Aircraft Stabilizers and Elevators Quiz

AVAV 4107 Flight Controls Handout

• This manual is for training purposes only
• The document contains a table of contents, listing topics within flight controls, with page numbers for referencing

Introduction

• Aircraft axis flight dynamics is the science of air vehicle orientation and control in three dimensions
• The three critical flight dynamics parameters are pitch, roll, and yaw, about the center of mass
• Control systems for a vehicle's orientation (attitude) include actuators and forces, or moments, about the center of gravity
• Pitching moment is a vertical force applied forward/aft of the center of gravity
• Roll, pitch and yaw refer to rotations about respective axes (equilibrium state), with yaw known as "heading" and without slipping/skidding as coordinated

System Operation

• A conventional fixed-wing aircraft consists of control surfaces, linkages, operating mechanisms for controlling direction in flight, and engine controls
• Fundamentals of aircraft controls are explained in flight dynamics; this section focuses specifically on operating mechanisms

Mechanical Assistance

• Some mechanical flight control systems use servo tabs that provide aerodynamic assistance
• A servo tab (Flettner tab) is a small hinged device on a control surface. It moves in the opposite direction of the control surface
• It has leverage advantage and is located closer to the trailing edge, reducing a pilot's control force
• Some aircraft use servo tabs as the only pilot-control connection.

Anti-servo tabs

• An anti-servo tab moves in the same direction as the surface. It increases resistance during control surface movement and often is used with increased stability requirements of a particular axis

Flight Control Systems

• Stabilizers are either fixed or adjustable, and form the directional stability component of the pitch control system
• The adjustable stabilizer is used for trim control
• Trim tabs are small surfaces on the control surfaces and are used to counteract aerodynamic forces, stabilizing an aircraft in a particular desired attitude without a pilot's constant control input.

Elevator

• Elevators, usually at the rear of the aircraft, change pitch and angle of attack of the wing
• Nose up or down movement is related to ascending or descending
• An increased angle of attack produces higher lift; and a decrease produces lower lift, decreasing speed.

Ailerons

• Hinged surfaces, typically on the trailing edge of wings.
• Used to control aircraft roll and thus heading, or tilting of the lift vector
• One aileron goes up while the other goes down for coordinated turns (rolling moment about the longitudinal axis)

Adverse Yaw

• An unwanted side effect of aileron operation, resulting in a yawing moment in the opposite direction of the roll motion
• It is mostly affected by the change in drag on the left and right wings, the rising wing increasing lift and causing increased induced drag and the descending wing producing less lift and thereby reducing induced drag.
• Compensated by use of rudder, which creates a favourable yawing moment and helps coordination

Aileron Spades

• Metal plates usually attached to a lower aileron surface.
• Reduce force needed by the pilot to deflect the aileron
• Commonly found on aerobatic aircraft

Aileron Balance Weights

• Preventing control surface flutter (Aeroelastic flutter) by positioning the center of lift of the control surface behind the center of gravity
• Adding lead weights to the front of the aileron surface in some cases.

Types of Ailerons

• Frise Ailerons: Pivoted at 25-30% chord line, near bottom of wing's surface.
• Differential ailerons: The up aileron deflects more than the down aileron-helps to reduce the likelihood of a wing-tip stall.

Flaps

• Hinged surfaces on the trailing edge of the wing to increase lift coefficients (more lift for lower speed) and thus reduce stalling speed
• Extending flaps increases camber, thus requiring less speed for lift

Spoilers

• Plates on the top surface of a wing.
• Extending spoilers reduces lift and increases drag; often used in low-speed maneuverability.

Hydro-mechanical Controls

• A more complex mechanical flight control system commonly associated with larger aircraft to overcome muscular limitations
• Mechanical circuit connects cockpit controls to hydraulic circuits
• Hydraulic circuit includes parts like pumps, reservoirs, filters, pipes, valves, and actuators that convert pressure into surface movement.

Artificial Feel Devices

• Used with purely mechanical flight controls so a pilot can feel the aerodynamic forces on control surfaces
• A tactile feedback system in a hydro-mechanical system to overcome excessive control surface movement

Trim and Centering Mechanism

• A hydro-pneumatic system that provides variable amounts of opposition to pilot controls, and varies based on airspeed/inputs from the pitot system
• Used for some elevator systems

Full Power Controls

• Using aircraft pneumatic air to operate certain aspects of the flight control system and is based upon a pneumatically powered system

Electrically Powered Flight Controls

• Electric motors are commonly used for functions like flaps and trim on general aviation aircraft, and on some aspects of larger aircraft like flaps
• The use of an electronic interface substitutes manual controls with an electronic one (fly-by-wire) and computer calculation of control responses

Fly-by-wire Control Systems

• System replaces manual control with an electronic interface (Fbw)
• Signals from control movements are transmitted via wires to flight-control computers.
• These computers determine how to move actuators to achieve expected responses
• Signal conversions are also used in autopilots

Development of Fly-by-Wire Systems

• Mechanical and hydro-mechanical systems are heavy and can have limited ability to compensate for aerodynamic conditions
• Fly-by-wire systems are typically computer-controlled
• This allows flexibility for the control surfaces.

Automatic Stability Systems

• Computers operate control systems automatically in certain cases, such as reaction to changes in pitch, and yaw
• Gyroscopes, sensors, and computers relay movement data back and forth to control surfaces to keep the plane stable.

Turbulence Damping

• Reduces the effect of structural loads from turbulence

Safety and Redundancy

• Redundant computer systems (redundancy) prevent loss of control if a system fails
• Backup systems (analog, mechanical, or hydraulic) provide backup in the event of failure on some aircraft.

Yaw Damper

• A system used in most turboprops and jets to compensate for oscillations or undesirable yawing/rolling
• It utilizes yaw rate sensors and a processor (that send to a computer, which processes and sends commands through a system of actuators to drive the rudder to maintain a stable yaw rate) to provide control and feedback

Mach/speed Trim

• Compensates for a Mach tuck maneuver (when exceeding a certain speed and nose starts to drop)
• This input compensates for the aerodynamic stall and movement of the center of pressure

Rudder Limiter

• Automatically adjusts rudder movement levels, a function of aircraft speed
• Ensures the rudder does not extend beyond limits

Gust Lock

• A mechanism that locks control surfaces to prevent unexpected movements due to wind gusts

Stall Warning

• Devices/systems to prevent or delay stalling, or make recovery easier
• Includes aerodynamic devices on the wings, like stall strips or vortex generators
• Also commonly includes warning systems based upon speed, angle of attack or other factors

Balancing

• Positioning of mass balance weights to prevent flutter (oscillatory movement) in flight control surfaces.
• This is done to the ailerons, elevators, and rudders to ensure smooth operation.

Rigging General

• Correct rigging of flight controls is essential for proper aircraft performance
• Different types of mechanisms and systems (cablings, rods, electrical, hydraulic) are used to control surfaces.

Independent Checks

• Independent inspection is essential to ensure all flight controls are properly rigged and are operating in accordance with all specifications