Airframes, Aerodynamics, and Theory of Flight Flashcards
Stresses - Compression
Crushing or squeezing parts together
Stresses - Tension
Stretching or pulling apart objects
Stresses - Shearing
Cutting or sliding an object apart
Stresses - Bending
Pulls one side of an object apart while squeezing the other side
Stresses - Torsion
Twisting Motion
Fuselage Type - Truss Type
- Frame of wood beams or metal tubes (bolted or welded)
- Frame carries load and fuselage stresses
- Two types, Warren and “N” Girder
Fuselage Type - Monocoque
- “Stressed Skin”
- Skin carries some of the load
- Perfect Stressed Skin: Skin carries ALL of the load
- Formers maintain shape
- Bulkheads carry load
- Stringers run lengthwise and hold bulkheads together
Fuselage Type - Semi-Monocoque
- Combination of stressed skin and formers or frame system
- Includes a firewall, separates the engine compartment from the rest of the fuselage
- Cessna 172
Chord
Straight line joining the leading and trailing edges of wing
Camber
Upper curvature of the wing
Span
Distance from wingtip to wingtip
Wing root
- Inboard section of wing closest to fuselage
Load Factor
Actual load being imposed on the wings vs the weight of the aircraft
Spars
Run from wing root to tip and carry most of the load in flight
Ribs
- Give shape to the wing and prevent twisting
False Ribs
- Smaller ribs placed between leading edge and front spar
Compression Struts
Steel tubes placed between the spars to prevent compression/distortion of the wing
Drag/Anti-Drag Wire
Provide additional support to the wing
Wing Tip Bow
Curved metal tube giving the wingtip its shape
Semi-Cantilever Wing
Supported by external struts
Full Cantilever Wing
No external bracing
Stabilator
No fixed horizontal stabilizer
Canard
Horizontal stabilizer at front of aircraft
Control Systems
Ailerons - Torque Tube
Elevators - Push/Pull Rod
Rudder - Cable and Pulley
Nose Wheel Advantages
- Greater visibility over the nose
- Nose over tendencies eliminated
- Greater maneuverability on ground
Tail Wheel Advantages
- Less Drag
- Cheaper and easier to build and maintain
- Will sustain less prop damage
- More suitable for ski operations
Brakes - What to look for
- Hydraulic leak around main gear (red puddle)
- Cracks in the pucks
- Rusting over long periods due to lack of use
4 Forces
- Lift acts 90º to wing span
- Weight acts at C of G
Factors Affecting Lift
- Angle of Attack
- Velocity of the Airfoil
- Density of the Air
- Wing Area
- Shape of the Aerofoil
Coefficient of Lift
- Relative measure of aerofoil’s lifting capabilities
- Varies with angle of attack and aerofoil type
- Higher camber and flaps will yield greater CL
- Increases up to critical angle of attack, the decreases rapidly (stall)
Total Drag
Induced Drag + Parasite Drag
Parasite Drag
- Drag produced by any surface that doesn’t contribute to lift
- Interference Drag (Joining of two or more parts)
- Profile Drag (Form Drag + Skin Friction)
Form Drag
- Drag created by shape of body
- Reduce by streamlining
Skin Friction
Drag created by tendency of air flowing over a surface to stick to it
Wingtip Vortices
Greatest at low airspeeds, clean configuration, heavy
Reducing Induced Drag
- High Aspect Ratio (Ratio of span to average chord)
- Winglets (Reduce airflow around wing tip)
- Ground effect
Conventional Airfoil
- Different shapes and sizes
- Maximum camber is about 25% chord from leading edge
Laminar Airfoil
- Maximum camber occurs at 50% chord
- Maintains smooth laminar flow over greater percentage of chord
- Used on higher speed aircraft
- Stalls more violently at high angles of attack
Planform
Shape of wing as seen from directly above
Angle of Incidence
Angle at which the wing is permanently inclined to the longitudinal axis of the airplane
Washout
- Twist in the wing where the angle of incidence at the root is greater than at the tip
- Improves stall characteristics by having wing root stall before wingtips
- Enhances aileron control at low speeds
Stall Strips
- Strips attached to the leading edge of the wing near the root
- Purpose is wing root area to stall first
- Very similar to washout
Wing Fences
- Fin-like vertical surfaces attached to the upper surface of the wing to prevent spanwise airflow
- Wing Fences improve slow-speed handling and stall characteristics
Spoilers
- Long narrow strips arranged spanwise along the top surface of an aerofoil
- Purpose of spoilers is to increase drag and spoil lift
- Can replace ailerons as a means of roll control
Speed Brakes
- Metal plates used on high speed aircraft to increase drag withou t decreasing lift
- Located near trailing edge of airfoil
- Used to slow the aircraft at high speed when unsafe to deploy flaps or landing gear
Vortex Generators
- Small vertical plates arranged across the upper surface of the wing
- Purpose is to re-energize the boundary layer to reduce drag caused by turbulence airflow
Slots
- High lift device FIXED to the leading edge of an airfoil
- Used to maintain stability and control at low speeds
Slats
- High lift device on the leading edge of an airfoil that is RETRACTABLE
- Used to maintain stability and control at low speeds
Flap Design - Split Flap
Creates a low pressure area between the wing and the extended flap to create more drag than the plain flap with lesser angles of deflection
Flap Design - Fowler Flap
Combines camber change with an increase in wing area as well as the creation of a slot to obtain a smooth airflow
Flap Design - Zap Flap
Increases wing area without creating the slot
Flap Design - Double Slotted Flap
Combines camber changes and slots to obtain smoother airflow
Servo Tab
- Tab on trailing edge of control surface
- Moves opposite to control surface
- Eases amount of force required by pilot
Anti-Servo Tab
- Tab on trailing edge of control surface
- Moves in same direction as control surface
- Increases amount of force required by pilot
Aileron Drag
In rolling the wings, down-going aileron increases the drag on that wing, causing adverse yaw
Frise Ailerons
Up-going aileron projects into airflow, increasing form drag, balancing the induced drag on the down-going aileron
Differential Ailerons
Up-going aileron moves through a greater angle than the down-going aileron, increasing form drag, balancing the induced drag on the down-going aileron
Balanced Controls
- Aerodynamic Balance (Extending part of control surface in opposing airflow to hold surface in position)
- Mass Balance (Placing a mass ahead of the control surface hinge to prevent flutter at high speed)
Static Stability
Initial Tendency to return
Dynamic Stability
Overall tendency to return
Longitudinal Stability
- Stability about the lateral axis (or pitch stability)
- Influenced by the horizontal stabilizer and C of G position
Longitudinal Stability - Forward C of G
- Positive Static Stability
- More tail-down force required to balance weight ahead of the centre of pressure
- Effective weight increases, stall speed increases, TAS decreases
Longitudinal Stability - Less Forward C of G
- Less Positive Static Stability
- less tail-down force required to balance weight ahead of the centre of pressure
- Effective weight decreases, TAS increases
Longitudinal Stability - Aft C of G
- Neutral Static Stability
- No tail down force exerted
Longitudinal Stability - Canard
- Balancing force is ahead of the C of G
- Horizontal stabilizer will always be a positive force
- Less apparent weight, higher TAS
- aerodynamically efficient, however engine gets disturbed airflow in rear of aircraft
- Aft C of G more stable than forward C of G
Factors Affecting Lateral Stability - Dihedral
- Angle that a wing makes with the horizon
- Sideslip is produced in a wingdrop
- Lower wing meets relative airflow at greater angle of attack
- Aircraft will tend to roll back to straight and level
Factors Affecting Lateral Stability - Keel Effect
Occurs on high wing aircraft where the weight of the aircraft is primarily below the wing and acts as a pendulum to correct any lateral instability
Factors Affecting Lateral Stability - Sweepback
- Wing drops and creates a sideslip
- Leading edge of the lower wing presents itself at an angle perpendicular to the relative airflow
- Lower wing will create more lift, causing a roll back to straight and level
Yaw Stability - Vertical Stabilizer
- Creates a greater surface area aft of the C of G
- Any disturbance from the desired direction is automatically corrected (weather vaning)
Factors Affecting Lateral Stability - Sweepback
When aircraft is yawed, upwind wing has longer leading edge to the relative airflow, creating more drag on that wing, pulling the aircraft back straight
Calculating stall speed in turn
= regular stalls speed * square root of load factor
- Load factor = 1/cos(bank)
Adverse Yaw - Propeller Torque
- Clockwise spinning propeller causes an opposite counter-clockwise rolling action on the airframe
- Yaw to the left
Adverse Yaw - Asymmetric Thrust/P-Factor
- At high angles of attack, down-going propeller meets relative airflow at a greater angle of attack, producing more thrust on the right side of propeller
- Yaw to the left
Adverse Yaw - Gyroscopic Precession
- Propeller acts as a gyro
- Any force applied to spinning gyro acts as if that force had been applied from 90º in the direction of rotation
- When aircraft pitches down, yaw to the left
- Experienced by tail-wheel aircraft when tail wheel rises
Adverse Yaw - Slipstream
- Spiralling corkscrew of air strikes tail on left side
- Causes nose to pivot to left when power setting is high
- Reduction in power causes yaw to right
Service Ceiling
Highest altitude at which an aircraft can maintain a 100 fpm climb
Absolute Ceiling
Altitude at which an aircraft can no longer climb
Center of Pressure
- Point on wing where lift is assumed to act
- Center of pressure shifts as the angle of attack changes
Weight and the Stall
- Higher the weight, higher the stall speed
- Due to more downforce required, therefore increasing effective weight, needing more lift, higher angle of attack
C of G and the Stall
- Will stall at higher airspeed with forward C of G
- Aft C of G has higher TAS
Climbing Turns
Tendency to over-bank
Descending Turns
Under banking Tendency
