In order to increase the loads and ranges of their bombers and observation
planes, the German Air Force has resorted to overloading. Once in the
air, planes can fly with a considerable overload, although their speed is
somewhat reduced; the main operational difficulty lies in the take-off. A normal
take-off under overloaded conditions will require a runway of abnormal
length; this is generally impracticable. The Germans have devised other means which
have proven so successful that even smaller fields than heretofore are
now being used.
There are three main types of assisted take-off: the catapult, the winch, and the rocket system.
a. The catapult is costly and complicated, and is not mobile. It consists of a
dolly or car, upon which the airplane is placed. Upon a signal from the pilot, the
car is hurled forward by compressed air, and the plane with its engines full-on is
literally shot into the air.
The catapult is mainly used aboard ship where the take-off must of necessity be
extremely short. The aircraft employing this method must be reinforced to
withstand the sudden strain put upon it. The catapult has not proven
itself very adaptable for ground operations.
b. The winch system was adopted by the German Air Force in 1940 primarily to
assist overloaded Heinkel He-111 bombers in taking off from small airports, and now
appears to be standard. This equipment is believed to consist of a large drum-pulley
coupled by a clutch to a fly-wheel which is driven through gears by a powerful
aero-engine. The entire device is mounted on wheels and can be moved to the required
location by a tractor. A cable approximately 825 feet long is wound over the pulley and
attached by a hook to a shackle underneath the fuselage. The tail of the plane is
fastened by an electromagnetic coupling to a smaller winch.
The aircraft, after being placed in approximate take-off position, is pulled backward by the
smaller winch until the main cable is taut; the plane is thus held in starting position
for the take-off. After running up his engines to full throttle, the pilot presses a
switch which simultaneously drops the tail coupling and engages the clutch in the
main winch. The aircraft is pulled forward at a high speed and, as it rises and
flies over the winch, the main cable is disengaged by its own weight. The clutch
is thereupon automatically disengaged and a brake applied to the winding drum. Attachments
found on planes such as the Do-17 lead to the belief that devices of this or similar types are
probably in general use.
c. The cheapest and most convenient form of assisted take-off is probably
the rocket device now in use by the German Air Force on the Ju-88, Me-110, and
other aircraft. It usually consists of two large pear-shaped rockets attached by
special fittings to the underside of each wing. These rockets may have a
venturi-type discharge nozzle and are believed to be activated by slow-burning
cordite or some other fuel and compressed air. It is possible that if it is
cordite, the powder is stowed in sections or layers which are progressively
ignited by electrical means.
After a short take-off run the pilot presses an electrical switch, igniting
the rockets; should the need arise, he may extinguish them almost instantaneously by
turning off the switch. The thrust of these rockets lasts about 30 seconds. When the
aircraft has risen about 500 feet, the rocket gear, which is quite large and
heavy, is jettisoned and drops to the ground by parachute. It is believed that the
rockets can be reloaded and used again.
While aircraft must be specially equipped to use this device, the apparent
simplicity of the rocket method will no doubt increase its use for planes
operating from restricted fields under conditions of overload.