code0
26th Nov 2012, 14:02
Greetings! May be all the prop masters can give me a feedback on this one.
I am trying to understand the Propeller rather gas turbine or piston - Constant speed propeller positions relative to the aircraft's phases.
I have just drawn a diagram (my illustrator skills rock!) with the position of the propeller blade in different phases of the aircraft.
http://flightlevel350.tumblr.com/image/36592655596
please refer the image shown or
pls click http://flightlevel350.tumblr.com/image/36592655596 if not displayed
Simply as at a glance this looks like an alien spider from Andromeda, let me give a small insight!
The Blade airfoil shows 5 positions of the propeller. it is simply straight fwd as they are labeled. POR - Plane of Rotation and the propeller blade is moving down shown by the arrow under the airfoil.
The red arc is the Throttle positions
The Blue arc is the relative airflow
Now going one-by-one as numbered...
No1. Now, if I start the engines, the initial position of the blade is parallel to the airflow of rotation of the blade which directly meet the leading edge from the ground arrow at the bottom. Since there is no AOA, it does not produce any thrust.
No2. Now when taxiing, you set the pitch little more up (Ground Fine) so that the little increase AOA produce a little thrust fwd. Now at the take off run since because the aircraft is now moving fwd the resultant airflow will move towards up-left along the blue arc. So you move the blade angle further more to compensate the best AOA.
No.3 Now at the cruise aircraft at it's cruise speed and meet the maximum continuous airflow from the front hence the resultant relative airflow will move further up along the blue arc. To compensate this the blade angle is increased more to Coarse.
No.4 Now, boom! during in-flight engine shutdown! when the engine is shutdown the props stop rotating so there is no prop rotation induced airflow from the bottom, so only airflow is from the front, so to avoid windmilling the blade is set parallel to the incoming airflow, no AOA, hence no thrust no drag (well less drag!)
No.5 Reverse thrust!
Is this diagram perfect enough to understand the operation of a Constant speed propeller at a glance? or any suggestions or corrections?
Thanks and sorry for the lengthy post!
Cheers
Code0
I am trying to understand the Propeller rather gas turbine or piston - Constant speed propeller positions relative to the aircraft's phases.
I have just drawn a diagram (my illustrator skills rock!) with the position of the propeller blade in different phases of the aircraft.
http://flightlevel350.tumblr.com/image/36592655596
please refer the image shown or
pls click http://flightlevel350.tumblr.com/image/36592655596 if not displayed
Simply as at a glance this looks like an alien spider from Andromeda, let me give a small insight!
The Blade airfoil shows 5 positions of the propeller. it is simply straight fwd as they are labeled. POR - Plane of Rotation and the propeller blade is moving down shown by the arrow under the airfoil.
The red arc is the Throttle positions
The Blue arc is the relative airflow
Now going one-by-one as numbered...
No1. Now, if I start the engines, the initial position of the blade is parallel to the airflow of rotation of the blade which directly meet the leading edge from the ground arrow at the bottom. Since there is no AOA, it does not produce any thrust.
No2. Now when taxiing, you set the pitch little more up (Ground Fine) so that the little increase AOA produce a little thrust fwd. Now at the take off run since because the aircraft is now moving fwd the resultant airflow will move towards up-left along the blue arc. So you move the blade angle further more to compensate the best AOA.
No.3 Now at the cruise aircraft at it's cruise speed and meet the maximum continuous airflow from the front hence the resultant relative airflow will move further up along the blue arc. To compensate this the blade angle is increased more to Coarse.
No.4 Now, boom! during in-flight engine shutdown! when the engine is shutdown the props stop rotating so there is no prop rotation induced airflow from the bottom, so only airflow is from the front, so to avoid windmilling the blade is set parallel to the incoming airflow, no AOA, hence no thrust no drag (well less drag!)
No.5 Reverse thrust!
Is this diagram perfect enough to understand the operation of a Constant speed propeller at a glance? or any suggestions or corrections?
Thanks and sorry for the lengthy post!
Cheers
Code0