Notes

Outline

Cover

References

Aerodynamics

Airfoils

Airfoil Sections

Airfoil Section Shapes Airfoil Shapes  Small Center of Pressure Shift Less Lift, Less Desirable Stall Characteristics Asymmetrical Larger Center of Pressure Shift Better Lift/Drag Ratios and Stall Characteristics

CP Symmetrical Airfoil

CP Asymmetrical Airfoil

Airfoil Layout

Airfoil Terminology

Airfoil Terminology (cont)

Forces on Airfoils

Results of Forces

Lift Theories

Equal Transit Time

Equal Transit Time (cont1)

Equal Transit Time (cont2)

Reaction Lift

Reaction Lift (cont1)

Reaction Lift (cont2)

Suction Lift

Suction Lift (cont1)

Suction Lift (cont2)

Suction Lift (cont3)

Suction Lift (cont4)

Bernoulli's Theorem

Circulation Lift

Magnus Effect

Magnus Effect (cont)

Combination Theory

Drag

Drag (cont)

Production of Drag

Observations About Drag

Production of Lift

Production of Lift 2

Stall

Lift vs Drag

Lift Coefficient

Power Required

Observations About Lift & Drag

3D Airfoil

Trailing Edge Vortices

Observation About Vortices

Helicopter Flight Forces

The 4 Forces

Hovering Flight

Collective & Angle Of Attack

Gyroscopic Precession

Effect of Rotation

Coning and Flapping

Blade Coning

Coriolis Force Conservation of Angular Momentum Causes the Blade to Speed Up  (or Slow Down) It’s Angular Velocity This force is known as:  Coriolis Effect – The tendency of a mass to increase or decrease its angular velocity when its radius of rotation is shortened or lengthened To Reduce Stress and Avoid Bending A Vertical (Lead/Lag) Hinge is Added to the Hub & Blade A Lead/Lag Damper is Added to the Hub and Blade to Reduce Oscillation and Keep Blades in Phase An Underslung Hinge May Be Used on a Semi-Rigid Rotor System

Tail Rotor Contibution

Tail Rotor Effects

Directional Control

Pilot's Primary Controls

Primary Controls

Cyclic Pitch

Cyclic Pitch & Hunting

Collective Pitch

Hover Airflow

Ground Effect

Ground Effect (cont) Induced Flow is Restricted, Greater Lift Vector Lower Blade Angle = Less Induced Drag Increase in Recirculation Flow Tip Vortices Reduced – Larger Portion of Blades Producing Lift

Hover IGE

Hovering OGE Induced Flow is Not Restricted Tip Vortices Increase Recirculation is drastically reduced More Pitch is Required to Obtain Required Angle of Attack, Creating More Drag, Increasing Power Required

Hover OGE (cont)

Forward Flight

Acceleration & Climb

Dissymmetry of Lift

Transverse Flow

Transverse Flow Theory 1

Transverse Flow Theory 2

Transverse Flow Theory 3

Transverse Flow Theory 4

Realities Of Transverse Flow Recirculation Flow is Required to Reduce the Power Required. As the Aircraft Moves Forward, the Rotor Wash (Recirculation) Moves Through the Fuselage of the Aircraft and the Retreating Side Moves Into Its Shedded Tip Vortex. As the Recirculation is Disturbed or Destroyed by the Airframe & the Tip Vortex,  Less Resultant Lift is Created by the Rear Left Quartering Portion of the Disk. A Short Duration Roll is Induced that Occurs 90 Degrees Later in the Plane of Rotation (Precession). Vibrations are Felt in the Airframe Due to the Unequal Lift and Flow Interference. The Roll and Vibrations Disappear as the Recirculation Flow Elongates Past the Rear of the Airframe. The Pitchup of the Nose is Likely a combination of the High Pressure Flow Field of the Retreating Side Crossing Over the Horizontal Tail and Dynamic Pressure Effects on the Rear Portion of the Rotor Disc.

Translational Lift

Deceleration & Rearward Flight

Turning Flight

Vibrations

Stability

Stability & Control Coupling

Stability Augmentation