A Theory For Predicting The Rotational And Vortex Noise Of Lifting Rotors In Hover And Forward Flight

A Theory for Predicting the Rotational Noise of Lifting Rotors in Forward Flight, Including a Comparison with Experiment

A theory and resultant calculations are presented, predicting the noise generated by a lifting rotor in forward flight. With suitable adjustments in parameters, this theory reproduced (by numerical integration) the closed form results of Garrick and Watkins in their investigation of noise produced by a propeller. The theory presented here accounts for (1) asymmetry of inflow, lift, and drag; (2) non-linear section characteristics, compressibility, and reverse flow; (3) first harmonic and steady rigid blade flapping and pitching; (4) rotor shaft tilt; and (5) chordwise distribution of lift and drag forces. Sound pressure levels were evaluated for up to 20 harmonics at a general field point translating with the rotor hub, for the H-34 and HU-1 helicopters. A comparison with experiment is also presented. (Author).

Helicopter Theory

The history of the helicopter may be traced back to the Chinese flying top (c. 400 BC) and to the work of Leonardo da Vinci, who sketched designs for a vertical flight machine utilizing a screw-type propeller. In the late 19th-century, Thomas Edison experimented with helicopter models, realizing that no such machine would be able to fly until the development of a sufficiently lightweight engine. When the internal combustion gasoline engine came on the scene around 1900, the stage was set for the real development of helicopter technology. While this text provides a concise history of helicopter development, its true purpose is to provide the engineering analysis required to design a highly successful rotorcraft. Toward that end the book offers thorough, comprehensive coverage of the theory of helicopter flight: the elements of vertical flight, forward flight, performance, design, mathematics of rotating systems, rotary wing dynamics and aerodynamics, aeroelasticity, stability and control, stall, noise and more. Wayne Johnson has worked for the U.S. Army and NASA at the Ames Research Center in California. Through his company Johnson Aeronautics, he is engaged in the development of software that is used throughout the world for the analysis of rotorcraft. In this book, Dr. Johnson has compiled a monumental resource that is essential reading for any student or aeronautical engineer interested in the design and development of vertical-flight aircraft.

NASA Technical Note