Radar System Engineering

SEC. 922] STREA MLIA”ING 315
function, radome materials, transmission of radar energy, structural
requirements, aerodynamics, access to the radome cavity, and specification
and test.
In this discussion only the three major items—aerodynamics, electrical
transmission, and structural design—will be discussed, and these
only briefly. N’one of these items can take preeminence over the others
since a design aerodynamically or structurally poor can prevent the radar
set from being useful, just as would a radome that had faulty transmission
characteristics. The radome design must, therefore, be a compromise
of these three major factors if accuracy and effectiveness of the airborne
unit are to be secured.
9.22. Streamlining. -There is no simple foolproof answer to the
aerodynamical problem. Each installation has peculiarities of its own,
depending upon its location on the airplane in question, the plane itself,
the speed of the plane, and the size and shape of the radome. A few
simple considerations can be set forth but the real answer can only result
from careful test in a wind tunnel.
Although, from an electrical viewpoint, the circular cylinder is the
most desirable shape for a radome, aerodynamically it is objectionable
due to its high drag. By streamlining a cylinder its air resistance can be
reduced to a sixth or less. Any radome extending beyond the fuselage
line of the airplane should therefore be streamlined.
The drag for a protuberance of given shape increases in approximate
proportion to its frontal area. It is therefore desirable to reduce the
projected area of the radome as much as possible even to the extent of
having the radome surface coincide with the skin of the plane.
If a protuberance is necessary, the drag can be minimized by locating
the radome at a position where there is already some disturbance of the
airflow. The turbulence of the air stream tends to be a maximum toward
the tail of the plane. R’bile practically no protuberance is permissible
near the nose of a high-speed airplane, one etiending several inches amidship
or further aft may cause a hardly noticeable increase of drag.
The truly satisfactory design, however, can be verified only by tests
in the wind tunnel where very slight differences in aircraft performance
are readily detectable. The wind-tunnel test can also be used to furnish
pressure distributions on the radome surface, which are necessary for the
structural design computations.
The location of the antenna on the airplane must also be the result of
operational requirements and compromises with the other components.
For navigation and bombing it is desirable to have the antenna scan 360°
in azimuth. This can best be realized in a location on the belly of the
-e about midship, but generally only by adding a large protuberance.
A location in the “chin” of the airplane offers a more favorable location