THE INSTALLATION OF CAMERAS AND MOUNTINGS IN PLANES
=Conditions to Be Met.=—The characteristic difficulty in installing the
airplane camera is that there is no place for it. After the gasoline
supply, the armament, the wireless, the oxygen tank, the bombs, and
other necessities are taken care of there is neither space available nor
weight allowable. Where space may be found it will be inaccessible, or
accessible only through a maze of tension and control wires; or it will
be in a position where any weight will endanger the balance of the
plane. Plane design has in fact been more or less of a conflict between
the aeronautical engineer, who is designing the airplane primarily as a
machine to fly, and the armament and instrument men, who look upon it as
a platform for their apparatus. Lack of appreciation of the extreme
importance of aerial photography resulted, during a large part of the
war, in the camera installation being neglected until the plane was
supposedly entirely designed, and even in production. At that stage the
installation could be but a makeshift. Only in the later stages of the
war, when plane design became a matter of coöperation between all
concerned, were fairly convenient and satisfactory arrangements made for
the camera. Always, however, the rapid succession of new plane designs,
with various shapes of fuselage and details of structure, made camera
installation in the war plane a matter calling for the greatest
ingenuity.
The problem was met in part by constructing both cameras and mountings
in sections, to be laboriously wormed in through inadequate apertures,
in part by later structural changes in the planes, such as the
substitution of veneer rings or frames for the tension wires. In certain
cases the rear cockpit controls were omitted, thereby freeing accessible
and often adequate space for the larger cameras. Rear controls were
never used in the German planes, so that their standard practice was to
carry the camera forward of the observer. This, together with the
general restriction to the 13 × 18 centimeter size plate, made the
installation problem less difficult in the German aircraft than in the
Allied.
=Practical Solutions.=—An important feature of camera installation has
already been mentioned, but may well be repeated for emphasis. The
camera and its anti-vibration mounting should always be considered as a
unit, and should be so designed that simple bolts or straps will suffice
to fasten it in its place in the plane. Even should the spacing of the
structural parts of the plane not correspond to that anticipated by the
mounting design, the ingenuity of the man in the field may be depended
upon to make the necessary alterations or additions to the plane. The
design of the camera suspension itself cannot, however, be left to
uneducated ingenuity.
Assuming the camera and mounting supplied, the next step—a very
difficult one—is to insure uniformity in the structures to be built into
the planes for the purpose of supporting the camera mountings. With this
uniformity must, however, be combined the greatest possible flexibility
to provide for various designs of cameras.
In the English service the standard camera installation consists of
wooden uprights with cross bars athwart the plane, adjustable as to
height (Fig. 95). A distance between the cross bars of 13¼ inches has
been standardized, and all camera cradles and mountings are notched or
otherwise spaced to fit this dimension. The installation adopted in the
American planes is similar, but with a distance of 16 inches between
cross bars. These uprights and cross bars are ordinarily situated in the
bay behind the observer, but can be placed in any available space. Fig.
83 shows, in a model bay, the arrangement of uprights and cross bars in
the American DH 4, with the L camera in place in its cradle. It is just
possible to introduce camera and cradle separately from the observer's
cockpit through the tension wires, and, by uncomfortable reaching,
magazines may be changed.
[Illustration:
FIG. 95.—“LB” camera with 20-inch lens, mounted on bell-crank
suspension in skeleton fuselage. Stream-lined hood below to cover
projecting end of lens cylinder. Propeller and Bowden release in
place.]
A step in advance is made when the top tension wires and superstructure
are replaced by a rigid frame with an opening large enough to admit the
entire camera and mounting. When this is done considerably larger
cameras may be accommodated in the same sized bay, as shown in Fig. 96.
A further advance, from the standpoint of accessibility and convenience
of installation, follows when the tension wires between observer's and
camera bay are replaced by a ply-wood ring, as shown in Fig. 97. Here
the only serious limitations are those due to the vertical height of the
camera, and of course its weight.
Openings for the lens to point through are simply provided in the fabric
covered aircraft, by cutting through the canvas and stiffening the edge
of the hole by wire. Tension wires are often in the way. They may either
be disregarded, since they merely cut off a little light, or replaced in
part by metal rings, as shown in Fig. 96. In veneer covered fuselages
the hole must of course go through the wood. This may be undesirable,
since the veneer is depended on to furnish structural strength, a point
which further emphasizes the importance of the photographic requirements
being thoroughly considered while the plane is being designed.
Single seater or scout planes do not lend themselves to the insertion of
such standardized uprights and cross-pieces, because of their small size
and the common utilization of all space inside the fuselage for gasoline
tanks and control wires. Some French scouts, whose fuselages are very
wide, due to the rotary engines, have been fitted with compartments for
contemplated automatic film cameras. The most commonly used camera in
the single seater was, however, the Italian 24-plate single-motion
apparatus (Fig. 49). This camera and its carrying tray occupy very
little lateral space and have in actual practice been carried beneath
the seat or pushed up through an opening in the bottom of the fuselage
under the gasoline tank. Whatever criticism may be made of the adequacy
of the mounting, it must be said that the camera, as used, is perhaps
the most eminently practical of all developed in the war, as its use on
scouts testifies.
[Illustration:
FIG. 96.—U. S. type “K” film camera on bell-crank mount, in camera bay
of DeHaviland 4. Veneer frame at top of bay in place of usual
cross-wires.]
[Illustration:
FIG. 97.—Section of fuselage of veneer construction affording superior
accessibility to camera.]
=Special Photographic Planes.=—As cameras grew in size, the difficulty
of installing them in planes built without regard to photographic
requirements greatly increased. Few planes could carry even the 50
centimeter focus camera obliquely without the necessity of poking its
nose through the side where it would catch wind and oil; while the 120
centimeter camera could be carried obliquely only in the fore and aft
position. Even vertical installation of the latter camera was really
feasible in but few planes; sometimes the camera was carried to the
exclusion of the observer—and, in fact, this size was never used by the
English, whose fuselages were small in cross-section.
This situation led, late in the war, to steps toward producing planes
designed primarily for photographic reconnaissance. In these the camera
would be entirely accessible, and cameras of any size could be carried
in any desired position. One scheme which properly belongs under this
heading was the provision of a special removable photographic cockpit,
for the front or nose of a twin-motored three seater. Other noses, for
bombing and heavy machine guns, were also planned, all to be
interchangeable. Since the regular photographic bay with uprights and
cross-pieces was also provided to the rear, this special photographic
ship could on occasion do two classes of work, such as long focus
spotting and short focus mapping.
The most completely worked out photographic plane was probably the model
designated P1 by the United States Air Service. This is a modified
DeHaviland 4 in which the rear controls have been removed and the
cowling raised and at the same time made squarer in cross-section. The
space formerly occupied by the rear controls provides ample room for all
types of camera. These are carried on uprights at the standard distance
apart, 16 inches, with cross-pieces adjustable as to height. The camera
space is accessible not only from the observer's cockpit, but from
above, upon folding back the metal cover. Doors at the bottom and at
each side permit not only vertical but oblique exposures. The latter are
not interfered with by the wings, as they would be in some designs of
plane if the camera occupied the same position relative to the cockpits.
Fig. 91 shows the deRam camera in place, as seen from the rear. Figs. 98
and 99 show the 18 × 24 centimeter film camera, set both for vertical
and oblique views.
Negative lenses are provided for both pilot and observer, the one for
the pilot permitting him to see from a point far ahead to directly
underneath, while the observer's is furnished with cross wires below and
etched rectangles of the camera field sizes on the upper surface.
Windows of non-breakable glass assist in sighting obliques. The
accompanying picture (Fig. 100) of the plane showing an oblique camera
in position gives an excellent idea of its appearance. Its special
features are worthy of copying in peace-time photographic aircraft.
=Installation of Auxiliaries.=—It is quite necessary that the camera
lens be protected from splashing mud and often from oil spray due to the
motor. For this purpose an easily opened and closed door is essential,
unless the camera is carried well up in the plane. An alternative,
possessing certain advantages, is to incorporate into the camera
protecting flaps operating in front of the lens, which open only when
the exposure is made. If the camera projects beyond the fuselage,
_stream lined hoods_ (Fig. 95) must be provided to protect the camera
nose with the minimum of air resistance.
[Illustration:
FIG. 98.—20-inch focus automatic film camera mounted obliquely in
photographic DH-4.]
[Illustration:
FIG. 99.—20-inch focus automatic film camera mounted vertically in
photographic DH-4.]
[Illustration:
FIG. 100.—DeHaviland 4 re-constructed as a special photographic plane,
showing 20-inch camera mounted for oblique photography.]
The mounting of the regular camera auxiliaries—releases, sights,
propellers, speed controls, motors—is usually a great bother, due to
lack of space and to the severe restrictions on methods of fastening.
Screws in longerons or uprights are taboo. Metal straps to go around
structural parts are the approved device, but with variations in the
size of these members, the holes, straps, bolts and nuts provided are
very apt not to fit. Changes of construction, such as that from
skeletons covered with fabric to veneer bodies, also interfere with any
standard means of attachment, and leave this, like many other problems
in war-time aerial photography, to the resourcefulness of the man in the
field.
Magazine racks must be tucked away in any available space. Under the
seat is a position frequently utilized. Especially with plates is it
desirable to carry the extra magazines in a position to interfere as
little as possible with the balance of the plane. In the DH 4 this means
that they should be carried if possible forward of the observer, even
though he must turn completely around to get and insert each magazine.
IV
SENSITIZED MATERIALS AND CHEMICALS