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Theory of Flight Airplane Axes. Reference. From the Ground Up Chapters 2.1.3, 2.1.4: The Axes of an Airplane, Stability Pages 23 – 26. Introduction. - PowerPoint PPT Presentation
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Sep 2012Lesson 2.3
Theory of Flight
Airplane Axes
Reference
From the Ground UpChapters 2.1.3, 2.1.4:The Axes of an Airplane, StabilityPages 23 – 26
Introduction• There are three axes around which an
airplane moves. Each run through the C of G, are controlled by the pilot, and are stabilized by features in the aircraft.
Outline• Airplane Axes• Balanced Controls• Stability
Airplane Axes
Longitudinal Axis(nose to tail)
Vertical (or Normal) Axis(vertical through C of G)
Lateral Axis(wing tip to wing tip)
Longitudinal Axis
Movement around: RollControlled by: AileronsAttitude: Left/Right Bank
Lateral Axis
Movement around: PitchControlled by: ElevatorAttitude: Nose Up/Down
Vertical Axis
Movement around: YawControlled by: RudderAttitude: Nose Left/Right
Balanced Controls• Control surfaces sometimes balanced to help
pilot move them and reduce flutter
• Inset Hinge/Horn Balance– Part of control surface in front of hinge– Airflow helps pilot to move it
• Mass Balance– Streamlined mass in front of control surface hinge– Reduces flutter
Balanced Controls
Horn Balance Mass Balance
Stability• Stability
– Tendency of an airplane in flight to remain in straight, level, upright flight and to return to this attitude, if displaced, without corrective action by pilot
• Inherent Stability– Stability from design features of an aircraft– Affected by weight and C of G
Stability
Straight flight disturbedby upward gust of wind
Static StabilityInitial tendency to return to original position
Dynamic StabilityOverall tendency to return tooriginal position, after seriesof oscillations
Stability
Straight flight disturbedby upward gust of wind
Positive StabilityAircraft returns to original position
Neutral StabilityAircraft continues in disturbed position
Negative Stability (AKA Instability)Aircraft moves further away fromdisturbed position
Longitudinal Stability= Pitch Stability = Stability around Lateral Axis = Corrects unwanted pitch
Horizontal StabilizerAirflow hitting stabilizer pushes aircraft back to original position if disturbed
Longitudinal StabilityCenter of GravityC of G affects nose up/down tendenciesif too far rear/forward of C of P
* Airplane must never be tail-heavy, orunable to recover from stalls
Lateral Stability• Lateral Stability = Roll Stability = Stability around Longitudinal Axis
• Dihedral– Angle that each wing makes with horizontal– If wing is displaced downwards, airplane slips into that direction
causing more airflow to down going wing and lifting it
• Keel Effect– High-wing aircraft have weight below wings acting as pendulum to
return aircraft to original position if wing displaced
• Sweepback– If aircraft is disturbed and a wing dips, lower frontward wing is
exposed to more airflow– This creates more lift in frontward wing, thus picking it up
Lateral Stability
Keel Effect:
Directional Stability= Stability around vertical/normal axis = Corrects unwanted yaw
Vertical StabilizerAirflow hitting vertical stabilizer pushes aircraft back to straight flight when disturbed
Directional StabilitySweepbackAirflow hitting one wing is more perpendicular to relative airflow, creating more drag and pushing it back
Next Lesson
2.4 - Theory of FlightFlight Performance
From the Ground UpChapters 2.1.5, 2.1.6, 2.1.7:Flight Performance Factors, AirspeedLimitations, Mach NumberPages 26 - 33