Refinements In The Aeroprediction Code Based On Recent Wind Tunnel Data

Refinements in the Aeroprediction Code Based on Recent Wind Tunnel Data

Refinements in the Aeroprediction Code Based on Recent Wind Tunnel Data

The 1998 (AP98) and prior versions of the aeroprediction code are based primarily on slender body and perturbation theories at low angle of attack and empirical constants that represent the nonlinear aerodynamics as a function of angle of attack, Mach number, aspect and taper ratio, and other missile geometric parameters. The primary data base upon which these empirical nonlinear constants were derived was based on the NASA/Tri-Service component data base taken in the 1970s. This data base was limited in body radius to wing semispan plus body radius ratios (r/s) of 0.5. A more recent data base taken by NASA and the former McDonnell Douglas Corporation, investigated other values of the parameter r/s of 0.25, 0.33 and 0.5. As a result of this new data base, the empirical constants in the AP98 were fine-tuned. This fine-tuning has shown the average normal force coefficient errors to be reduced by anywhere from 10 percent to over 40 percent on various missile configurations. The largest reductions in error were for configurations where the AP98 average accuracy was the worst. These new improved empirical constants will be a part of the next planned release of the aeroprediction code in 2002 (AP02). The AP98 average error on normal force coefficient of +/- 10 percent will therefore be somewhat better for the AP02.

The 2002 Version of the Aeroprediction Code

A new version of the aeroprediction code (APC), the AP02, has been developed to address the requirements arising from advanced weapon concepts. The AP02 was formed by adding significant new technology and several productivity improvements to the previous version of the APC, the AP98. New technology added included 6 and 8 fin aerodynamics, improved nonlinear aerodynamics, improved pitch damping predictions, improved power-on base drag estimates, base-bleed effect on base drag estimation, improved axial force of nonaxisymmetric bodies and trailing-edge flap capability. Other improvements and productivity enhancements include an aerodynamic smoother, ballistic and three degree-of-freedom simulation modules as well as refinements for the pre- and post-processor for inputs and outputs of the AP02. Comparison of the predicted aerodynamics of the AP02 to AP98 and experimental data showed the AP02 to be slightly better than the AP98 in most cases that both codes would handle. However, due to the additional new technology incorporated into the AP02, many new options are available in the AP02 that are not available in the AP98. Therefore, the AP02 is more robust and, on average, is slightly more accurate than the AP98 in predicting aerodynamics of weapons.