Gyro Horizon; Air Driven Attitude Horizon; Electrically Driven Attitude Horizon - Piper PA-44-180 SEMINOLE Maintenance Manual

1. Carefully lay teflon tape on the threads allowing one thread to be visible from the end of the fitting. Hold in
place and wrap in the direction of the threads so tape will remain tight when fitting is installed.
2. Apply sufficient tension while winding to assure that tape forms into thread grooves. One full wrap plus 1/2
inch overlap is sufficient.
3. After wrap is completed, maintain tension and tear tape by pulling in direction of wrap. The resulting
ragged end is the key to the tape staying in place.
4. Press the tape well into the threads.
5. Screw fitting into port being careful not to exceed torque requirements as noted on decal on gyro cover.

GYRO HORIZON.

Both air and electric attitude horizons are used depending on the option package installed. Both types are
displacement type gyros with "free" rotors mounted in gimbal assemblies. It is important to consult the A.F.C.S.
Manufacturer's Service Manual if a flight director or autopilot is coupled to the attitude horizon.

AIR DRIVEN ATTITUDE HORIZON.

The air driven attitude horizon is driven by the pneumatic system which is supplied by engine driven dry
pneumatic pumps either on pressure or vacuum. It is of prime importance to realize that air VOLUME and not air
pressure, spins the gyro rotor. The air filter can become contaminated and restrict air flow reducing gyro rotor
speed while the pressure regulator will automatically adjust air pressure within proper limits.
The gyro air filter must be clean or replaced prior to adjusting gyro air pressure.
Airflow directed at the gyro buckets causes the rotor spin approximately 17,000 to 22,000 rpm thus producing
the gyroscopic ability to remain rigid in space. The instrument case moves freely about the spinning gyro rotor in
three dimensions by use of a gimbal assembly. The resulting displacement in both pitch and roll is mechanically
displayed on the instrument face, providing an artificial horizon reference which portrays airframe attitude at any
given moment. The display is stable and can show minute attitude changes of only 1°. Unlike the directional
gyro, the erection mechanism activity can be seen by a rapidly wobbling and leveling horizon bar when power is
first applied. The instrument can be adjusted for parallax through a knob on the instrument face. This knob, when
held in the "IN" position, engages forks which cage the gyro rotor.

ELECTRICALLY DRIVEN ATTITUDE HORIZON.

These gyros contain rotors which are electrically driven with the gyro rotor acting as the armature of an
induction motor. Brush assemblies are not used since the friction would result in abnormal precession. The
rotor/armature is inductively excited. The electric attitude horizon is subject to the same operational requirements
of the air driven attitude horizon, except for the method of obtaining rotor rotation and the design of the erection
mechanism.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
— Note —
2J4
3 4 - 2 3 - 0 3
Page 34-10
Revised: May 15, 1989