' ABB No. L'^23 ^y I NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGlNALLy ISSUED April 19*^5 as Advance Restricted Beport L5C23 FLIGHT TESTS OF THE LATERAL COHTROL CHARACTERISTICS OF AN F6F-3 AIE^PLANE EQUIPPED WITH SPRING-TAB AILERONS By Walter C. Williams Langley Memorial Aeronautical La"boratory Langley Field, Va. NACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid dlstribuUon of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. L - IU9 DOCUMENTS DEPARTMENT MCA ARR No. L5C25 "i^ (j ^ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS ADV.^.rCE RESTRICTED REPORT FLIGHT TESTS OF THE LATERAL CONTROL CHARACTERISTICS OP AN f6f-5 AIRFLAITE equipped VITH SPRING-TAB AILERONS By VJalter 0. Williams SUMI".ARY Flight tests were n-.ade to determine the lateral con- trol characteristics of an f6f-5 airr>lane equipped, with spring-tab ailerons, which were developed hy the Grumtnan Aircraft Engineering Corp. and have "been made a production installation on F6r airplanes. The flight tests showed that the spring-tab ailerons liad desirably light stick forces and no tendency to over- balance. Although the tabs were not mass-balanced, no flutter tendencies were indicated at speeds up to LoO relies per hour, and any oscillations following abrupt control deflections were heavily damped. The spring- tab ailerons gave 80 percent higher values of effectiveness with a 50-pound stick force at l\.00 m.lles per hour than the original ailerons on the p6f-3 airplane. At speeds lower than 275 ^'^^iles per hour, the spring-tab ailerons were less effective than the original ailerons because of restricted aileron travel as a result of the use of large stick deflection to deflect the spring tab. Recommendations are made for m.odif ications that would increase the aileron effectiveness at low speeds without affecting the lateral control at high speeds. The m.odif ications consist of increasing the available aileron deflection and modifying the spring-tab arrangement. Such an arrangement might, however, be m.ore susceptible to flutter than the produc- tion Installation. INTRODUCTIO] Flight tests were m.ade to determine the lateral con- trol characteristics of an f6f-5 airplane equipped with spring-tab ailerons, which were developed by the GruiTunan Aircraft Engineering Corp. and have been made a production NACA ARR No. L^C;:i3 installation on f6f airplanes. Considerable interest has been shown in the use of spring tabs as a means of balancing control surfaces on high-speed airplanes, because spring tabs per.-Dlt light control forces to be obtained at high speeds without iiiaking the balancing action critical to siriall changes in control-surface contour. These advantages are obtained because the balancing action provided by a spring tab is proportional to the applied control force, and. very close aerodynamic balance of the control surface is not required. AIRPLANE AND AILERONS The p6f-5 airplane is a low-wing, sin^;le-place, single-engine, fighter- type monoplane. A three -view drawing of the airplane is shown as figure 1. The spring- tab ailerons nave a Frise typo nose balance and are identical to the original I'6f-3 ailerons except that a spring tab has been installed on each aileron. These spring tabs are identical in size and location to the trim tab on the original FbF-J ailerons; in the case of the spring-tab ailerons, however, the tab on the left •r.ileron is a combination trim and spring tab. Details of the spring- tab aileron arrangement are shown in fig- ures 2 and J, which were furnished by the Grummo-n Aircraft En.gineering Corp. Dimensions pertinent to the aileron characteristics are as follows: 7/ing- span, feet 1^2.85 Aileron span (each), feet o.375 Distance from, center line of airplane to inboard end of aileron, percent sem.isTDan .... 6I4. Aileron chord, percent wing chord 20 Aileron area behind hinge line (each), square feet . 7 • &U Spring-tab area (each), square foot O.I|.6o Spring-tab span (each), feet 1'375 Stick force required to deflect spring tab 1^, pounds 1.6 No preload was used in the spring of the arrangem.ent tasted and the tabs had no mass balance. The variation of stick position with right-aileron spring-tab angle with the aileron held neutral is shown in figure [| . The tab angles are measured in degrees from the aileron. The relation between stick position and right- and left-aileron angle, with no load on the control system, is shown in figure 5' The aileron angles are referenced to neutral. NAG A ARZi Ko. L5C23 INSTRUMENTATION Striidard NAOA photographic record-jng inptnameiits , synchronized by an electrlccil timer, viere used to measure airspeed, rolling velocity, silsi'on stick force, and the position of the spring tab, eileron, and stick. Correct service inlicated airspeed V- used herein is defined s aj "" s ^i'o^ where T<: = li5.08 f„ ccri-'preGsi Dill ty correction at sea level q^ Impact pressure, measured differovxce betiween static and total-head pressures corrected for position error, inches of v/ater TEST RESULTS Ai:.:D DISCUSSION Tests were made to determine whether the spring-tah ailerons tended to oscillate or flutter in the speed range to 1;00 miles per hour. These tests consisted of m.aneuvers in which the pilot abruptly deflected and released the aileron control at various speeds. Typical time histories of the maneuvers are shovn in figure 6, vhich Indicates thr.t any oscillation of the aileron or spring tab was heavily damped and disappeared completely within two cycles. The pilot reported no flutter in the speed rf^snge up to ):.00 miles per hour. The lateral control charscteristlcs were measured in abruot aileron rolls with the rudder held fixed as described in reference 1. These rolls were m.ade at increments of 'yO miles per hour from, ariproximately 100 to I|.00 miles per hour. The results are given as the variation of helix angle pb/2V and change in aileron stick force at various speeds v.-lth the change in total aileron angle in figure 7 ^^id with stick position in figure 8. No force data are shovm in these figures for ]|. MCA ARR No. L5C23 most of the end points on the 2— curve?' because the con- 2V trol stick was against the stops snd the forces recorded were a r-easure of hov; hard the pilot was pushing against the stops rather than a measure of the force required to deflect the silerons. Limited stick deflections vere used r,.t 35*^ and iiOO miles per hour in order that the structural design loads of the system would not be exceeded. Figures 7 and 6 show that the aileron stick forces are quite light and there 1? no tendency toward overbalance. It should be noted hov/ever that, although the end test points in figure 7 Indicate partial aileron deflection, figure o shows that substantially full stick travel was used to obtain these aileron deflections. This condition occurs because considerable stick travel is used to deflect the spring tab. In all flights for which data are presented herein, the transmitter of an FACA electrical control-position recorder was mounted externally on the right aileron to measure the spring- tab angles. A flight made without the transmitter, hov/ever, showed tnat this protuberance caused no change in the aileron characteristics. The results of the measurements of spring-tab angles during the abrupt plleron rolls are shown in figure 9 as the variation of spring-tab angle on the right aileron with deflection of that aileron. The similarity of these curves to curves of IrUige-rnoment coefficients for a Frise type aileron, such as is used on the p6f-3 airplane, indicate that the tab angle is proportional to the stick force required to deflect the aileron. That is, for the dovm-aileron deflections, the large tab angles indicate little aero- dynam.ic balance; while for the up-aileron deflections the negative tab angles tend to oppose the aileron travel, which indicates aerodynamic overbalance, until separation occurs about the nose. Separation decreases the aerodynamic balance and causes the spring tab to deflect in a direc- tion to aid in deflecting the ailerons. The over-all efficiency of the spring-tab ailerons is compared with tnat of the original f6f-5 ailerons in figures 10 and 11. These figures present, respectively, the pb/2V and the rolling velocity at an altitude of 10,000 feet obtained throughout the speed range with full stick deflection or JO-pound stick force, whichever occurred first. The data for the original ailerons were obtained from a flifOrit Investigation (unpublished) of the handling qualities of the f6f-5 airplane. These data show that NACA ARR No. L5C23 the spring-tab ailerons aro less effectivo than the original ailerons at speeds lower than approxiinately 275 Tf'-iles per hour. The loss in effectiveness of the spring-tab aij.erons is caur.ecl by the lircited aileron travel, v/hloh results from the use of large stick deflection to deflect the spring tab. At speeds greater than 275 iiiiles per hour, the effect of the lighter stick forces of the spring-tab ailerons beconies 'iredomlnant and, as a result, the aileron effectiveness obtained v/ith a 50-pound stick force at b.QO miles per hour is approxirriately 80 percent higher vith the spring-tab ailerons than the aileron effectiveness obtained with the original ailerons. The loss in effectiveness of the spring-tab ailerons can be decreased at lovv speeds without affecting the desirably light stic'': forces at high speeds if a stiffer spring is used and if, at the same time, the length of the tab actuating arm (fig. 2) is so Increased that the ratio of stick force to tab deflection is kept the same as in the spring-tab aileron tested. In this suggested arrangement, the stick deflection required for full tab deflection would be decreased and this decrease would allow larger aileron deflection. Such an arrangement, however, might m,ake the tab installation m.ore susceptible to flutter (reference 2); that is, the tab would have a greater m.echanical advantage over the control system than the spring-tab tested and, therefore, inertia effects of the tab voould be more likely to cause flutter. Further increases in ailei'on effectiveness at the lower speeds could be accomplished by increasing the down-aileron deflection to the sam.e value as the present up--aileron deflection. Increases in the uo-aileron deflection are not recom^mended , however, since figure 9 indicates flow separation about the nose balance and any increase in up-alleron deflection m.ight therefore result in aileron buffet at full deflection. Although the increase in do-rm-aileron deflection might result in somewhat higher stick forces throughout the spaed range, some reduction could be made in the spring stiffness to reduce the stick forces to the present values and, at the same tim.e, retain increased aileron effectiveness at low speeds. C0NCLnSI0i;3 Plight tests to determine the lateral control char- acteristics of an f6f-5 airplane equipped with spring-tab ailerons indicated the fcllowim? conclusions: 6 KACA ARR No. L5C23 1. The spring-tab oilsrons on the F'6f-3 airplane shoved no tendency to flutter in the speed range up to Ij.OO rniles per hour, and any oscillations following abrupt control deflection were heavily damped. 2. The spring-tab ailerons had de?;irably li.^ht stick forces mthout any tendency to overbalance. 5. The sprln£-tab ailerons gave 30 percent higher values of effectiveness with a JO-pound stick force at ilOO miles per hour than the original f6f-5 ailerons. At speeds lower than 275 iTil^s per hour, the spring-tab ailerons had less effectiveness than the original ailerons because of restricted aileron travel as a result of the use of large stick deflection to deflect the spring tab. [j.. The available aileron effectiveness with the spring-tab ailerons at the lower speeds could be increased without affecting high-speed lateral control by an increase in the available aileron deflection and a rriodlficatlon of the spring-tab arrangeinent. Such an arrangement might, however, be more susceptible to flutter than the produc- tion Installation. Langley Memorial Aeronautical Laboratory National Advisory Cominittee for Aeronautics Langley Field, Va. REFERENCES 1. Jolinson, Harold I.t FAGA Procedure for Flight Tests of Aileron Characteristics of Airplanes. NACA EB No. 5G2l[, IQIlJ. 2. Collar, A. R. : The Prevention of Flutter of Soring Tabs. Rep. No. S.M.E. 52[l9 , British R.A.E., May 19U5. NACA ARR No. L5C23 Fig. 1 13' I- DIAM. THREE- BLADE HAniLTON STANDARD PROPELLER GROUND-LINE STATIC LOAD II' 0" TREAO- LEVEL-GPOUND-LINE S TATIC LOAD NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Figure 1.- Three-view drawing of F6F-3 airplane. Digitized by tlie Internet Archive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/flighttestsoflatODIang NACA ARR No. L5C23 Fig. 2 IbrcfiM rod /s free to rotate, at this (znd Tab actuating arm Torqu 0) Q) • C C -H bo U C d) w .-( n3 <-! Id td cj 1 -H bo < C •H C u cd a E to e ^ Ci bo •H >> Ui ^ tt-J T3 O O) S M 0) -H •H C > t-1 •H n3 j:: +J cx Q t^ bo I O to o OJ D-, U — 3 bo NACA ARR No. L5C23 Fig. 4 • / / / / / ir / I ^ /v-^^y /J37 'U/ 'C/0///£XDCy )/J//p CO CO _i o «3 Y Q 't- I '^ 0) Li bo NACA ARR No. L5C23 Fig. \ / I 1 \ • / \ ^ / \ 1/ \ \ / / oo- si- ll _l C3 O UJ ^ \ / \ \. / / \ / \ \ / / \ / / \ ^ / \ ^^ / \^ / \ Ss / ^ \ ^ -y / \, / \ » 5ii ^ ^ o-^ \ U^X 5J! c o Li (U ■H -I C OJ O I ♦J T3 c i U Eb CO (Sj (£> >> > fe. CO I • ■-\ • CO o .-H -iJ 0) bo G L. 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