Navigation path

Decrease textIncrease textDividerPrint versionRSSDivider

Integration of Technologies in Support of a Passenger and Environmentally Friendly Helicopter


Today’s helicopters need to be improved further to gain more environmental and public acceptance. Helicopters generate external noise, cabin noise and vibration due to the complex nature of their dynamic systems and suffer from NOx emissions, like other transport systems. It is therefore essential that these issues are addressed to improve the situation for new generation rotorcraft, to make them environmentally friendly and acceptable to the general public

Project objectives

  • Acoustic footprint areas reduced between 30% and 50% depending on the flight condition.
  • 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.
Reduction of internal and external noise
Reduction of internal and external noise

Description of the work

In the area of short-term objectives:

1) Noise Abatement Flight Procedure

As a short-term goal of external noise reduction, the impulsive noise (blade slap noise) during the particularly sensitive approach phase will be tackled by dedicated flight procedures, which also take into account aspects of safety and certification. The goal is to identify a combination of glide path angle and flight speed to circumvent the area of high blade slap. The procedures will be demonstrated in-flight by different helicopter types and will be introduced as extensively as possible into the respective flight manuals. A microphone array will record noise footprints to measure significant noise annoyance. To optimise this method, a common noise footprint prediction tool will be established, based on the partners’ existing codes.

2) Cabin Noise Reduction

The reduction of the cabin noise level will be addressed in a twofold way:

A. by tackling cabin noise emission at the source:

In order to favourably influence the emission characteristics of the gearbox, main gearbox elements will be modified and damping features will be added. In addition, at the interfaces between gearbox and fuselage, active elements will be implemented to interrupt the transmission of structure-born noise. Dedicated rig- and flight-tests are planned.

B. by reducing cabin noise in the cabin itself:

Applying active structure control, mainly acting on cabin panelling, will reduce structural and aerodynamic noise. In order to focus the cabin treatment measures on critical areas, methodologies to identify acoustic leaks will be developed. Identification technology and effectiveness of the cabin treatment will be verified by flight-testing.

3) Engine Noise Reduction

The engine noise emission will be tackled by acoustically treating the engine inlet and outlet ducts with noise absorbing structures. The lessons learnt from the Fifth Framework Programme HORTIA project will be used among others. In this project, first attempts to treat the engine outlet acoustically have been started. After a dedicated concept study, bench- and flight-tests will prove the efficiency of the actions taken.

In the area of long-term objectives:

4) Active Blade Control

In order to accomplish in the long term:

  • larger noise reductions
  • lower NOx emissions
  • minimised cabin vibrations.

the technology of active blade control (ABC) through actuation distributed along the blade surface will be brought to maturity and validated. This technology will allow:

  • blowing away the blade tip vortices responsible for the blade slap noise
  • use of thin blade tips but with delayed flow separation through high blade incidence angles leading to a lower power requirement
  • generation of secondary excitation loads counteracting the original unsteady forces and moments at the rotor hub.

For this reason, distributed piezo-ceramic actuators will be integrated into the rotor blade skin, generating dynamic blade twist and camber adapted to the flight condition at any given time.

In detail, tests will be carried out on:

  • the integration aspect by blade rig-tests of full scale blade segments
  • the controllability of the rotor blades through a Mach-scaled model rotor in hover conditions.

These tests will represent a decision point for continuation in the form of intensive wind tunnel- and subsequently also flight-tests planned for the Seventh Framework Programme.

Expected results

The activities envisaged are to provide a number of key deliverables. All of these will have undergone intense efficiency testing, mostly by flight tests. They will consist of the following:

  • for Noise Abatement Flight Procedures:
    • flight guidelines/flight manuals enabling helicopter pilots to perform noise abatement flight procedures
    • a software tool, to be used by helicopter designers, local heliport authorities as well as noise certifying authorities, and even architects, to predict the noise around heliports.
  • for Engine Noise Reduction:
    • design proposals for appropriate inlet and outlet geometries
    • liners for quiet air intakes and exhaust nozzles
    • recommendations for airworthiness and performance aspects.
  • for Cabin Noise Reduction:
    • acoustic leak detection methods
    • a quiet main gearbox
    • an active reduction of structure-borne gearbox noise
    • actively and passively-damped cabin trim panels.
  • for Rotor Noise Control:
    • an experimentally validated technology for an active reduction of noise, vibrations and fuel consumption
    • a proof of blade controllability by model rotor blade spin tests
    • evidence of actuator endurance and integration appropriateness by full-scale blade sample tests.