2V full-scale rate of descent, ft/sacalculated angle of attack at model orairplane center of rotation,a=arctan(tan(a)cos(f)), degaq+90, angle between model fuselagereference waterline and vertical inSpinTunnel, degbcalculated sideslip angle at model orairplane center of rotation,b=arcsin(sin(a)sin(f)), degdaaileron deflection, degdddifferential horizontal stabilizerdeflection, degdfleading-edge flap deflection, degdrrudder deflection, degfroll angle, degmrelative density ofmodel orairplane,m/rSbnkinematic viscosity of air, ft2/srdensity of air, slugs/ft3sratio of air density at altitude tothat atsea levelqpitch angle, degWfull-scale spin rate about vertical axis,deg/syyaw angle, degAbbreviations:A against the spinc.g. center of gravityD leading-edge flap deflected down, orother control surface deflected trailing-edge downDOF degrees of freedomIPMP inertia pitching moment parameter, Iz-Ixmb2IRMP inertia rolling moment parameter, Iy-Izmb2IYMPinertia yawing moment parameter, Ix-Iymb2MSPSModel Space Positioning System, SpinTunnel data acquisition systemRCS radar cross sectionU inner wing up, or control surface deflectedtrailing edge upW with the spinModelAn existing 1/28-scale model of the NASAF-18 High Alpha Research Vehicle (HARV),fabricated at the NASA Langley Research Center,was tested inthe Langley 20-Foot Vertical SpinTunnel. The thrust vectoring vanes and actuators onthe HARV airplane were not represented onthemodel. The model was modified sothat thevertical tails were removable at the surface of thefuselage. The rudders could beactuated for testswith the tails installed. The dimensionalcharacteristics of the airplane are presented intable 1. A three-view drawing ofthe unmodifiedmodel appears in figure 1. A drawing ofthe modelwith the vertical tails removed appears infigure2.Photographs ofthe model as-tested with thevertical tails installed appear in figure 3.The model was ballasted to obtaindynamic similarity tothe airplane at analtitudeof 25 000 ft(r= 1.065 x 10-3slug/ft3) using Froudescaling. The dynamic scaling relationships,discussed indetail inreferences 3 and 4, arepresented intable 2. The mass characteristics,center of gravity, and moment ofinertiaparameters used for the airplane and for the modelas-tested are presented in table 3.