VIBRATION & BALANCE
Vibration, shimmy and other
similar conditions are usually blamed on improper tire balance. Imbalance is a
well-known and easily understood cause for vibration. In many cases though,
this may not be the cause. There are a number of specific aspects of the tire,
wheel and gear assembly which can be the cause or contribute to aircraft
vibration. As with any concern, a systematic approach should be taken to
isolating its cause.
that the tire has been inflated to the proper inflation pressure.
the airframer's recommendation.
sure an accurate calibrated pressure gauge has been used.
that dual tire inflation is equalized between tires and per the operating
that the tire reached full growth before it was installed on the aircraft.
at least 12 hours at operating or rated pressure for the tire to attain
that the beads of the tire have been properly seated.
the tire for flat spotting or uneven wear. If flat spotting does not
extend to the protector ply (Radial) or reinforcing ply (Bias) and
vibration is acceptable, the tire can be left in service.
that tires have been properly mounted. For tubeless tires, the red balance
mark on the lower sidewall of the tire should be aligned with the wheel
valve. For tube‑type tires, the balance mark (light spot) on the
lower sidewall of the tire should be aligned with the balance mark (heavy
spot) on the tube.
for air trapped between the tire and tube. Use a soapy solution to check
for leakage at the base of the tube valve stem where it exits the wheel.
Rolling the tire by taxiing will generally work any trapped air out from
between the tube and tire.
the tube wrinkled because of improper inflation procedures?
the wheel out of balance because of improper assembly?
the wheel manufacturer's instructions for properly aligning wheel
balance mark on the tire should be aligned with the valve mounted on the
wheel, unless otherwise specified by the wheel manufacturer.
the condition of the wheel to see if it has been bent.
for a loose wheel bearing caused by an improperly torqued axle nut
for poor gear alignment as evidenced by uneven wear
for worn or loose landing gear components.
Certain aircraft have nose landing gears
which are sensitive to vibration. For these cases, assemblies should be
checked for balance and wheel weights added when required