Adaptive Rotor Blades for Rotorcraft Vehicles

Rotorcraft is another category of aircraft for which adaptive compliant structures technology offers significant promise. While the resarch is not as far along as that for fixed-wing aircraft, applying variable-geometry technology along both the leading and trailing edge of rotor blades could have an even greater impact.

An Army-funded research project recently resulted in a variable-geometry helicopter rotor blade section with an embedded compliant mechanism. The variable-geometry leading edge, with 0-10° deflection capability, modifies the aerodynamics so that dynamic stall on the retreating blade is delayed, giving the craft higher speed and better maneuvering performance.

In this program, we designed and fabricated a 3-ft-span, full-scale chord rotor blade to demonstrate 0-10° leading-edge camber change at 6 Hz (once per revolution). The blade was designed with high-strength materials to withstand pressure loads and centrifugal loads for 4,500 hr of service life (220 million cycles fatique life).

In a helicopter blade, the blade cross-section that is best for the advancing blade is far from optimal for the same blade in its retreating phase. This shape mismatch results in reduced lift, dynamic shock as the blade azimuth changes, vibration stress, audible sound, and structural wear. These problems substantially limit rotorcraft performance (e.g. maximum speed and altitude), decrease the structural life of rotor blades, and increase the cost of operation and maintenance.

The morphed leading-edge structure begins with the airfoil shape optimal for good high-speed performance in the advancing blade phase and then changes to a cambered design that optimizes airfoil performance as the blade retreats. It then cycles back to the advancing blade configuration, once per revolution or at a rate up to seven times per second. This behavior allows the morphing aircraft structure to maintain an optimal profile through its entire azimuthal circuit, thereby offering substantial gains in speed and maneuverability (12-25%) and about 10% incrase in payload.

The reductions in drag, vibration, and wear will significantly improve the performance of next-generation rotorcraft far beyond the current achievable maximum, promising higher speeds, lower drag and fuel requirements, better maneuverability, and quieter operation, not to mention longer usable blade life and reduced maintenance.

Video

This video shows the prototype helicopter blade with variable-camber leading edge. (2.46MB .wmv movie)

Pictures

All Pictures Copyright 2006 by FlexSys, Inc. Please contact FlexSys for permission to use the pictures on this site.

This graphics shows airflow over an advancing and retreating rotorblade without camber change.	This graphic shows airflow over an advancing and retreating rotorblade with camber change.
This graphic shows a side-by-side comparison of airflow with and without leading edge morphing (camber change).