Abstract
Helicopters are still an indispensable addition to aviation in this day and age. They are characterized by their ability to master both forward flight and hover. These characteristics result in a wide range of possible operations. Key for the design of the rotor blades is a blade design that always represents a compromise between the different flight conditions, which enables safe and efficient flight in the various flight conditions. In order to operate the rotor blade even more efficiently in all flight conditions, a new morphing concept, the so-called linear variable chord extension, has been developed. Here, the blade chord length in the root area is changed with the help of an elastic skin to adapt it to the respective flight condition. The simulations performed for this concept showed a promising increase in overall helicopter performance. The fabrication of the resulting demonstrator as well as the tests in the whirl-tower and wind tunnel are presented in this paper. The results of the tests show that the concept of linear variable chord extension has a positive influence and a great potential for hovering flight.
Highlights
Helicopters continue to be an indispensable part of aviation, as their variable speed of travel allows them to cover a wide range of operations
The design of helicopter rotor systems is always a significant compromise between the flight conditions, for example, between hover and forward flight. This results in rotor blades that are not optimal for all flight conditions, not even taking into account the different aerodynamic conditions on each rotation during forward flight
Concepts such as discrete trailing edge flaps, “servo” flaps, as well as active twist have been proposed and wind tunnel tested (Boeing/DARPA/ARMY/AIR FORCE SMART HELICOPTER ROTOR [6]), and the Blue PulseTM flap solution was even demonstrated by an in-flight test [7]
Summary
Helicopters continue to be an indispensable part of aviation, as their variable speed of travel allows them to cover a wide range of operations. Most of this work focusses on higher harmonic excitation, which would reduce the disadvantages of the highly different aerodynamic conditions on the advancing and retreating side of the rotor in forward flight Concepts such as discrete trailing edge flaps, “servo” flaps, as well as active twist have been proposed (see Maucher [5] for a comprehensive review) and wind tunnel tested (Boeing/DARPA/ARMY/AIR FORCE SMART HELICOPTER ROTOR [6]), and the Blue PulseTM flap solution was even demonstrated by an in-flight test [7]. In contrast to the state of the art, the concept shows a non-uniform chord extension, which is more of what is needed for performance increase An advantage of this concept is the closed contour for any airfoil section without gaps and openings into the inside of the mechanism.
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