Types of Aircraft Propellers

While most people think of modern jet engines when they think of planes, it’s important to acknowledge the huge role “traditional” aircraft propellers played in the evolution of the aeronautics industry. Today, propeller driven planes still serve a valuable role for beginners, hobbyists, and the cost conscious, and are essential for the needs of the global economy and military. Read on to learn more about the various types of propellers, their technological evolution, the impact therein, and why certain propellers fill specific needs.

Types of Aircraft Propellers

Most modern propeller variations are distinguished by whether the blades, or airfoils, have a fixed pitch or angle of attack on the air, or have some kind of adjustable pitch. We will dive into the nuances throughout this article, but you can think of the different “types” of aircraft propellers as split between fixed or variable position propellers.

Fixed position propellers cannot change after installation, while variable position propellers may be referred to as: ground adjustable, two-position, controllable pitch, and constant speed propellers. 

Modern aircraft benefit from myriad design updates and an explosion of innovation since WW2. But did you know that there are many different types of propellers and all of them have specific pros and cons? When understanding the role of propellers in different types of aircraft, it’s important to grasp that all propeller types represent trade-offs between speed, altitude potential, durability, intended operating conditions, and the forces surrounding takeoff, climbing, and cruising.

You may hear aircraft propellers referred to as one of the eight types below:

1. Fixed pitch propellers

This is the simplest aircraft propeller type, wherein the blade pitch, or angle, is set at installation, and is typically associated with smaller piston aircraft. (Or likely what you imagine when you think of the original aircraft before today’s modern jet engine aircrafts.) Fixed-pitch propellers are typically metal or wooden in their construction and are mechanically linked directly to the engine. 

Unlike some of the other propeller configurations we’ll discuss next, and as the name suggests, once the fixed pitch propeller is built, changing the angle is impossible. The largest performance challenge with a fixed pitch propeller is that the blade angle has to work under many different conditions, and thus represents a compromise between cruise performance (coarser pitch), climb, and take-off (finer pitch).

Since there is a direct link between the propeller and the aircraft engine, the propeller’s rotation speed is a direct function of the speed of the engine. As such, the speed of the propeller will vary with altitude and airspeed, as well as engine throttle settings.

Fixed-pitch propellers are built for high efficiency at a forward and rotational speed. They are designed to fit a set of conditions around the airplane’s needs and engine speeds, and any alteration in these conditions lowers the efficiency of both the engine and the propeller. As a pro – or a con, depending on what you’re looking for – fixed pitch propellers don’t require or accept any additional pilot input since their pitch is static. For all its impact historically and the benefits of simplicity, a fixed-pitch propeller configuration tends to result in lower speeds, range, and altitude when compared to modern airplanes. Although it represents a set of constant compromises, its reduced complexity does create a simpler and ultimately cheaper plane, which can be desirable.

Wooden Fixed Pitch propellers

Before World War II, business and personal aircraft almost exclusively had wooden propellers. Today, wooden propellers aren’t as popular as metal propellers in modern aircraft due to the advancements and benefits offered by modern metal composites.

A wooden propeller is built using several layers of specially selected and prepared wood. They are not cut from a solid block. Black walnut, yellow birch, sugar maple, and black cherry were the most common woods used in building these “vintage” fixed propellers.

Metal fixed pitch propellers

The first metal fixed propellers were used by the military in 1940. They were crafted using high-strength, heat-treated aluminum alloy. Metal propellers are now common for all types of aircraft. The appearance of the metal propeller is generally similar to the wooden propeller but with thinner sections.

The aluminum alloy makes these propellers incredibly strong and durable. They are also heat treated to enhance their properties and make them less vulnerable to warping from cold or heat.

Understanding Variable-Pitch Propellers

Variable pitch propellers have the huge advantage of blades that can alter their pitch on their long axis and thus can adapt to conditions as needed by their pilots. To highlight why this is ideal, imagine a stationary aircraft with the propeller spinning. In those conditions the relative wind vector acting upon each blade will be from the sides of the blade. But once a plane is moving forward, and increasingly so at higher speeds, the relative wind vector will come from the front and the more surface area exposed to oncoming wind the higher the blades’ drag. All propellers are basically at the mercy of this basic concept: the blade pitch that is ideal for taking off or climbing will be inefficient for cruising, and what is good for cruise performance could stall an aircraft at lower speeds. A lower pitch offers better performance against high resistance (strong relative wind vectors at higher speeds) but provides little thrust, while a higher pitch provides more thrust under conditions with lower forward resistance but necessitates higher engine RPM and lower fuel efficiency at higher speeds. As a result, variable-pitch propellers were a huge innovation on fixed propellers, and constant speed propellers offer an ideal solution by approaching constant efficiency across broad ranges of airspeeds.

Since WW2 the vast majority of planes either have had a fixed pitch propeller or a constant speed propeller on them, though there are additional variable pitch propellers worth being familiar with.

2. Ground adjustable pitch propellers

The ground adjustable propeller functions like a fixed-pitch propeller, except that the pilot can physically change the blade pitch, or angle, when the propeller is on the ground.  This change is accomplished by loosening the clamping mechanism that keeps the blade in place to allow the transition. After tightening the clamping mechanism, it is not possible to change the blade’s pitch in flight to fit varying flight requirements. This is among the reasons why present-day aircraft don’t often use ground-adjustable propellers.

3. Two-position propeller

A two-position propeller is an aircraft propeller whose blades are limited to two blade angles, one for takeoff and climb (low pitch and high RPM)  and the other for cruising (high pitch and low RPM). This propeller allows for the pitch to be changed from one position to the second position by the pilot during flight.

4. Controllable Pitch Propellers

The controllable pitch propeller, as the name suggests, allows a pilot to manually change the blade angle, or pitch, in-flight while the propeller is running. The advantage is that the propeller can be altered for the best performance or goal given a specific flight condition.

However, depending on the model and specifications of the plane, the pitch position angles may be limited, conceptually similar to a two-position propeller, within a certain set of designated increments. Or the pitch might be adjusted to any angle between the propeller’s minimum and maximum blade pitch settings. The unique design characteristics of controllable pitch propellers make it possible to achieve a desired engine RPM and thus optimal efficiency for specific flight conditions.

Controllable pitch propellers are sometimes confused with constant speed propellers. Controllable pitch propellers directly allow the pilot to change the angle during flight. On the other hand, constant speed propellers, which we will discuss next, allow the blade angles to change automatically with the help of a governor.

5. Constant Speed Propeller

Constant speed propellers offer the huge advantage of letting pilots toggle a specific engine RPM and allowing the constant speed unit, or propeller governor, to adjust the blade pitch automatically. The end result is high engine efficiency and better performance across a wide variety of conditions.

An early constant speed propeller design, known as a counterweight propeller, relied on centrifugal force and a set of weights and springs to adjust the pitch based on engine RPM. Most current constant speed units, or CSUs, rely on oil pressure and a complex set of springs, flyweights, and valves to adjust oil pressure which then directly alters pitch as the blades interact with various wind speeds. Most high performance propeller-driven planes rely on CSUs for optimal performance so this is the most likely propeller you will encounter today outside of fixed propellers. A notable advantage of this configuration besides its mechanical elegance, is that if the engine pressure or CSU fails the propeller will automatically feather, which reduces drag, and serves as an excellent transition into our next section.   

6. Full Feathering

Blade feathering allows for the intentional or default mechanical response of  adjusting the blade pitch such that the chord line is nearly parallel to the oncoming wind vector. While most variable pitch propellers provide for blade feathering, it is worth highlighting the specific importance of these propellers given their historical importance in military applications. When a propeller is feathered, it significantly reduces drag on multi-engine aircraft, since there is a minimum amount of resistance to incoming wind. Since the propeller blades are parallel to the airstream, the propeller stops rotating, and windmilling, if any, is minimized.  These properties can be life saving by reducing drag from a failed engine, like one rendered unusable by enemy fire, or more commonly these days, mechanical failure. In single engine aircraft this reduction in drag increases how far a plane can glide and improves the options available for a forced landing.  

7. Reversing propeller

A reversing propeller is a controllable propeller with blade angles that can be changed to a negative value during a flight. The reversible blade pitch feature creates a negative propeller blade angle, producing thrust that’s opposite the normal forward direction.

Typically, the pilot can move propeller blades to a negative pitch, or reversed, after landing to slow the aircraft and make it come to a complete stop. As the propeller blades go into a negative pitch, the power of the engine increases negative thrust. This negative thrust aerodynamically slows down the plane and limits ground roll. Plus, reversing the propellers decreases airplane speed quickly after its touchdown and limits airplane brake wear.

8. Test Club Propeller

A test club propeller is used to test and break-in reciprocating engines. These propellers are designed to provide the correct engine load during the test break-in time. A multi-blade test club propeller also creates extra cooling airflow when engines are being tested.

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