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