Aerodynamic Sensing as Feedback for Ornithopter Flight

Flapping wing vehicles, or ornithopters, have proven difficult to control due to the unsteady flow generated by the high-speed flapping surfaces. To-date, research has focused on computational models from which fixed flapping strokes are optimized. These strokes are then fixed and executed open-loop in practice with flapping speed as the primary control output for climb and descent. This paper investigates the use of a distributed pressure sensing system embedded in the flapping wing surfaces to provide real-time aerodynamic force estimates. These measurements could ultimately be used as a source of feedback for an ornithopter autopilot system. This paper describes the design, construction, and testing of flat plate and airfoil ornithopter wings into which pressure lines were embedded during construction. The embedded pressure lines were tethered to external high-precision pressure sensors, while the wings were mounted to a commercially-available ornithopter body then affixed to an instrumented flap stand. A series of exploratory low-speed wind tunnel tests were conducted during which pressures, airspeed, wing deflections, and overall forces/torques were acquired. Initial data is consistent and is observed to match trends obtained from a panel method simulation used to generate comparative pressure measurements over the flapping stroke. Nomenclature b = wingspan, m c = chord, m h = stroke amplitude, m f = frequency of oscillation, Hz U = free stream velocity, m/s Re = Reynolds number, cVti