mi\ L'^o i^ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED Fetruary 19^5 as Eestrlcted Bulletin L5A13 THE USE OF GEARED SFRIRG TABS FOR EKEVATOE CONTROL By Willi am H. Phillips Laj3gl©y Memorial Aeronautical Latoratory Langley Field, Va. MAC A 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- j vlously 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. ^-^0 DOCUMENTS DEPARTMENT Digitized by tlie Internet Arcliive 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/useofgearedsprinOOIang 11.1 7'- NACA RB Mo. L5A13 RESTRICTED MTICMAL ADVISORY C0?miTT3E FOR AERONAUTICS RESTRICTED BULLETIN THE USE OF GEARED SPRING TABS FOR ELEVATOR CONTROL By William H. Phillips SUMNIARY Equations are presented for the stick force per g in maneuvers obtained with a geared spring tab. A geared spring tab, as defined herein, differs from an ordinary spring tab in that, when the elevator is moved v;ith the stic^c free at zero airspeed, the tab m.oves with respect to the elevator in the same manner as a conventional geared, or balancing, tab. The geared spring tab is shown to present the theo- retical possibility of obtaining a value of force per g independent of speed regardless of the spring stiffness. If the geared spring tab is used in conjunction with an elevator that has zero variation of hinge moment v;ith angle of attack, the force per g may be made independent of speed at any center-of -gravity location. A suitably designed geared spring tab will provide adequate ground control, small sensitivity of the control forces to slight changes in the elevator hinge -moment parameters, and sub- stantially no variation of stick force per g with speed. The geared spring tab is shown to be most suitable for application to large airplanes. INTRODUCTION An analysis of the elevator control forces obtained ith spring tabs was presented in reference 1. Tvifo types of spring tab were discussed: the ordinary, or ungeared, spring tab (fig. 1) and the geared spring tab (fig. 2). The geared spring tab differs from the ordinary spring tab in that when the elevator is moved with the stick free at zero airspeed, the tab moves with respect to the elevator in the same manner as a conventional geared, or balancing, tab. Although the calculations and discussion of reference 1 were concerned mainly with ordinary spring w RESTRICTED 2 NACA R3 No. L^AIJ tabs, the advantages of gearsd spring tabs 'were pointed out. The geared ?priiig tab presents the theoretical possibility of obtaining a value of force per g in r:aneu- vers that docs not vary v:lth speod even though a stiff spring is used to provide adequate ground control. The present report b.^lefly outlines the theory of the geared spring tab, gives formulas for use in design, and indicates more cor.pletely the practical possibilities and limitations of the device . DISCUSSION Difficulties have been experienced with conventional types of elevator balance on largo airplanes, because the elevator must be very closely balanced and because small changes In the hinge -mo:;ient parameters cause large changes in the control forces. The possibility of using a servo- tab to avoid these difficulties -.vas explained in reference ] In tests of a control surface equipped with a servotab, which is defined as the system shov/n in figure 1 with the spring o^'-itted, the pilots considered this arrangement undesirrble because the elevator did not follow sraoothly movements of the stick when the airplane was on the ground, taxying, or making landings and take-offs. A banging action of the control v\ras experienced because the elevator did not r:ove until the tab had hit its stops. A spring tab provides a mechanical connection between the stick and the elevator that relieves this difficulty. Vihen a spring tab is used, the force per g varies with speed. This variation may be reduced to an acceptable amount by using a tab spring sufficiently flexible to make the control behave essentially as a servotab at normal flight speeds. The ground control provided by this flexible spiring might be considered acceptable but a stlffer spring would be very desirable, especially on large airplanes that have elevators with high moments of inertia. The equations for the stick forces with a spring tab were presented in reference 1. In the appendix of the present paper, these equations are extended to allow cal- culation of the stick forces with a geared spring tab. The force per g obtained with an ordinary spring tab has been shown to vary with speed. As the speed approaches ?.ero the force per g approaches that obtained with the tab fixed and, at very high speeds, approaches the value for NACA RS No. L5A13 5 a servotab. 7/lth a glared spring tab, as the speed approaches zero the force per g is shov/n to approach that of an equivalent balancing tab and, at very high speeds, is shown to approach the value for a servotab. The geared spring tab therefore provides a means of reducing the force per g at lov/ speeds v«i2le leaving the force per g at high speeds unchanged. The force per g may theoretically be made to remain constant throughout the speed range, no matter what spring stlfihess is used. This arrangement therefore embodies the advantage provided by either the conventional balance or the servotab, namely, that the stick-force gradient does not vary with speed. The unde- sirable sensitivity of the conventional balance to small changes in hinge-moment characteristics and the poor ground control of the ?ervotab are avoided by the geared spring tab. In order to compare the merits of conventional types of balance, ungeared spring tabs, and geared spring tabs, the stick-force characteristics have been computed for an airolane of the medium-bomber class (weight, 50>000 lb) with the various types of elevator control. The results of those calculations are sh ovm In figure 3« '^^■^^ charac- teristics of the airplane and of the tab s7/stem.s that were used in the calculations are given in tables I and II, respectively. (All ?ynibols are defined in appendix A.) The stick forces of a closely balanced elevator with con- ventional balance (as, for example, a balancing tab) are shown in figure 3(a) • The critical natui-e of the balance is also shovm by the large changes in stick-force gradients caused bj changes in dCj^ /^^e ^^^ ^^ /6arp of -0.001 per degree. Variations of this order of m.agnltude may result from slight differences in contours of the elevator, v;ithin production tolerances, on different airplanes of the same type. The characteristics of an ungeared spring tab are Illustrated in figure J>(h), The spring constant has been chosen to provide a fair degree of ground control without excessive variation of force per g v/ith speed at norm.al flight speeds. The criterion for the choice of this spring stiffness was presented in reference 1. For the airplane under consideration, the spring stiffness is such as to require a stick force of 100 pounds to deflect the tab 1 radian at zero airspeed when the elevator is held fixed. The characteristics of a geared spring tab that was designed to provide the same control-force characteristics k NACA RB No. L5A15 as the conventional balance are shown In figure 5(c). The method of calculating the values of the hinge-mornent parameters and gear ratio that v;ere used to obtain stick- force gradients independent of speed is given in appendix B. The sa;-ne characteristicv'5 will be obtained with any spring stiffness. The exact values of hinge -trioment parameters required to give the characteristics shown in figure Jfc) will not be attained in practice. It is therefore desirable to investigate the effects of changing the hinge -moment parameters slightly. If the spring in the geared spring tab had infinite stiffness, the system would be identical with the balancing tab (fig. 5(a)) and the stick forces would be equally sensitive to small changes in hinge- moment parameters. The spring stiffness m.ust therefore be liraited to a point at which normal changes in 60^ /^^e and 6C;i-^ /darp do not cause large changes in the stick- force characteristics. In order to determine the effects of errors in the values of dC]-^ /^^e ^'^^ ^'^h /<^ctT when a finite value of sprlrig stiffness is used, the stick forces have been computed for a geared spring tab that has the same spring stiffness as the ungeared spring tab of figure 3(b). The effects of changing dCy^ /6d^ and dC^ /da^ by -0.001 for the geared spring tab are shown in figures /-i-(a) and I-!-(b), respectively. Some variation of force per g with speed is introduced but the variation is considerably smaller than that normally encountered with the ungeared spring tab (fig. 3(b)). Inasmuch as a greater variation of force per g with speed probably can be tolerated, an increase in spring stiffness to improve the ground control appears desirable. The changes in do^i /6 5q and dCh /da^ cause changes in the order of magnitude of the stick forces as well as some variation in force per g with speed. These changes are, however, much smaller than those tliat occur with the conventional balance (fig. 3(a)). At high speeds, in fact, they approach the changes that would occur if a servotab were used. The effect of changing the gear ratio of the geared spring tab from its ideal value is shown in figure J^Cc ) . NAGA R3 No. L5A15 5 The effect of chan;];ing the gear ratio is nearly equivalent to changing- the value of dOj^ /^^e- An error in providing the ideal value of 6Cv^ /65o on an actual airplane may ^e/ ® therefore be corrected by suitable adjustment of the gear ratio . The £-eared spring tab used to obtain the character- istics shown in figure 3(c) had values of the hinge -moment parameters dCv^ /(^ttrp and 6Cy^ /^°^T ®'^^^1 ^° zero. The equations given in appendix ■? sho'.v that this condition must be satisfied if the stick-force gradient is to be independent of speed at any center-of -gravity location. The value of 60y^ /^o'.,p, in practice, may be made equal to zero by use of elevators with a beveled trailing edge or with horn balances. The value of 60^. /daT i- nor- mallj'- very small and m.ay likewise be adjusted by varying the trailing-edge angle. If the values of dC^ /darp and ACvi, /^arp are not equal to zero, the force per g may still be made independent of speed by use of a reared spring tab for one particular center-of-gravity location, but the force per g v;ill vary somewhat with speed at other center-of-gravity locations. The effect of an increase in altitude on the stick- force gradients obtained with a geared spring tab is to shift forward the center-of-gravity location for zero force per g (the maneuver point) and to leave the slopes of the curves of force per g against center-of-gravity location unchanged. In this respect, the geared spring tab may be shown to follow the same rules as a conventional elevator. The stick-force variation with speed in straight flight is related to the force per g in maneuvers in the same v>ray for a spring-tab elevator as for a conventional elevator . The application of spring tabs to airplanes of various sizes was considered in refei-ence 1. The results of this analysis, in general, may be applied to the geared snring tab. In order to avoid excessive stick-force variation with speed v;ith an ordinary spring tab, the spring must be sufficiently flexible to make the control behave essentially as a servotab in the norm.al -flight speed range. T'he stick-force gradient obtained v;ith a geared spring tab must also equal that of a servotab if l^mCA RB No. L5A13 force variation, v/ith speed iz- to be avoided. Because the stick forces obtained with, a servotab i-esult frora the aerodynamic hinge moments on the tab, some difficulty may be encountered in providing sufficiently heavy stick-force gradients vn* th norm.al tab designs on airplanes much sm.aller than the 50,000-pound airplane considered in the present report. The calculations of reference 1 indicated that sufficiently heavy stick forces may be provided on an airplane weighing about l6,000 pounds, but a large tab-to- stlck gear ratio and a tab havln;: a rather wide chord are required. These features increase the difficulty of preventing flutter. Because the stick-force gradients obtained with a spring tab on small airplanes are ii.ndesirably low, the use of a bobwelght in conjunction with the spring tab has been 'oroposed to obtain desirable stick-force gradients in steady maneuvers. Flight tests shov/ed this arrangement to be unsatisfactory because of i^ndue lightness of the stick forces for sudden or rapid movements of the control stick. The reason for this undesirable control "feel" is that the elevator may be suddenly moved to large deflec- tions because the aerodynamic hinge moments on the tab are small. After a certain time lag, the acceleration builds up and causes the bobwelght mom.ent to be felt by the pilot. These effects are discussed more fully in x-eference 2. The preceding conslderabicns indicate that the geared spring tab may prove unsatisfactory on small airplanes. On large airplanes, for vi/hich sufficiently large stick forces result fro:"- the aerodynamic hinge moments on the tab, the geared spring tab should be satisfactory . C0NCLTJ3I0.NS An analysis of the characteristics of geared spring tabs for elevator control has led to the following con- clusions : 1. Py m.eans of a geared spring tab, it is theoreti- cally possible to provide a value of stick-force gradient in maneuvers that does not vary with speed, no matter what spring stiffness is used. If the geared spring tab is used in conjunction with an elevator that has zero variation of hinge moment v;ith angle of attack, the force MCA RB No. L5A15 per g may be madG independent of speed at any center-of- gravity location. 2, A geared spring tab may be designed to provide adequate ground control and small sensitivity of the control forces to slight changes in the hinge -moraent pararaeters. The poor ground control associated with a servotab and the sensitivity of a conventional balance to small changes in hinge-moment parameters may therefore be avoided. 5. The geared spring tab appears to be most suitable for application to large airplanes. Langley J'emorial Aeronautical Laboratory ^Tational Advisory Committee for Aeronautics Langley Field, Va . 8 MCA RB No. L5A15 APP'iNDTX A SYTOOLS W weifht b span S wing area c chord I tail length Srp tail area w ~6 ±jrri slope of lift curve of wing € dov/nv.'ash angle q dynami c pr e s s ur e C-^ lift coefficient I elevator moment of inertia variation of lift coefficient of tail with e elevator angle. elevator effectiveness factor 6Cl /653 dC Irp/^aT K-j^ ratio of stick Tr.ovenent to elevator deflection, tab fixed; norrr.ally positive K2 ratio of stick novement to tab deflection, elevator fi:^:ed; nornially negative Kz ratio of stick force to tab angle at zero airspeed, elevator fixed; nornally positive NAG A aB No. L5A13 9 Ki ratio of stick force to elevator angle at zero ^ airspoed; elevator held in deflected position by external jueans, tab deflection held at zero by apDllcation of required force at control stick; positive for balancing tab H hinge moment Cj^ hinge-monent coeffi( 6q elevator deflection (positive down) 5-f- tab deflection from elevator (positive down) Xg stick deflection (positive forward) F stick force (pull force positive) a angle of attack of wing Grr. angle of attack of tall p mass density of air n nor-nal acceleration in g units g acceleration of gravity (52,2 ft/sec^^ X distance between center of gravity and stick- fixed neutral point in straight flight (positive when center of gravity is rearward) 4-'^ A = —. ^ ' + gJil ■A'X 1 n "-^'Ln, q *6e T (^ variation of elevator hinge-moment coefficient with anp;le of attack of tail, measured with ^^ tab free 10 NACA RB Fo. L5A13 -j variacj'.on of elevator hinge-moment coefficient \'^^e/^f with elevator angle, rneasured with tab free Subscripts : t tab e elevator T tail h value for equivalent balancing tab MCA H3 Nc. L5A13 11 APFEATDIX B SQ'JATIOFS FOR ELEVA'POR FOIGES V/I'TH T-IilARED SPRING- TA^ The talD sypteir. considered is shown in figure 2. The mechanical characteristics of the linkage are coinpletely deter.nined when four constant r are specified. These constants are defined by tno follovving equations* ■l^e ^2^t (1) K36,, + K|,e.^ (2) Equation (2) applies when the airspeed is zero. The ratio between the tab deflection and the elevator deflec- tion, stick fixed, equals — — and the ratio between the tab def].ection and the elevator deflection at zero air- speed, ctick free, equals -T' ■h The ratio K: ?: -k is defined -5 ^^5 as the linkage ratio of an equivalent balancing tab. Vi/hen the syjitem is in equilibrium, the i-elaticns between stick force, elevator hing'e moments, and tab hinge moments are 5;iven in terns of these constants by the expressions AHe - A^It I AF = AT? = K- AH^ n. K: + K:r A6^ + -^ A5 h K2 ^51 t K. (5) The changes in elevator and tab hinge moments for any type of maneuver are given by the equations AIL ( Aarp d arp + A5, 60h ^^^h 6 6, -- + ASf 'e 65 e \ , 2 qrpDgCe ik) 12 A?^ 6Ch^ 6 0,,.^ d(^.. -■- oarp cOq oot ' ■ NACA RB No. L5A13 (5) In t-io present report, as in reference 1, the stick fores required in a gradual pull-up is used as a criterion of the elevator-control characteristics. The stick force required in a pull-up, or any other maneuver, may be determined b^-^ substituting the appropriate values for Aan and A5g, and solving equations C3)> (k), and (5) simul- taneously. If the tab is assumed to have a negligible effect on the lift of the tail, the values of Aam and Aoq in a gradual pull-up are A5r. ^^\l + " (n - 1) 1) (6) (7) For convenience, the solution of these equations for an ungeared spring tab (Ki = 0), vs^hich was derived in reference 1, is presented first. The force per g is given by - n = '¥x AO^ irp 1-p d5, and (9) are the values that would be measured on the ele- vator With the tab free and are riven by the expressions <^'^> 66, 664- V 6C h4 A5t J (10) The force per g for a r^eared ?prin{- tab, obtained by sLnultaneous solution of equations (3), (k) , and (5), may be fc:jfpresFed by the sa^iie equation as vvas derived for an ordinary spring tab (equation (b)), provided that certain substitutions are made for some cf the parameters These su.bstituted values may be interpreted physically ^ NACA RB No. L5A15 as the characteripticG of the equivalent balancing tah previously defined. The complete equation is 6f 6n 0^i)i A + _iiliiii oc + B 'dCh, K2K3' Vc6e /b d5 e /tf ^^ht ZbT ^t^*'^" qT 2 — beCe bpC e^e t/v KpK7 To 6c, ht >, „ 2 "'-^ht „ ^_,2 WbF57''t°t" T5?'lTVt (11: where the qu.antities with the subscript b are defined in the followinrr table: Quantity Definition Physical sin;nif Icance (%)| Ratio between stick travel and elevator deflec- tion for equiva- lent balancing tab e^e Value of cChe/'^^e for equivalent balancing tab ^^ darp Kk ''"^H ^f^t' Value 01 6Cv K^ daT b^cp2 for equivalent e'-e oa±ancing tab 'h, 1% ^''^ht btct^ d&t ^"3 65t bece^ Value of 6Che/65t for equivalent balancing tab, measured, with tab linlc connected. Physical signifi- cance may be visu- alised as effect of deflecting tab as a trim tab by changing length of tab link NACA R3 No. L5A15 15 The stick-force characteristics of an ordinary spring tab wore discussed in reference 1. At very high speeds, the stick force per g normal acceleration was shown to approach t]ie value obtained with a servotab and, at low speeds, the force per g was slicwn to approach the value obtained with the tab fixed. By similar reasoning, the stick-force rradient w?th a geared spring tab may be shown to approach that of a servotab at high speeds and to approach that obtained with the equivalent balancing tab at lo-.v speeds. 3y varying the gear ratio, the foi-ce per g at low speeds may be adjusted to any desired value without affecting the force per g at high speeds. In particular, the force per g at low speeds may be adjusted to the value obtained at high speeds. The stick-force gradient, in this case, is found to be independent of the speed. The conditions that must be satisfied in order to provide a force gradient independent of speed may be found from equation (11). The assumption is made that the ratio qip/q is independent of s]3eed - a condition approxi- mately true at maneuvering speeds. The force per g will be independent of speed if the ratio of the terms in the numerator that contain q-p to the terms in the denomii- nator that contain qrp is the same as the ratio of the rem.aining terms in the numerator to the remaining terms in the denominator. For one partioiilar center-of-gravity location, this condition may alway/s be satisfied by suitable choice of the gear ratio. If it is desired to provide a force gradient independent of speed at any center-of-gravity location, the following relations must be satlsfiedr V^dop/tf K2l -— -) OeCe' \6St/v (12) 1 - b (^l) to b d5t ht l6 KACA RB No. L5A13 C ■dCv, \ (13) ^^ht. (^^i).-Hf^^^ In practice, equation (12) can be satisfied only by making '^Cllg/'(^a^[l and dCj^x^/carp very close to zero. Equation (13) may then be used to deterraine the gear ratio Kl/Kz that must be er.jployed to provide a value of force per g which does not vary v;ith speed. An example of the application of equation (13) to the air-olane with the characteristics given in table I is presented. If the values for (K]_), , ( ^j , and 65 t. D given in the preceding table are substituted in formula (13), the follov\fing relation is obtained: ''d^ 6-.. 2 t 'Ki,f ^S H<^t^ ■•3/ ^5t ^e = e^ (lU) All of the quantities are assi-ciied to be known except the gear ratio PIJ^/Kj . It v;ill be noted that, because the quantities Ki and K^ always occur as a ratio and Kr MCA R?, Fo. L5A15 1? and Kv are both increased in the same ratio when the spring stiffness is increased, no li-nitation is placed on the spring stiffness. If an attempt is made to solve e [uation CI/4) exolic- itly for the ^^ear ratio Ku/Y.-z,, a f if th-de^vree equation is obtained. This complication may be avoided, however, by solvlnp; equation ( lJ+ ) by a method of successive approximations. This process is applicable because a change in the value of K[,_/K5 has a marked effect on the value of the right-hand side of equation (li^) and a relatively small effect on the value of the left-hand side. As a first approximation, the value of Kk/Kz is assu:ned to be zero where it occurs in the left-hand side of equation (li^) and bhe equation (nov/ a quadratic) is solved for r:[i /K3 . This approximate value is substituted in the left-hand side of the equation, and the equation is again solved for Kh/Kz. The process converges very rapidly and this second approximation generally will be sufficiently accurate. If the values for the airplane and elevator charac- teristics given in table I are substituted in equation fli;) and the valxies of Y.u/Y-z on the left-hand side are assumed to equal zero, the follov/ing equation is obtained; 1 . (-0-1^3) (-0. 303) (?U.o) (2.2)^ ^3 (i.eo)(-o.oo5)(7.35)(o.8)^ . ^^(g) (7.33) (0.8)^ ^5 (3U.0) (2.2)2 + ( — (-0.005)^ ^3/ (3i+.0)(2.2)2 This quadratic equation has the solutions ^ = 0.863 -^ = 20.2 K5 l8 NACA R3 No. L5A15 Of these two solutions, only ths smaller value Is of practical interest. The larger value v.'ould result in excessive tab deflections that would cause the lift incre- ment due to the tab, which has been neglected in the present analysis, to reverse the direction of lift on the surface. If the va]ue tt^ = 0.868 is substituted in the left-hand side of equation (II4.) and the equation is again solved for Fl/k^, the second approximation for the gear ratio is obtained as — ^ = O.SS. Fu.rther approximations K3 do not change this value appreciably. The following criterion for determining approximately the minimum value of the spring stiffness reqixired for satisfactory ground control was given in reference 1; 1 -^He 2 -f s—— = 200 foot-pounds per foot per slug-foot For a geared spring tab, the variation of elevator hinge moment with stick deflection v;hen the elevator is held fixed is given by the formula ^^^^h^\ .2 , ^'^ht 2 611 e + _ - _ (1^5} 6X3 K2 K2 Kp2 2 If it is desired to satisfy the criterion at zero airspeed, the terms containing qrp may be neglected and the fol- lov:lng relation is obtained; 1 ^I'e i ^ = 200 I 6x3 -(Ki)^^^5 K2I This expression may be used to solve for K2, which determines the spring stiffness. For the exam.ple under consideration, NACA RB No. L^AlJ I'5 = K2(200)I 19 (-0.[^^)(2C0)(].3) -i.Soli Co.33)r-o.i^-S)' i.eo 95.0 pounds per radian A value of K2 of 100 pounds per radian has been used In the ezampleF of this paper, ^•'oni the value of Kl/Kz determined previously, the value of K], may be readily obtained . 20 NACA RD No. L5A15 1. Phillips, William H.: AppDlcation of Spring Tabs to Elevator Controls, IJACA ARR No. 1J4H28, 19i|lj.. 2. Jones, Robert T., and Greenberg, Harry; Effect of Hinge -Moment ParaiuCters on Elevator Stick Forces in Rapid Maneuvers. NACA ARR No. Li4.J12, ISkk. MCA R-3 Fo. LSA15 21 TABLE I AIRPLA^IE CHARACTER TSTICS W, lb 50,000 ^, sq ft 1,000 c, ft 11.18 I, rt 55 Srp, sq ft 200 bg, ft 514- Ce, ft 2.2 bt, ft 7.55 c^, ft 0.8 , per radian 4.5 da/^; 1 - ^ 0.55 da T 0.5 -, per radian I.7 ^ 1.0 q I, slus-ft^ 1.5 NAT I Or'A L ADV I S OR Y C0l3vlITTP,£ FOR ALROIIAUTICS NACA PB No. L5AI3 ZZ TABLE II C OMTR GL-SYST SI.I CH AlAGTER IS'^ I OS Conventional balance ffif. 5(a)) Un.^'eared cnring tab Cfi-. ^fb)) beared poring tab Cfig. 5rc)) ¥.-]_, ft per radian 2.18 1.60 1.80 K2 , f': per radian -o.ls -o.l5 K2, lb per radian 100 100 K),, lb per radian 3 s •^^^e .,..„ .„_ "7 > i"^-'- ^<^b oarp -^e -0.00058 -0.005 -0.003 d5e -0.005 -0.005 66t ' ''^ 0"^^ '^arp ^^ht d5e ^'^.u ^ -0.005 -0.005 65t ' "^^ ^^'' HAT I OFAL ADVI S ORY COIillTTSE FOR AERONAiri^ICS NACA RB No. L5A13 Figs. 1,2 51 l\ Spr/r?^-. rfz-ee l/nK NATIONAL ADVISORY COMMinEE FOR AERONAUTICS Figure 1.- Mechanism for ordinary spring tab. Free ImH NATIONAL ADVISORY COMMinEE rOR AERONAUTICS Figure 2.- Mechanism for geared spring tab. Fig, NACA RB No. L5A13 1 1 I t. ^ / / / p Va ^ is CO O 1 i^ -^ /v A// f 5 t A// :2^ ^ 00 to a <5> . •§ § "^i"^ is^ J8 ^ ^ r ^ J ^ y ^ ^ ^ 5 ^ '# ^ I ^ ^ 4 1 l\ ^ ^ ■^ «^) O t3 *3 O, 3 o o .H "^ 'S U B U m o u ^ « o J3 /;/ 1 1 \ / // t 1 (U at V, '^ / / / /^ V / / 1- ^^ ^ / 5^ ^- / / ^ ^ ^ > / .>: ^ ^ / / / \ ^ fe / / § Tin J «D ^ M- ^ ^ 3 J9d qx 'uoi^BJOXSooB iwajou 3 jod eojoj J05»a6X3 Hsnj NACA RB No. L5A13 Fif. 4 i I / 4 y/ji^ '^M^/ 1 ^ 1 ^^ 1 a \ ^^ 3 ...J 5^> Tina § <:i CM d 5 •a u 8> <5 > ^ y i '/ ^ / f / N I / 1 [. _,^ m » o •^l c « o B o * 1 K u o •-4 Ct U o 1 T) o J< f> u o to o •H c «H > «3 S) o o 1 o v4 i 1 ■N 1 1 /^ /: /ii\ $ A / '/^ 1 // ^ ^ ^t- "5) c 5 S 3 jed Qt 'uotlBjBXSOOB XBtnjou 3 aed eojoj jo^BAexa UNIVERSITY OF FLORIDA 3 1262 08104 948 7 UNIVERSITY OF HXJRIDA DOCUWa^TS DEPARTMENT 1 20 fAfiJRSrON SCIENCE LIBRARY RO. BOX 117011 GAINESVILLE. FL 32611-7011 USA