17.01.2009, 20:36
There are four common families of propeller,
They are fixed-pitch, ground-adjustable, inflight-adjustable and constant-speed. The last two are both examples of variable-pitch propellers.
The term Low and High were used in what I wrote above:
A (fine pitch propeller) has a ( low ) blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A (coarse pitch) propeller has a ( high ) blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is new>
The load on the engine is the propeller torque.
When the aircraft is stationary, with the engine throttle wide open, the propeller torque and the static thrust generated,(i.e. the efficiency of the engine and the propeller combination) depend on the propeller pitch.
If the pitch is zero or slightly negative, the static thrust will be zero and the propeller torque will be very low so that the engine will race — overspeed — and lose power because of inefficient cylinder charging, etc.
If the pitch is 'fine' ( low ), the propeller will generate near maximum static thrust and sufficient torque to maintain (high engine rpm), thus delivering ample power to the propeller shaft. This is the ideal situation to get the aircraft rolling for take-off and climb-out.
If the pitch is very 'coarse' ( high ), then static thrust is low but propeller torque is very high,
which will slow the engine. This is the worst situation for take-off ,
the aircraft will move forward sluggishly and, most likely, will never reach take-off speed.
I see how people come to refer to low/high
I still think it is a confusing term compared to fine or coarse, just my opinion though...
I have scoured through some more books at home here ,
in all the books I have the term Fine /Coarse is used ,with some only refering to low/high after the term fine or coarse is used. Most topics only fine or coarse are mentioned when describing pitch.
The automobile analogy>
A (fine pitch) propeller has a (low blade angle), will try to move forward a small distance through the air with each rotation, and will take a ('small' bite of the air). It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a ( low gear ) in your automobile.
Stick it Low and go.....Take-off
A (coarse pitch) propeller has a (high blade angle), will try to advance a long distance through the air with each rotation, and will take a(big 'bite' of the air). It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is like having a ( high gear ) in your automobile.
Get up there and stick it in High gear and cruise Man...
In escense the term low and high are in referance to a blade angle,
of a fine or a coarse adjustment to the pitch of the prop.
In my mind anyway.....but it went through the 60's and 70's Man..... 8)
Thanks for the read ,it's all been interesting
Everything both of us posted is correct....it's just confusing lol
It's all good Man...
Easy
They are fixed-pitch, ground-adjustable, inflight-adjustable and constant-speed. The last two are both examples of variable-pitch propellers.
The term Low and High were used in what I wrote above:
A (fine pitch propeller) has a ( low ) blade angle, will try to move forward a small distance through the air with each rotation, and will take a 'small' bite of the air. It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a low gear in your automobile.
A (coarse pitch) propeller has a ( high ) blade angle, will try to advance a long distance through the air with each rotation, and will take a big 'bite' of the air. It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is new>
The load on the engine is the propeller torque.
When the aircraft is stationary, with the engine throttle wide open, the propeller torque and the static thrust generated,(i.e. the efficiency of the engine and the propeller combination) depend on the propeller pitch.
If the pitch is zero or slightly negative, the static thrust will be zero and the propeller torque will be very low so that the engine will race — overspeed — and lose power because of inefficient cylinder charging, etc.
If the pitch is 'fine' ( low ), the propeller will generate near maximum static thrust and sufficient torque to maintain (high engine rpm), thus delivering ample power to the propeller shaft. This is the ideal situation to get the aircraft rolling for take-off and climb-out.
If the pitch is very 'coarse' ( high ), then static thrust is low but propeller torque is very high,
which will slow the engine. This is the worst situation for take-off ,
the aircraft will move forward sluggishly and, most likely, will never reach take-off speed.
I see how people come to refer to low/high
I still think it is a confusing term compared to fine or coarse, just my opinion though...
I have scoured through some more books at home here ,
in all the books I have the term Fine /Coarse is used ,with some only refering to low/high after the term fine or coarse is used. Most topics only fine or coarse are mentioned when describing pitch.
The automobile analogy>
A (fine pitch) propeller has a (low blade angle), will try to move forward a small distance through the air with each rotation, and will take a ('small' bite of the air). It requires relatively low power to rotate, allowing high propeller speed to be developed, but achieving only limited airspeed. This is like having a ( low gear ) in your automobile.
Stick it Low and go.....Take-off
A (coarse pitch) propeller has a (high blade angle), will try to advance a long distance through the air with each rotation, and will take a(big 'bite' of the air). It requires greater power to rotate, limiting the propeller speed that can be developed, but achieving high airspeeds.
This is like having a ( high gear ) in your automobile.
Get up there and stick it in High gear and cruise Man...
In escense the term low and high are in referance to a blade angle,
of a fine or a coarse adjustment to the pitch of the prop.
In my mind anyway.....but it went through the 60's and 70's Man..... 8)
Thanks for the read ,it's all been interesting
Everything both of us posted is correct....it's just confusing lol
It's all good Man...
Easy