A Beginner’s Guide to Propeller Terminology

Remember back to school days when you had vocabulary tests? Most students cringed at all those words where you had to memorize the spelling and definition. Quick: what is the definition of a variable pitch propeller?

All joking aside, in the flying world, it is essential to have a basic understanding of the terminology used in the industry.

At Stockton Propeller, we have a passion for flying and everything that makes it happen. Call us if you have any governor, or metal and composite propeller, overhaul or maintenance needs.

Why learn terminology?

While it might seem somewhat elementary, understanding the basic terminology is essential to understanding the field. When you interact with other pilots or artisans in the aviation world, it is critical everyone is using the same language.

However, one of the best reasons to learn basic terminology is the ease of business. Imagine taking your machine to a mechanic and finding out you speak different languages! It can feel similar to that when both parties don’t adhere to the same definitions.

When you need maintenance or repairs, it is much more convenient when you understand everything the mechanic is talking about, and you can clearly describe the issues or problems you have noticed.

If you need another reason, how about the joy of learning new things? A lifelong student is always learning up-to-date and helpful information. You never know when you will learn something that will be important down the road.

Now, on to defining some terms and learning a little more about them.

Propeller terminology word cloud

Major propeller components

Hub: The main housing that attaches to the engine output shaft and holds the blades and pitch change mechanism together.

Blade: Two to seven blades are held in place by the hub, which connects to the engine through an output or crankshaft.

Pitch Change Mechanism: The assembly that converts hydraulic energy to mechanical motion to rotate the blades.

Feathering springs: Continually push blades toward a high pitch.

Counterweights: Also move the blades toward a high pitch or feather angle when there is a loss of oil pressure.

Spinner: The spinner dome is positioned over the propeller hub and creates an aerodynamic cover that assists in engine cooling and streamlining the airplane.

Spinner Bulkhead: This component connects the spinner to the rest of the propeller assembly protecting the pitch change mechanism and hub.

Other terminology

Governor: Oil pump with flyweights that controls the engine speed or RPM by changing the blade pitch.

Propeller Pitch: The propeller blade pitch is the angle the blade presents to the rotation of the propeller.

Fixed pitch propeller: The angle of this propeller is set at installation and cannot be changed while the aircraft is in flight. It is a compromise of best take-off and cruise performance.

Variable pitch propeller: The pilot can adjust the angle of a variable pitch propeller during flight to optimize the efficiency for take-off, climbing, and cruising.

Constant speed propeller: Like a variable pitch propeller, the blade angle of this propeller can be adjusted during flight. However, this propeller automatically adjusts its design pitch to maintain revolutions per minute (RPM).

Propeller control systems: There are two main kinds of control systems you should be aware of: single-acting systems and double-acting systems.

Single-acting systems utilize oil pressure to change the blade pitch in one direction and aerodynamic forces and a spring, or blade counterweights and a spring, in the opposite direction..

Double-acting systems utilize oil pressure to change the blade pitch in both directions.

Orange Green and Red engine with propellers

A few more key terms

Flat pitch: The blade angle with minimum torque, usually around 0 degrees. The blades are flat, facing the direction of travel. If an angle is below 0 degrees, the pitch is considered reverse.

Reverse thrust: The pitch angle can be changed to the point of producing reverse thrust. This helps stop an airplane upon landing, or backing it up as needed. This is very helpful on seaplanes for backing away from the dock.

Coarse or high pitch: The maximum in-flight pitch available for reducing rpm and gaining cruise speed.

Feather: The angle that results in slow or no rotation when the engine is not running. This angle is just under 90 degrees and used to reduce drag on a “dead” engine on a multi-engine airplane to allow the plane to be more controllable.

Blade Twist: For the propeller to achieve optimum aerodynamic performance, blades need to be twisted at specific angles. To understand this angle best, you need to consider both the plane’s forward speed, which is constant and the propeller’s rotational speed, which increases as you move from the root of the blade to the tip.

The blade twist creates this disparity of speed along with the propeller, which will get you the maximum amount of lift along the blade.

Thrust: Thrust is the force that moves the craft. Propellers create this thrust similar to how wings produce lift. As evidence, propellers somewhat resemble wings. Air flows over the wing, forming a pressure differential, creating lift.

In the case of the propeller, air flows over the blade at an angle that causes a similar pressure change, producing lift. This created lift in the propeller makes the airplane move forward instead of vertically.

Vintage Airplane with close up on propeller

Partner With Stockton Propeller Today

While this is a simplified list and only enough to get you started, you now have a basic understanding of terms that will help you going forward. When you need to speak to a real propeller terminology expert, contact Stockton Propeller.

We have experts in blade overhaul and reconditioning, as well as experts that can repair damaged blades to specification, or modify experimental blades to achieve an extra percentage of performance.

Whether you are flying with something as simple as a fixed-pitch metallic propeller, trying to keep your warbird flying, or fine-tune your experimental aircraft, contact us for a free quote on your repair or maintenance needs today.