LANGLEY’S LARGE AËROPLANE.
(Courtesy Smithsonian Institution.)
Many runs along the track were made to test the working of this great apparatus before trusting it to launch forth in free flight. Dynamometers gave independently the thrust of the screws, and the lift of the wings on the front and rear axles. The ascensional planes for controlling the fore and aft equilibrium were tested during the run, as also the practical operation of the propelling plant. During the trials of 1893 the machine frequently lifted clear of the lower track, and flew forward resting against the guard rails above the wheels. Finally, on a gusty day, the lift against the upper track caused this to give way, whereupon the machine rose into the air with Mr. Maxim and his assistant, then toppled over on the soft earth, suffering some damage to its framework. Here the experiments were discontinued for lack of funds, having indeed demonstrated that a large weight can be carried in dynamic flight, but having proved little as to the feasibility of controlling an aëroplane in launching, in free flight, and in landing.
Compared with the work of his contemporaries this achievement of Mr. Maxim was herculean, both in construction and expenditure, the cost being reported as nearly one hundred thousand dollars. It raised high hopes for aviation. It proved conclusively not only that a flying machine could be made to lift a pilot, but that it could carry hundreds of pounds additional weight. It still holds the world’s record for magnitude of machine and cargo. But it had two great defects; it was improperly balanced and it was inadequately powered; for, as Mr. Maxim says, “the quantity of water consumed was so large that the machine could not have remained in the air but a few minutes, even if I had had room to maneuver and learned the knack of balancing in the air.”[32] These defects, however, would soon be remedied by the work of others, and particularly by the costly experiments of the automobilists, who were rapidly developing a light gasoline motor suitable for aviation.
The inventors thus far noticed had developed most of the important features of the present-day flying machines, but had not provided adequate mechanism for preserving a steady lateral balance. The present writer had proposed the combination of a double rudder and torsional wings to steer and control a flyer, and had published a paper setting forth its general principle and describing a specific device; but inventors had little need for a third rudder till they encountered the dangers of dynamic flight in gusty weather. The paper referred to was presented to the Third International Conference on Aërial Navigation, in August, 1893, under the title, Stability of Aëroplanes and Flying Machines, and was published with the proceedings of the conference.[33] It discusses mainly the question of automatic stability and steadiness; but recommends personal control during the experimental period. It concludes as follows:
“We have been considering the question of automatic stability, in so far as it may be secured in the construction of the craft itself,[34] apart from a pilot, or special equilibrating devices. The application of the latter would give exercise to an infinite amount of ingenuity, and would, perhaps, best be left to the fancy of the individual inventor. One curious design, however, occurs to me, which, since I have not seen it described elsewhere, may be worth a moment’s notice.
“Suppose a Phillips’s machine (see [Plate XIV]) to be provided with a double tail, and to have a vertical fin extending longitudinally along its entire length, well above the center of gravity. These would steady its flight and promote stability. Suppose also that its sustaining slats were pivoted, so that a pilot could at pleasure change their inclination on the right and left side independently. He could then set the engine for a desired speed, sweep forward along the earth with the sustainer slats horizontal, and at will mount into the air, by giving the slats an upward inclination. Once in the air he could raise or lower the machine by slightly changing the angle of the slats; he could wheel to right or left by giving one set of slats a little different slope from the other; he could arrest all pitching, rocking and wheeling by a slight counter movement of the sustainers. It would be necessary, of course, to preserve a rapid forward motion, for it is a peculiarity of the compound aëroplane that, if it comes to a standstill in the air, it will drop plumb down with a frightful plunge until it acquires headway.”
The succeeding paragraph disclosed a specific contrivance embodying the principle just given. This showed two levers rotating drum shafts for actuating wires adapted to change the impact angles of the wing surfaces. Accordingly this much of the mechanism of control, together with the broad device of the torsion wings, has been the common property of inventors since the publication of that paper. Furthermore, the combination of torsional wings and a double rudder, either fixed or movable, has been public property since that date.[35]
Little was said about the manner of manipulating the double rudder and torsional wings; for the rules of manipulation would vary in different machines, depending upon structural design and external conditions. For example, if the proposed fin and vertical rudder were ample and suitably placed, the lateral balance could be controlled by merely twisting the wings, without touching the vertical rudder; but if the fin and rudder were not adequate, the lateral poise would be controlled by twisting the wings and working the vertical rudder conjunctively. A novice might prefer leaving the rudders fixed and controlling the poise in short flights by twisting the wings by means of a single lever having two independent movements, one to rotate the wings oppositely, the other to rotate them identically.
The principle of control expressed in italics had been set forth also in a preceding paragraph. Having proposed means for securing both stability and steadiness about each of the three axes of an aëroplane, the text continued: