The bearing cups are shrink-fitted into the hub of
the wheel casting; the bearing cups are the parts on
which the bearings ride. The bearings are tapered roller
bearings. Each bearing is made of a cone and rollers.
This type of bearing absorbs side thrust as well as radial
loads and landing shocks. These bearings must be
cleaned and lubricated in accordance with the NAVAIR
Figure 7-4.--Safe-core valve tool.
A three-piece grease retainer keeps the grease in
area. All wheel bearings should be lubricated at every
the inboard bearing and keeps out dirt and moisture.
tire change, and as required by the applicable
The retainer is composed of a felt seal and inner and
maintenance requirements cards (MRCs). All wheel
outer closure rings. A lockring secures the assembly
and bearing assemblies should be removed according to
inside the wheel hub.
the applicable maintenance instruction manual (MIM)
for that specific aircraft.
The hubcap seals the outboard side of the hub. It is
secured with a lockring. On some aircraft, the hubcap is
secured with screws.
All wheels designed to be used on the main landing
gear are equipped with braking components. These
When a wheel is to be removed from an aircraft,
components are attached to the wheel casting. They
the nitrogen or dry air must be removed from the tire
may consist of either a brake drum or brake drive keys.
prior to removing the wheel. This should be done
The wheel shown in figure 7-3 is equipped with drive
with the Palmer Safe-Core valve tool (P/N 968RB),
keys. This wheel is designed for disc brakes.
which traps the valve core in the body of the Palmer
Safe-Core valve tool. See figure 7-4. This precaution
The trend in the military is toward smaller, faster,
must be taken because of the possibility that the bolts
more powerful aircraft with increased load carrying
in split wheels might have been sheared and cause the
capabilities. This means heavier loads and higher
wheel halves to separate when the axle nut is
landing speeds. The friction of long landing rollouts
removed. A tire deflated (valve core removed) metal
and taxiing causes heat to be absorbed by the wheel.
tag should be installed on the valve stem prior to
Because of the heat, possible wheel failure may occur.
removing the wheel from the axle. See figure 7-5.
This may damage equipment and injure personnel. To
Several people have been killed because they failed to
prevent this situation, aircraft manufacturers have
remove the air from the tire before removing the axle
developed a safety device called a "fusible plug." The
fusible plug contains an alloy that will melt and permit
the tire to deflate. This action occurs in the event the
wheel is exposed to excessive heat. Wheels that contain
fusible plugs should have a metal tag affixed that reads
"Fusible Plugs Installed."
ORGANIZATIONAL-LEVEL TIRE AND
Corrosion and loss of bearing lubrication are two of
the major causes of failure or rejection of aircraft
wheels. It is extremely important that all organizational
maintenance activities take precautions to protect
aircraft wheels/bearings from water, particularly salt
water. Wheel bearing lubrication gets contaminated
and/or breaks down, from excessive heat and water,
more often than it is lost. When wheels are exposed to a
stream of water (such as a hose), it will usually
penetrate the hub area, contaminating the bearing
Figure 7-5.--(A) Deflated tire flag, (B) Storage of valve core
lubricant. This contributes to corrosion in the bearing
and cap using alternate deflated tire flag.