Overview
Today's helicopters need to be further improved in order to gain more environmental and public acceptance. Helicopters generate external noise, cabin noise and vibrations due to the complex nature of their dynamic systems. They also suffer from NOx emissions, as other transport systems. It was therefore, essential that these issues be addressed in order to improve the situation for the new generation rotorcrafts and to make them environmentally friendly and acceptable to the general public.
FRIENDCOPTER intended to achieve the following main goals:
- Acoustic footprint areas reduced between 30% and 50%, depending on the flight conditions;
- A reduction of up to 6% of fuel consumption for high-speed flight;
- Cabin noise levels below 75 dBA, similar to airliner cabins for normal cruise flight;
- Cabin vibrations below 0,05 g, corresponding to jet smooth ride comfort for the same flight regime.
Due to the large and fast rotating rotor, the non-symmetric rotor flow, the close vicinity of the main gearbox and passenger heads and the specific requests of maximum engine performance, the targets mentioned above were highly challenging, requiring a strong high tech initiative.
The project was structured as follows, into six work packages (WPs):
WP1 - Specifications
The objectives of WP1 were:
- To ensure well defined and harmonised start of the project by confirming and quantifying the project targets and key deliverables envisaged through the main helicopter manufacturers and the engine manufacturer;
- To provide guidelines for an overall integrated research approach on development and operation of environmentally friendly helicopters by specifying the methods to be applied;
- To take precautions against technical imponderabilities by a risk assessment with respect to the methods applied and by identification of potential alternative procedures.
The following methods were used:
- The provision of guidelines for the work planning of the other WPs;
- Rough quantification of the final results expected in the different WPs;
- Specifications of the methods planned including risk assessment.
A specification report defining targets and methods of the programme was issued.
WP2 - Noise abatement flight procedures
WP2 was concerned with the reduction of noise on the ground through operational means (noise abatement procedures) and the prediction of the acoustic impact of such rotorcraft flight operations. Specifically, WP2 aimed to:
- Develop methodologies for the design of operationally viable noise abatement procedures;
- Design and validate the necessary prediction tools to assess the acoustic impact of rotorcraft flight procedures on the ground and assist in the development of low-noise flight procedures.
In terms of noise reduction, the objective was to reduce acoustic footprint areas between 30 % and 50 %, depending on the flight condition.
The tasks within this WP were split into three main topics:
- Identification of the needs and specific objectives relating to noise abatement procedures;
- Development of the models needed to predict the noise emitted by helicopters during various phases of flight and the tools necessary to design low-noise flight procedures;
- Full scale flight tests on different helicopter models in order to provide noise data to the prediction models and assess the low-noise procedures.
WP3 - Engine noise reduction.
The objective of WP3 was to reduce a component of helicopter noise, relevant mainly during take-off and climb, i
Funding
Results
The project achievements by WPs were:
WP 1 Results:
- provision of guidelines for the work planning of the other WPs;
- rough quantification of the final results expected in the different WPs;
- specifications of the methods planned including risk assessment.
The achievements of the WP2 could be summarised as follows:
- A new noise footprint model was developed and validated (HELENA). This model takes into account the complexity of noise generation specific to rotorcraft.
- Fully automatic optimisation routines were demonstrated for the development of noise abatement procedures.
- Extensive noise measurement means were deployed and guidance was provided for future noise campaigns.
- Flight guidance hardware dedicated to noise abatement procedure was developed and successfully flight tested.
- Considerable noise footprint reduction was demonstrated on all three aircraft through the use of noise abatement procedures (up to 50 % noise footprint reduction, more than a 10 dB reduction at specific observer locations).
The deliverables of WP 3 were:
- design proposals for appropriate inlet and outlet geometries;
- liners for quiet air intakes and exhaust nozzles;
- related recommendations for airworthiness and performance aspects.
There are currently no turboshaft silent technologies flying on serial helicopters. Therefore, the demonstrated technologies have no known equivalent in helicopter industry. The exhaust liner made of titanium alloy beneficiated from the know-how acquired during the EU-funded HORTIA program as well as from a technology transfer from the airplane industry.
The new manufacturing process developed in FRIENDCOPTER for integrating acoustic liners in composite material reduces the manufacturing time and costs, increasing the technology's attractiveness and enabling the product to be offered to a broader range of potential applications.
An important outcome of the project was also the improvement of the state of the art measurement techniques through the use of acoustic antennas that allow the development of new methodologies to determine engine acoustic power both during static tests and in flight.
Results of WP4:
The work performed in WP4 has improved partners' professional knowledge and their capabilities to apply advanced measurement syst
Technical Implications
A number of the results of this project are now ready to be industrialised, covering both:
- evaluation methods, such as low frequency SEA and noise mapping with ultra sound methods as well as,
- abatement technologies, like modifications to the main gear box and advanced panelling and sealing.
On the other hand, new technologies, methodologies and measurement techniques, some of them applied in FRIENDCOPTER for the first time, such as:
- the Matrix inversion method and
- active noise reduction methods
will need further development.
Impact on industry or research sector
The investigated technologies have been significantly advanced during the FRIENDCOPTER project. For both low risk technologies, i.e. active twist and active trailing edge, the technology readiness level has been increased by more than two levels. The feasibility of the investigated technologies on sub-system level and on blade level could be proven. Transfer considerations to full scale industrial rotors established good confidence for future product application.
Concerning the achievable benefits, active rotor control is a major component to meet the overall FRIENDCOPTER targets. For industrialisation however, the results have to be applied to the complete system with all sub-systems contributing to noise, vibration and power consumption in order to assess the validity for the complete aircraft.
The benefits have been shown by numerical simulations that are widely used in industry and research centres and have been extensively validated on passive rotors in the past.
In the future, an important issue will be to validate these findings against experiments, either in model scale wind tunnel campaigns or full scale flight testing. Partially, the Green Rotorcraft Platform of Clean Sky will be a continuation of FRIENDCOPTER for selected active technologies.