Fight Control System. Introduction to Aircraft Design and Aviation Systems (ENG3005) 1. Introduction

Transcription

1 Fight Control System 1. Introduction Modern aircraft is a complex machine with a lot of electrical, electronic, mechanical, hydraulic or a combination of them.. This section will introduce some of its functions. Due to the complexity, each of its function can be classified as a system. Basically, The electrical system based on electrical power or electronic control and with mechanical and other control units, we will focus more on the electrical and control parts. In this topic, we will concentrate on the fight related control electrical unit. Without these parts, the airplane will not be able to leave the ground. Besides the electric system to provide the electrical energy discussed before, there are fight control system. The following will Flight Control Linkage Hydraulic Components Environmental Control Fig 1. The various control related to the fight system 1

2 2. Flight Control Linkage Fig 2: The X-Y-Z 3D view of aircraft flight Aircraft flies on a 3D terrain (X, Y, and Z) If the aircraft wishes to head into a new direction, it must make a turn (or a roll) on one of the X, Y, aor Z axis. Roll(along Y axis); pitch (along X axis); yaw (along z axis). The above are called Primary Flight Control. Secondary Flight Control refers to control of aircraft flight other than Primary Flight Control. Fig 3: The primary and secondary fight control surface 2

3 2.1 The primary flight controls The primary fight control is the ailerons, elevators, and rudder. Fig 4 A simplified diagram for Flight control surfaces on airliner Roll Ailerons Yaw Rudder Pitch Elevators A further evolution of the servo-assisted control is the fly-by-wire technique, based on signal processing of the pilot s demand before conversion into actuator control. The number and type of aerodynamic surfaces to be controlled changes with aircraft category. Fig. 3 and 4 show the classic layout for a conventional airliner. Aircraft has a number of different control surfaces: The primary flight control (Red, for colour print), i.e. pitch, roll and yaw control, basically obtained by deflection of elevators, ailerons and rudder (and combinations of them); The secondary fight control (blue, for color print) indicated in blue for the secondary flight control: high-lift and lift-dump devices, airbrakes, tail trimming, etc 2.2 Secondary Fight control They include wing flaps, slats, spoilers, air brakes and variable-sweep wings. The secondary controls available to give the pilot finer control over flight or to ease the workload. 3. Power actuated systems There are a number of actuation units, besides the primary and secondary fight control, there are 3

4 pump and other motion control. Flight Control Linkage has the following examples: Push-pull control rod (small planes) Hydraulically linked (larger planes) Fly by wire (advanced planes) 3.1 Push-pull control rod Fig 5: A push-pull rod control linkage (Hawk 200) It is a simple and classical system. It is all-mechanical and is suitable for small aircraft and low cost solution Other similar system also use: Cables and pulleys, sometimes motor assisted for larger plane. 3.2 Hydraulic control A few control surfaces on board are operated by electrical motors. The hydraulic system has demonstrated for actuation in terms of weight per unit power and flexibility, with respect to the 4

5 electrical system, then becoming the common tendency on most modern airplanes: the pilot, via the cabin components, sends a signal, or demand, to a valve that opens ports through which high pressure hydraulic fluid flows and operates one or more actuators. Fig 6: Example of hydraulic linkage in BAE 146 Comment: large force, mature technology, reliable and good response 3.3 Electrical actuation The hydraulic system requires considerable maintenance. The reliability is good, however, the oil involved requires good monitoring and dirty. For the last 20 decades, replacing the mechanical linkages to the valves with electrical controls, producing the "fly-by-wire" design, and more recently, optical networking systems in what is known as "fly-by-light". The combination of the hydraulic system with electric motor control is also used frequently in aircraft. They are known as electro-hydraulic actuation. 5

6 4. Engine Control For jet engine planes, engine control requires the control of the following: Fuel flow - to allow the change of engine speeds at will. Air flow to allow the engine to be operated efficiently, and with large safety margin. Exhaust Gas Flow to burn the exhaust gas and vary the nozzle area to obtain extra thrust. Fig 7: Schematic of engine control system in aircrafts Inputs: 1) throttle pedal position; 2) air speed and altitude data; 3) overall temperature; 4) engine speed; 5) engine temperature; 6) nozzle position (for afterburner jets); 7) fuel flow; 8) pressure position. Outputs: 1) fuel flow control using solenoid, or torque motor, or stepper motor; 2) air flow control using variable guide vanes or valves The power level of the motor related system is of high power. The pump is of scale of tens to 100 kw for large aircraft 6

7 Fig 9: The use of electric pump system A full authority control system as shown above in Fig 9 with electrically control signaling FCU- fuel control unit TGT- turbine gas temperature NH- speed of rotation of engine T1- intake total temperature Comments: sophisticated; more electrical; control engine through motor or actuator; All of them are driven by wire. The users will not need to feel for engine! A number of locations need motor drive system. References: Ian Moir & Allan Seabridge, Aircraft Systems, 2 nd Edition, Professional Engineering Publishing,