(7)
The AFCS design includes command limits in all A/T, AP or F/D airspeed modes designed to prevent the system from commanding speeds which exceed the flap placards, the gear placard or the VMO/MMO placards. In addition, reversion modes are provided, except when in an Altitude Acquire, Capture or Hold mode or when in Glideslope mode, to:
(a)
Enable the airspeed mode to limit the minimum speed commanded to a speed above alpha floor if in an airspeed mode.
(b)
Enable an airspeed mode, if speed was specifically deselected and the alpha floor ( ), flap placard, gear placard or VMO/MMO placard speed limits are close to being exceeded. These reversions will be made to A/T Speed mode.
(c)
Enable Level Change mode if the airplane cannot maintain speed because it is performance limited when the AP is in V/S mode and the A/T is in Speed mode.
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Oct 20/83 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 22-11-01 Page 25
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E. Roll Axis
(1)
The roll axis block diagram Fig. 8 represents the complete AFCS roll control from input signals, control, annunciation, F/D output, AP output to control surface commands and feedback signals.
(2)
The roll axis schematic Fig. 9 shows internal computation within the FCC for digital and analog computers. The digital computer provides cruise and F/D mode computations and the analog computer provides AP approach mode computation. Analog signal equivalent circuits are used within the digital computer area to show various signal relationships. The analog circuits only are shown for preset heading and preset course. The digital circuits consist of encoders within the MCP which provide digital data which is compared with analog (synchro) inputs in the FCC.
(3)
The analog computer can be divided into output amplifier command section and AP approach computer.
(a)
The output amplifier operates as a synchronizer or provides an output signal. Synchronizer operation is performed prior to system engagement and maintains a null output on the valve amplifier. This is accomplished by applying the valve signal thru summing point (17), thru a feedback amplifier back to point (15) and valve amplifier inputs. After engagement the synchronizer path is opened by S8, then S9 closes to null the feedback amplifier, then S10 is closed momentarily to synchronize the command to the aileron position. When hydraulic pressure is applied to the autopilot actuator, output signal from the valve amplifier operates the aileron AP actuator which controls aileron PCU to bank the airplane according to command signal. Feedback signals are provided by the LVDT when system is engaged.
(b)
The command amplifier receives an input signal from the D/A converter when in cruise mode, or from the AP approach computer when in approach mode. Either input is applied to point (11), then limited for bank angle command, depending on on-course logic, limited for bank angle rate, depending on the mode, then applied thru the command integrator limiter to point (14). Point (14) introduces the summed roll attitude and roll rate term. The summed signal is gain programmed as a function of computer airspeed and applied to summing point (15) in the output amplifier. Roll control wheel steering signal is also applied thru this amplifier, at summing points
(12) and (14). S5 provides a pre-engage synchronizer path to null the command limiter.
(c)
The AP approach computer provides computations for localizer approach after capture of the localizer beam. The V/L deviation signal at summing point (20) is applied to LOC on-course limiter thru closed S20, combined with gain programmed lateral acceleration, sent thru the integrator amplifier than tapped for the feedback loop to summing point (20) and applied to the LRRA gain programmer. The intercept limiter establishes maximum signal limits, then the signal is split for F/D use or summed with localizer course until approach on-course mode. Filtered acceleration signal and lagged roll signal is added after approach on-course. The output of (21) is applied to (11) when captured on localizer. The integrator, which monitors intercept limiter output signal, drives the deviation signal to null (beam center) to establish the required crab angle during cross winds and drift to maintain beam center during approach.
(4)
The digital computer can be divided into AP cruise computer and F/D computer.
(a)
The AP cruise computer initially converts input analog signals, synchro or dc to digital format. Synchro inputs from heading, preset heading and preset course are changed into sine and cosine components, then these voltages are demodulated and converted into digital words. The dc VHF NAV deviation and computer internal command limiter output signals are also converted into digital words.
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