TM 1-1500-204-23-2
Figure 4-163. Piston Damper Cross Section
2
Nose landing gear damper. Vane-
type dampers, such as the one shown in figure 4-168, are
used on the nose landing gear of some aircraft to eliminate
the shimmy tendency.
3
Stabilizer
bar
damper.
Some
helicopters have vane-type dampers, such as the one
shown in figure 4-169, that serve to control the degree of
sensitivity with which a helicopter responds to movement
made by the pilot on the flight controls. These dampers are
mounted on a bracket attached to the helicopter mast (main
shaft). The damper arms are interconnected with other
parts of the flight control system.
(2)
Shear-principle dampers. In dampers operating
on the shear principle, fluid is not forced out of one space
and into another within the damper as in the case of
displacement dampers. Instead, action on the fluid involves
tearing (shearing) a thick film of highly viscous fluid into two
thinner films that move with resistance in opposite
directions. A highly viscous fluid is thick bodied, syrupy,
and sticky.
Figure 4-164. Nose Landing Gear with Piston
Damper
Theory of operation. In a shear-prin-
ciple damper, two reacting parts are free
to slide or rotate past each other as the
damper operates. The surfaces facing
each other are relatively smooth, and
between them there is a preset gap of a
few thousandths of an inch. This gap is
filled with a highly viscous fluid. As the
parts of the damper move relative to each
other, the film of fluid In the gap between
them shears into two thinner films. Each
film adheres to and moves along with one
of the parts. It is the friction within the
fluid itself that causes resistance to move-
ment of the parts to which the films ad-
here. To better understand this principle,
imagine a puddle if syrup spilled on a
relatively smooth table top A sheet of
paper placed on top of the puddle would
move with considerable drag. This is very
much like what happens between the
parts of a shear-principle damper as the
damper operates.
Figure 4-162. Piston Damper
4-158
