Air vehicle flight in turbulence is generally treated as an anomalous part of the flying environment. Aircraft geometries and flight-control systems are often designed and tested for calm atmospheric conditions, where both steady winds and gusts are minor. As a result, the flight performance of small aircraft deteriorates in the presence of atmospheric turbulence, where gust disturbances can be large relative to the flying speeds. A better approach is needed in the aircraft and control system design process that specifically accounts for the effects of turbulence and provides a means of mitigating disturbances to improve the mission effectiveness of micro unmanned air vehicles and small unmanned air vehicles. The current research considers untethered flight tests of a small unmanned air vehicle in a large wind engineering tunnel that can be configured to replicate turbulence levels expected from urban and suburban environments. Systematic changes to the configuration of the fixed-wing aircraft are made to evaluate the role of metrics, such as c.g., mass, moment of inertia, wingspan, and wing loading to turbulence sensitivity. Estimates of the force and moment disturbances indicate that some parameters, such as moment of inertia, have simple and expected influences on the response to turbulence. Conversely, wing area and mass have conflicting effects due to the compounded influences on the aircraft response. The sensitivity of the various aircraft configurations to turbulence are presented as control equivalent turbulence disturbances, which equate forces and moments acting on the airframe to control deflections. This method normalizes the aircraft responses with respect to the ability to suppress disturbances with actuated controls. Nomenclature A = system dynamics a y = lateral acceleration a z = vertical acceleration B = control effectiveness b = wingspan C = state observation c = wing chord E = disturbance dynamics F = fit quality I x;y;z = moments of inertia I xz = product of inertia l = rolling moment m = pitching moment n = yawing moment p = roll rate q = pitch rate q = dynamic pressure r = yaw rate S = wing area u, = control input V 0 = velocity x = state vector Y = side force y = measurements Z = vertical force = angle of attack = angle of sideslip Subscripts d = disturbance force/moment lat = lateral lon = longitudinal T = total force/moment contributions a = aircraft-only force/moment contributions a = aileron e = elevator r = rudder

Aspects of the turbulent wind environment Micro Air Vehicles (MAVs) experience when flying outdoors were replicated in a large wind tunnel. An overview of the facility, instrumentation and initial flight tests is given. Piloting inputs and aircraft accelerations were recorded on fixed and rotary wing MAVs and for some tests, measurements of the approach flow (u,v,w sampled at 1,250Hz at four laterally disposed upstream locations) were made. The piloting aim was to hold straight and level flight in the 12m wide × 4m high × ~50m long test section, while flying in a range of turbulent conditions. The Cooper-Harper rating system showed that a rotary craft was less sensitive to the effects of turbulence compared to the fixed wing craft and that while the fixed wing aircraft was relatively easy to fly in smooth air, it became extremely difficult to fly under high turbulence conditions. The rotary craft, while more difficult to fly per. se., did not become significantly harder to fly in relatively high turbulence levels. However the rotary craft had a higher mass and MOI than the fixed wing craft and further work is planned to understand the effects of these differences.

No abstract

No abstract