Nose gear shock struts are provided with an upper
centering cam that is attached to the upper cylinder and
a mating lower centering cam that is attached to the
lower cylinder. See figure 13-10. These cams serve to
line up the wheel and axle assembly in the
straight-ahead position when the shock strut is fully
extended. This prevents the nosewheel from being
cocked to one side when the nose gear is retracted,
preventing possible structural damage to the aircraft.
These mating cams also keep the nosewheel in a
straight-ahead position prior to landing when the strut
is fully extended.
Nose and main gear shock struts are usually
provided with jacking points and towing lugs. Jacks
should always be placed under the prescribed points.
When towing lugs are provided, the towing bar should
be attached only to these lugs.
All shock struts are provided with an instruction
plate that gives, in a condensed form, instructions
relative to the filling of the strut with fluid and inflation
of the strut. The instruction plate also specifies the
correct type of hydraulic fluid to use in the strut. The
plate is attached near the high-pressure air valve. It is of
the utmost importance that you always consult the
Figure 13-9.--Landing gear shock strut (metering tube type).
applicable aircraft MIMs and familiarize yourself with
the instructions on the plate prior to servicing a shock
stroke and to prevent a too rapid extension of the shock
strut with hydraulic fluid and nitrogen or air.
strut, which would result in a sharp impact at the end of
The majority of shock struts are equipped with an
axle that is attached to the lower cylinder to provide for
tire and wheel installation. Shock struts not equipped
with axles have provisions on the end of the lower
cylinder for ready installation of the axle assembly.
Suitable connections are also provided on all shock
struts to permit attachment to the aircraft.
A fitting, which consists of a fluid filler inlet and a
high-pressure air valve, is located near the upper end of
each shock strut to provide a means of filling the strut
with hydraulic fluid and inflating it with air or nitrogen.
A packing gland designed to seal the sliding joint
between the upper and lower telescoping cylinders is
installed in the open end of the outer cylinder. A
packing gland wiper ring is also installed in a groove in
the lower bearing or gland nut on most shock struts to
keep the sliding surface of the piston or inner cylinder
free from dirt, mud, ice, and snow. Entry of foreign
matter into the packing gland will result in leaks. The
majority of shock struts are equipped with torque arms
attached to the upper and lower cylinders to maintain
correct alignment of the wheel.
Figure 13-10.--Nose gear shock strut.