TM 1-1500-204-23-2
Figure 4-170. Simple Shock Strut
of an aircraft. Therefore, a shock strut gives under load
and compresses until the air pressure builds enough to
support the aircraft
(b) Cushioning during taxiing. As an aircraft
taxies, the unevenness of the runway surface causes
the aircraft to bob up and down as it moves forward
(sometimes air currents contribute to this effect) The
inertia of the aircraft fuselage in opposition to such
up-and-down movements causes the force of the taxi
load to fluctuate This bouncing motion is held within
limits by the damperlike action of the shock strut. This
dampening results from resistance created by the back-
and-forth flow of fluid through the orifice as the shock
strut extends and compresses.
(c) Reducing shock during landing. The
aircraft will continue to descend at a high rate when
landing, even after the wheels touch the ground. In the
few remaining inches that the fuselage can move toward
the ground after the wheels touch, the descent of the
aircraft must be stopped. To perform this task, the shock
strut must remove a great amount of energy from the
downward movement of the aircraft. The Impact force is
very great compared to the force exerted by the mere
weight of the aircraft. The shock strut removes some of
the energy of motion-and thus some impact force-by
converting energy into heat and dissipating the heat into
the atmosphere. The resistance to fluid flow offered by
the orifice is the principal means of developing the heat.
Also, the temperature of the air Inside the strut rises as
the air is compressed.
1 Strut extension. The speed of a des-
cending aircraft while landing causes over-compression
of the air in the shock strut As a result, the air pressure
is greater than that needed to support the static load of
the aircraft. The excess pressure tends to extend the
shock strut and to bounce the aircraft back into the air.
For reasons of comfort and control of the aircraft, this
rebound has to be held to the lowest level possible. The
most common means of counteracting rebound involves
4-161
