Aircraft Design Fundamentals

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Questions and Answers

What is the primary consideration for designers when creating an aeroplane?

Manoeuvrability and low landing speed

Stability and manoeuvrability (correct)

Stability and high cruising speed

High utility and low cost

What is the purpose of secondary flight controls?

To control the aircraft's speed

To change the direction of the aeroplane

To assist or modify the effect of the primary controls (correct)

To rotate the aeroplane about its three axes

What determines the aerodynamic lift of a wing?

The colour and material of the wing

The speed and direction of the aeroplane

The shape and size of the wing aerofoil section (correct)

The weight and balance of the aeroplane

What is the easiest way to provide a greater pressure difference between the upper and lower wing surfaces?

Increasing the camber of the wing Signup and view all the answers

What are slots and flaps used for?

To increase lift, change the stall angle or change the aircraft's trim Signup and view all the answers

What type of secondary flight control modifies the amount of lift a surface produces?

Trailing edge high-lift devices Signup and view all the answers

What is the most universal lift-modifying device used on modern aircraft?

Flaps on the trailing edge of the wing Signup and view all the answers

What effect do flaps on the trailing edge of the wing have on lift and drag?

Increase lift and drag Signup and view all the answers

What is the purpose of trailing edge flaps?

To control the movement of the Krueger flap Signup and view all the answers

What is the function of a Krueger flap?

To work in conjunction with trailing edge flaps Signup and view all the answers

How does a drooped leading edge flap work?

By using a jack-screw arrangement to push the leading edge of the wing Signup and view all the answers

What is the primary purpose of slots in a wing?

To improve airflow conditions at high angles of attack and slow speeds Signup and view all the answers

What happens to the airflow around a wing when the angle of attack increases and slots are present?

More air is deflected through the slot Signup and view all the answers

What is the effect of a slat on the wing at high angles of attack?

It increases the extent of the low-pressure area over the wing Signup and view all the answers

Why are slots not used in high-speed aircraft?

Because they increase drag during normal flight Signup and view all the answers

What happens to the drag when a slat is present during normal flight?

It increases Signup and view all the answers

What is the main difference between a split flap and a plain flap?

The amount of drag produced at low lift coefficients Signup and view all the answers

Which type of flap is the most popular on aeroplanes today?

Slotted flap Signup and view all the answers

What is the purpose of the slot in a slotted flap?

To prevent the flap from stalling Signup and view all the answers

How do double and triple-slotted flaps achieve maximum increase in lift?

By allowing the maximum increase in drag without airflow separation Signup and view all the answers

What is the main characteristic of a Fowler flap?

It rolls back on a track, increasing the wing's effective area Signup and view all the answers

What happens when a slotted flap is lowered all the way?

Air from the high-pressure area below the wing flows up through the slot Signup and view all the answers

What is the effect of a slotted flap on the lift coefficient?

It increases the lift coefficient a good deal Signup and view all the answers

Where is the hinge of a slotted flap located?

Below the lower surface of the flap Signup and view all the answers

What is the purpose of mass balance weights in flight control surfaces?

To equalize the moment about the hinge line of the control surface Signup and view all the answers

Where can mass balance weights be located?

Either internal or external to the control surface Signup and view all the answers

Why is it necessary to rebalance the control surface after overhaul or repair?

To prevent flutter and ensure safe flight operations Signup and view all the answers

What is the purpose of the horn in flight control surfaces?

To house lead weights for mass balancing Signup and view all the answers

What determines the control force required to move a control surface?

Airspeed and control surface area Signup and view all the answers

What is achieved when a portion of the control surface is extended ahead of the hinge line?

Aerodynamic balance and reduced control force Signup and view all the answers

What is the term for the portion of the control surface extended ahead of the hinge line?

Overhang Signup and view all the answers

Why are controls often aerodynamically balanced?

To assist pilot input force during high-speed manoeuvres Signup and view all the answers

What is the primary function of a stall strip?

To produce vortex Signup and view all the answers

What is the purpose of flight control tabs?

To overcome difficulties in moving control surfaces during high-speed flight Signup and view all the answers

What is affected by airspeed variations in normal flight?

Longitudinal balance Signup and view all the answers

What is the purpose of trim tabs?

To fly the aircraft at the desired attitude with little or no control input Signup and view all the answers

How are trim tabs operated?

By separate controls in the cockpit Signup and view all the answers

What is the function of the jack screw mechanism in the elevator?

To adjust the length of the actuating rod to the tab horn Signup and view all the answers

What is the result of adjusting the length of the actuating rod to the tab horn?

The relationship between the tab and the elevator remains fixed for all positions of the elevator Signup and view all the answers

What is the location of the simple adjustable trim tab?

On the trailing edge of the elevator Signup and view all the answers

Study Notes

Design Considerations for Aircraft

Designers must balance between stability and maneuverability, high cruising speed and low landing speed, and high utility and low cost.
Primary flight controls rotate the aircraft about its three axes, while secondary controls are used to assist or modify the effect of primary controls.

Secondary Flight Controls

Secondary flight controls may be extended only when needed and tucked away into the structure at all other times.
Four basic types of secondary flight controls:
- Those that modify the amount of lift a surface produces (e.g., trailing edge high-lift devices, leading edge high-lift devices)
- Those that change the amount of force needed to operate the primary controls
- Those that control the aircraft's trim
- Those that induce drag

Lift-Modifying Devices

Flaps on the trailing edge of the wing change the camber of the wing, increasing lift and drag for any given angle of attack.
Types of flaps:
- Split flap
- Slotted flap (increases lift coefficient more than simple flap)
- Fowler flap (increases effective area of the wing and lowers the trailing edge)
- Krueger flap
Drooped leading edge flap uses a jack-screw arrangement to push the leading edge of the wing against a hinge on its lower surface, increasing camber and lift.

Slots and Slats

Slots are nozzle-shaped passages through a wing, designed to improve airflow conditions at high angles of attack and slow speeds.
Slots increase the stall angle by maintaining a streamlined flow around the wing.
Slats are fixed or retractable devices on the leading edge of the wing, which increase the extent of the low-pressure area over the wing at high angles of attack.

Flight Control Tabs

Introduction to flight control tabs: used to overcome difficulties in moving and holding control surfaces in deflected positions during high-speed flight.
Types of tabs:
- Trim tab (used to adjust the downward tail load as airspeed changes in flight, allowing for hands-off flight at any airspeed)
- Flight control surface mass balance (used to balance the control surface and prevent flutter in flight)

Aerodynamic Balance

Aerodynamic balance is achieved when a portion of the flight control surface is extended out ahead of the hinge line (known as a horn balance or overhang).
The purpose of aerodynamic balance is to assist the pilot's input force during maneuvers by reducing the control force required to move the control surface.

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Description

This quiz covers the fundamental principles of aircraft design, including the trade-offs between stability and maneuverability, cruising speed and landing speed, and utility and cost. It also explores the role of primary and secondary flight controls in aircraft operation.