Experience, both with models 5 and 6, and with the quarter-size model, had also demonstrated the necessity of providing some means whereby the aerodrome frame would be relieved of the torsional strains produced upon it by a side wind striking the under surface of the wings when the aerodrome was mounted on the car preparatory to a test. The means for preventing these torsional strains in the case of the models, when “overhead” type of launching car was used, has been described in Chapter X of Part I [◊]. However, with the “underneath” type of launching car, a different means was necessary. A plan, in which outriggers projected from the body of the car and wires running from these outriggers up to the main ribs of the wings, with means for releasing the wires just before the car reached the end of the track, was used with the “underneath” car in the tests of models 5 and 6 in the summer of 1899, but the outriggers were frequently deranged by the sudden stopping of the car at the end of the run and they were replaced by a simpler arrangement. In this plan the torsional strains were relieved by providing, at the forward and rear ends [p159] of the car, smaller hinged uprights furnished in their upper part with a small slot into which a pin projected from the bottom of the forward and rear guy-posts, respectively. The guy-wires from wings being connected to the lower ends of the guy-posts the torsional strain produced by a side wind was immediately transmitted from the wings through the guy-wires to the guy-post, whence it was transmitted to the car itself, and thus prevented from acting on the metal frame of the aerodrome, as shown in Plate [39]. These additional short struts for taking up the torsional strain were first added to the small launching car in 1901, and in the succeeding tests made with the quarter-size model no trouble of any kind was indicated as likely to be caused by them. As it was these extra struts which were directly responsible for the accident in the launching of the large aerodrome October 7, 1903, at the time of its first trial, and possibly also for that on December 8, 1903, at the time of the second trial, special attention is here called to them.

The length of travel which could be provided for the launching car in the case of the large aerodrome, as well as in that of the models was necessarily very limited, owing to the fact that the track had to be constructed on the top of the house of the boat. It was therefore necessary, in order that the aerodrome might attain a speed sufficient for soaring before being launched, to keep the weight of the launching car as small as possible, a given spring tension being capable of accelerating a given mass a definite amount in a given length of travel. With a heavier launching car the spring tension would have to be increased. Moreover, since the blow which would be struck when the car was suddenly stopped at the end of the track, would depend on its mass as well as its velocity, there was an additional reason for trying to keep the weight of the car as small as possible.

While it was found perfectly feasible to keep the weight of the launching car for the model low enough for practical purposes, in designing the launching car for the large aerodrome it was only by eliminating all flooring of the car and providing merely a box frame with necessary cross-braces, that its weight was kept within what appeared reasonable limits. Even then the blow which it would strike when it reached the end of the track was found by calculation to be exceedingly formidable.

Referring to the drawings of Plate [40], Figs. 1, 2 and 3, it will be seen that the large launching car consisted essentially of two parallel longitudinal side members 6 inches deep by 1.5 inches thick by 19 feet long, connected by three main sets of cross-members: one set near the rear, at the point at which the rear struts for supporting the aerodrome were mounted; a second rather heavier set about the middle of its length, at the point where the strut which carried the clutch-hook was mounted; and a third near the front, at the point where the front struts were mounted. Projecting from the forward end of each of the [p160] longitudinal side members were piston rods, on which were mounted leather-cup pistons, which co-acted with buffer cylinders fixed at the extreme front of the track to absorb the blow when the car reached them at the end of its travel. The car was supported on each side by means of four hangers (Figs. 4 and 5) which carried grooved wheels having ball-bearings and running on a steel track consisting of flat plates fastened on the side of the timbers of the launching track. On the extreme lower point of these hangers were small guide pulleys, so placed as to be just below and out of contact with a guard rail on the side of the launching track, thus preventing any possibility of the launching car being raised from the track either during its forward motion or by a side wind striking underneath the wings.

Aerodrome “A.” (Details 13 Full Size) PL. 40. GENERAL PLAN AND DETAILS OF LAUNCHING-CAR [◊] [lgr]

FIG. 1. FIG. 2. FIG. 3. PL. 41. AERODROME ON LAUNCHING-CAR [◊]

PL. 42. DETAILS OF CLUTCH POST FOR LAUNCHING-CAR [◊] [lgr]