Aircraft Secondary Flight Control Systems
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Questions and Answers

What is the primary reason for deploying slats in conjunction with flaps on large transport category aircraft?

  • To decrease the overall camber of the wing, reducing drag during landing.
  • To reduce the stall angle, thus ensuring the aircraft can land at higher speeds.
  • To increase the stall angle and lift coefficient by energizing airflow over the wing. (correct)
  • To minimize the increase in lift coefficient caused by flaps, maintaining consistent handling characteristics.

How do fuselage-installed aerodynamic brakes primarily function?

  • By increasing drag. (correct)
  • By decreasing drag and increasing lift.
  • By increasing lift and decreasing drag.
  • By decreasing both lift and drag.

During which flight maneuver is the 'ground spoiler' function typically activated?

  • During rapid descent to increase drag.
  • During takeoff to reduce ground speed.
  • During cruise to adjust altitude.
  • Upon landing, after both main landing gear legs are compressed. (correct)

What distinguishes the function of spoilers used as 'speed brakes' from their function as 'ground spoilers'?

<p>Speed brakes are used in flight to increase drag and control descent, while ground spoilers are used on landing to kill lift and improve braking. (D)</p> Signup and view all the answers

Which of the following correctly describes the effect of deploying flaps on the stall angle of an aircraft?

<p>Flaps decrease the stall angle, but the associated increase in lift allows for a lower stall speed. (A)</p> Signup and view all the answers

If a pilot commands a roll order during approach, what happens to the speed brake function?

<p>The speed brake function is overridden; roll order has priority. (A)</p> Signup and view all the answers

What is the primary purpose of secondary flight controls in an aeroplane?

<p>To assist or modify the effects of the primary controls. (B)</p> Signup and view all the answers

Why is increasing the camber of a wing an effective way to increase lift?

<p>It creates a greater pressure difference between the upper and lower wing surfaces. (D)</p> Signup and view all the answers

What is a key benefit of using flaps on the trailing edge of a wing?

<p>They enable landing at slower speeds and shorten runway requirements. (A)</p> Signup and view all the answers

What typically happens when flaps are deflected to their maximum extent without the use of leading edge slots or slats?

<p>The airflow separates from the upper surface, leading to a loss of lift and increased drag. (B)</p> Signup and view all the answers

What best describes the functionality of plain flaps?

<p>Sections of the wing's trailing edge, inboard of the ailerons, hinged from the top. (C)</p> Signup and view all the answers

In aircraft design, what does the need to compromise between stability and maneuverability suggest?

<p>Enhancing one aspect often diminishes the other, requiring a balanced design approach. (C)</p> Signup and view all the answers

What is the relationship between aerodynamic lift and the shape and size of a wing's aerofoil section?

<p>The shape and size of the aerofoil section directly determine aerodynamic lift. (C)</p> Signup and view all the answers

What are slots and flaps primarily used for in aircraft design?

<p>To increase lift, change the stall angle, or adjust the aircraft’s trim. (B)</p> Signup and view all the answers

What is the main reason plain flaps are seldom found on modern aeroplanes?

<p>Their effect on lift and drag is minimal compared to more advanced flap designs. (C)</p> Signup and view all the answers

Which type of flap is characterized by a portion of the lower surface of the wing's trailing edge hinging down into the airstream, significantly increasing drag at low lift coefficients?

<p>Split Flaps (D)</p> Signup and view all the answers

What is the primary advantage of using slotted flaps on an aircraft wing?

<p>They prevent air separation by re-energizing the boundary layer. (D)</p> Signup and view all the answers

How do Fowler flaps primarily enhance lift during their initial deployment phase?

<p>By substantially increasing the wing area. (D)</p> Signup and view all the answers

What is a flaperon, and how does it function on an aircraft?

<p>It is an aileron that can also act as a flap, combining both control surfaces. (A)</p> Signup and view all the answers

What is the purpose of leading edge flaps on high-performance aircraft?

<p>To allow a higher angle of attack before airflow separation. (A)</p> Signup and view all the answers

Why are Krueger flaps used on large turbine-engine transports with swept wings?

<p>To increase lift at low speeds. (B)</p> Signup and view all the answers

How does a drooped leading edge flap function to increase lift?

<p>By drooping the leading edge of the wing, increasing camber. (B)</p> Signup and view all the answers

What is the primary function of slots in an aircraft wing?

<p>To improve airflow at high angles of attack. (B)</p> Signup and view all the answers

What is the primary disadvantage of fixed slots in a wing, especially for high-speed aircraft?

<p>They cause a substantial increase in drag at higher speeds. (A)</p> Signup and view all the answers

How do movable slats overcome the limitations of fixed slots on aircraft wings?

<p>By minimizing drag during normal, low angle of attack flight. (B)</p> Signup and view all the answers

Flashcards

Aeroplane Design Compromises

Balancing stability, speed, cost, and utility in aircraft design.

Primary Flight Controls

Controls that rotate the aircraft about its three axes.

Secondary Flight Controls

Controls that assist or modify the effect of primary controls.

Aerodynamic Lift

The upward force generated by the wing due to its shape and size.

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Flaps

Devices on the trailing edge of the wing that increase lift and drag.

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Trailing Edge Flaps

Flaps located on the back edge of the wing to enhance lift.

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Leading Edge Slots

Devices used to maintain airflow over the wing at high angles of attack.

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Plain Flaps

Simple flaps that slightly deflect the trailing edge of the wing.

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Wing Camber

The curvature of the wing that affects lift generation.

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Stall Angle

The angle of attack at which airflow separation occurs, causing a loss of lift.

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Lift Coefficient (CL)

A dimensionless number that represents the lift characteristics of a wing design.

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Spoilers

Control surfaces that disrupt airflow to reduce lift and increase drag, aiding in descent and braking.

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Aerodynamic Brakes

Devices that increase drag and help in descent, often used in landing and rapid approach.

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Ground Spoilers

Types of spoilers activated on landing to increase tire contact and improve braking efficiency.

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Split Flaps

Flaps that hinge down from the wing's trailing edge to increase lift but also increase drag significantly.

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Slotted Flaps

Flaps that create a duct when lowered, improving lift by allowing high-pressure air to flow over the top.

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Fowler Flaps

Flaps that roll back on a track to increase wing area and camber for more lift with minimal drag increase.

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Slotted Fowler Flaps

Combination of Fowler flaps with slots to enhance lift while managing drag during different flight phases.

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Flaperons

Ailerons that also function as flaps, allowing for both roll control and increased lift.

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Leading Edge High-Lift Devices

Devices on the leading edge of wings that increase camber to allow for higher angles of attack.

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Krueger Flaps

Devices that hinge down from the leading edge to increase wing camber and enhance lift at low speeds.

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Drooped Leading Edge Flap

Flap mechanism that lowers the leading edge of the wing to increase camber for better air deflection.

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Slots

Nozzle-shaped passages in the wing that improve airflow at high angles of attack for better stall management.

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Drag Coefficient

A measure of the drag force acting on the wing as the angle of attack changes, affecting lift efficiency.

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Study Notes

Aircraft Flight Control Systems

  • Aircraft design involves compromises between stability, maneuverability, speed, utility, and cost.
  • Primary flight controls manipulate the aircraft about its three axes.
  • Secondary controls modify or assist primary controls.
  • Secondary controls are retractable, used only when needed.

Aerodynamic Lift and Control

  • Wing shape and size determine lift.
  • Lift modification is done through slots and flaps.
  • Wing camber increase is easier for lift enhancement, especially during takeoff and landing when speed/angle adjustments aren't practical.
  • Slots and flaps affect lift, stall, and trim.

Types of Secondary Flight Controls

  • Lift Modifiers:
    • Trailing-edge high-lift devices (flaps)
    • Leading-edge high-lift devices (slots, slats)
  • Force Modifiers:
    • Assists in controlling primary functions
  • Trim Controls:
    • adjust balance of lift
  • Drag Inducers:
    • increase drag to influence flight path.

Trailing Edge Flaps

  • Flaps on the trailing edge are the most common lift modifiers.
  • Flaps increase lift and drag.
  • Flap extension and angles can be adjusted from the cockpit.
  • Flap configurations vary.
  • Full flap deflection can cause airflow separation, leading to lift loss; slots can prevent separation.

Flap Types

  • Plain Flaps: Simple, minimal effect, mainly used for low-speed aircraft
  • Split Flaps: Less common today, previously used, produced similar lift change as a plain flap but higher drag.
  • Slotted Flaps: Most common modern type, increases lift coefficient significantly, uses a slot to prevent airflow separation at stall. Double/Triple-slotted flaps maximize lift increase without stalling.
  • Fowler Flaps: Increases wing area, initial high lift with low drag, but increases drag and turbulence as the flap extends further.

Leading Edge High-Lift Devices

  • Leading-edge devices increase camber and allow higher angles of attack before stall.
  • Krueger Flaps: Increase camber on swept-wing aircraft for low-speed lift. Electric or hydraulically actuated.
  • Drooped Leading Edge Flaps: Alter the leading edge of the wing to improve lift.
  • Slots: Improve airflow at high angles of attack and low speeds, slightly increase drag.

Aircraft Flaps and Slats Behavior

  • Slats and flaps together are preferred designs
  • Slats increase lift when deployed with flaps
  • Slats also increase camber

Aerodynamic Brakes

  • Devices that increase drag, reduce lift.
  • Wing-installed: Increases drag and reduces lift
  • Fuselage-installed: Increases drag
  • Used for approach/descent, landing, and ground braking through spoilers

Spoilers

  • Destroy lift by disrupting airflow.
  • "Speed brake" function on approach and descent to increase drag and control descend rate.
  • In landing, spoilers increase braking efficiency by increasing tire/ground contact pressure

Flaperons

  • Ailerons that can function as flaps, combine the functions of flaps and ailerons.
  • Boeing 767, 777 and 787 use the ailerons as flaperons.
  • Function as ailerons during cruise.
  • Function as flaperons during landing.
  • Function as aileron and spoiler during landing rollout.

Coefficient of Lift (CL) and Stall Angle

  • Lowering flaps reduces the stall angle but improves lift at lower speeds.
  • Deployment of slats together with flaps restores normal stall angle and increases it beyond flap-less position.

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Description

Explore aircraft secondary flight control systems. Secondary controls like flaps, slots and slats modify lift. Trim controls maintain lift balance, while drag inducers adjust the flight path.

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