Uncontrolled copy not subject to amendment Principles of Flight

Principles of Flight Learning Outcome 5: Be able to apply the principles of flight and control to rotary wing aircraft Part 1

REVISION

Questions Name the Forces Acting on a Glider in Normal Flight. a. Force, Weight and Lift. b. Drag, Weight and Thrust. Drag, Weight and Lift. Drag, Thrust and Lift.

Questions How does a Glider Pilot Increase the Airspeed? a. Operate the Airbrakes. b. Lower the Nose by pushing the Stick Forward. Raise the Nose by pulling the Stick Back. Lower the Nose by pulling the Stick Back.

Questions A Viking Glider descends from 1640 ft (0.5 km). How far over the ground does it Travel (in still air)? a. 17.5 kms. b. 35 kms. 70 kms. 8.75 kms.

Questions When flying into a Headwind, the distance covered over the ground will: a. Be the same. b. Decrease. Increase. No change.

Propellers Objectives: Define Blade Angle and Blade Angle of Attack. Show with the aid of a diagram the Aerodynamic Forces acting on a Propeller Blade in flight. Explain Aerodynamic and Centrifugal Twisting Moments acting on a propeller. 4. Explain the effect of changing forward speed on: a. A Fixed Pitch propeller. b. A Variable Pitch propeller. (and thus the advantages of a variable pitch propeller). 5. Explain the factors causing swings on take-off for: a. A Nose-Wheel aircraft. b. A Tail- Wheel aircraft.

Propellers PICTURE MOD

Propellers (Terminology) Airflow due to rotational velocity Induced flow This is the air drawn through the disc. Relative airflow Where is AOA? (Chord line/relative airflow) Always looking for optimum AOA, which is? (4) What is other angle? (Chord line/Airflow due to rotational velocity) Quick look at AOA of blade from hub to tip to maintain 4o AOA (If prop stationary then the airflow through would be TAS)

Propellers (Terminology) Airflow due to Rotational Velocity

Propellers (Terminology) Induced Flow Airflow due to Rotational Velocity

Propellers (Terminology) Induced Flow Airflow due to Rotational Velocity Relative Airflow

Propellers (Terminology) Induced Flow Airflow due to Rotational Velocity Chord Line Relative Airflow

Propellers (Terminology) Induced Flow Airflow due to Rotational Velocity Chord Line Relative Airflow  = AofA

Propellers (Terminology) Induced Flow Airflow due to Rotational Velocity Chord Line Relative Airflow  = AofA = Blade Angle 

Propellers Blade Twist Rotational Velocity Approx 4o Angle of Attack PROPELLER BLADE TWIST What is the problem with a prop blade? What is the tip doing relative to the hub? Total Inflow

Effect of Airspeed Induced Flow Airflow due to Rotational Velocity   At Zero Airspeed

Effect of Airspeed TAS + Induced Flow = Total Inflow Airflow due to Rotational Velocity (Same) -  EFFECT OF AIRSPEED Induced flow + TAS does what to AOA? Less efficient How do we counter this?  At a Forward Airspeed

Effect of Airspeed TAS + Induced Flow = Total Inflow Airflow due to Rotational Velocity (Same) -  EFFECT OF AIRSPEED Induced flow + TAS does what to AOA? Less efficient How do we counter this?  At a Forward Airspeed Need larger  for same 

Effect of Airspeed Fine Propeller Efficiency Coarse at Max Power _ 100% Fine _ 75% Propeller Efficiency at Max Power Coarse _ 50% _ 25% True Airspeed

Pitch of Propeller Blade _ 100% Variable Pitch Fine _ 75% Propeller Efficiency at Max Power Coarse _ 50% _ 25% True Airspeed

Why a different Number of Blades? EXAMPLES OF PROPS WHY DIFFERENT? Depends on Power output of the engine

Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity 

Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity  Total Reaction

Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity  Drag Lift Total Reaction

Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity  Thrust Total Reaction

Aerodynamic Forces Total Inflow Airflow due RAF to Rotational Velocity  Thrust Prop Rotational Drag Total Reaction

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust Slow Speed Fixed Pitch Total Reaction

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust High Speed Fixed Pitch Total Reaction

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust High Speed Fixed Pitch Total Reaction

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust High Speed Fixed Pitch Total Reaction

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust High Speed Fixed Pitch NB: Rotational Drag reduced, RPM ?

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust High Speed Fixed Pitch NB: Rotational Drag reduced, RPM increases. Don’t exceed limits.

Aerodynamic Forces (Effect of High Speed) TAS+Induced Flow Airflow due to Rotational Velocity RAF  Thrust Slow Speed Variable Pitch Total Reaction

Aerodynamic Forces (Effect of High Speed) Faster TAS+Induced Flow RAF Airflow due to Rotational Velocity  Thrust (eventually reduces) High Speed Variable Pitch Total Reaction (same or possibly greater)

Windmilling Propeller Negative  TAS WINDMILLING PROPELLER Negative AOA Normally the prop will fine-off to maintain rpm (rotational drag) This will even try to drive the engine (oil failure) Could cause engine failure so: we want the blade to produce zero torque and reduce drag to a minimum How is this done? Airflow due to Rotational Velocity

Windmilling Propeller Negative  TAS TR Airflow due to Rotational Velocity

Windmilling Propeller Negative  TAS TR Negative Thrust (Drag) Airflow due to Rotational Velocity

Windmilling Propeller Negative  TAS TR Negative Rotational Drag (Driving The Propeller) Negative Thrust (Drag) Airflow due to Rotational Velocity

Windmilling Propeller Negative  TAS TR Negative Thrust (Drag) Negative Rotational Drag (Driving The Propeller) This may cause further damage, even Fire. Airflow due to Rotational Velocity

Feathered Propeller SLIDE 40 FEATHERED PROPELLER The idea is to reduce the drag Although twisted, in aggregate, blade at “Zero Lift α”. Therefore drag at minimum. Note that in Firefly/Tutor prop goes to “Fine Pitch” if engine rotating, “Coarse Pitch” if engine seized

Take-Off Swings All Aircraft: Torque Reaction means greater rolling resistance on one wheel Helical slipstream acts more on one side of the fin than the other TAKE-OFF SWINGS Prop rotating clockwise from cockpit All Aircraft: Torque Reaction means greater rolling resistance on one wheel. (Newton’s 3rd Law) More weight supported by wheel  more drag. USE MODEL Helical slipstream acts more on one side of the fin than the other Rotating clockwise from behind - Tail wheel aircraft only: Asymmetric blade effect Top picture both propeller sections are equal also distance travelled are equal. Picture exaggerated but downgoing blade has greater AOA more thrust. Distance travelled by downgoing blade greater. Gyroscopic effect When tailwheel raised all effects are zero (until rotate?) But, force applied to top of disc (gyro) then clockwise rotation will cause yaw to the left Obviously anticlockwise all reversed. Affect all aircraft on rotate? Don’t forget crosswind effect. (if yaw to left because of slipstream then get a crosswind from the right)

Take-Off Swings

Tail wheel aircraft only: Asymmetric blade effect Gyroscopic effect Take-Off Swings Tail wheel aircraft only: Asymmetric blade effect Gyroscopic effect

Take-Off Swings

Affect all aircraft on rotate? Take-Off Swings Affect all aircraft on rotate?

All Aircraft: Don’t forget crosswind effect! Take-Off Swings All Aircraft: Don’t forget crosswind effect!

Centrifugal Twisting Moment This makes it more difficult for the pitch changing mechanism when increasing pitch. Better to increase the number of blades rather than make larger Tries to fine blade off

Aerodynamic Twisting Moment Relative Airflow Total Reaction AERODYNAMIC TWISTING MOMENT Tries to increase AOA, this partially offsets CTM When windmilling in a steep dive the ATM is reversed and enhances CTM. This could prevent pitch mechanism from working Tries to coarsen blade up

Aerodynamic Twisting Moment Windmilling Total Reaction Relative Airflow Tries to fine blade off

ANY QUESTIONS?

Propellers Objectives: Define Blade Angle and Blade Angle of Attack. Show with the aid of a diagram the Aerodynamic Forces acting on a Propeller Blade in flight. Explain Aerodynamic and Centrifugal Twisting Moments acting on a propeller. 4. Explain the effect of changing forward speed on: a. A Fixed Pitch propeller. b. A Variable Pitch propeller. (and thus the advantages of a variable pitch propeller). 5. Explain the factors causing swings on take-off for: a. A Nose-Wheel aircraft. b. A Tail- Wheel aircraft.

PICTURE

Questions Blade Angle of Attack is between? a. The Chord and Relative Airflow. b. The Rotational Velocity and the Relative Airflow. The Total Reaction and the Chord. Lift and Drag.

Questions Increasing speed with a fixed pitch propeller will? a. Be more efficient. b. Reduce efficiency. Make no difference. Increase the Engine speed.

Questions The Forces trying to alter the Propeller Blade Angle of Attack are? a. ATM and CTM. b. CDM and ATM. CTM and REV. AOA and ATM.

Questions The Resultant Forces that a Propeller produce are? a. Lift and Thrust. Thrust and Propeller Rotational Drag. Drag and Total Reaction. d. Drag and Thrust.