Development of an Air Data System for Ducted Fan Unmanned Aircraft

Analysis and wind tunnel testing performed as part of a development program for a family of ducted fan unmanned aircraft has generated a significant database of wind tunnel data. These include force and moment data as well as duct lip surface pressures over a range of flight velocities, fan speeds, and vehicle tilt angles. In recognition of the need for a simple, lightweight, and robust air data system for this class of UAV, a study was undertaken to correlate duct pressure data to freestream flow velocities. Sample pressure data and a simple correlation methodology is presented in this paper. Results from this study indicate a strong correlation is present between duct pressures and freestream flow velocities, with very good system sensitivities at flow speeds at and well below 5 knots for the vehicles studied. Nomenclature c = duct chord Cp = pressure coefficient d = inner duct diameter n = fan speed (1/sec) p = surface static pressure (dimensional, usually psi) pwindward = pressure on windward side of duct pleeward = pressure on leeward side of duct V, Vx = freestream velocity xb = body x axis yb = body y axis zb = body z axis = vehicle angle of attack = air density I