A Simplified Method For Predicting Aerodynamics Of Multi Fin Weapons

A Simplified Method for Predicting Aerodynamics of Multi-fin Weapons

A Simplified Method for Predicting Aerodynamics of Multi-Fin Weapons

A new semiempirical method was developed to compute aerodynamics of multi-fin missile configurations using cruciform missile aerodynamics as a baseline. The method was developed using full Euler Computational Fluid Dynamics codes to compare computations with wind tunnel data bases for cruciform missiles as a function of Mach number, angle of attack, and aspect ratio. The Euler codes were then used for the same free stream conditions and missile configurations except the number of fins were increased from four to six and eight respectively. A table of coefficients was then formed for the aerodynamics of six- and eight-fin configurations compared to that of four-fin cases for use in the aeroprediction code or other semiempirical codes. It was concluded that this approach worked well except for subsonic Mach numbers at moderate to large angles of attack, where the Euler codes failed to predict the leeward plane flow field adequately. It is believed that full Navier-Stokes solutions could be used to improve upon this semiempirical model. Engineering judgement, in conjunction with low angle-of-attack Euler solutions were used in the regions where Euler solutions were suspect. In comparing the new semiempirical method to a limited amount of wind tunnel data on several configurations, it was concluded that the model worked well at all the conditions where data was available. However, additional wind tunnel data at higher angles of attack on six- and eight-fin configurations is needed before the method can be truly validated.

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.