Boots – shoes – and leggings
Patent
1989-02-10
1990-08-07
Lall, Parshotam S.
Boots, shoes, and leggings
36442401, 384 71, 244 1N, H04R 2700, B64C 1150
Patent
active
049473565
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatus for controlling cabin noise in propeller or fan driven aircraft.
Several proposals for reducing noise are reviewed in an article entitled `Strategies for reducing propeller aircraft cabin noise` by F B Metzger in Automotive Engineering, 1981, Vol 2, No. 1, Page 5. In particular, the use of synchrophasing to reduce noise levels in multi-engine transport aircraft is reviewed. Synchrophasing is the automatic control of one or more propellers to provide a fixed phase relationship between the circumferential blade locations of the propellers in relation to a reference propeller. By maintaining an accurate phase relationship between the propellers the annoying beat characteristic of unsynchronsied propellers is avoided. Cabin noise levels may be reduced by careful adjustment of this phase relationship.
There have been a number of proposals for large unducted fan aircraft engines for operation at cruising speeds of between 0.6M and 0.8M. Such engines are mounted at the rear of an aircraft fuselage and a number of proposed designs include contra-rotating forward and rearward fans. The rearward fan reduces residual swirl from the forward fan and improves the overall efficiency of the engine. Cabin noise arising from the use of such engines is likely to be a major problem.
The present invention provides an improved form of aircraft cabin noise control using synchrophasing and active noise control techniques.
According to the present invention, cabin noise control apparatus for a propeller or fan driven aircraft includes means for varying, during flight, the phase relationship between a reference propeller or fan of the aircraft and one, some or all of the other propellers or fans of the aircraft characterised in that the phase relationship is varied in response to the output from a signal processor connected to receive and analyse signals from a plurality of transducers located inside the cabin.
The transducers may be microphones in which case the signal processor may form part of an active noise control system which generates sound waves in anti-phase with ambient noise waves. Such a system may, for example, be as claimed in UK Pat. No. 2149614. This system provides apparatus for reducing noise in an enclosed space where the noise, generated by an external source, has a fundamental frequency f.sub.O and a series of harmonics thereof. The value of f.sub.O is monitored and communicated to a signal processor and the sound pressure level in the enclosure is monitored by a plurality of microphones and also communicated to the processor. The processor outputs signals to a plurality of loudspeakers, these signals being in antiphase with the input signals so as to minimise the sound pressure level in the enclosure.
Alternatively, the transducers may be mounted, for example, on a vibrating part of the aircraft which radiates sound into the cabin. The signal processor linked to such accelerometers may also form part of an active noise control system similar to that just described. Microphones and accelerometers may also be used in this way in combination with one another.
In an aircraft having multishaft engines, the phase varying means may be arranged to vary the phase relationship between the reference propeller or fan on one shaft and a propeller or fan on the other shaft of the same engine.
An embodiment of the invention will now be described with reference to the drawings of which:
FIG. 1 is a schematic diagram of aircraft cabin noise control apparatus in accordance with the invention,
FIG. 2 is a block diagram of a computer simulation of the apparatus of FIG. 1,
FIGS. 3, 4 and 5 are graphs showing the results of the simulation of FIG. 2,
FIG. 6 is a graph showing error functions for systems with and without active noise control.
In FIG. 1, an aircraft cabin 1 (only part of which is shown) contains four
microphones 2, 3, 4, 5 and two loudspeakers 6, 7 which form the active elements of a cabin noise control system. Outputs from the microphones 2, 3, 4, 5 are fed via amplifier
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patent: 4245955 (1981-01-01), Lambertson
patent: 4566118 (1986-01-01), Chaplin et al.
patent: 4589133 (1986-05-01), Swinbanks
patent: 4659283 (1987-04-01), Niessen et al.
patent: 4689821 (1987-08-01), Salikuddin et al.
patent: 4715559 (1987-12-01), Fuller
Journal of Aircraft, vol. 23, No. 2, "Propeller Model for Studying Trace ocity Effects on Interior Noise".
Automotive Engineering, vol. 89, No. 10, Oct. 1981, Society of Automotive Engineers, Inc. (N.Y., U.S.), F. B. Metzger, pp. 107-113, International Search Report.
Elliott Stephen J.
Nelson Philip A.
Lall Parshotam S.
The Secretary of State for Trade and Industry in Her Britannic M
Zanelli Michael
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