Aeroplane Aerodynamics and Flight Control Systems

Flashcards covering aeroplane axes, primary and secondary flight controls, high-speed flight aerodynamics (Mach number, shock waves), and advanced flight control systems (Fly-by-wire, stall protection).

What common reference point do the three axes of an aeroplane pass through?

The centre of gravity (CG).

What are the three axes of rotation for an aircraft?

Longitudinal, Lateral, and Vertical (Normal) axes.

What is the specific motion and control classification associated with the longitudinal axis?

Motion is called roll, and control about this axis is called lateral control.

Which primary flight control surfaces provide roll control?

Ailerons and roll spoilers.

What is the effect of flight control movement on an aerofoil?

It modifies the camber, which changes the lift and drag produced by the surface.

Describe the undesirable effect known as adverse yaw.

Aileron drag caused by the downward-moving aileron, which pulls the nose in the opposite direction of the turn.

How do differential ailerons minimize adverse yaw?

The aileron moving upwards travels a greater distance than the one moving downwards to create parasite drag that counteracts induced drag.

What is a Frise aileron?

An aileron with a leading edge that extends below the lower surface of the wing when the aileron moves up, producing parasite drag.

What percentage of the roll rate can roll spoilers account for when a large amount of aileron is used?

$$80\%$$

In pitch control, what happens when the control wheel is pulled back?

The trailing edge of the elevator moves upwards, increasing the download on the tail and rotating the nose upwards.

What is a stabilator?

An all-movable horizontal tail surface that has no fixed stabiliser.

What is the purpose of an anti-balance tab on a stabilator?

To decrease the sensitivity of the stabilator by moving in the same direction as the surface.

How is a variable incidence stabiliser usually adjusted?

By means of screw spindles driven hydraulically, electrically, or by a combination of both.

What is the safety advantage of a canard configuration during a stall?

The canard stalls first, causing the nose to drop and speed to build up while maintaining full aileron control.

What is the function of a rudder limiter?

To limit the maximum deflection of the rudder as a function of aircraft speed to protect the structure from excessive loads.

Define elevons.

Control surfaces used on tailless aeroplanes that combine the functions of ailerons and elevators.

What are ruddervators?

Movable surfaces on a V-tail configuration that combine the functions of the rudder and the elevator.

What type of flap consists of a portion of the wing's trailing edge rolling back on a track to increase effective wing area?

Fowler Flaps

Which Boeing aircraft models use the inboard aileron as a flaperon?

Boeing $767$, $777$, and $787$

What are Krueger flaps?

Leading edge high-lift devices hinged to a wing’s leading edge that lie flush with the lower surface when stowed and extend forward/down when deployed.

How do vortex generators prevent or delay airflow separation?

They pull high-energy air down into the boundary layer using tip vortices.

What is the purpose of wing fences on swept-wing aircraft?

To prevent air from flowing outwards along the span of the wing, which prevents tip stalling and pitch-up.

What is the Mach number formula?

$$M = \frac{\text{True Airspeed}}{\text{Local Speed of Sound}}$$

What is the speed of sound at standard sea level?

$$661.7\,kt$$

Define the critical Mach number ($M_{crit}$).

The flight speed at which some portion of the air flowing over the wing first reaches the speed of sound ($Mach\,1.0$).

What are the three types of pressure waves in high-speed flight?

Normal shock waves, oblique shock waves, and expansion waves.

Describe the Area Rule for transonic aircraft design.

The cross-sectional area of the aircraft body should be consistent throughout its length to produce the least amount of drag.

To what temperature can the leading edges of the Concorde's wing reach due to aerodynamic heating?

$$127\,^\circ C$$

What is the function of Active Load Control (Load Alleviation)?

To reduce wing bending loads and improve ride quality by rapidly actuating flight controls in response to turbulence.

What is the purpose of a Wing Tip Brake (WTB)?

To mechanically stop and lock the flap or slat transmission system if the control computers detect a failure such as asymmetry or runaway.

In a fly-by-wire system, what characterizes the 'Direct Configuration'?

A direct relationship between the sidestick and the surfaces, typically used on the ground or after multiple flight protection failures.

What is a 'Q-feel' system?

An artificial feel system where the feel force varies with the dynamic pressure of the air, sensed by pitot-static elements.

What is 'Mach Tuck'?

A nose-down pitching moment caused by the centre of pressure moving aft when an aerofoil exceeds its critical Mach number.

What is the purpose of a duplicate inspection in flight control rigging?

It is a mandatory safety requirement by regulatory authorities after the assembly or adjustment of aircraft flight and engine controls.

How does a stick shaker provide a warning to the pilot?

It uses an electric motor with an unbalanced flywheel to induce a forceful, noisy tremor in the control yoke to warn of an imminent stall.

What is the pneumatic logic for a stick pusher to operate?

It operates only when both stall computer channels simultaneously give an output to energise solenoid valves connected in series.