f EB No. Ll^E31 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED May \S)iX as Restricted Bulletin IAE31 MAXIMnM RATES OF CONTROL MOTION OBTAIHED FROM OODND TESTS By De E. Beeler Lacgley Memorial Aeronautical Laboratory Langley Field, Ya. NACA WASHINGTON NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution 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 tec.'i- nically edited. All have been reproduced without change in order to expedite general distribution. 100 DOCUMENTS DEPARTMENT Digitized by tine Internet Arcliive in 2011 with funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/maximumratesofcoOOIang 111. 110 u NACA RB No. lLF31 KESTRICTSD NATION^i ADVI30KV C ! IT-IT TTZE P'OR AERONAUTICS RESTRICTED BUT.LF.TIN MAXIIvIUM RATES OF OOIITROL MOTION OBTAINED FROIvi GROUND TESTS By De E. Heeler SUI.HVIARY Ground tests were conducted In a specially constructed cockpit rig to determine the iraximuT; rates of control- stick (elevator) motion and the corresponding maximum stick forces that coald be exerted, as based on results obtained ".'i th a number of pilots. The measurements indicate that the m.aximum rate of push on the control stick is greater than the m.aximum rate of pull; that the maximum, rate of either push or pull is less v-hen a mental restriction is imposed upon the pilot; and that the maximum, rates at which the pilot thought he v;ould apply elevator control forces in flight are considerably less than the rates at v/hich he could appl:/ these forces with the same stick stiffress. INTRODUCTION The m.aximum rates of control motion as well as the rnaxim.um. forces that a pilot can exert on the elevator controls mu5?t be taken into account in the formulation of rational design criterions for dynamic tail load com.pvita- tions. The maxim.um. tail loadi consistent with the load factor in vertical -plane maneuvers results when an elevator m.otion is specified in which the elevator is moved as rapidly as possible to a maxim.um. value and held there for such a time that, vhen the controls are abi^'uptly reversed. RESTRICTED "AC A RB No. LiiEJl the maximum allowable positive load factoi'' is .past reached, Several investigations that have some bearj.ng on this suo- ject (references 1, 2, and 5) have already been comnleted, but they do not yield safflclent data on the rate of control motion. In references 1 and 2 the emphasis is placed on the quickness v/ith v/hich a maximum force can be developed, whereas in reference 5 tests of the maximum steady foi'ces applied oj a pilot in various positions v;as renorted. The question of how the pilot actually moves the con- trols denends on such unpredictable variables as the physiological and psychological makeup of the pilot, which are in turn influenced by the "feel" of the airplane. This subject is largely outside the scope of the present papep, which presents mainly the re-^^ults of tests made expressly to determine the effect of several variables on the m-aximum possible rates of stick motion. Nine pilots, var;^rlng in physical fitness and In flying experience, participated in the performance of these tests. APPARATUS The rig used in the tests (see fig. 1) consisted of an adjustable bucket-type pilot's seat, a control stick, and a rudder bar that wore mounted on a heavy wooden table. The relative positions of the seat, stick, and rudder bar were similar to those used in present-day fighter air- planes, A resisting force was applied to the stick by means of two preloaded spiral springs, which v/ere attached at one end to a movable shelf that was Installed under the table top. The other ends of the springs were attached to a collar, v.-hich could slide on a projection of the stick that extended below the table top. Adjusting the height of the shelf and of the collar permitted different spring restraints to be imposed on the stick. lb was realized at the otitset that general relatlon- sh.'ps that would hold for all cases could not be estab- lished between the force and the stick deflection. With the type of control motion contemplated, an adjustment of the springs such that an additional restraint would be imposed during the return motion appeared necessary. This adjustment would be in accordance with conditions that would occur in flight when an angular velocity was present and a convergent elevator was used. For this purpose, an NACA RB No. lIjEJI 5 adjustable nonreturn nechanlsn v.'as attached to the spring supplyin3 the restraint in the pull direction. The action of this apparatus is illustrated in figure 2, which shov.-s the time variation obtained for the stick position and the stick force with the mechanism in operation. A diagrammatic view of the stick system is also shown on this figure. A strict interpretation of the results of figiire 2 in terms of the corresponding aei'odynamic parame- ters of the substitute elevator is not possible because varying values of the parameters would be obtained for different parts of the cui've , The position of the stick v;as recorded by a control- position recorder mounted on top of the table. A timer, also mounted on top of the table, was used to im.press timing signals on the control-position record in order that accurate time histories could be obtained. The relation between the stick position and the stick force was obtained hj separate calibrations for which the stick was pulled back slowly by a spring scale with the shelf in each of the positions used during the tests. A thigh belt v/as used to secure the pilot in the seat. Although the belt restricted the reach of the pilot, the results obtained by its use were believed to be more consistent than v/ould be obtained if no belt were used. r-TETHOD AND TESTS Three types of stick motion were investigated. For each tjrpe, resisting forces of 55»5j l6.6, 8.3, and [|..2 pounds per inch of control-stick displacement were imposed on the control stick. For the first part of the investigation, measurements were made of the maximum rate and corresponding maximum force obtained when the stick was pulled and then pushed as rapidly as possible with no limitation as to either displacement or force. In addition, one pilot was instructed to move the control stick in this same manner v;ith no resisting force other than inertia on the stick. For the second part of the investigation, the pilot was requested to use only one-half the displacement ob- tained in the first part. This condition was thought to simulate more nearly the flight condition inasmuch as the h TTACA RB No, L[^E31 ■pilot v;onld genei-ally be constrained as to amount of de- f].eotion by the knowledge that in flight he might obtain larger accelerations th'.n he coTild comfortably stand. For the third part of the investigation, measurements were made of the maximum rate and corresponding maxim-um forces at which the subject pilot thought he would move the control stick to pull out from a diving attitude if forces similar to those applied to the cockpit rig were experienced in the dive. These measurements are limited in that they depended on the extent of flying experience and imagination of each of the subject pilots. The maximum rates for the tests of the three types of stick motion v/ere obtained directly from the record films by measuring the maximum slopes thereon and. the rate of film travel at the midpoint of the maximum slope. Maximum forces also were obtained from the film records by reading the maximum deflections of the stick. ACCITRAOY The measurements of the control-stick rates are believed to be accurate to ilO inches per second, whereas the neasurem.ents for maximum stick forces are accurate to tj pounds. These values are largely based upon the accuracy to which the film records can be read. RESULTS AND DISCUSSION The results of the measurements made to determine the maxim'om rates at v»hich a pilot can move the control stick with various restraints in the control system are presented in figures 5 to 12. These figures shov/ that considerable scatter exists in the data. When this scatter was first noted, consideration was given to plotting the maximum rate of stick movement for each pilot against the pov/er exei'ted at the time of raaximum rate in order to reduce the scatter. The scatter, however, still persisted and it was finall3r decided to plot the maximum ratss against either the maxim-om force or the maximim stick displacement for a given run vvithoat distinguishing between -Dilots. II NACA R3 No. Li;i:31 5 All the results given in figures 3 to 6 have one thing in cominon; that is, v/ith an increase in the maximum stick force there is a definite decrease in the maximum rate of stick motion. This result contradicts results of previous tests (reference 1), v/hich report that forces have little or no effect on the rate of control movements provided they are vv'ithin the pilot's capability. Figures 7 to 10 show that the maximixm rate also increases v/ith stick displacemant . This variation is to he expected from the results in figures 5 to 6, hov/ever, because with the system used the force is proportional to the displacement. Comparison of the results shown in figure 11 and 12, which represent the measurements made to determine the maximum rates of stick motion during simulated dive pull- outs, with results shovv-n in figures 9 ^^d 10 shows that the maximum rates at "which the pilots think they would move the stick is considerably lower than the rate at v;hich they could move the stick. All the pilots were of the opinion that the highest value of restraint used in the tests was more than would be experienced with present- day airplanes; however, records of such forces obtained in flight on fighter -bomber airplanes indicate that re- straints of this magnitude may exist, A summary of the rates of stick motion given in table I shov/s that the rate of motion is from 25 to 60 percent greater in the push direction than in the pull direction. Factors that contribute to this difference are: (1) the returning force introduced by the system used effected the first part of the pushing motion, (2) the distance the stick may be moved is greater in the push direction, and (5) the pilot is in a more favorable position for performing the pushing operation. From the s-iimmary given in tab].e lit may also be seen that the maximum rates obtained in either direction o'f' motion with no restriction were from 20 to 50 percent greater than those obtained v/ith a restriction as to the amount of travel. This difference in the rate seems a reasonable one in viev/ of the restrictions imposed. It also seems reasonable that different results vv'ould be obtained if a different restriction had been imposed on the -Dilot, NACA RB No, lI+EJI CONGLUSIOJTS Testa conducted by rreans of a specially constructed cockp'' t rig to deter^.ine maximum rates of control-stick TTotton indicate the follcving conclusions; 1. The iT!a:/:5rrium rates of stick move- rrient are greater in the push direction than in pull whether there is a mental restriction or nc restriction irposed on the pilot as to stick travel. 2. The rr'axitruT rates of stick movement increase both with a decrease in maxirrixTi stick force and with an in- crease in iroxfrnuTT. stick displacement, ■-5. The maxirum rate at which a pilot believed that he wQiild move the control stick is considerably lower than the rate at v.hich he cculd move the stick. Langley IV;em.orial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va. FEFERENCEJ Superintendent, Royal Aircraft Factory: Experiments on the Possible ^.ate at ViTnlch a pilot Can Pull Back the Control Column in an Aeroplane. R. & I". Fo. 262, oritish A.C.A. , I916. Hertel, Heinrich: Hetermin'^. tion of the I'.iaxlm.um Con- trol lorces and Atto.inaDle qj.uickness in the Opera- tion of Airplane Controls, NACA TM Ko. ^Gj, 1950, (lough, F. N. , and Beard, A. P.: Limitations of the Pilot in Applying' P'orcea to Airplane Controls. NACA TN No. 5'3C, I936 . NAG A RB No. Lij^3''- CO d n D rO Cd < h-1 M n " CO •H OS 0) o o o •rH +:> CO -P +J CD '— •H S • d (D f:; fn rH ^ 0) P-r-1 p, 00 - — •H CM O o o CO -It O O fo, O n-{ o CO LPs t^- OJ C\J NA VO NA e • o O -d- CO ViD KN rH rOi CO o M H !>H r-> t; -^ o £5 c/? O M (>1 >- fel c:i -■i; < ry- 1-1 o ■;l' I-- o w M tJ H F-^ ■:;; H S M *--■ ■c t r* O o NACA RB No. L4E31 Fig. 1 ^^w^ A. ^^^^^^^^^M^^^^ . .^^Mf^ f ,. ^ I : im PH^'...^., . ^ .. W i. 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A o A C D □ O 1 A 2 a D H n ^ 2 4 6 Maximum rate of 8 ^ 12 14 /6 stick motion , m-/sec (pull) g I I I Figure //. - l/ar/at/on of maximum rate of stick motion with maximum stick c/isp/acement obtained in ground tests during a simulated pull -outj pt/J/ /brce exeriad. ^pr/rt^ Arce per 6 ///7 D 33.3 A 16.6 "y ' /T O 83 O 42. - li <• o o o A ■> D D t '< A o t o IS ^__ ] >• NATIONAL ADVISORY c COMMITTEE FOR AERONAUTICS ^ 2 4 6 8 Maximum rate of stici: 10 12 /4 16 motion ^ in./sec (push) Figure /2. - l^anat/on of maximum rate of stick motion ii^ift) maximum stick displacement obtained /n ground tests during a simulated pu//-out.j pu^/j force exerted. UNIVERSITY OF FLORIDA iiiiiiniiiiii " 3 1262 08 04 990 9 G^NESV/OE, a 3261,-70,, USA