Aircraft Stabilizers and Elevators Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of a horizontal stabilizer?

To stabilize the aircraft's roll

To control the yaw of the aircraft

To stabilize the aircraft's pitch (correct)

To provide lift to the aircraft

How is an adjustable horizontal stabilizer typically controlled?

Only manually through cables

Through a joystick in the cockpit

By altering the flap positions

Using a trim actuator driven by multiple sources (correct)

What effect do elevators have on an aircraft?

They increase the aircraft's drag

They stabilize the aircraft against wind turbulence

They change the aircraft's angle of attack (correct)

They adjust the aircraft's roll axis

A fixed horizontal stabilizer does not allow for which of the following?

Automatic pitch adjustments Signup and view all the answers

What typically drives the stabilizer trim indicator?

The stabilizer trim control switch Signup and view all the answers

What happens to the speed of an aircraft when the angle of attack decreases?

The speed increases Signup and view all the answers

What is a stabilator?

An elevator directly acting as a stabilizer Signup and view all the answers

What is the primary function of Mach/speed trim in aircraft?

To compensate for aerodynamic stalls due to over-speed conditions Signup and view all the answers

Why does the wing root stall before the tips in most aircraft designs?

To allow pilot control over ailerons for better stall recovery Signup and view all the answers

What occurs at the critical Mach number of an aircraft's wing?

The airflow over the wing becomes supersonic, leading to a shock wave Signup and view all the answers

What happens to the center of pressure when the wing root stalls?

It moves towards the wing tip, reducing total lift Signup and view all the answers

Which design feature is commonly associated with aircraft that approach the speed of sound?

Swept wings to delay shock wave formation Signup and view all the answers

What is the blow down limit in large transport aircraft?

The largest achievable angle of a rudder in flight Signup and view all the answers

How does the speed of an aircraft affect the blow down limit?

It decreases the blow down limit. Signup and view all the answers

What is a trim tab used for in flight controls?

To counteract aerodynamic forces and stabilize the aircraft Signup and view all the answers

Which statement about the relationship between the trim tab and the larger control surface is true?

The trim tab can greatly influence the movement of the control surface. Signup and view all the answers

What is the primary function of flaps in aircraft?

To reduce stalling speed and enhance lift Signup and view all the answers

How do flaps affect the aircraft during takeoff and landing?

They enable the aircraft to fly safely at lower speeds. Signup and view all the answers

What is a significant feature of how trim tabs function?

They adjust the resting position of control surfaces. Signup and view all the answers

What determines the effective angle of a trim tab?

The angle of attack of the larger control surface Signup and view all the answers

What is NOT a characteristic of flap operation?

Decreases drag when extended Signup and view all the answers

What is the purpose of the mechanical feedback linkage in older jet transports?

To provide tactile feedback of airspeed to the pilot Signup and view all the answers

What risk is associated with hydro-mechanical flight control systems compared to purely mechanical systems?

Loss of tactile feedback on control surfaces Signup and view all the answers

How does a typical spring and cam operated feel unit work?

As the cam rotates, it stretches feel and centering springs, creating a force against control input. Signup and view all the answers

What role does the control trim actuator play in the feel unit mechanism?

It adjusts the neutral point of the centering mechanism. Signup and view all the answers

Which aircraft model is noted for using a hydro-pneumatic system to provide variable feel to elevator systems?

Boeing 737 Signup and view all the answers

What is a disadvantage of true hydro-mechanical control systems?

There are no mechanical backup capabilities. Signup and view all the answers

What is the function of the air-data system in hydro-pneumatic systems?

To adjust the amount of control surface feedback based on airspeed. Signup and view all the answers

What happens to the centering springs in a feel unit when the control input force is reduced?

They force the roller into the detent of the cam. Signup and view all the answers

Which of the following best describes the purpose of artificial feel systems in flight control?

To mitigate the sensation of aerodynamic forces on pilots. Signup and view all the answers

What effect does increasing airspeed have on the opposition to pilot input in a hydro-pneumatic system?

It increases the resistance felt by the pilot. Signup and view all the answers

What is the primary function of the hydraulic systems in aircraft?

To operate flight controls using pressurized fluids Signup and view all the answers

How do pneumatically powered leading edge flaps operate in aircraft like the B747?

Employing pneumatic energy from the aircraft's pneumatic system Signup and view all the answers

Which statement accurately describes electric flight controls in larger aircraft?

They utilize electric motors to operate control surface trim Signup and view all the answers

What distinguishes a fly-by-wire (FBW) system from traditional flight control systems?

It utilizes electronic signals transmitted by wires Signup and view all the answers

What are the advantages of fly-by-wire systems compared to mechanical systems?

They are more adaptable to changing aerodynamic conditions Signup and view all the answers

Which of the following is true about the use of electric motors in flight controls?

They provide alternate power sources for flap systems Signup and view all the answers

What might be a disadvantage of mechanical and hydro-mechanical flight control systems?

They require careful routing and can be cumbersome Signup and view all the answers

What is the concept of 'fly-by-light' in flight control systems?

It uses fiber optic cables for electronic signal transmission Signup and view all the answers

What role do autopilot systems play in relation to flight control systems?

They are used to reduce pilot workload with electrical servo motors Signup and view all the answers

What is a critical characteristic of electrical hydraulic pumps in aircraft?

They offer redundant power sources for hydraulics Signup and view all the answers

Study Notes

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

Studying That Suits You

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

Description

Test your knowledge about the essential components of aircraft stability, particularly the functions and control of horizontal stabilizers and the role of elevators. This quiz covers key concepts related to aerodynamics and control surfaces crucial for flight performance.