Contra Rotating Propellers
Chapter 1: Introduction
Spitfire Mk XIX, Tu-95 Russian strategic bomber, Douglas XB-42 Mixmaster, what makes these Aircrafts different. For most vehicles, the primary power consumer is the propulsion system. Advances in CFD and fabrication have increased the efficiency of the single propeller significantly. However, further increases in efficiency can sometimes be obtained from having two propellers in a contra- rotating configuration. 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 minimize the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs, where similar issues and principles of torque apply Axially-aligned contra-rotating propellers have long been recognized as an extremely efficient arrangement. The two propellers are designed such that the aft propeller removes the swirl induced by the forward propeller; as a result, a dual contra-rotating propeller will be on the order of 10% more efficient than a single propeller of equivalent power. An additional benefit is that the two propellers are torque balanced, which is advantageous in directional control and reduced heeling moment of single-shaft vessels. Contra-rotating propellers were installed in two U. S. Navy submarines in the late 1950’s to early 1960’s. These propellers were
1
mounted co-axially on a concentric shaft line; each shaft was powered by a separate motor. Significant problems with shaft seals and bearings precluded installation on
Spitfire Mk XIX, Tu-95 Russian strategic bomber, Douglas XB-42 Mixmaster, what makes these Aircrafts different. For most vehicles, the primary power consumer is the propulsion system. Advances in CFD and fabrication have increased the efficiency of the single propeller significantly. However, further increases in efficiency can sometimes be obtained from having two propellers in a contra- rotating configuration. 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 minimize the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs, where similar issues and principles of torque apply Axially-aligned contra-rotating propellers have long been recognized as an extremely efficient arrangement. The two propellers are designed such that the aft propeller removes the swirl induced by the forward propeller; as a result, a dual contra-rotating propeller will be on the order of 10% more efficient than a single propeller of equivalent power. An additional benefit is that the two propellers are torque balanced, which is advantageous in directional control and reduced heeling moment of single-shaft vessels. Contra-rotating propellers were installed in two U. S. Navy submarines in the late 1950’s to early 1960’s. These propellers were
1
mounted co-axially on a concentric shaft line; each shaft was powered by a separate motor. Significant problems with shaft seals and bearings precluded installation on
References: [1] A Design Method and an Application for contra rotating propellers, by Benjamin Y.H. Chen and Arthur M. Reed. [2] Design Method for Contra-Rotating Propellers for High- Speed Crafts: Revising the Original Lerbs Theory in a Modern Perspective by Stefano Brizzolara, Davide Grassi and Emilio P. Tincani. [3] A Numerical Method for the Design and Analysis of Counter-Rotating Propellers , S.C. Ylayie, K. D. Korkan, and E. Von Lavante, Texas A&M university, College Station, Texas. [4] Marine contra-rotating propeller apparatus, Inventor: Hiroshi Nohara, Nagasaki, Japan, Patent Number: 4642059, Feb 10, 1987 [5] Aircraft adapted for vertical ascent and descent, Inventor Charles L. Cochran, Overland Park, Kanas, Patent Number 553808, Dec 19, 1955 [6] Tilt-Rotor Aircraft, inventor: Robert Graham Burrage, The Chestnuts, Abingdon, Oxfordshire (GB), Patent Number: 784923 B2, Sep 8, 2009. [7] Contra-Rotating Propellers – Combination of DP Capability, Fuel Economy and Environment, DYNAMIC POSITIONING CONFERENCE, October 17-18, 2006, Hannu Jukola, Steerprop Ltd., Finland; Teuvo Ronkainen, Steerprop Ltd., Finland [8] White paper on, Integrated Contra-Rotating Propulsion Drives for Thrust-Dense Propulsion Systems, C. Chryssostomidis*, J. L. Kirtley Jr., A. Slocum, J. Chalfant, Massachusetts Institute of Technology [9] A design method for contra rotating propellers based on exact lift surface correction, Emilio Tincani, Davide Grassi, Stefano Brizzolara, Marine CFD group, Department of Naval Architecture and Marine Technology, University of Genoa, Italy 25