Hand calculation procedures for predicting aerodynamic noise from propellers, rotors, and lift fans

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A review of aerodynamic noise from propellers, rotors, and lift fans

HE present and future use of helicopters as flexible air transportation in and out of highly restricted heavily populated areas is threatened by the community noise problems associated with these vehicles. In the next generation of vehicles, noise requirements may play a major role in the design process.1 It is important to have in the early stages of the design process an estimate for the effect of a given design change upon both the noise and DOC of the vehicle. This Note presents a correlation of existing data on main rotor vortex noise which is, at the present state-of-the-art, an irreducible effect of operating the main rotor. Although basic research into the effect of airfoil cross-section and tip planform shape on the noise from main rotors may eventually lead to noise reductions below this curve, an examination of the present data can also serve as a base to compare later improvements. For the typical helicopter, aerodynamic noise is produced by the main rotor, the tail rotor, and the engine. Current efforts in design should succeed in reducing the noise from the tail rotor and engine to a point where the dominant source of noise is the main rotor.

A Correlation of Vortex Noise Data from Helicopter Main Rotors

: This report summarizes the state-of-the-art in helicopter noise. It includes a bibliography of reports on all components of helicopter noise including main rotor, tail rotor, engine and gearbox. Literature on helicopter noise reduction and subjective evaluation of helicopter noise were also included. Capsule summaries of important reports are included which describe the purpose of the report, summarizes the important results, compares the report with others on the same subject, and provides a critical evaluation of the work presented. It is concluded that the available prediction methodology provides a means for estimating helicopter sources on a gross basis. However, the mechanisms of noise generation are still not fully understood, although the experimental and theoretical tools are now available to conduct the definitive experiments and establish the mathematical models needed for accurate definition of helicopter noise generation mechanisms. Spectrum analyses of helicopter noise show that main rotor, tail rotor, and engine sources contribute significantly to annoyance. In cases where these sources have been heavily suppressed, gearbox noise will also appear as a significant contributor to annoyance. Therefore, quieter helicopters must include suppression of all of these components. For certification, the liter

/pdf/a-comprehensive-review-of-helicopter-noise-literature-332ii664qy.pdf

A Comprehensive Review of Helicopter Noise Literature

Noise Implications for VTOL Development

An increase of background noise has accompanied the steady growth of industrial society. Rapid growth of air travel has focused special attention on aircraft noise, and need for abatement. Anticipated growth of short-haul air transport will bring vertiports into established commercial areas and low-altitude flyovers to populated areas. Noise intrusion may be assessed in perceived noise (PNdb) for residential communities, but a more realistic yardstick for commercial/industrial sections might be speech interference level (SIL). Achievement of the ideal goal—no intrusion of noise above ambient levels—requires reduction of powerplant noise but may be limited by aerodynamic noise from the vehicle itself. Consideration of powerplant noise in terms of "disk loading," progressing from jets at the high end down through fans, propellers, and rotors, leads to selection of rotors and propellers for shorthaul propulsion. Further noise reduction below current state-of-the-art levels will require intensive long-range development programs. Parallel to concentrated effort by industry to provide aircraft acoustically acceptable to the community, the community should plan for these aircraft by judicious selection of vertiport sites and utilization of zoning and building-code functions for development of surrounding neighborhoods.

N. Shapiro

Papers

A realistic assessment of the vertiport/ community noise problem.