Basic Aerodynamics
Terms
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- 5 Factors Affecting Lift
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1. Surface Area
2. Angle Of Attack
3. Velocity Of Airflow
4. Air Density
5. Blade Stall - Coriolis Effect
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- Blade Acceleration & Deceleration
- As CenterMass (CM) Moves Closer To The Axis Of Rotation There Is An Increase In Velocity & ViseVersa
- Figure Skater Analogy
- Fixed By Underslinging - Bernoulli's Principle
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- If We Increase Velocity, We Decrease Pressure
- The Venturi Effect
- Air Must Move Faster Accross The Top Of The Airfoil To Rejoin Air On The Bottom Of The Airfoil - Drag
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- The Force That Resists Movement Of Objects Thru The Air
- Byproduct Of Lift
- Always Parallel To Relative Wind (RW) - Coning
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- The Upward Sweep Of The Rotor Blades In Their Plane Of Rotation
- Caused By Centrifugal Force (CF) & Lift
Coning Hinge:
- Causes Less Stress On The Rotor Blades - Translating Tendency (Drift)
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- The Tendency For The Helicopter To Drift In The Direction Of Tail Rotor Thrust
Counteraction:
1. Transmission Rigging
- Main Rotor Mast Has A Built-In Tilt Opposite Tail Rotor Thrust
2. Cyclic Centering
- When The Cyclis Is Centered, The Disc Is Actually Slightly Tilted The Opposite Of TR Thrust
3. Pilot Correction (R22)
- Pilot Holds Slight Lt Cyclic To Maintain Positon
- Cause Lt Skid To Hang Low - Dissymmetry Of Lift
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- Unequal Lift Accross The Rotor System
- As Heli Moves Thru The Air The Advancing & Retreating Sides Of The Rotor Disc Feel Different Amounts Of Lift
- If This Were Allowed To Persist, The Helicopter Would Roll Left
- In Reality The Blades Are Allowed To Flap
- Via The Teetering Hindge
- As A Unit
- To Equality
Note:
Blowback:
- Max Flap Up Over The Nose
- Max Flap Down Over The Tail
- Tip Path Tilts Rearward - Translational Lift
- - Any Horizontal Airflow Across The Rotor System
- Parasite Drag
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- Caused By the Movement Of Any "Non-Lifting" Component Thru the Air
Example:
- Cabin
- Tail Boom
- Landing Gear
- ETC... - Pendular Action
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- Since The Helicopter Is Suspended By A Single Point
- It Is Free To Osillate
- Either Longitudinally Or Laterally
Note:
- Keep Control Movements To A Minimum - Profile Drag
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- Drag Developed By Friction Of Airfoil Traveling Thru The Air
2 Types:
1. Form Drag
- Turbulent Wake
- Caused By The Seperation Of Airflow From A Stucture
- Caused By Size & Shape (Form)
2. Skin Friction
- Surface Roughness - Induced Flow
- - Large Amounts Of Air Being Sucked Down Thru The Rotor System
- Gyroscopic Procession
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- The Resultant Action Or Deflection Of A Spinning Object
- When A Force Is Applied To It
- Will Register That Force 90 Degrees After It Has Been Applied
- In It's Plane Of Rotation
Note:
Pitch Horns:
- Compensate For G.P. By Applying The Control Input 90 Degrees Prior To The Desired Output - In-Ground Effect
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- Benificail Influence On Helicopter Performance
- When Within One Rotor Diameter Of The Surface
- 2 Ft Skid Clearence (R22)
- As Airflow Contacts The Airfoil It Is Deflected Downward
- In the Form Of Downwash
- As The Airflow Contacts The Surface It Is Impeded By Surface Friction
- The Downwash Stacks Up On Itself
- Catching Blade Tip Vortices And Pushing Them Outward
Note:
- Best In A NO Wind Condition Over A Hard Surface - Out-Of-Ground Effect
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- As Helicopter Gains Altitude With No FWD Airspeed
- Induced Flow (IF) Is No Longer Restricted By Surface Friction
- There Is A Decrease In Outward Airflow
- Resulting In Blade Tip Vortex Increase
- Highter Pitch Angle Is Required For The Same Amount Of Lift