sep 2012 lesson 2.4 theory of flight flight performance
TRANSCRIPT
Sep 2012Lesson 2.4
Theory of Flight
Flight Performance
Reference
From the Ground Up
Chapters 2.1.5, 2.1.6, 2.1.7:
Flight Performance Factors, Airspeed
Limitations, Mach Number
Pages 26 - 33
Introduction
• There are many factors that affect an aircraft’s flight performance. As well, the four forces are manipulated to be able to maneuver an aircraft.
Outline
• Flight Performance Factors• Climbing, Gliding & Turns• Stalls, Spins & Spiral Dives• Load Factor & Airspeed
Torque
In nose-engine aircraft, propellerrotates clockwise (as seen by pilot)
Result: Roll to left (counterclockwise rotation from equal and opposite reaction)Correction: Slight right-turning tendency built-in to aircraft
Asymmetric ThrustAt high angles of attack and high power setting (i.e. take-off), descendingpropeller blade has greater angle of attack than ascending blade
Right side of prop produces more thrust then left side
Result: Yaw to leftCorrection: Use right rudder
PrecessionSpinning propeller acts like a gyroscope: When force applied to spinninggyro, force acts as if it was 90° in direction of rotation
Result:Quick Nose-Up = Sharp yaw rightQuick Nose-Down = Sharp yaw leftCorrection: Use opposite rudder
Tail-wheel aircraft prone to precession when nose pushed forward on take-off
Slipstream
Propeller pushes air back in corkscrew motion which hits left side offin (pushing it right)
Result: Constant yaw to left (depending on power setting)Correction: Offset fin, trim, right rudder
Climbing
Weight
Drag
LiftThrust
Angle of AttackIncrease: More lift, less speedDecrease: Less lift, more speed
Ability to climb dependent on thrust: More thrust needed at higher altitudes
Climbing
Best Rate of Climb (Vy)Most altitude in least time(used on normal take-off)
Best Angle of Climb (Vx)Most altitude in leasthorizontal distance(used for obstacles)
- Longer Time- Shorter Distance
- Shorter Time- Longer Distance
Normal ClimbUsed during cruise
GlidingGliding = 3 forces (Weight, Lift, Drag)
Weight
Drag
Lift
Thrust = Horizontalcomponent of weight
Glide Reaction= Resultant of liftand drag, opposesweight
Gliding
Best Range SpeedFurthest distance per altitude lost
Best Endurance SpeedMost time in air peraltitude lost
- Longer Time- Shorter Distance
- Shorter Time- Longer Distance
Turns
Weight
Lift
Angle of Bank
Centripetal ForceHorizontal component of lift,pulls aircraft into turn
Vertical Component of LiftKeeps aircraft in air (opposes weight)
Centrifugal ForceImaginary force thatpulls aircraft outside ofturn (is really inertia)
TurnsShallow Bank- Lesser turn rate- Larger turn radius- Lower Stall Speed- Less Wing Loading
Steep Bank- Greater turn rate- Smaller turn radius- Higher Stall Speed- More Wing Loading
Turns
Faster Airspeed- Lesser turn rate- Larger turn radius
Slower Airspeed- Greater turn rate- Smaller turn radius
Same bank angle
Turns
Load Factors in TurnsAngle of bank increase= Load factor increase
60° bank = 2 G's
DangersHigh load factor= Possible structural failure(overload)
Increased load factor= Increased stall speed
Stalls• Definition: Wing can’t create enough lift to support
weight
• When Critical Angle of Attack (Stall Angle) reached, turbulent airflow surpasses laminar airflow on wing
• C of P rapidly moves towards trailing edge
• Aircraft can stall at any airspeed or attitude if critical angle of attack is exceeded
• Aircraft will stall at same indicated airspeed regardless of altitude
Factors Affecting Stall• Weight
– More weight = higher angle of attack (closer to stall angle)
• C of G– Forward = higher stall speed– Rearward = lower stall speed
• Turbulence– Upward vertical gust could cause aircraft to exceed stall angle
• Turns– Angle of bank increase = Stall speed increase (load factor/weight)
• Flaps– Increasing lifting potential of wing = Stall speed decrease
• Aircraft Condition– Snow, Frost, Ice, Dents = Disrupted laminar flow (increases stall speed)
Spins
• Definition: Auto-rotation which develops after aggravated stall
• When wing drops in stall:– Down-going wing has greater angle of attack– Wing receives less lift, drops more rapidly– Drag on down-going wing increases, further
increasing angle of attack– Wing stalls further, nose drops, auto-rotation starts
Spins
Spiral Dives
• Definition: Steep descending turn in which airplane has excessive nose down attitude
• Characteristics:– Excessive angle of bank– Rapidly increasing airspeed– Rapidly increasing rate of descent
• Structural damage can occur if airspeed increases beyond limits
Spiral Dives
Spins vs Spiral Dives
• Spin:– Aircraft stalled– Airspeed constant and low
• Spiral Dive:– Aircraft not stalled– Airspeed increasing rapidly
Airspeed Limits• Never Exceed Speed (VNE)
– Max speed airplane can be operated in smooth air
• Normal Operating Speed (VNO)– Design cruise speed, should not be intentionally exceeded
• Maneuvering Speed (VA)– Max speed at which flight controls can be fully deflected
without damage to structure
• Maximum Flaps Extended Speed (VFE)– Max speed at which full flaps can be used
Mach Number
• Ratio of speed of body to speed of sound (in air surrounding body)
• Mach 1 = Speed of sound
• Varies with air temperature, pressure and density
Next Lesson
2.5 - Theory of Flight
Flight Instruments
From the Ground Up
Chapter 2.2:
Flight Instruments
Pages 33 - 44