Fig. 89.—Tests of camera mountings: (a) deRam camera on bell-crank-and-spring mount, below the center of gravity; (b) same, at center of gravity; (c) type “K” film camera on universal mounting (Fig. [88]).
Tests on the English design made in the United States Air Service appear to show that the chief virtue of the mounting lies in the approximation of the point of support to the center of gravity in the English cameras. A deRam camera supported by its cone, so that its center of gravity was considerably above the center of support gave rather poor results (Fig. [89]a), but when the bell cranks were attached near the center of gravity, highly successful results were obtained (Fig. [89]b). The French deRam camera as ordered for the American Expeditionary Force was fitted with a bell crank supported in this position.
Figures 90 and 91 show a bell crank mounting furnished with a rotating turret. This was designed to facilitate the changing of magazines in the English B M camera, which is swung around through 90 degrees from the exposing position to bring the magazine near the observer. The camera shown in the mounting is the American hand-operated model (type M), in which there is the same necessity for turning in order to manipulate the bag magazine easily. The camera is shown in both exposing and plate changing positions. An important detail of these mounts is a safety catch, which must be fastened before the plane lands, in order to prevent the shocks of landing from producing oscillations sufficient to throw the camera out of the mount.
Center of Gravity Rubber Pad Supports.—Given a camera whose center of gravity does not change during operation, a simple and entirely adequate anti-vibration support is furnished by a ring of sponge rubber in the plane of the center of gravity. But if provision has to be made for oblique views or for adjusting the camera to the vertical, something more elaborate is necessary.
Fig. 90.—U. S. model deRam camera on anti-vibration mounting adjustable for the angle of incidence of the plane.
Fig. 91.—U. S. deRam camera and mount installed in photographic DeHaviland 4 (Fig. [100]). Viewed from above the observer's cockpit.
Fig. 92.—U. S. type “K” film camera on universal mounting, vertical position.