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PROPELLER SYSTEM 1st - Look at how lift is generated
Then see how it applies to propellers
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How lift is generated PROPELLER SYSTEM
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Pressure Decreases here Pressure Remains Constant here
In this example In this direction Pressure Decreases here Pressure Remains Constant here The result is LIFT How lift is generated PROPELLER SYSTEM
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Greater Pressure Decrease here Small Pressure Increase here
The result is MORE LIFT Small Pressure Increase here How lift is increased PROPELLER SYSTEM
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The difference in direction of travel and aerofoil incline is called:-
The ANGLE of ATTACK How lift is increased PROPELLER SYSTEM
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How does lift apply to PROPELLORS?
On Propellers, LIFT is called THRUST And propeller Blades work the same way as aircraft wings When a propeller spins and the aircraft moves forward, the tips of the propeller blades move in a ‘corkscrew’ path This path is called a HELIX PROPELLER SYSTEM
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How the HELIX ANGLE is generated
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
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How the blade tip travel produces the HELIX ANGLE
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How the blade tip travel produces the HELIX ANGLE
Rotation - Number of Rotations per Minute Forward Speed - Distance Travelled over One Minute How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the blade tip travel produces the HELIX ANGLE
Forward Speed RPM How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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How the HELIX ANGLE is changed by engine rpm and forward speed
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Changes in FORWARD SPEED and RPM will change the Helix Angle
How an increase in RPM changes the Helix Angle Faster RPM RPM Forward Speed How the blade tip travel produces the HELIX ANGLE PROPELLER SYSTEM
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Changes in FORWARD SPEED and RPM will change the Helix Angle
Faster Forward Speed RPM Forward Speed How an increase in FORWARD SPEED changes the HELIX ANGLE PROPELLER SYSTEM
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Direction of blade through the air with forward speed
Let’s take a closer look at the blade aerofoil and the Helix Angle and thrust (lift) generation Direction of rotation Direction of blade through the air with forward speed This is the Helix Angle If the Helix Angle changes, then we need to change the blade angle. This is the Angle of Attack Remember (from the comparison with the aircraft wing), the optimum Angle of Attack is required to maintain most efficient thrust generation. PROPELLER SYSTEM
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Mechanical STOPS and blade angles
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All propeller blades are actuated by the same mechanical linkage
Actuating Lever Sliding Piston Propeller Blade Fine Pitch Direction of Rotation Direction of Flight Coarse Pitch Actuating Link Hard Stops All propeller blades are actuated by the same mechanical linkage PROPELLER SYSTEM
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The blade angle changes through 90deg with piston travel
Direction Of Rotation Coarse pitch Or ‘Feathered’ Fine pitch Maximum resistance to forward speed Minimum resistance to forward speed Maximum resistance to rotation Minimum resistance to rotation At this hard stop the blade is in this position At this hard stop the blade is in this position Piston travels between ‘hard’ stops Note: - blade angle is relative to piston travel PROPELLER SYSTEM
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Zero pitch – or Ground Fine Pitch
Good for:- Maximum resistance to forward speed Easier Starting of engine Running engine with no/minimal thrust Direction of Rotation High drag – braking effect on ground Minimum resistance to rotation Bad for:- In-flight – loss of control In-flight engine failure – loss of control and engine disintegration Direction of travel Importance of set blade angle PROPELLER SYSTEM
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Maximum pitch – or Feathered Minimum resistance to forward speed
Bad for:- Starting of engine Could cause engine burn-out if running Direction of Rotation Low drag – NO braking effect on ground Maximum resistance to rotation Good for:- In-flight – loss of control In-flight engine failure – control maintained and engine stops rotating minimizing damage Direction of travel Importance of set blade angle PROPELLER SYSTEM
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Reverse Pitch PROPELLER SYSTEM
Used for:- High drag – high braking effect on ground Air pushed forward giving reverse thrust Direction of Rotation Usually for military aircraft only Minimal resistance to rotation Bad for:- In-flight – loss of forward speed, aircraft stalls In-flight engine failure – loss of control and reverse rotation increasing engine disintegration Direction of travel Importance of set blade angle PROPELLER SYSTEM
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Flight Fine and Cruise Pitch PROPELLER SYSTEM
Flight Fine pitch Used for:- Low drag on final approach Direction of Rotation Cruise pitch Used for:- In-flight descent – faster forward speed than final approach Both give minimal drag at low power settings Direction of travel Importance of set blade angle PROPELLER SYSTEM
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Blade Twist
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PROPELLER SYSTEM Typical Blade Typical 3 Blade Prop Blade Twist ROOT
TIP MID-SPAN COARSE ANGLE MEDIUM ANGLE FINE ANGLE BLADE ANGLE RELATIVE TO DISTANCE (AND THEREFORE SPEED) TRAVELLED BY ROOT, MID-SPAN AND TIP DISTANCE TRAVELLED BY ROOT, MID-SPAN AND TIP THICK FOR STRENGTH THINNER FOR STRENGTH AND THRUST THIN FOR THRUST Blade Twist PROPELLER SYSTEM
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