ConstantSpeedPropPart2

constant speed propeller part 2 the mechanics of a constant speed propeller hi my name is Cora Valerie and I blog at expert a beat or calm this is the second in a series of videos looking at constant speed propellers in part 1 We discussed the purpose and operation of the constant speed propeller today we are going to learn the mechanics of how the propeller works, if you have not done so already, I invite you to watch part 1 of this video. There will be links to where you can find that video or you can go. to expert aviator communication and find it there.

A transcript of this video along with links to suggested reading is also available as resources used in this video and you may find that it also had expert aviator communication so no need to take notes, sit back, relax and enjoy. the show why constant speed propeller as a review of part one the constant speed propeller is a device that allows us to efficiently convert engine power into thrust remember that a constant speed propeller attempts to keep the engine at constant rpm by adjusting the Blade angle and therefore propeller pitch Propeller pitch is the distance in inches that the propeller would pass through the air in one rotation.

When we change the angle of the blade, we change the pitch of the propeller and we use the term controllable pitch propeller, therefore, when we change the angle of the blade, we are changing the distance the propeller would spin through the air and we are controlling the pitch of the propeller, that's why we call them controllable pitch propellers. It is really a simple operation to control the RPM of the engine if you just think about the angle of the blade and the results, by changing the angle of the blade using the propeller control on the airplane first we have an engine that converts its power to turn a large shaft that is attached to the propeller.

This twisting or rotational force is called torque. When you open a jar of peanut butter you are converting the energy of your muscles into rotational or twisting force. The amount of torque depends on the size of your muscles and the tools you use to open it. a jar, such as a plastic jar opener if you have a very large jar. of peanut butter, you may need to use more torque to open the jar. Likewise, if you have a large propeller blade angle, you will need a much greater force to rotate the propeller through the air, which produces resistance. similar to the one on the cover. in the jug we can't just see the air with our eyes, but we know it's there if you reduce the blade angle, there is less drag on the propeller, less torque is needed and the engine speed RPM will increase slightly now if you increase the blade angle the amount of torque needed increases and the propeller decelerates, causing the engine to slow down or decrease engine RPM.

The propeller in flight constantly changes pitch to maintain the selected rpm setting that we choose for our light conditions, for example we would want a low pitch setting so that the engine can produce the highest rpm during takeoff and turnaround, but In cruise flight we would like to set the propeller pitch higher, thus reducing the RPM, thus reducing fuel consumption and decreasing the amount of slip, and for a description of slip, you can see part 1 of the series on propellers constant speed or go to the website. Okay, change the propeller pitch to do this. I'm going to use one of my favorite free McCawley propeller systems brochures.

There is a link to this brochure in Calm. and I highly recommend that you save it for future reference. Another great reference is Rob Machado's Private Pilot's Manual, where Ron's wonderful illustrations make complex topics easy to understand. The propeller uses a device called a governor to maintain engine speed by varying the angle of the blade. and propeller pitch A governor is a mechanical device but it controls the speed of the engine by varying the pitch of the propeller to match the selected rpm before we learn how this governor changes the angle of the propeller blades and therefore Therefore, the step we need first Learn how to move the propeller angles as well to further simplify our discussion, since changing the blade angle directly changes the pitch.

I will use the term pitch to mean changing the angle of the blade to stay or the discussion again every time we change the angle of the propeller blade we are changing the pitch of the propeller, furthermore we will discuss the propellers used in most general aviation aircraft that are not flagged. Look for a discussion on fully flagged propellers in an upcoming episode so let's first look at the forces acting on the propeller and our Constant Velocity Propeller as the engine spins the propellers since it is not fixed there is a force of torsion called centrifugal torque, this causes the propeller, this twisting force to go at a low pitch if it was not attached to anything else, but the propeller is attached to something. which allows us to move it and overcome this torque to move the propeller blades we connect each blade to a piston inside a dome that contains oil the link between the piston and the propeller is called a driven link it is fixed to each end using pins when the piston moves the driven link and then moves the propeller to increase the propeller pitch.

Oil is pumped into the dome creating more pressure which then moves the propeller now to slow the pitch. The oil is simply drained, furthermore there are two forces that move the piston towards the front of the dome spring resistance and centrifugal torque of the propeller the first force is produced by a spring attached to the piston the spring is designed to push the piston towards the dome and therefore forces the propeller to a low pitch setting the second The force is called apology, caused by the rotating propeller, the rotating propeller causes a torque of the moving propeller itself the piston towards the front of the dome and therefore when oil is pumped into the dome, it moves the piston away from the front. of the dome I am overcoming these two forces one force is a spring the second force is the centrifugal torque of the rotating propeller when the desired rpm setting of the engine has been reached a state of equilibrium is reached in which no oil is pumped The oil is drained from the propeller if any flight condition changes this balance, such as if we push the nose down, increase airspeed, the engine RPM will begin to increase and the governor will cause the system to pump more oil into the engine. the dome, thus increasing the pace.

Propeller Understanding the mechanics of a constant speed propeller is easy once you can understand the basics of how the propeller works. I have found that most people need to review this meat material several times to fully understand the concepts. I invite you to review this video again and Imagine yourself using the propeller control system in the next section. I will analyze the system that pumps the oil to the dome and how the propeller governor works. I will also discuss some abnormal system operations, such as what will happen if it loses pressure or the engine stops running.

I will also talk about cold weather operations and engine operation before takeoff. I hope you enjoyed this video and it helped you understand how a constant speed propeller works. I hope to see you again soon and look for another video on The mechanics of the constant speed propeller ensure your safety.