Transcript Flight Performance

Theory of Flight
Flight Performance
Lesson 2.4
Sep 2012
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, propeller
rotates 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 Thrust
At high angles of attack and high power setting (i.e. take-off), descending
propeller blade has greater angle of attack than ascending blade
Right side of prop produces more thrust then left side
Result: Yaw to left
Correction: Use right rudder
Precession
Spinning propeller acts like a gyroscope: When force applied to spinning
gyro, force acts as if it was 90° in direction of rotation
Result:
Quick Nose-Up = Sharp yaw right
Quick Nose-Down = Sharp yaw left
Correction: 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 of
fin (pushing it right)
Result: Constant yaw to left (depending on power setting)
Correction: Offset fin, trim, right rudder
Climbing
Ability to climb dependent on thrust: More thrust needed at higher altitudes
Thrust
Lift
Angle of Attack
Increase: More lift, less speed
Decrease: Less lift, more speed
Drag
Weight
Climbing
Best Angle of Climb (Vx)
Most altitude in least
horizontal distance
(used for obstacles)
- Longer Time
- Shorter Distance
- Shorter Time
- Longer Distance
Best Rate of Climb (Vy)
Most altitude in least time
(used on normal take-off)
Normal Climb
Used during cruise
Gliding
Gliding = 3 forces (Weight, Lift, Drag)
Lift
Glide Reaction
= Resultant of lift
and drag, opposes
weight
Drag
Thrust = Horizontal
component of weight
Weight
Gliding
Best Range Speed
Furthest distance per altitude lost
Best Endurance Speed
Most time in air per
altitude lost
- Longer Time
- Shorter Distance
- Shorter Time
- Longer Distance
Turns
Vertical Component of Lift
Keeps aircraft in air (opposes weight)
Lift
Centrifugal Force
Imaginary force that
pulls aircraft outside of
turn (is really inertia)
Weight
Centripetal Force
Horizontal component of lift,
pulls aircraft into turn
Angle of Bank
Turns
Shallow 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 Turns
Angle of bank increase
= Load factor increase
60° bank = 2 G's
Dangers
High 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