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AUTO FLIGHT - GENERAL - DESCRIPTION AND OPERATION
1. General
A. The auto flight systems consist of an Autopilot and Yaw Damper System and a Mach Trim
System. Partial provisions for an Auto Throttle System are also installed on the airplane.
B. Autopilot and Yaw Damper Systems
(1) The autopilot system controls the airplane about the pitch and roll axes and provides
automatic airplane stabilization whenever the pitch and roll channels are engaged.
Automatic stabilizer trim, which is a function of the pitch channel, compensates for
changes in airplane trim due to fuel burnoff etc. Each autopilot channel may be engaged
separately and, in some modes, are not dependent upon each other. Various mode
selections enable the pilots to command the autopilot to fly the airplane onto a selected
heading, maintain altitude, or fly to a selected VOR, localizer or OMEGA course as well as
make automatic approaches to runways equipped with ILS facilities. The pilots may also
manually control the airplane in a normal manner with the control wheel/column (control
wheel steering) without disengaging the pitch or roll axes of the autopilot system. Pilots
can then assist the autopilot system in flying to a selected heading or course. Use of
control wheel steering does not disengage either channel of the autopilot system.
(2) The yaw damper system provides airplane stabilization about the yaw axis. Automatic
damping of dutch roll is sensed and corrected for by the yaw damper system whenever
the system is engaged. Rudder deflections are not felt by the pilots since the rudder
pedals are not moved by the yaw damper system. No interlocks are provided between the
yaw damper system and the autopilot system.
(3) The autopilot and yaw damper systems operate in conjunction with hydraulic power
control units which drive the airplane ailerons, elevators and rudder. Refer to Chapter 27,
Flight Controls.
C. Mach Trim System
(1) The mach trim system provides automatic repositioning of the elevators as a function of
mach number. As the airplane enters the mach tuck region, the elevator is repositioned to
provide a new neutral in an upward direction which is proportional to the increase in mach.
The mach trim system operates with or without the autopilot system engaged.
(2) The mach trim system operates in conjunction with the elevator hydraulic power control
units and stabilizer/elevator neutral shift mechanism. Refer to Chapter 27, Elevator and
Tab Control System.
D. Auto Throttle System
(1) The autothrottle system (if installed) automatically monitors airplane airspeed and adjusts
throttle settings to maintain a selected airspeed. The autothrottle system is intended to
assist the pilots in maintaining a constant airspeed when making landing approaches. The
autothrottle system is independent of the autopilot system and operates with or without the
autopilot system engaged.
AUTO FLIGHT-GENERAL - MAINTENANCE PRACTICES
1. General
A. In order to maintain the integrity of the auto flight systems, it may become necessary to replace
electro-hydraulic components on the elevator, aileron, and rudder power control units. This
would involve handling BMS 3-11 hydraulic fluid. The following information is provided to aid in
handling BMS 3-11.
2. BMS 3-11 Handling Procedure
A. BMS 3-11 is the general specification for the fluid that is used in all hydraulically operated
systems. BMS 3-11 is a fire-resistant base fluid to which suitable additives have been
incorporated. All fluids meeting this specification can be intermixed in any amount with no
separation, precipitation or cloudiness. All airplane equipment using BMS 3-11 are identified by
nameplates.
CAUTION: BMS 3-11 FLUID IS NOT COMPATIBLE WITH MIL-H-5606 FLUID. MIXING
THESE FLUIDS, IN ANY AMOUNT, WILL COMPLETELY RUIN THE INTEGRITY
OF THE HYDRAULIC SYSTEM.
B. Areas where hydraulic fluid may leak are designated as possible BMS 3-11 contamination
areas. Special paint and protective finishes are used to prevent damage in these areas. Refer
to Chapter 51, Structures - Protective Finishes.
C. BMS 3-11 has little or no effect on the metals used in aircraft construction up to 240F. Only
materials compatible with BMS 3-11 fluids, such as ethylene propylene, butyl rubber and teflon,
are used for system seals, gaskets, O-rings, and hose linings.
D. Skin irritation in the form of dry or cracked skin may result from prolonged or repeated contact
with BMS 3-11. It also causes painful but temporary irritation to the eyes and may produce a
burning sensation to other sensitive parts of the body. Inhalation of the fluid in the form of spray
of fine mist may cause irritation of the upper respiratory tract. To minimize contact with BMS
3-11, wear gloves, goggles, face shields or safety glasses whenever there is danger of
exposure. If exposure occurs, flush the eyes immediately with water and report to medical for
observation.
WARNING: BMS 3-11 HEATED TO TEMPERATURES ABOVE 450F CAN BE
DECOMPOSED INTO TOXIC FUMES AND GASES. AVOID INHALATION OF
FUMES AND VAPORS FROM OVERHEATED BMS 3-11. IF IT IS NECESSARY
TO WORK IN THESE FUMES AND VAPORS, SAFETY APPROVED EYE AND
RESPIRATORY PROTECTION ARE MANDATORY.
1. General
A. The Sperry SP-77 Automatic Flight Control System (autopilot and yaw damper system)
provides automatic operation of airplane flight controls to maintain altitude, attitude and heading
references, yaw damping, automatic tracking and control of omnirange navigation throughout
the various flight regimes, and automatic approach.
B. The autopilot and yaw damper system is characterized by the following features:
(1) Control wheel steering (CWS) for pitch and bank rate maneuvering.
(2) Full time series yaw damping with control cabin self-test and full-time yaw damper position
indicator.
(3) All angle radio beam capture with control wheel steering maneuvering.
(4) Solid state (microelectronic) interlock, and operating circuits.
(5) Plug-in modules on hinged cards for ease of maintenance.
C. The autopilot and yaw damper attains optimum smoothness and stability of control by the use
of error information based not only on the magnitude of the airplane and its control surface
displacements from reference positions and angles, but also on the rate of change of these
displacements. Optimum sensitivity and accuracy in maintaining system integrity are attained
by integrating the displacement errors with respect to time and by making control surface
movement a function of indicated airspeed. The following is a brief explanation of these
principles of operation:
(1) Physically, when a sudden change in airplane or control surface position or angle occurs,
a large rate of change of position exists before there is time for a significant displacement
actually to take place. By applying control forces based on this rate of change instead of
waiting for a significant displacement to build up, the initial control forces are greatest at
the inception of the error and consequently are most effective when needed. Thus,
considerable
corrective action is accomplished before the displacement becomes large and the
possibilities of large deviations from reference conditions are greatly reduced. The rate at
which these displacement corrections take place is damped by input rate information to
assure return to reference conditions with practically no overshoot. When the
displacement error is no longer changing, the rate signals fall to zero and the error existing
at that instance is acted upon by control forces that are proportional only to the error
magnitude. The combination of displacement control and rate control provides the desired
smoothness and stability of operation.
(2) Integration in the autopilot provides an extremely accurate means of automatically
retaining reference flight conditions when sustained or recurring displacement from the
references caused by wind or loading changes exist. A persistent displacement error, from
a flight reference, may exist at such a low level that it will not actuate the associated servo
channel to cause corrective action. Errors of this nature will produce increasing errors in
airplane displacement as they are permitted to remain. Small signal errors are integrated
against time to build up small displacement errors to usable values so they will correct the
error through the associated servo channel. The integrated signal remains at the value
required to overcome the displacement error, compensating for required changes in the
original flight references.
(3) The response of the airplane to control surface movement is aerodynamically a function of
dynamic air pressure. As the dynamic air pressure increases there is a decrease in the
amount of control surface movement required to produce a given change or rate of
change in airplane attitude. Therefore, to maintain accurate control of the airplane at all
airspeeds, continuous adjustment of the autopilot channel control surface gains is
provided. | 
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发表于 2011-6-14 09:22:00
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