FLIGHT CONTROL SYSTEMS

(FCS, ATA 27)

List of Questions FCS Module

1. What does it mean with positiveness in FCS

2. What kind of failures where the aircraft must be able to continue safe flight and landing?

3. How many types of signal transmission and power

transmission in FCS? Explain them.

4. How many types of actuation system based on their complexity? Explain them.

5. What is nulling? Explain the feedback method (moving

piston) and the follow up method (moving body).

6. Explain the protection in elevator. How many modes are available?

7. Explain the redundancy in aileron. How many modes

are available?

FLIGHT CONTROL SYSTEMS

(FCS, ATA 27)

- Function: enables the pilot to control the aircraft with the use of control surfaces during all flight phases within the flight envelope.

- Use of power supplies and 'feel' systems.

Airworthiness

Requirements

FAR

Sub-part B

Airworthiness Requirements Controllability and Maneuverability § 25.143 General. (a) The airplane must be safely controllable and maneuverable during - (1) Takeoff; (2) Climb; (3) Level flight; (4) Descent; and (5) Landing. (b) It must be possible to make a smooth transition from one flight

condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane limit load factor under any probable operating conditions, including -

(1) The sudden failure of the critical engine; (2) For airplanes with three or more engines, the sudden failure of the

second critical engine when the airplane is in the enroute, approach, or landing configuration and is trimmed with the critical engine inoperative; and

(3) Configuration changes, including deployment or retraction of deceleration devices.

Critical engine: the failure of the engine most adversely affect AC performance or handling abilities

(c) The following table prescribes, for conventional wheel type controls, the maximum control forces permitted

during the testing required by paragraphs (a) and (b) of this section:

Airworthiness Requirements

Airworthiness Requirements

Control Systems § 25.671 General. (a) Each control and control system must operate with the ease,

smoothness, and positiveness appropriate to its function. (b) Each element of each flight control system must be designed, or

distinctively and permanently marked, to minimize the probability of incorrect assembly that could result in the malfunctioning of the system.

(c) The airplane must be shown by analysis, tests, or both, to be capable of continued safe flight and landing after any of the following failures or jamming in the flight control system and surfaces (including trim, lift, drag, and feel systems), within the normal flight envelope, without requiring exceptional piloting skill or strength. Probable malfunctions must have only minor effects on control system operation and must be capable of being readily counteracted by the pilot.

(1) Any single failure, excluding jamming (for example, disconnection or failure of mechanical elements, or structural failure of hydraulic components, such as actuators, control spool housing, and valves).

Airworthiness Requirements

§ 25.671 General (cont’d) (2) Any combination of failures not shown to be extremely

improbable, excluding jamming (for example, dual electrical or hydraulic system failures, or any single failure in combination with any probable hydraulic or electrical failure).

(3) Any jam in a control position normally encountered during take off, climb, cruise, normal turns, descent, and landing

unless the jam is shown to be extremely improbable, or can be alleviated. A runaway of a flight control to an adverse position and jam must be accounted for if such runaway and

subsequent jamming is not extremely improbable. (d) The airplane must be designed so that it is controllable if

all engines fail. Compliance with this requirement may be shown by analysis where that method has been shown to be reliable.

Airworthiness Requirements

Flight Control Principles Control transmission Mechanical:

Cables and pulleys or push-pull rods Dual mechanical systems Parallel operation (pilot selects)

First failure must be detected Electric control (signaling)

Signal from the pilot or FCC by electrical means Multiple electrical channels are required Need monitoring, voting and protective switching

Optical signaling High data rates (not necessary for FC) Input and output still electrical Protects from EMI (Electromagnetic Interference: lightning,

radiation)

Not critical to cable brake-out

Powering of FC

Degrees of powering

Un-powered

Normally powered/degraded un-powered

Fully (only) powered

Involved systems on FCS: 27 00 00 9 The status display of active systems: 27 00 00 13

FCS Pilot Interface: 27 00 00 10

FCS 27 00 00 1 -2

Primary flight control:

1. Elevator

2. Ailerons

3. Rudder

Supplementary flight control:

1. Stabilizer

2. Rudder trim

3. Aileron trim

Secondary flight control:

1. Flaps

2. Lift dumpers

3. Speedbrakes

Characteristics of power supply and actuation

Hydraulics supply accurate

simple, self-lubricating low chance of jamming one leak, whole system disable (same hydr system) limited methods of protection (fuses) hydraulic fluid is aggressive and flammable.

Electrical supply

need gear box to reduce speed the actuator is heavy and complicated less accurate

less reliable higher chance of jamming advantage: separate the (failed) sistem

Actuation complexity (ascending): Simple mechanical actuation, hydraulically powered Mechanical actuation with simple electromechanical features (e.g.

autopilot) Multiple redundant electromechanical actuation with analogue

control inputs and feedback

Simple mechanical

actuation

Example: Aileron and Spoiler 27 00 00 3

Mechanical actuation with simple electromechanical features (e.g. autopilot)

The servo valves convert the electrical signal to mechanical power (from hydraulic power) to move the control valves.

Multiple redundant electromechanical actuation with analogue control inputs and feedback

27 03 00 3

Direct drive when electric signals from pilot interface

are directly sent to the ACE

Advanced actuation methods:

Example of application: Screw Jack on Horizontal Stabilizer

The changes of operation modes of FCC: 27 00 00 11

Method of Servo Valve Nulling

Follow Up Method (Moving body)

Actuator follows the movement of the servo valve.

Method of Servo Valve Nulling

Follow Up Method (Moving body)

Actuator follows the movement of the servo valve.

Method of Servo Valve Nulling

Feedback Method (Moving piston)

Feedback linkage

will return the servo

valve into its original

position

Method of Servo Valve Nulling Feedback Method (Moving piston)

Feedback

linkage will

return the

servo valve

into its

original

position

Artificial Feel

Elevator of F28

Elevator Boost Unit of F28

Elevator: Hydraulic Mode Two parallel units (hydr 1 and 2), solenoid controlled, normally deenergized. Initial movement: Rotation Point (RP) on line C because the piston has not moved yet. When moving: RP on line D because Backlash Lock out Cylinder is pressurized. End of movement: RP on A/B because the piston position has moved (feedback method)

Elevator: Manual Mode Both Backlash Lock-Out Cylinder are de-pressurized. Idle bar is not able to move, Rotation Point is on the servo valve line. The piston is moved by other piston and bypassing the hydr fluid.

Protection

Protection (Elevator)

Sticking Servo Valve (27 30 00 7)

AILERON The ailerons are fully hydraulically operated (with mechanical backup) and hinged at the trailing outboard edge of the wings

HYDRAULIC MODE

HYDRAULIC MODE

MANUAL MODE

MANUAL MODE

FCS Electronics: 27 03 00 1

27 10 00 11

Rudder failure: 27 20 00 13

Stick Shaker (27 30 00 13)

Elevator hydraulic Press loss: 27 30 00 14

Flap: 27 00 00 7

27 50 00 1, 7

Flap Extension: 27 50 00 8, 9

Slat mechanism: 27 80 00 1

Runaway

Thank You