MICHAEL PHELAN / LONDON
The US Defense Advanced Research Projects Agency (DARPA) has conducted flight tests of an unsteady active flow control system on the Bell XV-15 experimental tiltrotor that promises dramatic reductions in download forces during hovering.
The tests, conducted under DARPA's Micro Adaptive Flow Control (MAFC) programme, demonstrated that the technology can provide a 14% reduction in download forces on the airframe during hover by controlling the flow of air around the wing.
The technology is intended to enable control of large-scale aerodynamic flows using adaptive control techniques with small-scale actuators, such as synthetic micro-jets, micro-electromechanical systems (MEMS)-based actuators, pulsed-blowing, combustion actuators and smart structures. The XV-15 demonstration used small synthetic jets to delay flow separation. DARPA says the tests show that using MAFC, a 25,000kg (55,000lb) tiltrotor can carry about 450kg more payload.
The goal of the MAFC programme is to demonstrate military applications and develop design software to enable the technology to be used in new aircraft designs. But major technical challenges include the development of robust actuators with the required force, displacement and bandwidth for real applications, and the integration of combustion gas actuators, phased plasma actuators, and synthetic jets with MEMS-based flow sensors and adaptive controllers.
Further applications could include adaptive lift-on-demand for agile missiles and unmanned combat air vehicles, supersonic boundary layer control, lightweight gas turbine engines, and low-drag, non-intrusive methods to steer projectiles.
The XV-15 MAFC effort included more than 6h of flight tests conducted by Bell and Boeing, and programme participants included the Illinois Institute of Technology, Tel Aviv University, Israel, and the University of Arizona. NASA Langley is also partially funding the MAFC Adaptive Vehicle Integrated Technologies project, an effort to create a high-lift aerodynamic separation control system suitable for the proposed Boeing Advanced Theater Transport.
Source: Flight International
