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The conventional helicopter is close to the edge of its performance envelope. In the future emphasis is on making it a more efficient, environmentally friendly mode of transport. Both, vibration and noise, are major nuisance to aircraft occupants. In addition, they increase the pilot's strain during flight and reduce his capability to safely pilot the aircraft.
Noise radiated from aircraft is a general nuisance for the community. Vibrations cause major problems for the operation and maintenance of the aircraft. Induced by the complex interaction between main rotor and airframe, vibrations may cut the fatigue life of helicopter components down to 50% creating major costs for the aircraft operator.
Helicopter noise not only bothers helicopter occupants, but the total flight environment of the aircraft. Recognising that police and health/rescue services helicopters are often operated in populated areas, noise reduction is of major importance and a strong marketing aspect. A quite helicopter is benefit for the community in quest of a quite environment.
HeliNOVI's overall research objective is the enhancement of helicopter performance, safety and ride comfort.
In detail the objectives are to:
The methodology within the 'Tail Rotor Noise Reduction Potential' will comprise:
The methodology for the 'Vibration Reduction Potential' consists of the following key topics:
European Commission, Directorate-General for Research (DG Research)
The first major step in the programme was the creation of a data base capable to cover interactional phenomena between main rotor, tail rotor and fuselage. Such data base is necessary firstly to evaluate the noise and vibration reduction potential. Secondly it allows evaluating the simulation capability of the prediction tools with respect to interactional phenomena. Once the tools have been validated, they can be used to locate the main noise and the vibration radiating areas of the aircraft as basis for future research and design work.
There is high interest of the industry to tackle noise and vibration phenomena which have significant impact on type certification, crew and passenger comfort, and the life cycles of helicopter components.The goal of reducing noise by 60% was achieved by changing the tail rotor sense of rotation from "Advancing Side Down" to "Advancing Side Up". When comparing with tail rotor in "Advancing Side Down" mode, an average noise reduction of between 5 to 8 dBA has been measured depending on the flight condition. There was no performance penalty observed by the reversing tail rotor sense of rotation.
As a result of tip speed reduction, an averaged noise reduction value of more than 2 dBA was observed for all flight conditions. The reduction of main rotor BVI noise, especially in the retreating side area, was even more than 3dBA.
The experimental acoustic set up of the model helicopter (in DNW-LLF 8m by 6m open jet) measures the noise pattern and directivity. . The microphone array (red plane) - with more than 120 microphones - moves with the microphone traverse. The helicopter model is a 40% Mach scaled Bo-105. The diameter of the main rotor is 4 meter. In most of cases the experimental noise reduction benefits were confirmed in numerical simulations.
Tail rotor modifications were also analysed in order to study the vibration reduction potential based on interactional aerodynamics. The investigations and also the theoretical results confirmed that the tail rotor configuration can be optimised without affecting the vibratory behaviour.
In particular the clearance between main rotor and fuselage was studied in some detail. The Bo-105 as small helicopter has a large relative clearance leading to an interference factor of 0.6 compared to transport helicopters with small main rotor shaft lengths. The latter are showing high interference factors between 1 and 3. In a parametric study clearance between main rotor and fuselage was systematically reduced in order to analyse the hereby increasing vibration level of a top fairing of the wind tunnel model. The interference factor of the wind tunnel model was modified to approximately 2 by the top fairing.
The aerodynamic influence of the fuselage on vibratory loads increases with flight speed underlining the high importance of this interaction for operational needs.
The higher harmonic vibratory flap bending loads in the rotating system contribute to the 4/rev roll and pitch moments in the airframe system leading to a difference of at least 33%. Higher differences are expected for increased wind speeds. The theoretical results are consistent to the experimental data.
These HeliNOVI test results confirm the importance of interactional aerodynamics on helicopter vibration characteristics for industrial design considerations. They underpin the importance of the comprehensive data analysis and code validation work performed in this project. In summary the following results are available:
See key results
See key results
Mr Juergen Langer
DLR - Deutsches Forschungzentrum für Luft-und Raumfahrt
Tel: +49 531 295 2696
Fax: +49 531 295 2641
TRIP is funded by the European Commission's Directorate General for Mobility and Transport under the Seventh Framework Programme for Research and Technological Development (FP7).