1、I NASA TECHNICAL NOTE NASA TN D-5361 I F * IM z + 4 m 4 z CASE FILE - COPY ANALYSIS OF LATERAL-DIRECTIONAL I STABILITY CHARACTERISTICS OF A TWIN-JET FIGHTER AIRPLANE AT HIGH ANGLES OF ATTACK by Joseph R. Chumbers und Ernie L. At2glin Langley Research Center Langley Stdon, Humpton, Vu, NATIONAL AERON
2、AUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. AUGUST 1969 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. I 2. Government Accession No, NASA TN D-5361 17. Key Words Suggested by Author(s) 4. Title and Subtitle ANALYSIS OF LATERAL-Dl
3、 RECTIONAL STABILITY CHARACTER1 STICS OF A TWIN-JET FIGHTER AIRPLANE AT HIGH ANGLES OF ATTACK 18. Distribution Statement 7. Author(s) JoseDh R. Chambers and Ernie L. Analin 19. Security Classif. (of this report) Unclassified 9. Performing organization Name ond Address NASA Langley Research Center La
4、ngley Station Hampton, Va. 23365 20. Security Classif. (of this page) 21. No. of Pages 22. PriceX Unclassified 47 $3.00 2. Sponsoring Agency Name and Address National Aeronautics and Space Administration Washington, D.C. 20546 15. Supplementary Notes 3. Recipients Catalog No. 5. Report Date August 1
5、969 6. Performing Organization Code 8. Performing Organization Report No. L-6723 IO. Work Unit No, 126-62-01-01-23 11. Contract or Grant No. 13. Type of Report ond Pertod Covered Technical Note 14. Sponsoring Agency Code 16. Abstract An investigation was conducted to determine the factors producing
6、a directional divergence at high angles of attack for a twin-jet swept-wing fighter airplane. The study consisted of static wind-tunnel tests, tuft-flow visualization tests. and calculations of the dynamic lateral-directional stability characteristics of the airplane. Several modifications to the ba
7、sic configuration were evaluated in an attempt to delay or eliminate the instability. Lateral-directional stability Dynamic stability Stability at high angles of attack Unclassified -Unlimited For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151
8、Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANALYSIS OF LATERAL-DIRECTIONAL STABILITY CHARACTERISTICS OF A TWIN-JET FIGHTER AIRPLANE AT HIGH ANGLES OF ATTACK By Joseph R. Chambers and Ernie L. Anglin Langley Research Center SUMMARY An investigati
9、on was conducted to determine the factors producing a directional divergence at high angles of attack for a twin-jet swept-wing fighter airplane. The study consisted of static wind-tunnel tests, tuft-flow visualization tests, and calculations of the dynamic lateral-directional stability characterist
10、ics of the airplane. Several modifica- tions to the basic configuration were evaluated in an attempt to delay or eliminate the instability. The results of the investigation indicated that the directional divergence exhibited by the airplane was brought about by a simultaneous loss of directional sta
11、bility and effec- tive dihedral at high angles of attack. The loss of directional stability resulted from a combination of an adverse sidewash region at the rear of the airplane and a reduced dynamic pressure at the vertical tail location. The adverse sidewash was generated by the wing-fuselage comb
12、ination and was related to stalling of the leading-wing panel during a sideslip at high angles of attack. The loss of effective dihedral was also attributed to leading-wing-panel stall. The apparent directional divergence was determined to be, in reality, a highly unstable Dutch roll oscillation. Th
13、e only geometric modification studied that significantly delayed the divergence was wing leading-edge droop. INTRODUCTION The National Aeronautics and Space Administration is currently conducting a series of investigations of the poststall characteristics of a high-performance swept-wing fighter air
14、plane. Recently, concern has arisen over the existence of directional divergence (sometimes termed “nose slice“) at angles of attack near the stall. Tactical training and air combat maneuver requirements imposed on the airplane have resulted in operational angles of attack near the stall and the ass
15、ociated directional divergence which in turn has produced inadvertent poststall gyrations and spins. Inasmuch as instabilities of this type can seriously limit the maneuvering capability of an airplane, the present investigation was conducted (1) to identify the various factors producing the directi
16、onal divergence and (2) to define geometric modifications or fixes which might eliminate or postpone the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-instability to angles of attack farther removed from the operational flight envelope. The study c
17、onsisted of static wind-tunnel force tests, flow visualization tests, and calculations of the dynamic lateral-directional stability of the airplane. SYMBOLS All aerodynamic data with the exception of lift and drag are presented with respect to a body system of axes. Moment data are presented with re
18、spect to a center-of-gravity position of 33 percent of the wing mean aerodynamic chord. Dimensional values herein are given in both U.S. Customary Units and in the International System of Units. A,B,C,D,E coefficients of lateral-directional characteristic equation (see appendix A) wing span, ft (m)
19、mean aerodynamic chord, ft (m) mean aerodynamic chord of horizontal tail, ft (m) drag coefficient, FD/q,S lift coefficient, FL/q,S rolling-moment coefficient, MX/q.,Sb pitching-moment coefficient, My/q,Sc yawing- moment coefficient, Mz/ q,Sb side-force coefficient, Fy/q,S differential operator, d ds
20、b drag force, Ib (N) lift force, lb (N) side force, lb (N) horizontal tail deflection (positive when trailing edge is down), deg I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I i JX IY ! Iz moment of inertia about longitudinal body axis, slug-ft2
21、 (kg-ma) moment of inertia about lateral body axis, slug-ft2 (kg-m2) moment of inertia about normal body axis, slug-ft2 (kg-ma) product of inertia, slug-ft2 (kg-ma) radius of gyration in roll about principal longitudinal axis, ft (m) radius of gyration in yaw about principal normal axis, ft (m) nond
22、imensional radius of gyration in roll about principal longitudinal axis, kXO/b kZO/b nondimensional radius of gyration in yaw about principal normal axis, vertical tail length, distance from moment reference center to aerodynamic center of vertical tail measured along fuselage center line, ft (m) ai
23、rplane mass, slugs (kg) Mach number rolling moment, ft-lb (m-N) pitching moment, ft-lb (m-N) yawing moment, ft-lb (m-N) rolling velocity, rad/sec period of oscillation, sec effective dynamic pressure at vertical tail location, lb/ft2 (N/m2) free-stream dynamic pressure, lb/ft2 (N/m2) yawing velocity
24、, rad/sec 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-S wing area, ft2 (m2) sb nondimensional time parameter based on wing span, Vt/b t time, sec time required for amplitude of oscillation to decrease by a factor of 2, sec velocity, ft/sec (m/s
25、ec) angle of attack, deg or rad angle of sideslip, deg or .rad constants used in solution of characteristic equation root of lateral-directional characteristic equation Ah4 + BX3 + CA2 + Dh + E = 0 lateral-directional relative-density factor, m/pSb mass density of air, slugs/ft3 (kg/m3) sidewash ang
26、le, deg angle of bank, deg or rad angle of yaw, deg or rad Cnp = pb a- 2v - - nr e 2v aCY cyr = - rb a- 2v 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IZ - - C sin (Y n0,dynamic = cn B Ix increment of C due to vertical tail ACnk “B Model compon
27、ent designations: F fuselage H horizontal tail V vertical tail W wing DESCRIPTION OF AIRPLANE The airplane studied in the investigation is a two-place twin- jet high-performance fighter designed for land and carrier-based operations. A three-view sketch showing the general layout of the configuratio
28、n is presented in figure 1, geometric characteristics of the airplane are listed in table I, and typical mass characteristics for normal flight opera- tions (no external stores) are presented in table II. The longitudinal control system of the airplane consists of an all-movable horizontal tail (sta
29、bilator) which incorporates 23O negative dihedral (droop) to satisfy longitudinal stability requirements in the normal oper- ational flight range. The airplane lateral control system consists of upper-surface spoilers and ailerons. The control system is mechanized such that the ailerons deflect down
30、ward only while the spoilers deflect upward. The left aileron and right spoiler oper- ate simultaneously as do the right aileron and left spoiler. The directional control sys- tem consists of a conventional rudder. The maximum control-surface deflections are as follows: Rudder deflection, deg . i30
31、Stabilator deflection (trailing edge), deg. 21 up, 9 down Aileron deflection, deg 0 up, 30 down Spoiler deflection, deg 45 up, 0 down Mass loadings such as those presented in table I1 are typical of those of modern high-performance fighter airplanes and result from the fact that the major portion of
32、 the airplane mass is distributed along the fuselage; therefore the values of IZ and Iy are several times as great as those of IF This type of inertial distribution has significant 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-effects on dynamic
33、lateral-directional stability at high angles of attack as is discussed subsequently. FLIGHT MOTIONS The directional divergence exhibited by the airplane at high angles of attack is illus- trated by the time histories presented in figure 2. Shown in figure 2 are flight recorder traces of the major fl
34、ight variables and control- surface deflections during an accelerated stall at 25 000 feet (7620 m) with the airplane configured for cruise flight (M = 0.4). Unfortunately there is no record of yaw angle or yaw rate. The maneuver was initiated by rolling to a 60 banked turn to the left. Angle of att
35、ack was then increased at an approximately constant rate. The normal acceleration trace indicates airframe buffet occurred at angles of attack as low as loo. At about 38 seconds the magnitude of the normal acceleration trace starts to decrease, even though angle of attack is increasing, thereby indi
36、cating major stall. The angle of attack at this time was about 18; this value should be remembered when analyzing the force test results presented subsequently. As the angle of attack increased further, lightly damped lateral oscillations about the longi- tudinal body axis (termed “wing rock“) becam
37、e noticeable. At about 44 seconds severe wing rock was experienced; at about 50 seconds the oscillation diverged violently and the airplane entered a 2i-turn spin to the right. The flight path was about 40 below the horizon during the spin; therefore the spin appears as a continuous roll with refere
38、nce to the earth axes. The angle of attack at the time of directional divergence was between 20 and 25O; this range of angle of attack should also be remembered for subsequent reference. METHOD OF ANALYSIS Static wind-tunnel force tests were conducted to determine the aerodynamic charac- teristics o
39、f the airplane at high angles of attack. Airframe components were tested indi- vidually and in several combinations to determine the contributions of the isolated com- ponents to the overall stability characteristics of the airplane and to determine mutual interference effects. Several geometric mod
40、ifications or fixes to the basic configuration were evaluated in an attempt to delay or eliminate lateral-directional instability near the stall. The dynamic stability characteristics of the airplane were calculated by using linear three-degree-of-freedom equations of motion. The static and dynamic
41、aerodynamic sta- bility derivatives used as input data in these calculations were measured quantities deter- mined in wind-tunnel tests of a model of the airplane. 6 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Model and Test Equipment The wind-tu
42、nnel data presented herein were obtained with a l/ll-scale model tested at the Langley Research Center in a low-speed wind tunnel with a 12-foot (3.66-m) octag- onal test section. Additional data obtained at higher values of Reynolds number during tests of a 1/15-scale model at the Ames Research Cen
43、ter are also presented for purposes of correlation. The two models differed in external engine inlet configuration and hori- zontal tail leading-edge configuration as shown in figure 3 - the inlets and horizontal tail of the l/ll-scale model being representative of those of an earlier airplane confi
44、guration and the inlets and horizontal tail of the 1/15-scale model being representative of those of a later airplane configuration. Both models had blocked inlets - that is, flow through the engines was not simulated. A number of geometric modifications to the basic airplane configuration were eval
45、uated as possible fixes for the lateral-directional stability problem during the course of the study. These modifications, summarized in figure 4, consisted of vertical end plates on the stabilator, afterbody strakes, nose strakes, wing apex notches, wing fences, wing leading-edge droop, and two mod
46、ified vertical tail surfaces. Tests Wind-tunnel force tests of the l/ll-scale model were conducted at low-subsonic speeds at a Reynolds number of 0.5 X 106 based on the mean aerodynamic chord of the wing. Measurements were made of the six force and moment components over an angle- of-attack range fr
47、om Oo to 400 for a range of angle of sideslip of doo. The wing, fuselage, vertical tail, and horizontal tail were tested in several combinations. Tuft-flow visualiza- tion tests were conducted to aid in the interpretation and understanding of the force test results. A limited number of dynamic-press
48、ure and sidewash measurements at the verti- cal tail location were also made in conjunction with an analysis of the effectiveness of the vertical tail at high angles of attack. Additional low-subsonic force test data measured at a Reynolds number of 4.3 x lo6 at the Ames Research Center are also pre
49、sented. Calculations The dynamic stability characteristics of the lateral-directional modes of motion were calculated for the basic and modified airplane configurations by uslng the linearized three-degree-of -freedom equations of motion presented in appendix A. The calculated characteristics included the period P and time to half-amplitude t of the Dut
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