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71 Cards in this Set
- Front
- Back
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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
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4 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
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3 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
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Translating Tendency (Drift)
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The Tendency For The Helicopter To Drift In The Direction Of Tail Rotor Thrust
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3 Counteraction
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Transmission Rigging and Cyclic Centering and Pilot Correction
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Transmission Rigging
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Main Rotor Mast Has A Built-In Tilt Opposite Tail Rotor Thrust
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Cyclic Centering
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When The Cyclis Is Centered The Disc Is Actually Slightly Tilted The Opposite Of TR Thrust
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2 Pilot Correction
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- Pilot Holds Slight Left Cyclic To Maintain Positon - Cause Left Skid To Hang Low
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Dissymmetry Of Lift definition
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Unequal Lift Accross The Rotor System
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3 Dissymmetry Of Lift characteristics
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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
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3 Blowback
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- Max Flap Up Over The Nose - Max Flap Down Over The Tail - Tip Path Tilts Rearward
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Translational Lift
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Any Horizontal Airflow Across The Rotor System
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Parasite Drag definition
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Caused By the Movement Of Any Non-Lifting Component Thru the Air
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4 Induced Drag
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1 Created By Airflow Circulation Around The Rotor Blades 2 As They Create Lift 3 High Pressure Meets Low Pressure at Blade Tips 4 More Angle of Attack equals More Induced Drag
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3 Effective Transaltional Lift definition
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1 When Translational Lift Becomes Effective 2 Occures at Airspeeds of 16 - 20 Kias3 At This Speed Rotor Blades Move Out Of Their Vortices And Are In Undisturbed Air
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4 Effects of Effective Transaltional Lift
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1 Reduced Induced Flow 2 Reduced Induced Drag 3 Increased Angle Of Attack (Angle of Attack) 4 More Lift Is Felt
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3 Effective Transaltional Lift - Helicopter Control
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1 Nose Pitch Up 2 left Yaw because Tail Rotor Becomes More Efficiant 3 Requires forward Cyclic & right Pedal
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Pendular Action
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Since The Helicopter Is Suspended By A Single Point it Is Free To Osillate either Longitudinally Or Laterally
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Profile Drag
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Drag Developed By Friction Of Airfoil Traveling Thru The Air
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2 Profile Drag Types
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Form and Skin Friction
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3 Form Drag
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1 Turbulent Wake 2 Caused By The Seperation Of Airflow From A Stucture 3 Caused By Size and Shape (Form)
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Skin Friction
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Surface Roughness
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Induced Flow
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Large Amounts Of Air Being Sucked Down Thru The Rotor System
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Gyroscopic Procession
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1 The Resultant Action Or Deflection Of A Spinning Object 2 When A Force Is Applied To It 3 Will Register That Force 90 Degrees After It Has Been Applied 4 In It's Plane Of Rotation
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Compensate For Gyroscopic Procession (Pitch Horns)
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By Applying The Control Input 90 Degrees Prior To The Desired Output
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2 Transverse Flow occurs As
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The Helicopter Accelerates In forward Flight
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2 During Transverse Flow Induced Flow at the Rotor Discs
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1 Induced Flow (IF) at The Front Of The Disc - Is Reduced To Near Zero 2 Induced Flow (IF) at The Rear Of The Disc - Remains The Same
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3 Transverse Flow characteristics
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1 This Aerodynamic Increases In Angle of Attack at The Front Of The Disc 2 Causes The Blades To Flap Up Trying To Reduce Angle of Attack 3 The Opposite Takes Place At The Rear Of The Disc
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Because Of Gyroscopic Procession - The Max Displacement (Flap) Of The Rotor Blades Will Occur
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90 Degrees Later In The Plane Of Rotation
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2 Because Of Gyroscopic Procession Max Flap will be
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1 Up at left Side Of Disc 2 Down at right Side Of Disc
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Gyroscopic Procession Max Flap will result in a
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right Rolling Tendency
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8 In-Ground Effect
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1 - When Within One Rotor Diameter Of The Surface 2 - 2 Ft Skid Clearence (R22) 3 - As Airflow Contacts The Airfoil It Is Deflected Downward 4 - In the Form Of Downwash 5 - As The Airflow Contacts The Surface It Is Impeded By Surface Friction 6 - The Downwash Stacks Up On Itself 7 - Catching Blade Tip Vortices And Pushing Them Outward 8 - Best In A NO Wind Condition Over A Hard Surface
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5 Out-Of-Ground Effect
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1 - As Helicopter Gains Altitude With No forward Airspeed 2 - Induced Flow (IF) Is No Longer Restricted By Surface Friction 3 - There Is A Decrease In Outward Airflow 4 - Resulting In Blade Tip Vortex Increase 5 - Highter Pitch Angle Is Required For The Same Amount Of Lift
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torque
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tendency of the helicopter to turn in the direction opposite the main rotor direction
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tip-path-plane
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The imaginary circular plane outlined by the rotor blade tips as they make a cycle of rotation
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aircraft pitch
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movement about helicopter's lateral (side-to-side axis) tipping helicopter forward or aft
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aircraft roll
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movement about helicopter's longitudinal axis (forward/aft axis) tipping helicopter to either side
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angle of attack
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angle between chord line and relative wind
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pitch angle
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angle between chord line and ref. plane containing rotor hub
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magnus effect
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pressure differential created by circulation around an object (e.g. a rotating cylinder)
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bernoulli's principle
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pressure differential on the air foil due to constriction of space (in a constricted tube)
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steady-state-flight
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when an aircraft is in straight-level unaccelerated flight and all forces are in balance
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disc loading
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ratio of weight to the total main rotor disc area
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rotor disc area
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area swept by the blades of a rotor
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solidity ratio
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ratio of the total rotor blade area to the rotor disc area
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rotor blade area
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combined area of all the main rotor blades
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aircraft yaw
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movement of the helicopter about its vertical axis
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drag
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force that resists the movement of a helicopter through the air
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profile drag
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drag from the frictional resistance of the blades passing through the air
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3 profile drag characteristics
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1 - does not change much w/ change of angle of attack 2 - increases moderately with airspeed
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induced drag
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drag from the airflow circulation around the rotor blade as it creates lift
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2 induced drag characteristics
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1 - high pressure air and low pressure air meet creating vortices at the blade tips creating a downwash. This inclines total lift aft. 2 - high with high angle of attack (thus high at low airspeeds)
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parasite drag
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drag created by friction of nonlifting components of the aircraft
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major cause of drag at higher airspeeds
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parasite drag
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total drag
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sum of profile induced and parasite drag
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L/Dmax refers to the point
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where the lift-to-drag ratio is greatest
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translating tendency or drift
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tendency of single-rotor helicopter to move in the same direction as antitorque rotor thrust
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fuselage
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the central body of an aircraft
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coriolis effect
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the tendency of a rotor blade to increase or decrease its velocity in its plane of rotation when the center of mass moves closer or further from the axis of rotation
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underslung
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a rotor hub that rotates below the top of the mast as on semirigid rotor systems
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ground effect
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a usually beneficial influence on rotorcraft performance that occurs while flying close to the ground. it results from a reduction in upwash downwas and bladetip vortices which provide a corresponding decrease in induced drag
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gyroscopic precession
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an inherent quality of rotating bodies which causes an applied force to be manifested 90 degrees in the direction of rotation from the point where the force is applied
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translational lift
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the additional lift obtained when entering forward flight due to the increased efficiency of the rotor system - the rotor moves out of its vortices - the airflow is also more horizontal which reduces induced flow and drag with a corresponding increase in angle of attack and lift
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rotational velocity
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the component of relative wind produced by rotation of the rotor blades
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induced flow
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the component of air flowing vertically through the rotor system resulting from the production of lift
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resultant
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relative wind airflow from rotation that is modified by induced flow
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transverse-flow effect
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a condition of increased drag and drecreased lift in the aft portion of the rotor disc caused by the air having a greater induced velocity and angle in the aft portion of the disc
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dissymmetry of lift
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the unequal lift across the rotor disc resulting from the difference in the velocity of air over the advancing and retreating blades
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blowback
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the tendency of the rotor disc to tilt aft in forward flight as a result of flapping
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centripetal force
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the force that attracts a body toward its axis of rotation
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centrifugal force
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the opposite of centripetal force
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