Rotor of the future: Key technologies for the environmentally friendly helicopter

Kurzfassung

In 2007, the helicopter community celebrated 100 years of helicopter flight. Since these early days, helicopters experienced a tremendous improvement in performance, safety, controllability and handling qualities. Yet still a niche product, they concurred their market and cannot be replaced by any other aircraft. The ability to take-off and land vertically, to hover and the excellent low speed flight performances and handling qualities in comparison to other VTOL aircraft enable and consolidate this success. On the other hand, helicopters still suffer from many problems that hinder a further increase in their market share. Most pronounced are the high level of vibrations and the noise generated by the rotor. While vibrations are a concern of pilot and passenger comfort, but also give rise to an increase in maintenance effort and costs, the high levels of noise limit the acceptance of helicopters in the public, e.g. landing of helicopters on or close to hospitals during EMS missions. High noise levels also lead to an early aural detection during military missions. Further drawbacks of helicopters are the high fuel consumption in high speed forward flight due to the excessive power required, the limited speed of flight, the low range for the same reason, low lead-lag damping etc. Noise and power consumption are of environmental concern. With the increasing utilization of helicopters in large cities like Los Angeles and New York, increasing complaints of the public on the annoyance caused by helicopter generated noise were noticed. In the future, manufacturers have to address low noise profiles of helicopters as one design target much stronger, before politicians and authorities have to respond to the public opinion. Power and hence high fuel consumption drive operating cost as well as emissions which become increasingly of concern for any aircraft. This motivates design engineers to focus on key technologies for the environmentally friendly helicopter. The rotor as the mayor contributor to noise and power demands plays a dominant role within further improvements. The presentation first will describe noise and power related aspects. It will highlight and comment the different sources and aspects for both. The presentation then will highlight two techniques, one passive approach and one active rotor control approach, to tackle especially the noise and power issue. The passive approach dates back to first initiatives of Onera and DLR in 1991, dubbed the ERATO-project, which finally has been matured by Airbus Helicopters such that the now Blue EdgeTM called rotor blade was presented to the public in 2015 on the H160 aircraft. The presentation will present selected wind tunnel as well as flight test results. The second approach of active rotor control goes back to an internal DLR initiative. It aims to combine the advantageous of Higher Harmonic Control (HHC) and Individual Blade Control (IBC). The resulting concept is called Multi-Swashplate. It was tested in the DNW-LLF in October 2015 using DLR’s rotor test rig using two different rotors: one old design featuring rectangular blades with NACA23012 profiles and one more modern design. Results on performance, noise and vibration will be shown.