Landing gear doors have specific allowable
clearances that must be maintained between doors and
the aircraft structure or other landing gear doors. These
required clearances can be maintained by adjusting the
door hinges and connecting links and trimming excess
material from the door if necessary.
On some installations, door hinges are adjusted by
placing the serrated hinge and serrated washers in the
proper position and torquing the mounting bolts, which
allows linear adjustments. Figure 13-7 shows this type
of mounting. The amount of linear adjustment is
controlled by the length of the elongated bolt hole in the
door hinge.
SHOCK STRUTS
Shock struts are self-contained hydraulic units.
They carry the burden of supporting the aircraft on the
ground and protecting the aircraft structure by
absorbing and dissipating the tremendous shock of
landing. Shock struts must be inspected and serviced
regularly for them to function efficiently. This is one of
your important responsibilities.
Each landing gear is equipped with a shock strut. In
addition to the landing gear shock struts, carrier aircraft
Figure 13-8.--Landing gear shock strut (metering pin type).
are equipped with a shock strut on the arresting gear.
The shock strut is essentially two telescoping
The shock strut's primary purpose is to reduce arresting
cylinders or tubes, with externally closed ends. When
hook bounce during carrier landings.
assembled, the two cylinders, known as cylinder and
Because of the many different designs of shock
piston, form an upper and lower chamber for movement
struts, only information of a general nature will be
of the fluid. The lower chamber is always filled with
included in this chapter. For specific information on a
fluid, while the upper chamber contains compressed air
particular installation, you should refer to the
or nitrogen. An orifice (small opening) is placed
applicable aircraft MIM or accessories manual.
between the two chambers. The fluid passes through
this orifice into the upper chamber during compression,
A typical pneumatic/hydraulic shock strut
and returns during extension of the strut.
(metering pin type) is shown in figure 13-8. It uses
compressed air or nitrogen combined with hydraulic
Most shock struts employ a metering pin similar to
fluid to absorb and dissipate shock, and it is often
that shown in figure 13-8 to control the rate of fluid
referred to as the "air-oil" type strut. This particular
flow from the lower chamber into the upper chamber.
strut is designed for use on the main landing gear.
During the compression stroke, the rate of fluid flow is
not constant, but is controlled automatically by the
variable shape of the metering pin as it passes through
the orifice.
On some types of shock struts now in service, a
metering tube replaces the metering pin, but shock strut
operation is the same. An example of this type of shock
strut is shown in figure 13-9.
Some shock struts are equipped with a dampening
or snubbing device, which consists of a recoil valve on
the piston or recoil tube. The purpose of the snubbing
Figure 13-7.--Adjustable door hinge installation.
device is to reduce the rebound during the extension
13-8
