Improved Aerodynamics for Configurations with Boattails

Abstract

Aeroprediction, Incorporated undertook a review of the 2005 version of the Aeroprediction Code (AP05) when applied to configurations with boattails. It was found the code gave poor results for roll and pitch damping for configurations with long boattails (boattails greater than about 1 caliber in length). It was found that center of pressure predictions needed improvement as well. As a result, several improved methods were developed and implemented into the AP05 which will be released in 2009 as the AP09. Comparison of the new methods to experimental data for projectiles, mortars, and low-drag bombs showed significant improvement in roll and pitch damping predictions, as well as improvement in normal force and center of pressure. NomenclatureA ref = reference area, maximum cross-sectional area of body, if a body is present, or planform area of wing, if wing alone), ft 2skin friction, and wave components, respectively, of axial force coefficientbased on reference area and body diameter, if body present, or mean aerodynamic chord, if wing alone C M B , C M T = pitching moment coefficient of body or tail alone, respectively C M q C M = pitch damping moment coefficient= normal-force coefficient of body alone C N , C N n;a;b = total normal-force coefficient derivative, per radian, and normal-force coefficient derivative of nose, afterbody, or boattail, respectively C P = pressure coefficient P Pc r , c t = local chord, root, and tip chord, respectively c.g. = center of gravity location, cal, ft, or in. d B = body base diameter, ft d N = diameter of truncated nose tip, ft d ref = reference body diameter, ft F 6 , F 8 = empirical factors used to represent aerodynamics of six and eight fins based on four fin aerodynamics ', ' n , ' a , ' B = total body, nose, afterbody, or boattail length, respectively, ft or cal M 1 = freestream Mach number P L , P 1= local and freestream pressure, respectively, lb=ft 2 p, q = roll and pitch rate, respectively, rad=s Q L , Q 1 = local or freestream dynamic pressure, lb=ft 2 r B , r W = local body radius and body radius at wing, respectively, ft r r = reference body radius, ft X c:g:= distance to center of gravity, ft X c:p: , X c:p: n;a;b = center of pressure (in ft or cal from some reference point that can be specified) in x direction or center of pressure of a body component, respectively X c:p: =d = center of pressure (cal from some reference point) X LE , X AFT = distance from nose tip to wing leading edge or afterbody = angle of attack, deg = boundary-layer displacement thickness, ft b = boattail angle, deg = roll position of missile fins [ 0 deg corresponds to fins in the plus () orientation, 45 deg corresponds to fins rolled to the cross () orientation].