Fly in Comfort
Three individual light-weight systems should be designed, each targeting a specific noise-disturbance source
Active Vibrations Control System for engine vibrations reduction
Active anti-Noise Control System for engine vibration reduction
Active Fuselage-Floor anti-Vibration Control System
Project Abstract & Main Objectives :
In aircraft cabin environments, vibrations and noise co-exist which affect the passenger comfort and quality of flight. Vibrations are typically generated by two main sources: (1) the aircraft engines (turbojet or turboprop) rotating at high speeds and transferred via the engine mounts and the fuselage to passenger area; these vibrations typically lay in the range of 100-500Hz. (2) Additional vibrations are caused by the aerodynamic loads on the fuselage which may affect the global modal response of the aircraft and are finally transferred to the passenger area via the fuselage floor. The latter are significantly lower – up to frequencies of 20 Hz. The wide gap between the two frequency ranges, as well as the different transfer path, requires that each vibration source should be treated and mitigated independently. Noise is a special type of vibration, that causes acoustic discomfort. The Figure insert presents the main sources of external noise in a typical small business jet and the corresponding transmission paths towards the passenger cabin. A major source of noise is the aircraft engine, which can be highly tonal, as for e.g. in propeller driven aircraft, or of a more broadband nature as for e.g. jet driven aircraft. Other sources of noise may be of a more broadband and random nature, such as the aerodynamic excitation from turbulent bounder layers. Moreover, many sources of external noise may even have temporal characteristics, such as excitation from landing gears or aerodynamic control surfaces.
There are two related important challenges faced in new aircraft development.
Challenge 1: The comfort of passengers should be continuously improved.
Challenge 2: Most importantly, as more powerful and efficient aircraft engines are introduced and new light-weight airframes are adopted the intensity of engine and airframe vibrations is increased while the damping capacity of the fuselage is reduced, hence, the vibration and noise level in the cabin are increased, setting a barrier in the improvement of airframe and engine efficiency.
To address both challenges, special noise cancellation techniques should be employed. The proposed project aims to improve existing airframes and engine technology and efficiency, while sustaining the high level of the customer comfort through the introduction of novel integrated active technologies of noise and vibration reduction.
This is accommodated in two discrete, but highly related directions: (1) Active vibration isolation and control; and (2) Active noise control. The present project aims to technically improve current successful approaches and to adapt them for increased passenger comfort in business jets. The project objectives can be summarized as:
Obj. 1: Develop an Active Vibration Control System to accommodate engine vibrations using active engine mounts.
Obj. 2: Develop an Active Noise Cancelation System to reduce noise discomfort in the passenger area.
Obj. 3: Develop an Active Vibration Control System to attenuate aerodynamic vibrations transferred to passenger area via the fuselage floor.