Air-Oil Separator.--Oil and air in the vacuum pump are exhausted through the separator, which separates the oil from the air; the air is vented outboard, and the oil is returned to the engine sump.
Suction Relief Valve.-Since the system capacity is more than is needed for operation of the instruments, the adjustable suction relief valve is set for the vacuum desired for the instruments. Excess suction in the instrument lines is reduced when the spring-loaded valve opens to atmospheric pressure.
(See fig. 12-62.)
Pressure Relief Valve.-Since a reverse flow of air from the pump would close both the gate check valve and the suction relief valve, the resulting pressure could rupture the lines. The pressure relief valve vents positive pressure into the atmosphere.
Gate Check Valve.-The gate check valve prevents possible damage to the instruments by engine back-fire, which would reverse the flow of air and oil from the pump. (See fig. 12-63.)
Selector Valve.--In twin-engine aircraft having vacuum pumps driven by both engines, the alternate pump can be selected to provide vacuum in the event of either engine or pump failure, with a check valve incorporated to seal off the failed pump.
Restrictor Valve.--Since the turn needle operates on less vacuum than that required for other gyro instruments, the vacuum in the main line must be reduced. This valve is either a needle valve adjusted to reduce the vacuum from the main line by approximately one-half, or a springloaded regulating valve that maintains a constant vacuum for the turn indicator, unless the main line vacuum falls below a minimum value.
Suction Gage.-The suction gage is a pressure gage, indicating the difference in inches of mercury, between the pressure inside the system and atmospheric or cockpit pressure. The desired vacuum, and the minimum and maximum limits, vary with gyro design. If the desired vacuum for the attitude and heading indicators is 5" and the minimum in 4.6", a reading below the latter value indicates that the airflow is not spinning the gyros fast enough for reliable operation. In many aircrait, the system provides a suction gage selector valve, permitting the pilot to check the vacuum at several points in the system:
Suction Suction pressures discussed in conjunction with the operation of vacuum systems are actually minus or negative pressures (below sea level). For example, if sea level equals 17.5 p.s.i, then 1" Hg (1 inch mercury) or 1 p.s.i. vacuum is equal to
- 1 p.si. negative pressure or 10.5 positive pressure. Likewise 3" Hg= -3 p.s.i. negative pressure or +14.5 positive pressure.
Of course, for every action there is an equal and opposite reaction. Therefore when the vacuum pump develops a vacuum (negative pressure) it must also create pressure (positive). This pressure (compressed air) is sometimes utilized to operate pressure instruments, deicer boots and inflatable seals.
• Spring To vacuum pump -
• Wire screen FICURE 12-62. Vacuum regulator valve.
Air filter.-The master air filter screens foreign matter from the air flowing through all the gyro Cate check valve open Gate check valve closed instruments, which are also provided with indi- - Spring vidual filters. Clogging of the master filter will reduce airflow and cause a lower reading on the suction gage. In aircraft having no master filter Air flee from installed, each instrument has its own filter. With Air flens to vacuum pump an individual filter system, clogging of a filter will not necessarily show on the suction gage. FIGURE 12-63. Gate check valve.
Typical System Operation The schematic of a vacuum system for a twin-engine aircraft is shown in figure 12-64. This vacuum system consists of the following components; two engine-driven pumps, two vacuum relief valves, two flapper-type check valves, a vacuum manifold, a vacuum restrictor for each turn-and-bank indicator, an engine four-way selector valve, one vacuum gage, and a turn-and-bank selector valve.
The left and right engine-driven vacuum pumps and their associated lines and components are isolated from each other, and act as two independent vacuum systems. The vacuum lines are routed from each vacuum pump through a vacuum relief valve and through a check valve to the vacuum four-way selector valve.
Turn-and-bank selector valve Copilot's turn-and-bank Right T & B Needle valve Copilot's artificial horizon From the engine four-way selector valve, which permits operation of the left or right engine vacuum system, the lines are routed to a vacuum manifold.
From the manifold, flexible hose connects the vacuum-operated instruments into the system. From the instrument, lines routed to the vacuum gage pass through a turn-and-bank selector valve. This valve has three positions: main, left T&B, and right T&B. In the main position the vacuum gage indicates the vacuum in the lines of the artificial horizon and directional gyros. In the other positions, the lower value of vacuum for the turn-and-bank indicators can be read.
VACUUM-DRIVEN ATTITUDE GYROS In a typical vacuum-driven attitude gyro system, air is sucked through the filter, then through pas-
- Vacuum gage Left T & B Main Pilot's turn-and-bank Needle valve Pilot's artificial horizon Pilot's directional gyro Vacuum manifokl Check valve • Vacuum 4-way selector valve Relief valve Relief valve Check valve Right engine vacuum pump Left engine vacuum pump FICURE 12-64. Vacuum system for a multi-engine aircraft.
Precess Port Port A Applied force Gyro precesses, Precession Exhaust air equal increasing exhaust Precessing force at port A erects gyro, in all directions. from port A. exhaust air again equal at all ports.
Gyro erect.
FICURE 12-65. Erecting mechanism of a vacuum-driven attitude indicator.
sages in the rear pivot and inner gimbal ring, then into the housing where it is directed against the rotor vanes through two openings on opposite sides of the rotor. The air then passes through four equally spaced ports in the lower part of the rotor housing and is sucked out into the vacuum pump or venturi (figure 12-65).
The chamber containing the ports is the erecting device that returns the spin axis to its vertical alignment whenever a precessing force, such as bearing friction, displaces the rotor from its horizontal plane. Four exhaust ports are each half-covered by a pendulous vane, which allows discharge of equal volumes of air through each port when the rotor is properly erected. Any tilting of the rotor disturbs the total balance of the pendulous vanes, tending to close one vane of an opposite pair while the opposite vane opens a corresponding amount. The increase in air volume through the opening port exerts a precessing force on the rotor housing to erect the gyro, and the pendulous vanes return to a balanced condition (figure 12-66).
The limits of the attitude indicator specified in the manufacturer's instructions refer to the maximum rotation of the gimbals beyond which the gyro will tumble. The bank limits of a typical vacuumdriven attitude indicator are from approximately 100° to 110°, and the pitch limits vary from approximately 60° to 70°, depending on the design of a specific unit. If, for example, the pitch limits are 60° with the gyro normally erected, the rotor will tumble when the aircraft climb or dive angle exceeds 60°. As the rotor gimbal hits the stops, the FIGURE 12-66. Action of pendulous vanes.
rotor precesses abruptly, causing excessive friction and wear on the gimbals. The rotor will normally preceas back to the horizontal plane at a rate of approximately 8° per min.
Many gyros include a caging device, used to erect the rotor to its normal operating position prior to fight or after tumbling, and a flag to indicate that the gyro must be uncaged before use.
Turning the caging knob prevents rotation of the gimbals and locks the rotor spin axis in its vertical position.
PRESSURE-OPERATED GYROS The availability of pressure pumps on which no lubrication is necessary makes pressure-operated gyro systems feasible. In such installations, air is pushed under pressure through gyro instruments, rather than being sucked through the system. Positive-pressure pumps are more efficient than vacuum pumps, especially at higher altitudes.
VACUUM SYSTEM MAINTENANCE PRACTICES Errors in the indications presented on the attitude indicator will result from any factor that prevents the vacuum system from operating within the design suction limits, or from any force that disturbs the free rotation of the gyro at design speed.
These include poorly balanced components, clogged filters, improperly adjusted valves and pump malfunction. Such errors can be minimized by proper installation, inspection, and maintenance practices.
Other errors, inherent in the construction of the instrument, are caused by friction and worn parts.
These errors, resulting in erratic preccasion and failure of the instrument to maintain accurate indications, increase with the service life of the instru- For the aviation mechanic the prevention or correction of vacuum system malfunctions usually consists of cleaning or replacing filters, checking Possible Cause Isolation Procedure Correction
(1) No Vacuum Pressure or Insufficient Pressure Defective vacuum gage. On multi-engine aircraft check Replace faulty vacuum gage.
opposite engine system on the gage.
Vacuum relief valve incorrectly Change valve adjustment. Make final adjustment to proper adjusted. setting of valve.
Vacuum relief valve installed Visually inapect. Install properly.
backwards.
Broken line. Visually inspect. Replace line.
Lines crossed. Visually inspect. Install lines properly.
Obstruction in vacuum line. Check for collapsed line. Clean and test line. Replace defective part (s).
Remove and inspect. Replace faulty pump.
Make valve adjustment and note Adjust to proper pressure.
pressure.
Clean and adjust relief valve. Replace valve if adjustment fails.
sted. Adjust relief valve to proper setting.
Check calibration of gage. Replace faulty gage.
spond Visually inspect. Uncage instrument.
Check filter. Replace or clean as necessary.
Check vacuum setting. Adjust relief valve to proper setting.
Replace instrument.
Check lines and vacuum system. Clean or replace lines and replace components of vacuum system as necessary.
Instrument filter clogged. Visually inspect. Replace filter.
Defective instrument. Test with properly functioning Replace faulty instrument.
instrument.
(6) Turn-and-Bank Pointer Vibrates Defective instrument. Test with properly functioning Replace defective instrument.
instrument FICURE 12-67. Vacuum system troubleshooting.
and correcting for insufficient vacuum, or removing and replacing the instruments. A list of the most common malfunctions, together with their correction, is included in figure 12-67.
ELECTRIC ATTITUDE INDICATOR In the past, suction-driven gyros have been favored over the electric type for light aircraft because of their comparative simplicity and lower cost. However, the increasing importance of the attitude indicator has stimulated development of improved electric-driven gyros suited for light plane installation. Improvements relating to basic gyro design factors, easier readability, erection characteristics, reduction of induced errors, and instrument limitations are reflected in several available types. Depending upon the particular design improvements, the details for the instrument display and cockpit controls will vary among different instruments. All of them present, to a varying degree, the essential pitch-and-bank information for attitude reference.
The typical attitude indicator, or gyro horizon as it is sometimes referred to, has a vertical-seeking gyro, the axis of rotation tending to point toward the center of the earth. The gyro is linked with a horizon bar and stabilizes a kidney-shaped sphere having pitch attitude markings. The sphere, horizon bar, and bank index pointer move with changes of aircraft attitude. Combined readings of these presentations give a continuous pictorial presentation of the aircraft attitude in pitch and roll with respect to the earth's surface.
magnet attached to the top of the gyro shaft spins at approximately 21,000 r.p.m. Around this magnet, but not attached, is a sleeve that is rotated by magnetic attraction at approximately 44 to 48 r.p.m.
As illustrated in figure 12-69, the steel balls are free to move around the sleeve. If the pull of gravity is not aligned with the axis of the gyro, the balls will fall to the low side. The resulting precession re-aligns the axis of rotation vertically.
The gyro can be caged manually by a lever and cam mechanism to provide rapid erection. When the instrument is not getting sufficient power for normal operation, an "off" flag appears in the upper right-hand face of the instrument.
Gyro stabilized horizon bar Power failure warning flag Vertical index Bank index Bezel ' mask The gyroscope motor is driven by 115 v., 400 Hz alternating current. The gyro, turning at approximately 21,000 r.p.m., is supported by the yoke and pivot assembly (gimbals). Attached to the yoke and pivot assembly is the horizon bar, which moves up and down through an arc of approximately 27°.
The kidney-shaped sphere provides a background for the horizon bar and has the words climb and dive and a bull's-eye painted on it. Climb and dive represent about 60° of pitch. Attached to the yoke and pivot assembly is the bank index pointer, which is free to rotate 360°. The dial face of the attitude indicator is marked with 0°, 10°, 20°, 30°, and 60° of bank, and is used with the bank index pointer to indicate the degree of bank left or right.
The face of one type of gyro-horizon is shown in figure 12-68.
The function of the erection mechanism is to keep the gyro axis vertical to the surface of the earth. A Trim knob Caging knob FIcuRE 12-68. Gyro-horizon indicator.
Magnetic Compass The magnetic compass is a simple, self-contained instrument which operates on the principle of magnetic attraction.
If a bar magnet is mounted on a pivot to be free to rotate in a horizontal plane, it will assume a position with one of its ends pointing toward the earth's north magnetic pole. This end of the magnet is called the north-seeking end of the magnet.
Erection Magnet mechanism 44-48 г.р.m.
Reaction to precession forces
• 21,000 r.p.m.
Gyro universally mounted Caging mechanism FreuRE 12-69. Erecting and caging mechanisms of an electric attitude indicator.
The magnetic compass consists of = liquid-filled bowl containing a pivoted float element to which one or more bar magnets, called needles, are fastened. The liquid in the bowl dampens the oscillations of the float and decreases the friction of the pivot. A diaphragm and vent provide for expansion and contraction of the liquid as altitude and/or temperatures change.
If more than one magnet is used in a compass, the magnets are mounted parallel to each other, with like poles pointing in the same direction. The element on which the magnets are mounted is so suspended that the magnets are free to align themselves with the earth's north and south magnetic poles.
A compass card, usually graduated in 5° increments, is attached to the float element of the compass. A fixed reference marker, called a lubber line, is attached to the compass bowl. The lubber line and the graduations on the card are visible through a glass window. The magnetic heading of the aircraft is read by noting the graduation on which the lubber line falls. The two views of a magnetic compass in figure 12-70 show the face and the internal components of a magnetic compass, A compensating device containing small permanent magnets is incorporated in the compass to correct for deviations of the compass which result from the magnetic influences of the aircraft structure and electrical system. Two screws on the face of the instrument are used to move the magnets and thus counterbalance the local magnetic influences acting on the main compass magnets. The two setscrews are labelled IN-S and F-W.
Magnetic variation is the angular difference in degrees between the geographic north pole and the magnetic north pole. This variation is caused by the earth's magnetic field, which is constantly changing.
Since variation differs according to geographic location, its effect on the compass cannot be removed by any type of compensation. Variation is called west variation when the earth's magnetic field draws the compass needle to the left of the geographic north pole and east variation when the needle is drawn to the right of the geographic north pole.
The compass needle is affected not only by the earth's magnetic field, but also by the magnetic fields generated when aircraft electrical equipment is operated, and by metal components in the aircraft. These magnetic disturbances within the aircraft, called deviation, deflect the compass needle from alignment with magnetic north.
To reduce this deviation, each compass in an aircraft is checked and compensated periodically by adjustment of the N-S and E-W magnets. The errors remaining after "swinging" the compass are recorded on a compass correction card mounted near the compass.
Filler plug Magnetic compensator assembly Spring suspension Liquid chamber Lubber line E 6
• Card Siphon expansion chamber Float Pivot assembly FICURE 12-70. Magnetic Compass.
The "swinging" (calibration) of a compass can be accomplished in flight or on the ground. Ground swinging of a compass is usually done with the aircraft at rest on a compass "rose." A compass rose (figure 12-71) is a circle laid out or painted on a level surface and graduated in degrees. The directions marked on the compass rose are magnetic directions, although true north is also marked on some compass roses.
Compass compensation procedures vary, depending on the type of aircraft. Requirements are often set up on a flight-hour and calendar basis. Most facilities perform compass checks anytime that 360° 330° 30° * 300° 80°1
• 270° 90° 240° 120° 210° 150° 180° FICURE 12-71. Typical compass rose.
equipment replacement, modification or relocation might cause compass deviation.
An example of compass compensation is outlined in the following paragraphs. These procedures are general in nature and do not have specific application.
(1) The compensator should be set either to zero or in a position where it has no effect on the main compass magnets.
(2) The aircraft is placed directly on a south magnetic heading on the compass rose.
The tail of tailwheel aircraft should be raised to level-flying position.
(3) Note the compass reading and record it.
The deviation is the algebraic difference between the magnetic heading and the compass reading.
EXAMPLE:
On the south (180°) heading, the compass reading is 175.5°. This would be recorded as a deviation of +4.5° (180° - 175.5° = 4.5°). If the compass reading is too low, the deviation is plus; if the reading is too high, the deviation is minus.
(4) Align the aircraft on a magnetic north heading. Record the compass reading and compute the deviation.
EXAMPLE:
On the north (000°) heading, the compass reads 006.5°. Since the deviation is
6.5° too high, it is recorded as a minus deviation (-6.5°).
(5) The coefficient of north-south deviation is determined by subtracting, algebraically, the south deviation from the north deviation and dividing the remainder by 2:
Coefficient = (-6.5°) - (4.5°) N
- 11°
(10) Leaving the aircraft on an east magnetic heading, compute the coefficient of overall deviation. This coefficient is equal to the algebraic sum of the compass deviations on all four cardinal headings (north, east, south, and west), divided by 4:
(-65°) +0° +45° +(-6°) Coefficient = = - 5.5° The coefficient of north-south deviation, which is the average of the deviation on the two headings, is -5.5°. The northsouth compensator is adjusted by this amount, and the reading heading will now be 001°. This adjustment also corrects the south deviation by the same amount, so that on a south heading the compass will now read 181°.
--8° 4 = -2°.
If the coefficient is greater than 1°, further compensation is usually accomplished. The compensation is not done with the magnetic compensation device. It is accomplished by re-aligning the compass, so that it is mounted parallel to the longitudinal axis of the aircraft.
(6) Align the aircraft on a magnetic west (270°) heading on the compass rose.
Record the compass reading and compute the deviation. Suppose the compass reads 276°, a deviation of -6°.
(7) Align the aircraft on a magnetic east (090°) heading. Record the compass reading and compute the deviation. Suppose the compass reading is exactly 90° on the magnetic east heading, a deviation of 0°.
(8) Compute the coefficient of east-west deviation:
Coefficient = 0°- (-6°) + 6° = = + 3°
(9) While the aircraft is on the east heading, adjust the east-west compensator to add 3° to the compass reading. This reading then becomes 93° on the east heading and 273° on a west heading.
(11) After the initial compensation is completed, the aircraft will be compensated again on headings of 30°, 60°, 120°, 150°, 210°, 240°, 300°, and 330°. The compass readings for each heading are recorded on a compass correction card.
This card is then mounted as close as possible, to the instrument for ready reference. An example of a correction card is shown in figure 12-72.
The procedure described is a basic compensation procedure. Additional circuits around the compass rose should be made with the engine(s) and electrical and ratio equipment operating to verify the accuracy of the basic compensations.
Jacks, lifts, hoists, or any dolly needed to move and align the aircraft on the various headings of a compass rose should preferably be made of nonmagnetic material. When this is impossible, devices can be tested for their effect on the compass by moving them about the aircraft in a circle at the same distance that would separate them from the compass when they are being used. Equipment that causes a change in compass readings of more than onequarter of a degree should not be used. Additionally, fuel trucks, tow tractors, or other aircraft containing magnetic metals should not be parked close enough to the compass rose to affect the compass of the aircraft being swung.
AIRCRAFT COMPASS (5) The scale should be readable and its illumination good.
DATE
FOR STEER AUTOPILOT SYSTEM The automatic pilot is a system of automatic con- N 000° 000° trols which holds the aircraft on any selected magnetic heading and returns the aircraft to that head- 030° 033° ing when it is displaced from it. The automatic pilot 060° 060° also keeps the aircraft stabilized around its horizontal and lateral axes.
090° 095° 120° 120° The purpose of an automatic pilot system is primarily to reduce the work, strain, and fatigue of 150° 149° controlling the aircraft during long flights. To do S 180° 175° this the automatic pilot system performs several functions. It allows the pilot to maneuver the air- 210° 205° craft with a minimum of manual operations. While under automatic control the aircraft can be made to 240° 334° climb, turn, and dive with small movements of the W 270° 265° knobs on the autopilot controller.
300° 294° 330° 326° Calibrated by:
FIcURE 12-72. Compass correction card.
The magnetic compass is a simple instrument that does not require setting or a source of power. A minimum of maintenance is necessary, but the instrument is delicate and should be handled carefully during inspection. The following items are usually included in an inspection:
Autopilot systems provide for one, two, or three axis control of the aircraft. Some autopilot systems control only the ailerons (one axis), others control ailerons and elevators or rudder (two axis). The three-axis system controls ailerons, elevators, and rudder.
All autopilot systems contain the same basic components: (1) Gyros, to sense what the airplane is doing; (2) servos, to move the control surfaces;
and (3) an amplifier, to increase the strength of the gyro signals enough to operate the servos. A controller is also provided to allow manual control of the aircraft through the autopilot system.
(1) The compass indicator should be checked for correct readings on various cardinal headings and re-compensated if necessary.
(2) Moving parts of the compass should work easily.
(3) The compass bowl should be correctly suspended on an anti-vibration device and should not touch any part of the metal container.
(4) The compass bowl should be filled with liquid. The liquid should not contain any bubbles nor have any discoloration.
Principle of Operation The automatic pilot system flies the aircraft by using electrical signals developed in gyro-sensing units. These units are connected to flight instruments which indicate direction, rate-of-turn, bank, or pitch. If the flight attitude or magnetic heading is changed, electrical signals are developed in the gyros. These signals are used to control the operation of servo units which convert electrical energy into mechanical motion.
The servo is connected to the control surface and converts the electrical signals into mechanical force which moves the control surface in response to corrective signals or pilot commands. A basic autopilot system is shown in figure 12-73.
Aircraft on course Gyro input signal Amplitier Control surface feed back signal Feedback Servo circuit FIGURE 12-73. Basic autopilot system.
Most modern autopilots can be described in terms of their three major channels: (1) The rudder, (2) aileron, and (3) the elevator channels.
The rudder channel receives two signals that determine when and how much the rudder will move.
The first signal is a course signal derived from a compass system. As long as the aircraft remains on the magnetic heading it was on when the autopilot was engaged, no signal will develop. But any deviation causes the compass system to send a signal to the rudder channel that is proportional to the angular displacement of the aircraft from the preset heading.
The second signal received by the rudder channel is the rate signal, which provides information anytime the aircraft is turning about the vertical axis.
This information is provided by the turn-and-bank indicator gyro. When the aircraft attempts to turn off course, the rate gyro develops a signal proportional to the rate of turn, and the course gyro develops a signal proportional to the amount of displacement. The two signals are sent to the rudder channel of the amplifier, where they are combined and their strength is increased. The amplified signal is then sent to the rudder servo. The servo will turn the rudder in the proper direction to return the aircraft to the selected magnetic heading.
As the rudder surface moves, a followup signal is developed which opposes the input signal. When the two signals are equal in magnitude, the servo stops moving. As the aircraft arrives on course, the course signal will reach a zero value, and the rud der will be returned to the streamline position by the followup signal.
The aileron channel receives its input signal from a transmitter located in the gyro horizon indicator.
Any movement of the aircraft about its longitudinal axis will cause the gyro-sensing unit to develop a signal to correct for the movement. This signal is amplified, phase-detected, and sent to the aileron servo which moves the aileron control surfaces to correct for the error.
As the aileron surfaces move, a followup signal builds up in opposition to the input signal. When the two signals are equal in magnitude, the servo stops moving. Since the ailerons are displaced from streamline, the aircraft will now start moving back toward level flight with the input signal becoming smaller and the followup signal driving the control surfaces back toward the streamline position. When the aircraft has returned to level flight in roll attitude, the input signal will again be zero. At the same time the control surfaces will be streamlined, and the followup signal will be zero.
The elevator channel circuits are similar to those of the aileron channe., with the exception that the 512
Gyro Servoamplifier control unit Controller Elevator servomotor Amplifier Discriminator Pitch Pitcl Clutch transmitter channel Blevator Magnetic amplifier Servomotor Gear 1-1 -Gea Aileron amplifier channel Rate gen Gear Roll Roll Followup transmitter Rudder amp irier channe!
transmitter Rate Aileron servomotor transmitter Servo disconnect Rudder servomotor >>-- FICURE 12-74. Autopilot block diagram.
elevator channel detects changes in pitch attitude of the aircraft. The circuitry of all three channels can be followed by referring to the block diagram in figure 12-74.
The foregoing autopilot system description was used to show the function of a simple autopilot.
Most autopilots are far more sophisticated; however, many of the operating fundamentals are similar. Autopilot systems are capable of handling a variety of navigational inputs for automatic flight control.
BASIC AUTOPILOT COMPONENTS The components of a typical autopilot system are illustrated in figure 12-75. Most systems consist of four basic types of units, plus various switches and auxiliary units. The four types of basic units are:
(1) The sensing elements, (2) command elements,
(3) output elements, and (4) the computing ele- Command Elements The command unit (flight controller) is manually operated to generate signals which cause the aircraft to climb, dive, or perform coordinated turns.
Additional command signals can be sent to the autopilot system by the aircraft's navigational equipment. The automatic pilot is engaged or disengaged electrically or mechanically, depending on system design.
While the automatic pilot system is engaged, the manual operation of the various knobs on the controller (figure 12-76) maneuvers the aircraft. By operating the pitch trim wheel, the aircraft can be made to climb or dive. By operating the turn knob, the aircraft can be banked in either direction. The engage switch is used to engage and disengage the autopilot. In addition, most systems have a disconnect switch located on the control wheel (s). This switch, operated by thumb pressure, can be used to disengage the autopilot system should a malfunction occur in the system.
One type of automatic pilot system has an engaging control that manually engages the clutch mechanism of the servomotor to the cable drum. A means of electrically disengaging the clutch is provided through a disconnect switch located on the control wheel (s).
Sensing Elements The directional gyro, turn-and-bank gyro, attitude gyro, and altitude control are the sensing elements. These units sense the movements of the aircraft, and automatically generate signals to keep these movements under control.
Computer or Amplifier The computing element consists of an amplifier or computer. The amplifier receives signals, determines what action the signals are calling for, and ampli- 00 De fies the signals received from the sensing elements.
It passes these signals to the rudder, aileron, or elevator servos to drive the control surfaces to the position called for.
Output Elements The output elements of an autopilot system are the servos which actuate the control surfaces. The 513
Sensing elements Command elements Output elements Pressure source Directional gyro indicator он OтF Flight Aileron controller servo actuator Turn-and-bank indicator gyro Rudder servo actuator Computer Attitude indicator Elevator Navigation signals servo actuator Altitude control Heading selector Trim actuator FIGURE 12-75. Typical autopilot system components.
majority of the servos in use today are either electric motors or electro/pneumatic servos.
An sircraft may have from one to three servos to operate the primary flight controls. One servo operates the ailerons, a second operates the rudder, and a third operates the clovators. Each servo drives ita 514