TM 1-1500-204-23-2
Figure 4-169. Stabilizer Bar with Vane Dampers
is compressing, fluid is forced through the orifice into the
piston. The movement of fluid through the orifice,
together with the compression of the air, absorbs the
energy of motion of the descending aircraft. When the
load on the shock strut is lightened, the shock strut
extends. This extension is caused by the force exerted
by the compressed air in the shock strut and, during
takeoff, by the weight of the lower tube and the attached
landing gear. When the shock strut is extending, fluid in
the piston passes through the orifice from the piston into
the cylinder.
(2) Complex shock strut. Complex shock
struts work in essentially the same manner as simple
ones. However, they contain, in addition to two teles-
coping tubes, a number of parts that make for more
effective damping action than is possible with simple
struts. Design features found singly or in combination in
complex shock struts are metering pins, plungers, and
floating pistons.
(a) Metering pin. The metering pin is a
means of changing the effective size of the orifice so as
to vary the rate of fluid flow from one chamber of the
shock strut to the other. The diameter of the metering
pin varies along its length, being almost equal at the
ends and smaller in the middle. Note in figure 4-171 that
the unanchored end of the metering pin is located in the
orifice when the shock strut is fully extended. The large
diameter of the pin at this end provides a high resistance
to fluid flow, a condition that is required during landing.
The small diameter portion of the metering pin is located
within the orifice when the shock strut is in its taxi
position (partially compressed). This provides the low
resistance to fluid flow that is required for taxiing The
portion of the metering pin nearest is anchored end lies
within the orifice when the shock strut is completely
compressed. The large diameter of the metering pin at
this end provides increased resistance to fluid flow. The
design of the pin at this end ensures against bottoming
of the shock strut during unusually hard landings. The
gradual increase in the diameter of the pin toward the
anchored end prevents a sudden change in resistance
to fluid flow.
(b) Plunger. Some complex shock struts
are mounted on the aircraft with their cylinders upper-
most as shown in figure 4-172. In such a unit, a plunger
anchored in the cylinder extends downward into the
piston. The plunger forces fluid out of the piston and into
the cylinder during compression of the shock strut. The
plunger is hollow, and fluid enters and leaves its interior
through an orifice and through holes in its walls.
(c) Floating piston. In some shock struts,
the air charge is carried at the bottom of the shock strut
instead of at the top. Since air normally rises to the top
of a liquid, some means must be provided to keep the
air below the liquid. A floating piston serves this pur-
pose. In the floating-piston type shock strut, the upper
chamber of the strut decreases in size as the strut
compresses as shown in figure 4-173. This is because
compression of the shock strut forces fluid downward
out of the upper chamber into the lower fluid chamber.
The Increase in size of the lower fluid chamber, neces-
sary for accommodating the inflow of fluid, is obtained
by downward movement of the floating piston. Thus, in
addition to holding the air below the fluid, the floating
piston contributes to the movement of fluid through the
orifice as the shock strut compresses and extends.
(3) Uses of shock struts. Shock struts support
the static load of the aircraft, cushion jolts during taxiing
or towing, and absorb the shock of landing.
(a) Supporting static loads. The normal load
of a parked aircraft is static; that is, the force present is
fixed. The pressure of the air and fluid within a shock
strut tends to keep the shock strut fully extended. How-
ever, air pressure in a shock strut is not enough to keep
the strut fully extended while supporting the static load
4-160
