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AbstractAn investigation was conducted in theNASA Langley 20-Foot Vertical Spin Tunnel todetermine the developed spin and spin-recoverycharacteristics of a 1/28-scale, free-spinning modelof the NASA F-18 HARV (High Alpha ResearchVehicle) airplane that can beconfigured with andwithout the vertical tails installed. The purposeof the test was to determine what effects, if any,the absence of vertical tails (and rudders) had onthe spin and spin-recovery capabilities of theHARV. The model was ballasted todynamicallyrepresent the full-scale airplane at an altitude of2 5 000 feet. Erect and inverted spin tests withsymmetric mass loadings were conducted with thefree-spinning model. The model results indicatethat the basic airplane with vertical tailsinstalled (with unaugmented control system) willexhibit fast, flat erect and inverted spins fromwhich acceptable recoveries can bemade.Removing the vertical tails had little effect on theerect spin mode, but did degrade recoveries fromerect spins. In contrast, inverted spins without thevertical tails were significantly more severe thanthose with the tails installed.IntroductionCurrently, there is an interest in exploringthe feasibility of flight without the use of verticalstabilizers. The maturation of thrust vectoring hasallowed designers to begin considering taillessdesigns as a means o f reducing drag, for example.But the primary driver behind this interest ist hepursuit of low radar cross section (RCS), or?stealth? characteristics that are superior to thoseavailable oncontemporary designs such as t heF-117A and F-22. On these configurations, radar-reflecting vertical tails must be compensated forusing various stealth techniques. However, it isunlikely that any current technology could beexpected to provide the low-RCS characteristicsthat could berealized byremoving asource ofradar reflections altogether.An investigation was conducted in theNASA Langley 20-Foot Vertical Spin Tunnel todetermine what effects, if any, the lack ofverticaltails had on the spin and spin-recoverycharacteristics of a 1/28-scale free-spinning modelof the NASA F-18 HARV airplane. The HARVwas chosen asthe subject for this study because itrepresents acurrent fighter configuration and isequipped with thrust vectoring which could beused tocompensate for the lack of vertical tails.This investigation consisted ofdeveloped (i.e.,equilibrium) erect and inverted spins andrecoveries, with and without the vertical tailsinstalled. Both erect and inverted tests wereconducted. Data, in the form of motion timehistories, were obtained via an optical dataacquisition system installed inthe Spin Tunnel(ref. 1).Note that the present test was not anexhaustive free spin test (e.g., the F/A-18 testdescribed in reference 2). In a typical free spin testprogram, a model is launched into the Spin Tunnelupwards of one thousand times. With such alargenumber oftests, all ofthe equilibrium spin modesthat will bepossible for the airplane inquestionare identified. In contrast, the current test programwas meant only toidentify major trends in theresults that resulted from varying geometricparameters ona model whose basic spin modeswere already well documented. Therefore, all ofthe spin modes possible with the modified modelmay not have been identified in the present test.Symbolsb wing span, ftcwing mean aerodynamic chord, ftCnbody axis yawing moment coefficientIx, Iy, Izmoment of inertia about the x, y, or z body axis, respectively, slug-ft2llinear dimension, ftm mass of model or airplane, slugsN model-to-airplane scale ratioS wing area, ft2Re Reynolds number,Vln