40 Questions
What is the primary consideration for designers when creating an aeroplane?
Stability and manoeuvrability
What is the purpose of secondary flight controls?
To assist or modify the effect of the primary controls
What determines the aerodynamic lift of a wing?
The shape and size of the wing aerofoil section
What is the easiest way to provide a greater pressure difference between the upper and lower wing surfaces?
Increasing the camber of the wing
What are slots and flaps used for?
To increase lift, change the stall angle or change the aircraft's trim
What type of secondary flight control modifies the amount of lift a surface produces?
Trailing edge high-lift devices
What is the most universal lift-modifying device used on modern aircraft?
Flaps on the trailing edge of the wing
What effect do flaps on the trailing edge of the wing have on lift and drag?
Increase lift and drag
What is the purpose of trailing edge flaps?
To control the movement of the Krueger flap
What is the function of a Krueger flap?
To work in conjunction with trailing edge flaps
How does a drooped leading edge flap work?
By using a jack-screw arrangement to push the leading edge of the wing
What is the primary purpose of slots in a wing?
To improve airflow conditions at high angles of attack and slow speeds
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
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
Why are slots not used in high-speed aircraft?
Because they increase drag during normal flight
What happens to the drag when a slat is present during normal flight?
It increases
What is the main difference between a split flap and a plain flap?
The amount of drag produced at low lift coefficients
Which type of flap is the most popular on aeroplanes today?
Slotted flap
What is the purpose of the slot in a slotted flap?
To prevent the flap from stalling
How do double and triple-slotted flaps achieve maximum increase in lift?
By allowing the maximum increase in drag without airflow separation
What is the main characteristic of a Fowler flap?
It rolls back on a track, increasing the wing's effective area
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
What is the effect of a slotted flap on the lift coefficient?
It increases the lift coefficient a good deal
Where is the hinge of a slotted flap located?
Below the lower surface of the flap
What is the purpose of mass balance weights in flight control surfaces?
To equalize the moment about the hinge line of the control surface
Where can mass balance weights be located?
Either internal or external to the control surface
Why is it necessary to rebalance the control surface after overhaul or repair?
To prevent flutter and ensure safe flight operations
What is the purpose of the horn in flight control surfaces?
To house lead weights for mass balancing
What determines the control force required to move a control surface?
Airspeed and control surface area
What is achieved when a portion of the control surface is extended ahead of the hinge line?
Aerodynamic balance and reduced control force
What is the term for the portion of the control surface extended ahead of the hinge line?
Overhang
Why are controls often aerodynamically balanced?
To assist pilot input force during high-speed manoeuvres
What is the primary function of a stall strip?
To produce vortex
What is the purpose of flight control tabs?
To overcome difficulties in moving control surfaces during high-speed flight
What is affected by airspeed variations in normal flight?
Longitudinal balance
What is the purpose of trim tabs?
To fly the aircraft at the desired attitude with little or no control input
How are trim tabs operated?
By separate controls in the cockpit
What is the function of the jack screw mechanism in the elevator?
To adjust the length of the actuating rod to the tab horn
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
What is the location of the simple adjustable trim tab?
On the trailing edge of the elevator
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.
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.
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