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757 MAINTENANCE MANUAL
Vertical Speed Flight Director Command
1) The pitch path command provides the input for developing the pitch F/D bar command.
Pitch Rate Path Compensation
1) The sum of flight path acceleration and AOA rate filtered make up pitch rate path compensation. The flight path acceleration is modified as an inverse function of impact pressure and TAS. The AOA rate filtered is limited to a
1.0 deg/sec change to prevent rapid rate changes. The resultant signal is modified as a function of the cosine of roll attitude command. The pitch rate path compensation attenuates vertical accelerations and elevator activity during turbulance.
Flight Path Acceleration
1) Inertial flight path acceleration from the IRS and the flight path acceleration wind signal from the wind acceleration filter are summed to make up flight path acceleration. This is then modified as an inverse function of impact pressure and TAS. The modified flight path acceleration provides a desired pitch rate representing actual flight path acceleration and a small component of wind acceleration used in computing an integral command compensation signal to the elevator. This reduces vertical acceleration in the V/S mode.
AOA - Rate Filtered
1) The AOA rate filtered is computed from the computed AOA rate from the IRS. This is integrated and summed with corrected AOA (vane angle from the ADC and IRS) and applied through a low pass filter. The filter limits the signal to |1.0 deg/sec for damping of elevator movement. The AOA rate filtered represents a component of pitch rate path compensation to the elevator to allow for vertical wind gusts on the AOA vane.
Pitch Attitude Integrator Processing
1) The pitch attitude integrator establishes a pitch attitude reference. It integrates pitch commands from MCP manually selected modes, automatically selected modes, and navigation sources. It also generates pitch attitude error which is processed to provide the elevator servo command. Pitch signal summation to the pitch attitude integrator is provided from the pitch rate integral command, the pitch path command, and the versine command.
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22-12-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757 MAINTENANCE MANUAL
2) Vertical Speed Signal Logic
a) Switches 1, 4 and 5, remain as drawn since their control logic, TCLIM IN AIR NOT and TSYNC, are all zero. Switches 2, 3, and 6 transfer (IN AIR, TPATH, and PCE are logic one).
3) Vertical speed Signal Processing
a) The pitch rate integral command is summed with pitch attitude error to provide a long standing error washout at the rate of 0.1 deg/sec/deg.
b) Pitch path (proportional) command provides the immediate response elevator command. This is differentiated and summed with pitch rate integral command. V/S ENG allowing the composite pitch command signal to be summed with any possible signal.
c) The versine command is controlled as a direct function of IAS and as an inverse function of flap position. This is differentiated and summed to form composite pitch rate command.
d) The composite pitch command is integrated and its output is limited to |30 degrees of pitch angle. This is summed with the reference pitch attitude to provide a pitch attitude error command for processing.
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