Aerospace Principles Quiz

Control Movements

• Control surfaces change the surface's geometry when deflected
• Pitch: Control Column, elevator deflection, nose movement
• Rudder: Rudder pedals, rudder deflection, nose movement
• Ailerons: Control Column, aileron deflection, wing roll
• Trim: Alleviates pressure, normally a wheel or push/pull button

Forces Acting on an Airplane - Flight

• Thrust: Exerted by engine and propellers, pushing air backwards, causing forward motion
• Drag: Resistance to forward motion, directly opposed to thrust
• Lift: Upward force to sustain flight.
• Weight: Downward force due to gravity, opposes lift.

Equilibrium

• Steady motion, not a state of rest
• Thrust and drag are equal and opposite
• Lift and weight are equal and opposite

Lift

• Generated mainly through the wings
• Acts perpendicular to the relative wind and wingspan.
• Exerted through the center of pressure.
• Opposes weight
• During level cruise, lift equals weight

Airfoil

• Any surface designed to obtain a reaction from the air – lift!
• Curved/cambered shape produces most lift
• Upper surface generally has greater camber than the lower

Lift - Center of Pressure

• Center of pressure of an airfoil cross-section may differ from the entire wing
• The center of pressure of the wing may differ from the entire aircraft.

Airfoil Terminology

• Leading Edge: Forward edge of the airfoil
• Trailing Edge: Aft edge of the airfoil
• Chord: Line connecting the leading and trailing edges. Denotes the length of the airfoil.
• Mean Camber Line: Line drawn halfway between the upper and lower surfaces. Denotes the amount of curvature of the wing
• Point of Maximum Thickness: Thickest part of the wing expressed as a percentage of the chord

Angle of Attack

• Angle of attack is the angle between the chord line of an airfoil and the vector representing the relative motion between the body and the air.
• Angle of incidence is the angle between the chord line of the wing and the longitudinal axis of the aircraft. It is fixed by the manufacturer, between 2-4 degrees.

The Wing

• A wing is made up of many airfoils connected side-by-side
• The geometry of the airfoil may change from one part of the wing to another

Wing Terminology

• Wing root: Part attached to the fuselage
• Wing tip: Part farthest from the fuselage
• Wing span: Distance from wing tip to wing tip
• Mean aerodynamic chord: Average chord length of all the individual slices of the airfoil making up the wing
• Span x MAC gives wing area.

Aspect Ratio

• The ratio of a wing's span to its mean aerodynamic chord (MAC) or length/width.
• Sweepback: Wing in which the quarter chord line is not parallel with the lateral axis of the aircraft.

Wing Terminology - Dihedral & Anhedral

• Dihedral and Anhedral: Degree to which wings are canted upwards or downwards from the fuselage
• Washout/Washin: Change in angle of incidence from the root to the tip of the wing

How is Lift Created?

• Newton
• Bernoulli
• Coanda

Newton's Laws

• First Law: Law of inertia; an object in motion tends to stay in straight-line motion
• Second Law: Law of acceleration; external force applied will alter uniform motion of a body.
• Third Law: Law of action/reaction; when a force acts on an object, an equal force acts in the opposite direction

Newton - Lift

• For every action force, there must be a reaction equal in magnitude but opposite in direction.
• If no force acts on an object, it will continue at a constant velocity.
• By changing the direction of the flow, there must be some reaction force.

Bernoulli's Principle

• Swiss mathematician, Daniel Bernoulli (1700-1782)
• Formulated principle mathematically about 1755 (Leonhard Euler)
• Total energy of any system remains constant.

Law of Conservation of Energy :

• Energy cannot be created or destroyed, but can only change forms.
• In fluid flow, if velocity (kinetic energy) increases, pressure (potential energy) decreases, and vice versa.
• This explains the difference in pressure on top vs bottom of a wing in generating lift.
• The energy in fuel is dispersed in different forms such as work, heat etc.

Fluid in Motion

• The sum of potential energy (pressure or Ep) and kinetic energy (velocity or Ek) is constant for the total system energy.
• air is a viscous compressible fluid but compressibility is negligible below 40% speed of sound (about 600 knots) at lower flight speed (less than 240 knots) air considered incompressible

Laminar flow through a venturi

• Fluid velocity increase as the tube narrows, pressure decreases proportionally .

Volume in = Volume out

• A1V1 = A2V2

Coanda Effect

• Phenomenon whereby a jet flow attaches to nearby surfaces and remains attached even when the surface curves away from initial direction.

Airfoil Terminology

• Leading Edge- Forward edge of the aerofoil
• Trailing Edge- Aft edge of the aerofoil
• Chord- Line connecting the leading and trailing edge. Denotes the length of the aerofoil
• Mean Camber Line- Line drawn halfway between the upper and lower surface of the aerofoil. Denotes the amount of curvature of the wing

Parts of Wing Nomenclature

• Leading and Trailing edges
• Airfoil Terminology and definitions to differentiate various parts.
• Chord and Camber Lines.
• Locations of maximum thickness and camber.

Airfoil Terminology - Angle of Incidence and Angle of Attack

• Angle of Attack: Angle between the chord line of an airfoil and the incoming airflow.
• Angle of Incidence: Angle between the chord line of the wing and the longitudinal axis of the aircraft

Wing Design

• Low Lift - High Drag: Reflex trailing edge wing section, very little movement of centre of pressure, good stability
• Symmetrical: Cambered top and bottom wing sections, same as above
• GA/W-1: Thicker for better structure, lower weight, good stall characteristics
• Deep Camber: High lift, low speed, thick wing section
• Suitable for transports, freighters, bombers, etc and high lift, low speed, high thick wing section
• Suitable usage of thin wing section for high lift and low speed operations.

Wing Tip Design

• The main objective is to reduce the Induced Drag by reducing the vortexes.
• Controlling induced drag and wing tip vortices increase efficiency
• Wing tip tanks to increase range
• Distribute weight over more surface
• Aids preventing air from spilling over
• Wing tip plates
• Same shape as airfoil but thicker
• Droop wing tips and Winglets

Wing Designs - Wing Fences, Slats, Slots, and spoilers

Wing Designs - Flaps

• High lift devices increasing camber and some increased take off performance
• Greater flap deflection for generating more lift
• Steeper path without increasing AoA (Fowler type)
• Slow retraction of flaps (double slotted)

Axes of an Airplane

• Normal or vertical axis
• Lateral axis
• Longitudinal axis
• Centre of gravity

Axes of Movement

• Lateral axis: Pitching movement is about the lateral axis, controlled by elevators or stabilator
• Longitudinal axis: Rolling movement is about the longitudinal axis, controlled by ailerons
• Normal axis: Yawing movement is about the normal axis, controlled by rudder

Roll and Yaw

• Application of rudder to the right, left wing meets the relative airflow at higher speed producing more lift.
• Coordination of rudder and aileron movement for turns
• Aircraft yaws/turns away from the turn from aileron drag.
• Skids outwards requiring rudder movement

Yaw

• Dynamic Yaw: Normal movement around the normal axis
• Static Yaw: Condition where the aircraft is flying at some angle of sideslip, where the longitudinal axis is not aligned with the aircraft flight path.
• Sideslip: Aircraft yawing left or right.

Balanced Controls

• Some control surfaces are in front of hinge to reduce flutter and balance the forces acting on the control column.
• Air strikes the forward portion to assistant movement of the control surface.

Stability

• Static Stability: Aircraft's tendency to return to its original position when disturbed.
• Dynamic Stability: Aircraft's long term ability to return to its original position after being disturbed
• Positive, Neutral, and Negative Stability.
• Static stability in dynamic stability for design purposes

Longitudinal Stability

• Pitch stability: Lateral axis measured from wing-tip to wing tip, the size and position of the horizontal stabilizer impacts longitudinal stability.
• Larger horizontal stabilizer further from C of G to create more stability .

Lateral Stability

• Roll stability: Longitudinal axis. Dihedral- wings angle upwards or downwards from the aircraft fuselage.
• To compensate for disturbed wing, the lower wing creates greater uplift
• Keel Effect: High wing aircraft, most of the weight is below the wings. One wing drops, aircraft acts like a pendulum, returning to its original attitude
• Anhedral: The same as Dihedral but in opposite direction

Sweepback

• Leading edge of wing sweeps backwards
• Found on most large transport category aircraft
• Lower wing meets airflow at a more perpendicular angle to create more lift during a disturbance.

Directional Stability

• Yaw: Controlled about the vertical axis.
• Larger side area of the aircraft behind the centre of gravity provides more direction stability, with the vertical stabilizer.
• Vertical Stabilizer: Size/ shape affect directional stability
• Adverse Yaw: Various reasons cause unwanted yaw.

Slipstream

• Propeller rotation creates a spin to the slipstream, or corkscrew effect. This increased pressure on one side of the vertical fin causes unwanted yaw.

Asymmetric Thrust

• At high angles of attack. Descending blade of the propeller has a greater AoA than ascending blade.
• This produces more thrust from right side than left.
• Aircraft will yaw to the left

Torque

• Propeller rotating clockwise causes left turning tendency.
• This results in roll in flight, and yaw on the ground.
• Yaw correction methods : building a slight right turning tendency into the aircraft.
• Offsetting the vertical fin or offsetting the engine thrust line is done, in cruise,

Precession

• Spinning masses have a property called precession, which is that when a force is applied on an edge it will react as though the force has been applied 90 degrees to the rotation.

Turbulence

• Very difficult to control
• Rudder use is usually more effective in controlling roll from turbulence than aileron input.

Aileron Drag

• Ailerons create more drag (See lift/drag relationship)
• Aircraft tries to yaw to the opposite direction of the roll.
• Rudder input is needed.

Differential Ailerons

• Down going wing's aileron is deflected more than the up going aileron.
• This improves control effectiveness (Reduces drag on upper wing, and yaw on the lower wing during turn)

Frise Ailerons

• Leading edge of the down going wing's aileron extends into the airflow, creating more drag (reducing induced drag on up going wing).

Misuse of Rudder

• Rudder use must be coordinated with the amount of aileron displacement
• Occasionally, pilots press too hard or too lightly on rudder pedals which can cause yaw.

The End (or more...)

• There is more.

Climbing

• Elevators' function is to divide the engine produced thrust into speed and altitude, this is crucial during a climb.
• Effects during a climb without/with any increase in thrust
• Reaching absolute altitude during a climb is impossible.
• Best Rate Vy=least time
• Best Angle Vx=given distance

Gliding

• Thrust is no longer available
• Angle vs airspeed relationship in gliding
• Windmilling propeller providing negative thrust -> Drag
• Best Glide: AoA for max L/D, still air, any variations in wind reduce glide distance

Turns

• Lateral stability for climbing/descending turns is affected by relative airflow for each wing
• Descending : Inner wing – higher AoA
• Outer wing – travelling faster and more lift
• Climbing: Inner wing – smaller AoA, outer wing - higher AoA and greater speed.
• Compensate each other to keep angle of bank constant

Load Factor

• Load factor increases in turns
• Other maneuvers rapidly increase load factor.

Stall

• Aerodynamic stall is where the wing no longer produces sufficient lift to sustain flight.
• Stall occurs at too high angle of attack. The abruptness and predictability of this varies with wing and aerofoil design

Factors Affecting Stall

• Weight
• Centre of Gravity
• Turbulence
• Turns
• Flaps
• Contamination (snow, frost, ice, dirt, heavy rain)

Preventing Stall

• Why are wings not flat plates?
• High Lift Devices (Flaps)
• Vortex Generators
• Airfoil Shape
• Wash-out

Preventing Stall - Plain and Slotted Flaps

• The effect on keeping flow attached is very slight, they primarily increase camber/amount of deflection of flow/lift at lower angles of attack
• Slotted flaps leave a gap between the wing and the flap surfaceThis helps keep the flow attached to the upper surface of the flap
• Separation of flow is further ahead compared to other flaps for same AoA.

Prevention Stall- Slat

• Slots and Slats are leading edge devices which help keep the flow attached.
• Slots are permanently mounted
• Slats are retractable

Maneuvers

• Spin: Autorotation after aggravated stall. Increasing AoA reduces lift, and ailerons worsen effect, downward wing has higher AOA. Accelerates rolling moment
• Spiral: Excessive nose-down descending turns, Structural damage

Airspeed Limitations

• Rate of movement of aircraft relative to air mass.
• Never exceed/ Max Permissible Dive Speed
• Max structural cruise speed
• Normal operating limit spead
• Maneuvering speed
• Max Flap speed

Streamlining

• Smooth flow/reduced drag during flight.
• Design features affecting the streamlining.

Test your knowledge on key aerospace principles including the behavior of the Centre of Pressure (CofP), forces acting on an aircraft, and the relationship between thrust, lift, and drag. This quiz explores fundamental concepts critical to understanding flight dynamics and aircraft operation.