Although turbojet engines continue to dominate the aerospace propulsion market, propellers remain a viable option for aircraft models in a variety of applications. Due to their unmatched efficiency at lower airspeeds, propellers remain a staple for subsonic vessels. Despite some notable upgrades to materials and functionality, the operating principles behind propellers have continued without change. In this blog, we will explore the different propeller variants and in what circumstances each succeeds.
Each blade of a propeller can be thought of as a rotating wing. As such, they function using similar aerodynamic principles. In particular, propeller blades create a pitch, which is closely related to the angle of attack. Depending on the airspeed and stage of flight, the most optimal pitch in terms of fuel efficiency varies significantly over time. Being the most straightforward variant, fixed-pitch propellers maintain a set blade angle throughout the entire rotation. Although preventative and corrective maintenance is simple for these designs, they lack the efficiency that other propellers offer.
Variable-pitch propellers offer a controllable airscrew which allows the operator to adjust the angle of attack to be optimal over a wide range of conditions. Most manual versions actuate using oil pressure or hydraulic power, although some newer designs implement an electro-mechanical design. Depending on the configuration, the pilot may only have the option to choose between two or three blade positions, or an array of angles from minimum to maximum.
With the advent of variable-pitch propellers came a new paradigm of efficient operation. However, modulating the angle of attack throughout flight takes careful attention and time away from other critical tasks. Moreover, the given angle a pilot might choose may not always be optimal for the current condition. As a result, engineers created the constant-speed propeller which automatically adjusts pitch throughout flight to provide peak performance at all times. Although purchased at a higher premium than other options, constant-speed propellers are most likely to save the user on operating costs over time.
Unique to multi-engine aircraft, feathering propellers are a type of constant-speed variant which can produce a pitch angle of 90 degrees. In the event of an isolated engine failure, it is critical to decrease drag using all means necessary while also preventing windmilling if possible. Windmilling refers to the tendency of the propeller to turn from the force of the air. When implementing a feathering technique, the aircraft immediately assumes less drag, and the propellers essentially become immune from the effects of windmilling.
Although their mechanism might not seem intuitive, contra-rotating models employ two coaxial propellers which rotate in opposite directions. In doing so, the torque created by either set of blades is canceled out, allowing for more stability in flight. As a result, contra-rotating propellers are more efficient as they are able to generate more thrust with lower power inputs. Despite these benefits, this configuration is much louder than other designs, limiting its use in civil and military applications.
Stacked Aerospace is a leading parts distributor for the civil and defense aviation markets, and we are your number one choice for high-quality propeller components. Regardless of how mainstream or niche your application is, we are confident you will find the exact part required in our expansive 2-billion-item inventory. As you browse our various catalogs or use our comprehensive search engine, keep in mind you may initiate the purchasing process at any time using our Instant RFQ service. After submitting your request, you will be furnished with a customized quotation in just 15 minutes or less.
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