Variable Pitch Propeller / Constant Speed Propeller

5 Answers

1. 
   

   
   

   Brian on Oct 29, 2011

   A variable pitch is a propeller that can change pitch but RPM will act just like that on a fixed pitch propeller (i.e. go up with throttle increase or airspeed increase). Typically pitch varies between two or three setting for climb/cruise or climb/cruise/feather in the case of the motor glider I flew. A constant speed propeller will hold RPM constant, within system limitations, regardless of power or airspeed changes.
    
   Since RPM is held constant in a constant speed system it is unreliable for noting power changes. Instead, engine power is identified by a manifold pressure guage; this is changed with the throttle. RPM is controlled by a propeller controller. This propeller handle is usually identified with a blue handle between the throttle and mixture handles.
    
   For further information on the intricacies of a constant speed system see this link: http://www.avweb.com/news/pelican/182081-1.html

   +2 Votes 2 Votes  0 Votes

2. 
   

   
   

   Nathan Parker on Oct 29, 2011

   “In a Constant Speed Propeller , the Throttle makes the Blade – Pitch Adjustments and the Prop Lever controls just the MAP which is the output power of the engine .”
    
   Not exactly.  The blade angle setting is, strictly speaking, outside of the control of the pilot.  Instead, he sets a desired RPM on the propeller control.  The blade angle will change automatically to achieve that RPM.  Increasing the throttle setting will tend to increase the RPM, so the blade angle will increase automatically in order to prevent that.
    
   To determine the actual power output of the engine, you need to know the manifold pressure, RPM, and mixture setting.

   +4 Votes 5 Votes  1 Votes

3. Best Answer
   
   

   
   

   John D. Collins on Oct 29, 2011

   A variable pitch propeller is usually associate with a propeller system where the pilot is able to adjust the pitch of the propeller. The early Bonanzas had an electric prop that the pilot could control the pitch by turning a control (a rheostat) that would move the pitch of the propeller.  The pilot would use one pitch for climb and a separate one for cruise.  The speed of the propeller was controlled by the combination of the pitch setting and the throttle.  A constant speed propeller is a variable pitch propeller that has a governor that adjusts the pitch of the propeller to maintain a particular RPM.  In the case of the early electric propeller for the Bonanza, a governor was added to accomplish this.  In this case, the pilot set an RPM and the governor would manage the pitch to achieve the desired RPM.  Later on, props were designed to be controlled by oil pressure that was in turn controlled by a governor.  Again the governor would adjust the oil pressure to hold a constant RPM set by the pilot thru a prop control.
    
   With a constant speed prop system, the pilot controls the power by a combination of the throttle and prop control positions.  To know the power of such a system, you need to know the manifold pressure, the RPM, the altitude, and the temperature when the engine is operated rich of peak EGT, and to a lessor extent the mixture setting.  The POH usually lists the power settings in tabular form where all of the above parameters are included.  If the engine is capable of running smoothly when lean of peak, fuel flow determines power and this is true over a wide range of manifold pressures and RPM’s. 

   +19 Votes 21 Votes  2 Votes

4. 
   

   
   

   Earl Kessler on Oct 30, 2011

   Another form of variable pitch prop is the ground adjustable unit.  I have flown several light sport airplanes that have this attribute.  Flying from a high altitude field in the west, it is typical to use more of a climb setting than a cruise setting since we are much more prone to the effects of density altitude and have tall mountains to clear.  The props on Flight Designs with Rotax engines are 3 bladed and ground adjustable.  FAA rules for LSA dictate that these only be adjustable while not in flight.

   +2 Votes 3 Votes  1 Votes

5. 
   

   
   

   N Wellstead on Mar 26, 2013

   In a normaly aspirated constant speed prop aircraft
   1- the throttle (black lever) controls the MAP
   2- the prop pitch ( blue lever) controls the RPM
   Take off-apply full power until established in a

   climb
   First Reduce the throttle lever untill the MAP reads 25
   Reduce the prop pitch lever untill the RPM reads 25
   25 25 is known as running square
   Keep pushing the throttle back in as you climb to maintain 25 MAP

   Cruise
   First Reduce the throttle lever to read the recommended setting as per the POH (23-24) MAP
   Reduce the prop lever to read the recommended setting as per the POH (24) RPM

   Descent
   Reduce the throttle lever and keep reducing the throttle lever to keep the
   MAP at or under the RPM ( 25 25 ) or ( 24 25 )
   Push the prop lever up to full on short finals
   DO NOT allow the MAP to go over the RPM ( 26 25)
   This is known as running over square and this can do nasty things to your expensive engine.

   Rule of thumb (KISS)
   Throttle forward (Full Power)
   Prop lever forward (full Fine)
   Black MAP and blue RPM
   The RWY is BLACK and is under the BLUE SKY
   In other words keep the MAP at or under the RPM

   Good luck Happy flying and
   Do’nt forget to put the wheels down
   Noel Wellstead

   +11 Votes 16 Votes  5 Votes