FLIGHT CONTROLS | ftpcabair, Schemes and Mind Maps of Design

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FLIGHT CONTROLS

AXES OF CONTROL

FLYING CONTROLS

• There are 4 methods of actuating flying controls. These are:
  • Manual
  • Electric
  • Pneumatic
  • Hydraulic
• In addition, the non-manual systems can be sub-classified as either Power operated or Power assisted
• On large transport aircraft, both control surfaces and operating systems are duplicated (at least) to provide redundancy
• Effectiveness depends on:
  • Distance from aircraft CG
  • Control surface area
  • Degree of deflection
  • Dynamic pressure (IAS)
• Controls are said to be reversible if aerodynamic loads provide feedback (feel) to the pilot; they are irreversible if no such feedback is provided. Such systems need artificial feel

Basic Principle of

Fully Manual Control System

A manual flight control system uses a collection

of mechanical parts such as:

pushrods,

tension cables,

pulleys, counterweights,

sometimes chains

to transmit the forces applied to the cockpit

controls directly to the control surfaces.

Control column

Control lever

Pressure fluid (^) Pilot valve

Servo unit

Power Assisted

Movement of the control column will move both the flying control and the pilot valve

Reversible controls

Power Operated

Movement of the control column only moves the pilot valve

Irreversible controls

Pivot point

Pivot point

POWER ASSISTED & POWER OPERATED

CONTROL LOCKS

• Aircraft controls are normally locked on the ground to prevent damage caused by wind movement. In light aircraft these can be fitted either externally at the control surfaces or in the cockpit to prevent movement of the cockpit controls
• In larger aircraft, with electro-hydraulic systems, the controls lock automatically when power is removed. Other types of locks on larger aircraft consist of mechanical, lever and cable operated bolts or pins, that are engaged from within the aircraft

CONTROL STOPS

• Manually operated controls are fitted with stops to limit their range of movement. These are classified in 2 ways:
  • Primary stops are fitted to the control surfaces
  • Secondary stops are fitted to the cockpit controls

ARTIFICIAL FEEL (Q-FEEL)

• Artificial feel systems are designed to increase control column/rudder pedal forces to reflect increases in:
  • IAS (q) by sensing dynamic pressure
  • Control deflection in order to reduce the chance of overstressing the aircraft
• Normally duplicated and fitted in parallel with the control runs

Hydraulic Actuator

Servo

Feel unit

Feel unit

Control Column

ARTIFICIAL FEEL (Q-FEEL)

‘q’ Pot Static pressure

Hydraulic pressure

Pitot pressure

Diaphragm

Metering valve

Feel piston

Control spring

To control run

CONTROL POSITION INDICATIONS

• In addition to TOCWS, most large aircraft have control position indicators. A typical, non-EFIS system is shown below:

SPEED BRAKE INDICATION

SPEED BRAKE DO NOT

ARM illuminates with an amber coloured light when there is an abnormal condition

SPEED BRAKE ARMED illuminates green when the automatic system is operating correctly

TRIM TABS

Purpose is to zero control column/rudder pedal loads

a

b

F

F

TRIM CONTROLS

Elevator Trim

Rudder Trim

Servo Tab

Spring Tab

Control lever free to pivot against spring pressure

ANTI-BALANCE TAB

• The anti-balance tab makes it more difficult to move the controls