Standard Protections and augmentations The flight control system on the B777 is designed to restrict control authority beyond certain range by increasing the back pressure once the desired limit is reached. This is done via electronically controlled backdrive actuators (controlled by the ACE). The protections and augmentations are: bank angle protection, turn compensation, stall protection, over-speed protection, pitch control, stability augmentation and thrust asymmetry compensation. The design philosophy is: "to inform the pilot that the command being given would put the aircraft outside of its normal operating envelope, but the ability to do so is not precluded." In other words, the flight envelope protection system provides crew awareness of envelope margins and limitations by means of tactile, visual and aural cues and warnings. However, the protection functions of the system do not reduce or limit pilot control authority. Normal mode In Normal mode during manual flight, the ACEs receive pilot control inputs and send these signals to the three PFCs. The PFCs verify these signals and utilize information from other airplane systems in order to compute control surface commands. These commandas are then sent back to the ACEs which then send the enhanced signals to the flight control surface actuatos which convert them into analog servo commands. Full functionality is provided including all enhanced performance, envelope protection and ride quality features. When the auropilot is engaged, the autopilot system sends commands to the PFCs. The PFCs generate control surface commandas which are sent to the ACEs in the same manner as pilot control inputs. The autopilot commands move the flightdeck controls to provide autopilot feedback to the pilots. If a pilot overrides the autopilot with control inputs, the PFCs will disengage the autopilot and utilize the pilot control inputs. Note that the autopilot is not available should reversion to Secondary or Direct mode occur. Secondary mode Boeing Secondary mode is somewhat similar to the Airbus Alternate Law. When the PFCs can not support Normal mode operation due to internal faults or to loss of information from other aircraft systems, they automatically revert to Secondary mode. Reversion to Secondary mode results in the loss of the autopilot and the pilots must assume manual control of the aircraft. The ACEs still receive pilot control inputs and send the appropriate signals to the PFCs. However, due to the degraded mode of operation, the PFCs use "simplified" computations to generate the flight control surface commands. These commands are sent back to the ACEs from whence they are sent to the flight control surfaces in the same manner as during Normal mode operations. Aircraft handling qualities are affected by the simplified computations or PFC control laws that are utilized in Seconcary mode. While all flight control surfaces remain operative, the elevator and rudder are more sensitive at some airspeeds. The following functions are inoperative or degraded during Secondary mode operations: autopilot auto speedbrakes envelope protection gust suppression tail strike protection thrust asymmetry compensation yaw damping
Direct mode allows for full aircraft control while in flight and during the landing phase. Aircraft handling characteristics are very similar to those encountered while in Secondary mode. In addition to those functions lost during Secondary mode operations (as listed previously) the manual rudder trim cancel switch is inoperative. Mechanical Backup In the event of a complete electrical system shutdown, cables from the flight deck controls to the stabilizer and selected roll spoilers allow the pilots to maintain straight and level flight until the electrical system can be restored.
Will be posting my literature by my study hours of FCS
ReplyDeleteCONTROL LAWS OF BOEING 777
ReplyDeleteStandard Protections and augmentations
The flight control system on the B777 is designed to restrict control authority beyond certain range by increasing the back pressure once the desired limit is reached. This is done via electronically controlled backdrive actuators (controlled by the ACE). The protections and augmentations are: bank angle protection, turn compensation, stall protection, over-speed protection, pitch control, stability augmentation and thrust asymmetry compensation. The design philosophy is: "to inform the pilot that the command being given would put the aircraft outside of its normal operating envelope, but the ability to do so is not precluded." In other words, the flight envelope protection system provides crew awareness of envelope margins and limitations by means of tactile, visual and aural cues and warnings. However, the protection functions of the system do not reduce or limit pilot control authority.
Normal mode In Normal mode during manual flight, the ACEs receive pilot control inputs and send these signals to the three PFCs. The PFCs verify these signals and utilize information from other airplane systems in order to compute control surface commands. These commandas are then sent back to the ACEs which then send the enhanced signals to the flight control surface actuatos which convert them into analog servo commands. Full functionality is provided including all enhanced performance, envelope protection and ride quality features.
When the auropilot is engaged, the autopilot system sends commands to the PFCs. The PFCs generate control surface commandas which are sent to the ACEs in the same manner as pilot control inputs. The autopilot commands move the flightdeck controls to provide autopilot feedback to the pilots. If a pilot overrides the autopilot with control inputs, the PFCs will disengage the autopilot and utilize the pilot control inputs. Note that the autopilot is not available should reversion to Secondary or Direct mode occur.
Secondary mode Boeing Secondary mode is somewhat similar to the Airbus Alternate Law. When the PFCs can not support Normal mode operation due to internal faults or to loss of information from other aircraft systems, they automatically revert to Secondary mode. Reversion to Secondary mode results in the loss of the autopilot and the pilots must assume manual control of the aircraft. The ACEs still receive pilot control inputs and send the appropriate signals to the PFCs. However, due to the degraded mode of operation, the PFCs use "simplified" computations to generate the flight control surface commands. These commands are sent back to the ACEs from whence they are sent to the flight control surfaces in the same manner as during Normal mode operations.
Aircraft handling qualities are affected by the simplified computations or PFC control laws that are utilized in Seconcary mode. While all flight control surfaces remain operative, the elevator and rudder are more sensitive at some airspeeds. The following functions are inoperative or degraded during Secondary mode operations:
autopilot
auto speedbrakes
envelope protection
gust suppression
tail strike protection
thrust asymmetry compensation
yaw damping
Direct mode allows for full aircraft control while in flight and during the landing phase. Aircraft handling characteristics are very similar to those encountered while in Secondary mode. In addition to those functions lost during Secondary mode operations (as listed previously) the manual rudder trim cancel switch is inoperative.
Mechanical Backup In the event of a complete electrical system shutdown, cables from the flight deck controls to the stabilizer and selected roll spoilers allow the pilots to maintain straight and level flight until the electrical system can be restored.
There is nothing here??????????/
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