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Contra-rotating propellers have been found to be between 6% and 16% more efficient than normal propellers. [4] However they can be very noisy, with increases in noise in the axial (forward and aft) direction of up to 30 dB, and tangentially 10 dB. [4] Most of this extra noise can be found in the higher frequencies.
Propeller walk (also known as propeller effect, wheeling effect, paddle wheel effect, asymmetric thrust, asymmetric blade effect, transverse thrust, prop walk) is the term for a propeller's tendency to rotate about a vertical axis (also known as yaw motion). The rotation is in addition to the forward or backward acceleration.
An azimuthing propeller is a propeller that turns around the vertical axis. The individual airfoil-shaped blades turn as the propeller moves so that they are always generating lift in the vessel's direction of movement. This type of propeller can reverse or change its direction of thrust very quickly.
Counter-rotating propellers (CRP) are propellers which turn in opposite directions to each other. [1] They are used on some twin- and multi- engine propeller-driven aircraft . The propellers on most conventional twin-engined aircraft turn clockwise (as viewed from behind the engine).
A Soviet Ka-32 helicopter with coaxial contra-rotating rotors, in 1989. Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque.
A wheeled buffalo figurine—probably a children's toy—from Magna Graecia in archaic Greece [1]. Several organisms are capable of rolling locomotion. However, true wheels and propellers—despite their utility in human vehicles—do not play a significant role in the movement of living things (with the exception of the corkscrew-like flagella of many prokaryotes).
Axial – along the center of a round body, or the axis of rotation of a body Radial – along a direction pointing along a radius from the center of an object, or perpendicular to a curved path. Circumferential (or azimuthal ) – following around a curve or circumference of an object.
Axial (from Latin axis 'axle'): around the central axis of the organism or the extremity. Two related terms, "abaxial" and "adaxial", refer to locations away from and toward the central axis of an organism, respectively