1、NASA T!? 15 92 c .1 NASA Technical Paper 1592 Effects of Fuselage Forebody Geometry on Low-Speed Lateral-Directional Characteristics of Twin-Tail Fighter Model at High Angles of Attack Peter C. Carr and William P. Gilbert DECEMBER 19 79 Provided by IHSNot for ResaleNo reproduction or networking perm
2、itted without license from IHS-,-,-TECH LIBRARY KAFB, NM 0334765 NASA Technical Paper 1592 Effects of Fuselage Forebody Geometry on Low-Speed Lateral-Directional Characteristics of Twin-Tail Fighter Model at High Angles of Attack Peter C. Carr Dryden Flight Research Center Edwards, California Willia
3、m P. Gilbert Langley Research Center Hampton, Virginia National Aeronautics and Space Administration Scientific and Technical Information Branch 1979 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SUMMARY Wind-tunnel tests have been conducted with a
4、 modern fighter configuration to explore the effects of fuselage forebody geometry on lateral-directional characteristics at high angles of attack and to provide data for formulating general design procedures. The investigation consisted of low-speed, static, wind-tunnel tests of a fighter model ove
5、r a large angle-of-attack range with eight different forebody configurations; also included was consideration of forebody devices such as nose strakes, boundary-layer trip wires, and nose booms. Results were obtained in the areas of lateral-directional aerodynamic sym- metry and stability and longit
6、udinal stability. In general, forebody design features such as fineness ratio, cross-sectional shape, and devices like fore- body strakes and nose booms had a large influence on both lateral-directional and longitudinal aerodynamic stability. For the airplane configuration tested, results showed tha
7、t several of the forebodies produced both lateral-directional aerodynamic symmetry and strong favorable changes in directional and lateral stability. Hawever, the same results also indicated that such forebody designs could produce significant reductions in longitudinal stability near maximum lift a
8、nd could significantly change the influence which other configuration variables have on airplane stability. Furthermore, these tests indicated that the addition of devices such as flight-test nose booms to highly tailored fore- body designs could significantly degrade the stability improvements prov
9、ided by the clean forebody. INTRODUCTION High performance military airplanes designed for air-to-air combat are normally flown at extremely high angles of attack to obtain the turning perfor- mance required to maneuver effectively at subsonic speeds. The values of angle of attack reached during such
10、 vigorous air combat maneuvers often approach, and at times exceed, the angle of attack for maximum lift. At such extreme angles of attack, fighter configurations may experience Parge aerodynamic asymmetries, along with a severe degradation in stability and control characteristics; these degraded ch
11、aracteristics can result in inadvertent loss of control and spin entry. In view of the relative importance of high angle-of-attack flight char- acteristics for highly maneuverable aircraft, considerable emphasis has been placed on developing airframe and automatic-control-system concepts which pro-
12、vide a high degree of stability, control, and spin resistance for such flight conditions. Recent research conducted by the NASA Langley and Ames Research Centers (refs. 1 to 6) and by airframe contractors (ref. 7) has indicated that the relatively long, pointed fuselage forebody used for many curren
13、t fighter configurations can have significant, and sometimes predominant, effects on Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-aerodynamic characteristics at high angles of attack. These effects include the generation of extremely large asymmet
14、ric yawing moments and large varia- tions in static and dynamic directional stability. The present investigation was conducted to further explore the effects of geometric variations of fuselage forebody shape on lateral-directional and longitudinal characteristics for a current fighter configuration
15、 with twin vertical tails. The primary objective was to provide additional data for use in formulating general design procedures. The investigation consisted of low- speed wind-tunnel tests over a large range of angles of attack for a model with eight different forebody configurations. The forebodie
16、s tested included six different cross-sectional shapes and two forebody fineness ratios. The tests also included an evaluation of the effects of nose strakes, boundary-layer trip wires, and nose booms affixed to several of the forebodies. Previous inves- tigations (refs. 1 to 7) have shown that such
17、 add-on devices as nose strakes and nose booms (for flight-test air-data measurements) can strongly influence forebody aerodynamics at high angles of attack. In addition, a recent paper (ref. 8) has shown that small boundary-layer trip wires, when properly placed on the forebody, can suppress the de
18、velopnent of large yawing-moment asymme- tries at high angles of attack. The two aerodynamic parameters of primary interest in the present study were (1) the yawing moment measured at zero sideslip and high angles of attack, and (2) the variation of static direc- tional stability with angle of attac
19、k. All the lateral-directional results are presented herein, together with selected longitudinal data. Results of a water-tunnel flaw visualization study, which was conducted to parallel this investigation, are presented in reference 9. SYMBOLS AND ABBREVIATIONS All longitudinal forces and moments a
20、re referenced to the stability-axis system and all lateral-directional forces and moments are referenced to the body-axis system shown in figure 1. Moment data presented are referenced to a moment center located longitudinally at 26 percent of the wing mean aerody- namic chord. Dimensional quantitie
21、s are presented in both the International System of Units (SI) and U.S. Customary Units. Measurements were made in U.S. Customary Units, and conversions were made with the conversion factors given in reference 10. b wing span, m (ft) - C wing mean aerodynamic chord, m (ft) FD CD drag coefficient, -
22、ss FL CL lift coefficient, - ss 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Mv 1 C1B = rolling-mment coefficient, - ;i Sb Mv I pitching-moment coefficient, - ;is3 yawing-moment coefficient, - G* FY qs side-force coefficient, - drag force, N (lb
23、) lift force, N (lb) side force, N (lb) fuselage station rolling moment, N-m (ft-lb) pitching moment, N-m (ft-lb) yawing moment, N-m (ft-lb) free-stream dynamic pressure, Pa (lb/ft2) resultant airspeed water 1 ine body reference axes (see fig. 1) angle of attack , deg angle of sideslip, deg horizont
24、al tail deflection, deg 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Model designations: CIR circular cross section DKB duckbill cross section EMAH elliptical cross section with horizontal major axis EMAV elliptical cross section with vertical m
25、ajor axis SHK shark nose cross section BACKGROUND Historically, design trends for fighter configurations have resulted in rapid and dramatic variations in geometric airframe designs as depicted in fig- ure 2. The relative shape and length of the fuselage forebody have changed completely, from the sh
26、ort, blunt-nose geometry of fighters of World War I1 vintage to the long, pointed noses employed in current supersonic fighters. Because of the long moment arm between the nose and the center of gravity of the airplane, the long, pointed nose can generate strong vortex flows at high angles of attack
27、 which result in differential forces on the nose and extremely large aerodynamic moments. The munents produced by the fuselage forebody can be much larger than those produced by the tail and control surfaces. If the moments are beneficial, the stability and control characteristics of the air- plane
28、are significantly enhanced; however, if the moments are adverse, loss of control may occur. The aerodynamic effects produced by the forebody are of interest under conditions of zero and nonzero sideslip. As discussed in references 2 to 7, the large asymmetric yawing moments produced by long, pointed
29、 noses are of considerable importance to studies of departure and spin. As shown in fig- ure 3, flow separation on a long nose at zero sideslip tends to produce a sym- metrical pattern of vortex sheets at low angles of attack. This symmetrical flow pattern does not produce any side force on the nose
30、; consequently, no yawing moment is produced. At higher angles of attack, however, the vortices increase in strength; the flow pattern becomes asymmetrical; and the asymmetri- cal flow produces a side force on the nose which, in turn, produces a yawing moment about the airplane center of gravity. Fo
31、r extremely high angles of attack, such as those angles associated with post-stall flight and spins, these shapes have been found (refs. 2 and 7) to produce large asymmetric yaw- ing moments which can be much larger than the corrective moments produced by deflection of a conventional rudder. These m
32、oments may have a predominant effect on stall and spin characteristics and can, in fact, determine the ease and direction in which an airplane may spin. (See reference 2.) Although the aerodynamic asymmetries produced by sharp noses havebeen measured in past wind-tunnel investigations of airplane sp
33、in characteristics, the basic flaw phe- nomena were not well understood. As a result, the asymmetries either have often been ignored or have been attributed to poor wind-tunnel flow or significant model asymmetries. The more recent flight test results reported in reference 7 4 -I Provided by IHSNot
34、for ResaleNo reproduction or networking permitted without license from IHS-,-,-indicated that such asymmetries exist for full-scale aircraft and flight con- ditions and that the asymmetries can cause loss of control and spin entry. With regard to nonzero sideslip conditions, past studies such as tho
35、se discussed in references 2, 5, and 7 have shown that certain fuselage forebody designs can produce a high level of directional stability, and that geometric variables such as forebody fineness ratio and cross-sectional shape apparently can be used to take advantage of this potentially beneficial e
36、ffect. Moreover, results presented in reference 7 also point out that forebody geometry changes may substantially effect longitudinal characteristics (pitching moment). In order to derive quantitative design information on desirable and feasi- ble fuselage forebodies, research is required in two are
37、as. First, the aero- dynamic effect of forebody geometric variables such as cross-sectional shape, nose fineness ratio, and nose probes and booms must be determined; second, the effects of aerodynamically beneficial nose-radome-shapes on radar performance must be assessed. The primary objectives of
38、the present investigation were (1) to explore the beneficial aerodynamic effects produced by proper shaping of the fuselage forebody of a current fighter configuration and (2) to correlate the results with those obtained during past studies of other configurations. Thus, addi- tional data would be p
39、rovided to formulate general design procedures. DESCRIPTION OF MODEL The investigation was conducted with a 0.10-scale free-flight model which was used in the tests reported in reference 11 . The model was refurbished for the current testing and modified to accept several different fuselage forebody
40、 designs. A three-view sketch of the model is shown in figure 4, and some per- tinent dimensional characteristics of the model are presented in table I. As indicated in figure 4, the parting line used for mounting the various forebodies was located just forward of the canopy. Eight different fuselag
41、e forebodies were tested in this investigation, including the forebody of the basic model. The various forebodies are identi- fied in terms of fineness ratio and cross-sectional shape. The fineness ratio definition used in this study was the ratio of the forebody length (measured from the parting li
42、ne to the tip) to the forebody depth (vertical dimension measured at the parting line) as shown in figure 4. Note that several methods of defining fineness ratio have evolved in the literature and that the method used in this report may differ from definitions used in other studies. Fineness ratios
43、used in these tests were 2.3 for the basic model forebody and 3.5, which is representative of the forebody of the airplane discussed in reference 7. To facilitate ease of discussion of the various forebodies tested, a simple designation has been assigned for each forebody; the designation refers to
44、the forebody fineness ratio (either 2.3 or 3.5) and the forebody cross- sectional shape. Cross-sectional shapes are identified as follows: 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- Abbreviation or acronym CIR E“l EMAV SHK DKB . “. Shape Circ
45、ular Elliptical, with major axis horizontal Elliptical, with major axis vertical Shark nose Duckbill nose “. . . . “ . Using this scheme, the forebodies are referred to in this report as follows: Designation 2.3 CIR 3.5 CIR 3.5 SHK 3.5 DKB 2.3 EMAH 3.5 EMAH 3.5 EMAV Blunt Shape 0 0 0 Forebody descri
46、ption . . . Basic short forebody (2.3 fineness ratio) with circular cross section Long forebody (3.5 fineness ratio) with circular cross section Shark-nose forebody with 3.5 fineness ratio Duckbill forebody with 3.5 fineness ratio 2.3 fineness ratio forebody with elliptical cross section with horizo
47、ntal major axis 3.5 fineness ratio forebody with elliptical cross section with horizontal major axis 3.5 fineness ratio forebody with elliptical cross section with vertical major axis Blunt forebody representing fuselage with- out forebody In addition to tests of these forebody shapes, the study als
48、o included tests of several forebody add-on devices as listed in the following table: 6 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Forebody 2.3 CIR 3.5 CIR 3.5 DKB 3.5 EMAV “ . - . . - Strake J J J Add-on device Nose boom J J Photographs and ske
49、tches of the various forebodies and forebody add-on devices are shown in figures 5 to 9; a photograph of the model with the 3.5 DKB forebody is shown in figure 10. It is important to note that the trip wire shown in figure 9 is mounted on the forebody in a unique fashion and is most effective only if mounted in such a helical pattern (ref. 8). The diameter,
