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Shaft Engines
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
Contra-rotating propellers, also referred to as coaxial contra-rotating propellers or high-speed propellers, apply the maximum power of an engine (or engines) to drive two propellers one behind the other about the same axis in opposite directions.
UAS Airframe Design
Published in R. Kurt Barnhart, Douglas M. Marshall, Eric J. Shappee, Introduction to Unmanned Aircraft Systems, 2021
Michael T. Most, Michael Stroup
Torque effect is present in both fixed-wing and rotary-wing designs, but much more dominant in the latter. Torque effect develops as the result of Newton’s 3rd law, “for every action there is an equal and opposite reaction.” Power delivered to the rotor causes the fuselage to display the propensity to rotate in the direction opposite the rotor. This tendency varies linearly,—increase power, increase torque effect. Torque effect is countered on single-rotor helicopters, both manned and unmanned, by the tail rotor (aka, antitorque rotor). If the thrust produced by the tail rotor is less than torque effect, the fuselage will yaw in the direction opposite main rotor blade rotation; if thrust produced by the antitorque rotor is greater than the torque effect force, the fuselage will yaw in the direction of main rotor rotation. Using two rotors affords the advantage of torque cancellation, whereby the two rotor systems rotate in opposite directions and thus the torque of one cancels that of the other and no other antitorque system (e.g., a tail rotor) is necessary. Examples of UASs with two main rotor systems include both coaxial, contra-rotating, and tandem, counterrotating designs. The difference is that in the former example, the blades rotate around a common axis, while in the latter, rotation occurs about two independent axes. The first rotary-wing UAS, the QH-50 DASH, developed by Gyrodyne for the Navy in the late 1950s and early 1960s, was a coaxial, contrarotating design powered by a Boeing turboshaft producing 300 shaft horsepower. During the late 1980s and early 1990s, Sikorsky experimented with a coaxial unmanned design known as the Cipher and Cipher II, which subsequently evolved into the USMC’s Dragon Warrior UAS. Currently produced examples of a tandem, counterrotating UAS rotor system may be found on the unmanned version of the Kaman K-MAX, a helicopter capable of lifting an external load equal to its own weight, and the IAI Ghost, which resembles a Chinook manned helicopter in configuration. The K-MAX rotor system, wherein the blades mesh, much like those of an old-fashioned, mechanical egg beater, is also referred to as a synchropter or intermeshing rotor design.
Enhancing the roll dynamics of an AUV by contra-rotating-propellers
Published in Ships and Offshore Structures, 2021
Mohsen Ebrahimi, Ahmad Kamali, Madjid Abbaspour
A contra-rotating propellers system consists of a pair of propellers that are coaxial and rotating in the opposite direction. This system, mainly used as a propulsion system, has proper advantages such as high efficiency under high loads, low reaction torque, high maximum thrust power for a given diameter (Štorch 2017). The purpose of this paper is to study the roll control capability of the contra-rotating propellers system. At first, the roll dynamics of a Remus AUV using a single propeller system is investigated by developing a dynamics simulator. It is followed by developing the control system simulator and evaluations of using a contra-rotating propellers system as a roll control strategy.