How Propellers Generate Thrust


Many aircraft feature propeller assemblies that are used to generate the thrust necessary for flight, and it can be highly beneficial to understand how such processes work. Just like the wings on each side of the fuselage, propellers operate on the principle of lift, manipulating the flow of air to adjust air pressure for forward propulsion. In this blog, we will discuss propellers in more detail, allowing you to have a better understanding of their functionality and the method in which thrust is produced.

Propellers are airfoils, meaning that their cross-sectional shape is able to generate lift as it moves through a gas. Rather than producing lift in a vertical direction as would be seen with wings, the propellers generate lift in a forward direction. This forward lift is what we know as thrust. With their relation to other airfoils like wings, propellers also exhibit camber, chord lines, leading edges, and trailing edges. Additionally, one will notice that the angle of each blade will vary from its root to the tip.

During standard operations, the propeller assembly will rotate around a central crankshaft. As blades spin, the speed of the propeller blade tip will be higher than that of the root. Alongside this, the blade tip will also travel a farther distance than the root due to its orientation. As the root and tip must complete a full revolution in the same amount of time, engineers specifically design the root to have the highest blade angle. Furthermore, this also promotes a more uniform angle of attack across all sections of the blade, increasing efficiency. While this may not seem entirely important, a lack of varying angles and a non-uniform angle of attack would result in increased pressure differences and blade stalling.

For the actual functionality of the propellers, such assemblies act to transform the horsepower of the engine into thrust. As the blades spin, a lower static pressure will be created ahead of the aircraft, causing the vehicle to propel itself forward through the difference in pressures. To amply achieve acceleration, the generated thrust must surpass drag, and this can be done through increasing engine power and the RPM of the blades. Because a higher amount of acceleration also leads to more drag load and increased fuel-burning, pilots will typically balance settings to reach an equilibrium point that minimizes losses.

Depending on the need of a particular aircraft or application, there are three types of aircraft propellers that will differ in their control and design. The first is the fixed pitch propeller, that of which is the most simplistic type. These propellers are unchanging in their angle, thus they are specifically designed to be operated in specific conditions. Due to their various constraints, fixed pitch propellers are most often installed on single-engine aircraft that operate with a limited range, altitude, and/or speed.

Ground-adjustable propellers are the next step up from fixed pitch variations, allowing for pilots to adjust the pitch of their propeller while the aircraft is unpowered and on the ground. While this propeller does not allow for any changes to be carried out during flight, it does promote more flexibility as the pilot can make adjustments as necessary to compensate for changing atmospheric conditions. Because of their increased complexity over the basic fixed pitch propeller, they can be more expensive.

Constant speed propellers, otherwise known as controllable-pitch propellers, are the most advanced assemblies for propeller aircraft. Rather than only being adjustable while on the ground, constant speed propellers can be managed as needed during flight. As such, the variable pitch ensures the most optimal flight performance regardless of the present atmospheric conditions. As constant speed propellers grew in popularity, the ground-adjustable propeller soon became more obsolete.

As the diameter of propellers can have a major effect on efficiency, some will often claim that a variable-diameter propeller would be the best to achieve larger diameters for low airspeeds and smaller diameters for higher speeds. Despite this, the construction of such propellers would lead to issues concerning integrity, control, and weight, thus making them less practical for typical operations. Instead, manufacturers typically take advantage of medium-sized blades that balance operations across slow and fast speeds.

With more understanding of the functionality of propellers and how they go about generating thrust, one can best ensure efficiency throughout their operations. At ASAP Buying, we operate as a premier supplier of aviation, NSN, and electronic parts, all of which have been sourced from leading global manufacturers that we trust. With AS9120B, ISO 9001:2015, and FAA AC 00-56B accreditation, we stand by the quality of our inventory. If you find particular items on our website that you are interested in, fill out and submit an RFQ form at your earliest convenience, and a dedicated account representative will contact you within 15 minutes to provide a customized quote as a solution to your needs. Kick-off the procurement process today with ASAP Buying and see how we can fulfill all our customers’ needs with time and cost savings.


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September 28, 2021

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