Wind Tunnel Database Development Using Modern Experiment Design and Multivariate Orthogonal Functions

A wind tunnel experiment for characterizing theaerodynamic and propulsion forces and momentsacting on a research model airplane is described. Themodel airplane, called the Free-flying Airplane forSub-scale Experimental Research (FASER), is amodified off-the-shelf radio-controlled modelairplane, with 7 ft wingspan, a tractor propellerdriven by an electric motor, and aerobatic capability.FASER was tested in the NASA Langley 12-footLow-Speed Wind Tunnel. using a combination oftraditional sweeps and modem experiment design.Power level was included as an independent variablein the wind tunnel test, to allow characterization ofpower effects on aerodynamic forces and moments.A modeling technique that employs multivariateorthogonal functions was used to develop accurateanalytic models for the aerodynamic and propulsionforce and moment coefficient dependencies from thewind tunnel data. Efficient methods for generatingorthogonal modeling functions, expanding theorthogonal modeling functions in terms of ordinarypolynomial functions, and analytical orthogonalblocking were developed and discussed. Theresulting models comprise a set of smooth,differentiable functions for the non-dimensionalaerodynamic force and moment coefficients in termsof ordinary polynomials in the independent variables,suitable for nonlinear aircraft simulation.