Aircraft Control Systems Overview

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the purpose of the roll augmentation function in an aircraft?

To reduce any roll rate not commanded by the pilot.

What happens to the roll augmentation feature in the event of a spoiler panel malfunction?

It deactivates after five seconds and remains off for the duration of the flight.

How do roll spoiler deflections vary with flap position and airspeed?

The amount of roll spoiler deflection varies, with higher flap positions and airspeeds resulting in smaller spoiler deflections.

What is the role of the yaw damper in flight control systems?

To damp dutch roll oscillations using sensor feedback and rudder pedal input. Signup and view all the answers

In the long term, what happens to any persistent elevator offset greater than one degree in pitch trim?

It will be offloaded to the horizontal stabilizer. Signup and view all the answers

What are the main components of a pillow block assembly in the flap system?

Each pillow block consists of two ball bearings, an aluminum housing, and an externally-splined through-shaft that interfaces with the internally splined end fittings of the torque drive shafts. Signup and view all the answers

What are the three basic functions performed by the flap actuators?

The flap actuators perform three basic functions: 1) Conversion of high speed rotary motion at the input shaft to low speed linear motion at the translating nut, 2) Irreversibility (the translating nut cannot be back-driven in normal operation) and/or torque shaft or actuator disconnect system failure mode, and 3) System overload protection by limiting the maximum force that each actuator can apply. Signup and view all the answers

Explain the purpose of the force-limiting function in each flap actuator.

The force-limiting function in each flap actuator provides overload protection of the flight control system components and supporting structure by limiting the maximum actuator output load. In the case of a flap actuator system (FAS) jam or any other condition that results in increased FAS loading, the force-limiting device stalls the actuator, causing a 'trip' in one of the system safety monitors, which then completely disengages the FAS. Signup and view all the answers

How does the fly-by-wire technology in the flight control system ensure irreversibility of the flap actuators?

The fly-by-wire technology in the flight control system ensures irreversibility of the flap actuators through a mechanism where the translating nut of the actuator cannot be back-driven in normal operation, even in the event of a torque shaft or actuator disconnect system failure. Signup and view all the answers

Explain the purpose of the artificial feel mechanisms in the horizontal stabilizer system.

The artificial feel mechanisms in the horizontal stabilizer system are designed to provide the pilot with appropriate feedback and control forces, simulating the natural feel of a conventional control system. These mechanisms help the pilot maintain proper control and situational awareness during flight. Signup and view all the answers

Explain the purpose of the bungee rods in the flight control system.

The bungee rods act as a solid link between the wheel and column, allowing control in the event of a mechanical jam on the pilot or copilot side. They allow the control inputs from the pilots to be combined, preventing a jam on one side from completely overriding the other pilot's inputs. Signup and view all the answers

Describe the backup system for the flight control surfaces in the event that both Flight Control Computers (FCCs) are inoperative.

In the event that both FCCs (all four channels) are inoperative, the Backup Flight Control Unit (BFCU) controls the elevators, ailerons, outboard spoilers (roll control only, no speed brakes), and rudder, allowing the aircraft to be safely flown. Signup and view all the answers

Explain the purpose of the mechanical stops in the flight control system.

The mechanical stops are used to limit the maximum displacement of the flight control surfaces, providing appropriate "feel" forces to the pilots and preventing the control surfaces from exceeding their design limits. Signup and view all the answers

How are the pilot and copilot rudder pedals connected, and what is the purpose of this connection?

The pilot and copilot rudder pedals are mechanically connected with a hard link which cannot be overridden. This ensures that the rudder inputs from both pilots are combined, preventing a jam on one side from completely overriding the other pilot's inputs. Signup and view all the answers

Describe the role of the trim switches in the flight control system.

Trim switches are provided for the pitch, roll, and yaw axes, allowing the pilots to adjust the trim of the aircraft's control surfaces to maintain the desired flight attitude without constant input on the flight controls. Signup and view all the answers

What is the purpose of the hydraulic system in aircraft flight control surfaces?

The aircraft hydraulic system provides pressurized fluid to position and control the flight control surfaces. Signup and view all the answers

What is the role of the Regulating and Shutoff Unit (REU) in the aircraft hydraulic system?

The REU can electrically hold a solenoid to keep the actuator in an active state, or it can remove power from the solenoid to force the actuator into a damped bypass operation. Signup and view all the answers

Describe the 'damped bypass' mode of operation for an aircraft actuator.

In damped bypass mode, the actuator is in a passive condition that resists movement proportional to the rate at which the surface is moved, and hydraulic fluid is trapped within the actuator to prevent control surface flutter. Signup and view all the answers

What is the purpose of the Electrical Backup Hydraulic Actuator (EBHA) in an aircraft's flight control system?

The EBHA has three modes of operation: Hydraulically Active, Electric Backup, and Damped Bypass. In the event that a surface cannot be powered by an engine-driven hydraulic source, the EBHA's Electrical Backup (EB) hydraulic pump will provide hydraulic pressure to operate the flight control surface. Signup and view all the answers

How do pilots experience the behavior of damped bypass actuators during ground operations?

Pilots may directly experience the behavior of damped bypass actuators by rotating an aileron surface upward or downward with the palms of their hands during preflight when hydraulic pressure is not available to either the left or right system. Signup and view all the answers

Study Notes

Roll Augmentation

The roll augmentation function adjusts roll control surface deflections based on the magnitude of roll rate compared to the expected roll rate from wheel and pedal inputs.
It reduces uncommanded roll rates caused by wake turbulence or spoiler panel malfunction.
In the event of a spoiler panel malfunction, the roll augmentation feature will deactivate after 5 seconds and remain inactive for the duration of the flight.

Roll Spoiler Deflection

The amount of roll spoiler deflection varies with flap position and air speed.
Deflection can be as much as full deflection (55°).
Outboard and midboard roll spoilers are commanded to move together.

Yaw Control

The yaw damper is active using sensor feedback and rudder pedal input to damp dutch roll oscillations.

Pitch Trim

Pitch trim initially offsets the elevator.
Persistent elevator offset greater than 1 degree will be offloaded to the horizontal stabilizer.

Pillow Block Bearings

Each pillow block consists of two ball bearings, an aluminum housing, and an externally-splined through-shaft.
The bearings are sealed to prevent FOD and moisture ingress and are packed with grease.

Flap Actuators

Each flap surface is driven by two linear ballscrew flap actuators.
The actuators are lubricated with grease and vented to prevent corrosion.
The actuators perform three functions: conversion of high-speed rotary motion, irreversibility, and system overload protection.

Flap Position Sensors

The sensors have springs and dampers to provide appropriate "feel" forces and mechanical stops to limit their maximum displacement.

Flight Control System (FCS)

The system consists of two dual-channel Flight Control Computers (FCCs) and a Backup Flight Control Unit (BFCU).
The FCCs generate commands for the control surface actuators and house the operational logic (Control Laws) for control of the flight control surfaces.
Any one of the four FCC channels is independently fully capable of safely operating the entire aircraft FCS.

###.backup Flight Control Unit (BFCU)

The BFCU controls the elevators, ailerons, outboard spoilers (roll control only), and rudder in the event that both FCCs are inoperative.
The aircraft may be dispatched with one FCC channel inoperative or the BFCU inoperative with restrictions.

Hydraulic System

The system provides pressurized fluid to position the flight control surfaces.
Hydraulic pressure must be available and the actuator REU must electrically hold a solenoid.
The REU can force Damped Bypass operation by removing power from the solenoid.

Damped Bypass

The actuator is in a passive condition that resists movement proportional to the rate at which the surface is moved.
Hydraulic fluid is trapped within the actuator to prevent control surface flutter in flight and provides gust protection during ground operation.

Electric Backup Hydraulic Actuator (EBHA)

The EBHA has three modes of operation: Hydraulically Active, Electric Backup, and Damped Bypass.
In the event that a surface cannot be powered by an engine-driven hydraulic source, an Electrical Backup hydraulic pump will provide the EBHA actuator with hydraulic pressure to operate the flight control surface.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the components and mechanisms of aircraft control systems such as springs, dampers, bungee rods, and mechanical stops. Learn how these systems provide appropriate feel forces and limit displacement to ensure safe control of aircraft.