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ORIGINAL 2-126
2.27.2 Nosewheel Centering. The nosewheel is
automatically centered during gear retraction before the
nosewheel enters the wheelwell. During gear retraction
with weight off wheels, hydraulic pressure t?om the
combined system bypasses the steering unit shutoff
valve to center the nosewheel independent of rudder
pedal movement. Ifthe nosewheel is cocked beyond 15”
either side ofcenter after takeoff, the nosewheel is automatically
prevented Born retracting and the LAUNCH
BAR advisory light illuminates.
During carrier arrestmem, the nosewheel is centered
with weight on wheels and hook down when both throttles
are retarded to IDLE to prevent castoring during
rollback. After arrestment and rollback, the nosewheel
will remain centeredu ntil nosewheesl teeringi s engaged.
[WPIRUING)
Nosewheel centering can contribute to
launch bar misalignment in the catapult shuttle,
which could result in premature launch
bar separationd uring launch. The nosewheel
centering latching relay must be deactivated
by depressingt he nosewheels teeringb utton
after the hook check and prior to entering the
catapult. As this will also deactivate the
nosewheel steering automatic disengagement
function, the nosewheel steering must
be manually disengaged when entering the
catapult.
2.27.3 Shimmy Damping. Shimmy damping is pmvided
in the steering actuator. Increased shimmy damping
action is obtained with NWS disengaged.
m
If excessive nosewheel shimmy is encountered,
disengagen osewheels teering.
2.28 NOSEGEAR CATAPULT SYSTEM
Catapult connection components on the nose landing
gear shock strut piston provide nosegear catapult
capability. A launch bar attached to the forward face
of the nosegear steering collar guides the aircraft onto
the catapult track and serves as the tow link that engages
the catapult shuttle. A holdback fitting secures
the holdback restraint prior to launch. The two-piston
nose strut uses the stored energy catapult principle to
impart a positive pitch rotation movement to the air-
NAVAIR 0%Fl4AAD-1
craft at shuttle release, thus providing for a hands-off
launchflyawaytechnique.
2.28.1 Nose Strut Kneel. Prior to catapult hookup,
the nose strut is compressed 14 inches. Control of the
nose strut kneel function is provided by the NOSE
STRUT switch on the landing gear control panel (see
Figure 2-73.) The three-position (EXTD, OFF, and
KNEEL) toggle switch is spring loaded to return to the
detentedc entert o OFF. The position of the strut remains
in the last commandedp osition independento f electrical
or hydraulic power interruptions. In both cases, the
transfer control valve source of electrical power is the
essentialNo. 2 bus and combmedhydraulic system fluid
is used as the transfer medium. With external electrical
power on the aircraft, the combined hydraulic system
must bep ressurized( >500 psi) before the control switch
can command a position change of the transfer control
valve. The control switch need only be held momentarily
to effect a change in transfer control valve position.
Selectiono fKNEEL releasesh ydraulic fluid from the
shock strut transfer cylinder to the combined hydraulic
system return line, causing the weight of the aircraft to
compress the shock strut 14 inches. Stroking ofthe nose
strut causesth e aircraft to rotate about the main wheels.
The aircraft may be taxied or towed in the strut-kneeled
position except for the nuisance trip of the launch bar at
greater than 10” steering angle; this is the position used
for taxiing onto the catapult and enhances accessibility
to the forward fuselage compartments during ground
maintenanceS. ince the noses trut is bottomedd uring the
catapult launch stroke, the energy stored in the last 4
inches of strut-piston stroke is released upon shuttle
release at the end of the catapult stroke to impart a
noseup pitching moment to rotate the aircraft to the
fly-away attitude without any control required by the
pilot. All the stonede nergyi s expendedb eforet he nosewheels
leave the deck edge.
Note
Under certain launch conditions (high wind
over deck and light aircraft gross weights)
the nose strut will not be fully compressed
during the catapult stroke. Subsequentn ose
rotation following shuttle releasew ill be at a
less than normal rate. Aircraft launch bulletins
for the aircraft are written to ensure that
catapult launch pressures are sufficient to
provide safe launch pitch rates and flyaway
capability.
Full extensiono f then oses truta fter launcha ndw eight
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F-14D 飞行手册 Flight Manual 1(127)
