Justin Wastnage / Marseilles
Prototype Neighbourly Helicopter designed to be up to 9dB less noisy than proposed limits and could fly in two years
Eurocopter aims to fly a technology demonstrator within two years as part of plans to develop a civil helicopter up to 9dBquieter than internationally agreed noise limits.
The Franco-German manufacturer says its prototype Neighbourly Helicopter will incorporate an advanced blade design and active rotor and engine control, and will offer improved comfort.
Michel Polychroniadis, research programme director at Eurocopter's technical division, says reducing noise is "one of the most important" aims for its civil helicopter range. Maximum noise levels in cruise and hover have been regulated by International Civil Aviation Organisation standards for new helicopter designs since 1986, but national and local authorities often impose stricter requirements.
Polychroniadis says the Eurocopter EC155B1 is about 7dB inside ICAO's Annex 16 Chapter 8 noise limits, which restrict the effective perceived noise level (EPNL) for helicopters over 2,700kg (6,000lb) to 93dB.
Bringing helicopters more into line with fixed-wing noise restrictions was discussed by ICAO's environment protection committee at the organisation's general meeting in Montreal last December and helicopter operators fear a resultant reduction of the maximum EPNL to around 85dB.
The Neighbourly Helicopter should be 7-9dB quieter than the new proposed limits, depending on the final decision, says Polychroniadis. Civilian operators often have to comply with local government restrictions on landings at smaller pads and airports, which has led to research focused on descent noise reduction.
Central to the development is the advanced composite blade, which has twisted, swept tips and an active servo flap in the trailing edge to reduce noise in descent. The blade tips are slanted about 15¡ back, and are in full-scale development after producing noise reductions of around 6dB in studies, says Polychroniadis.
The use of angled blade tips is coupled with a reduction of about 4% in main rotor speed during cruise, controlled by the full-authority digital engine control.
"We will need to work with pilots to convince them of variable rotor speeds," says Polychroniadis. Eurocopter is working on the use of active rotor hub struts for high-frequency noise reduction, and has already flown a BK117 demonstrator. The company aims to fly a full demonstrator by the second quarter of 2005, says Polychroniadis.
Source: Flight International
