to the fact that the descent is not sheer. All of the machines failed to gain sufficient velocity to clear the cliff.
Those who wish to experiment with machines weighing only a few pounds will probably find that a height of seventy or eighty feet will be sufficient if the position gives a straight drop. When it comes to experimenting with a soaring machine as large as Lilienthal’s and carrying a weight representing that of a man, the summit of Mt. Willard, near the Crawford House, N.H., will be found an excellent place.