.. L./

~ ARR No. L5120

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

WAIWWIE REP(MWORIGINALLY ISSUED

February1946asAdvanceRestrictedReportL5120

FLIGHTMEASUREMENTSTO DETERMINEEFFECTOF A SPRING-LOADED

TAB ON LONGITUDINALSTABILITYOF AN AIRPLANE

By Paul.A. Hunterand JohnP. Reeder

LengleyMemorialAeronauticalLaboratoryLangleyField,Va.

,, ,,.

N“ACA””““’

WASHINGTON

NACA WARTIME REPORTS are reprintsofpapersoriginallyissuedtoproviderapiddistributionofadvanceresearchresultstoan authorizedgroup requiringthem forthewar effort.They were pre-ciouslyheldunder a securitystatusbutare now unclassified.Some ofthesereportswere nottech-nicallyedited.All have been reproduced withoutchangeinordertoexpeditegeneraldistribution.

31176013649604l-- r

.-. , ,.

NACA,ARRNoo L5120

NATIONAL ADVISORY COMMITTEE....... .......... ... . .

ADVANCE RESTRICTED

P(2I3AER3N..WI’ICS

.... .,.

REPORT

FLIGHT ME&SUR.EMENTS TO DhTEWINE EFFECT OF A SPRING-LOADD

TAB ON LONGITUDINAL STABILITY OF AN AIRPLN!!E

By paul ~. Hunter and John P. Fieeder

SUM?dARY

Ik conjunction with a program of research on thegeneral problem of stability of airplanes in the climbingcondition, tests have been made of a spring-loaded tab,

l~s~rlng~ ‘ab~,betab was ~r~%edwhich. is referred to as a . “ installed on theelevator of a low-wing scout bom-~er.to deflect upward with decrease in spei~, which caused anincrease In the pull f’orcerequired to trim at low speedsand thereby increased the stick-free static Iongltuc?inalstability ~f t~.eairplane.

It was found that the sprln~y tab would increase thestick-free stabillty in Ell flight conditi~ns, wouldreduce the danger of inadvertent stalling because of thedefinite pull force required to stall the airplane withpower on, would reduce the effect of’center-of-gravityposition on stick-free static stability, and would havelittle effect on the elevator stick forces in acceleratedf11ght . Another advanta~e of the springy tab is that Itmight be used to provide almost any dasired variation ofelevator stick force with speed by adjusting the tabhinge-moment characteristics and the variatton of springmoment with tab deflection. TJnlike the bungee and thebobweight, the springy tab would provide stick-freestatic stability without requiring a pull force to holdthe stick back while taxying. A davlce similar to thespringy tab may be used on the rudder .or,ailo.ronstoeliminate undesirable trim-force variations with speed.

INTROI)UCTION

The National Advisory Committee for Aeronautics hasinitiated a program of research on the general problem of

.. . .. .... . .

2

the stability ofconjunction with

NACA

airplanes in the climbing

ARR No. L5120

condition. Inthe iACA staff

stability at low speeds and yet does n~t affect the stick-free stability at high speeds. This.device consists of’a sying-loaded tab on the elsvator. This tab is arraingedto dei’lectupward with respect to the elevator and.tocause an increased pull farce for trim at low speeds. Asthe speed is increased, the upward tab Geflectian, andtherefore rl-eincrement cf pull force, is decreased untilat hi~h speed the tah reaches a st~p In its neutral posi-tian and ~s no further effect on the elevator forces.

A tab of %hla type, re2erre5 to herein as a ‘Ispringytsb,” was built and installed on the riLht elevator Qf alow-wing scaut bomber. ~ight fli@t tests were made orthe airplane with the springy-ta5 installation. The dataobtained in these i’li.#.tsure cmnparad herein with datapreviously obtained Ior the same uirplfme Vdtil the produc-tion thb lacked.

APPARATUS

A side view of the airplane used in this investi~a-tion is shown in figure 1. ~~ie~ro~uction r,oaels ~f the

airplane tested incorporate a tab on the rig:htelevahorthat is designed as a ?wlamhg tab but Is usually locked.This tab was utll:zed ~ar the springy-tab installation.The springy tab was statically and dynamically over-balanced bymovi~ its hin~e llne rearward 0.2b.inch andby adding wei~ht to its letiding ed~e. For the sprir&y-tah installation, the elevator mass balunce was increasedto obtain tha original mass overbalance of the elevator.A plan viex of the stabilizer, elevator, and tab is shownin figure 2.

A s~ring fiasinstalled as shmwn in figure 3 to pra-vide a moment about the tab hln:e line. Rhe link con-necting the sprin~ to the tab was piv~ted on the tab ata ?~int beb.ind the hi~e line so t-t the gradient of tab .hinge moment with deflection could be made either stableor unstable by adjusting the &eonetry of the system andthe spring characteristics. A small subtab was attachedto the trailing ed~e of the spi’i~y tab in order to adjustthe floating angle of the tab, and stops were provided tolimit the upward deflection of the springy tab to 21° and

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. .

NACA AR? ~~0. L5120 3

the.downward deflection to Oo. Photographs of the sprlngy-. . tab installation are given as-figures “~.and ~: .Unless

otherwise noted, the variation of’springy-tab hinge wxnentwith springy-tab angle (as measured on the ground) wkc!asshown in fi~mre 6 and tb.eangle of the subtab upward fromthe springy-tab center line was approximately 6.50,

The relation between the elevator angle, measuredfrom the stabilizer, and the stick position Is shown infigure 7. The friction in the elevator system is indi-

cated In figure 8 to be of the order of *2: pounds. The

airplane was fitted with a bobweight that required astick pull force of approximately 5 pounds. The bob-weight, which was installed for the tests of the airplanewith the original tab and with the s~ringy tab, is a pro-duction installation and had no effect on the relativestability of the two configurations. Elevator an~le,elevator st:ck farce, springy-tab un;le, velocitY,acceleration, and time were detemd.ned from standard NACArecording instl?UiiiOntS. Elev&tor angles were measured fromthe stabilizer in all cases, The airspeed used tF~ou@l-out, called ccrrect service indicated airspeed, IS theairspeed that would be ~;iveil by a stsndurd AN airspeedmeter if it were ccnnected to a ~itat-sttitic system freefrom positi~n error and is defined by

where

v~ s

f.

qc

correct service indicated airspeed, riles per hour

standard sea-level compressibility correctionfactor .

messured difference between total and staticpressures corrected for pitot-static positionerror, inches of water

The elevator-system mechanical advantage was changedbetween the time that the tests of the airFlane with theoriginal tab and tk.etests of the airplane with thespringy tab weve made. The stick forces for the airplane

i.-,—

. ..- ...- . . . . ... . ... . . ..... . I

.

4“

with the originalcorres~oad .tothe

NACA ARR No. L5120

tab, however, have been corrected tomechanical advantage of the airplane

with tfiespringy tab Installed. –

RESULTS AND DISCUSSION

Static Longitudinal Stability

The first several flights were made to adjust thecharacteristics of the springy tab to give the desiredeffects on the static longitudinal stability. In thesefllghts, the speed ran~e over wldch the tab operated wasfound to be too small and the friction in the tab system,too large. These faults were corrected by adjusting thetension in the spring, by adjusting the angle of’thesubtab, by chan:ing the position of’tunelink joint an thetab, and by installing ball beari~-s in all moving jointsof the springy-tab system. Unless otherwise noted, thedata on static longitudinal stability are from flightsr.ade subsequent to these changes.

~ Figures 9(a), 10(a), n(a) and (b), and 12(a) showthe static longitudinal stability characteristics of theairplane at both forward. and rearward center-of-gravitynositions with the springy tab installed. The test fliGht

conditions are defined in table I. Colnparable dhta pre-viously obtained wit-hthe airplane hati~ the orl.ginaltab locked at zera deflection are shows in figures 9(’b),10(b), 11(c) and (d), and 12(b). The stick-free stabilitycharacteristics of the airplane ‘fliththe oriainal tab andof the airplane l:~iththe sprine~ tab are compared infigure 13 for the climbing and gliding conditions at theresrward center-of-gravity position. I%e points indicatedas spat runs were obtained from short records taken whilethe airplane was in equilibrium in a given i’light condi-tion. The points designated continuous runs were readfrom longer records during which the speed was slowlydecreased.

The effects of the springy tab an the static longi-tudinal stability of the airplane as compared with theeffects of the original tab (figs. 9 to 13) may besummarized as follows:

(1) The springy tab increksed the stick-ih?ee stabilityin all flight conditions as manifested by larger negative

..

NACA ARR No... L5120 5. .. . ,,1

slopes of the curves of elevator stick force against air-speed. In power-on flight with the center-of-gravity

... ... position at approximately 32 p$rcent of the mean a6rody-natic chord - a condition in which the airplane with thewiginal tab had a large “degree of instability both stickfixed and stick free - the variation of stick force with

, airspeed became “stable throughout the speed range. Inthe power-off conditions, forcwhich the airplane with theoriginal. tab was stable, the ~11 forces required to trimat lQW speed were increased by the springy tab to anextent that was considered ”somewhat objectionable by thepilots, although,the pull force never exceeded 30 pounds.Some lightening of the pull force at the stall occurredin cases in which the springy tab reached its r,axirmmdeflection a I-&wmiles per hour above the stalling speedbut stick-force reversal occurred~only in the landingcondition at the rearward center-of-gravity position.Because the springy tab reached its stop at zero deflec-tion at approxir.ately 290 miles per hour, the highestspeed of the springy-tab tests, it would be expected tohave .no effect on the stability at higher speeds.

(2) The springy tab tended to reach maximum deflec-tion at a Gpeed near the stalling speed for all flightconditions despite tke variation of stalling speed withflight condition. The Increased dynamic pressure on thetall in power-on conditions probably accounts for thefact that the tab reached its maxkum def’lectlon at alower speed In these conditions.

(3) The Swiw’y tah reduced the effect OS center-of-gravity posltlon on the stick-free static stability. Thecurves of elevator stick force against airspeed, with thespringy tab installed, amost coincide In the low-speedrange at the two center-of-gravity positions tested. Theincreased up-elevator deflections recluired for trim withthe r.ore-forward center-~f-gravity positions resulted insmaller upward deflections of the tab beceuse of the &ero-dynsmic hinge mo~ent, due to elevator deflection, actingon the tnb.

()+)The stick-fixed static IonSitudinal stabilitywas slightly decreased by the action of..”thespringy.tab,as”shown by the smaller up-elevatoy ,or larger down-elevator deflections required for trb at low,speeds wibhthe “springy tab in operation.

6 NACA m KO. L5120

Dynamic Longitudinal Stahlli.ty

The results of the static-stability measurementsIndicated that the airplane with the springy tab installedwas stable with the stick free In all flight conditions.For conditions in which a large amunt of stick-fixedinstability existed, it was considered desirable .toinvestigate whether the airplane with the sprln~y tabInstalled would tend to return to its trim speed if thespeed were chan~ed sll~htly an<!the c,>rltrolstick released.The results of bests made in the cl.%blng Mnt.glidingconditions in which the stick was released at a speedsll~htly above the trim f3pGed”&r0 given in figure ~. Inthe climbing condition (fig. l~(a)), the airplane did nottend to return to its trim speed but ?.nsteud the speetiincreased slightly at f’irst. The stable variation ofstick force wltn speed in this condition (fig. ~(a)) wouldgive a chanEe in sticl:farce of less than 2 po:nds forthis change in trim speed. This amount O: change in stick~orce Is less than the friction in the elevat~r cantrolsystem. The elevator therefora rez!ained essentially fixeddurin~ this r.aneuver and the initial divergence from thetrim speed was caused by the stick-1’ixed instability inthis flight condition. Some sli~ht up-alevator mGtionoccurred naar the end of the maneuver and prevented thespeed from continuing to increase; in fact, the speedapparently began to decrease slightly.

In the gll”ling condition (fi.i:.l:;(b)), the airplaneinitially tended to return to its trim spead. Th&t thisstable tendency was due largely to the action of thesprln~y tab may be se~n from tha motion cd’the elevator .when the stick was released, Tna airplane also had asmall amount of sti.ck-fixed stability in this ccmtition(fig. lo(a)). Some lag in tliaaction of tiletab isindicated in fiwwre ~(b) anZ may have been caused partlyby the small amount ~f friction in the tab system andpartl~ by the elevator”r.ction. ~e~ause the airpiane wasnot in steady flight, the elevat~r m~les in tk.esetestsdid not be~r the ssxe relation to Llrspeed as in thestatic-stability tests (fig. id(a)). TY1e lti~in tl-leaction qf the tab ria~ h~ve caused the instability of’thelon~-~erioti oscillation shown In this Fia-re.bility Of

The sta-tne oscillatlan for tha air~luna with the

original tab was not investigated. Since the character-istics of the long-period oscillation huve been shown byprevious Investigations to have no correlation with tna

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.

NACA ARR NO. L5120 7

handling qualities of’an airplane, the oscillation shownin figure lb(b) ,1s not believed to be objectionable.. ..... ..... ...’- ....

The failure of the springy tab to cause the airplaneto tend to return to its trim speed when .dlsturbed, inflight conditions in which the airplane was very unstablewith sticlkfixed, indicates”that this device cannot over-come a deficiency in stlclc-fixed stability, at least netwith the sar.eamount of friction as was present in t-hecontrol system during these tests: The pilots did notconsider the clxmacteristics”,of the airplane to be satis-factory for any flight condition in which it was unstablewith stick fixed, although they believed that the controlcharacteristics were inmmoved by the springy tab.

f)neadvantage of the snringy tab is the reduceddanger of inadvertent stalling. With the springy tab inoperation, a definite pull farce was required to stallthe airplane; whereas! with the criglnal tab, a largenush force was required to prevent the stall in power-onconditions.

The variation of elevater stick f’orce and sprir@y-tab angle with norrr.alacceleration in turns at 196 milesper h~ur is shown in fi~ure 15. CarLparaL~lec’atafor theairplane with the original tab are Qvon in fi~ure 16.The springy tab appeared to have little effect on theelevator stick farces in accelerated fl~.gkt. For thasyingy-tab system, the test results showed a sli~tly

lower slcpe of’the curve of elevator stick force withnormal acceleration at rearware center-d’-~r~~tity pcsl-tions, e.smay be seen by comoarin~ figures 15 and 16.The effect of the tab on the force per & normal accelera-tion would be expected to be greater with the mare-f~rwardcenter-of-gravity nosit~ons because a lurger change inelevator an~le would be required to produce a given accel-eration and a Ereater tendency f~r the tab to i’lostdownwould exist. The sli~ht friction in the tab system mayhave caused the .fllghtmeasurements to differ f’rom theexpected tendency.

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8 NACA ARR “No.“L5120

Take-Offs

Time histories of take-offs of the airplane with aforward center-of-gravity position are given infigures 17(a) and (b) for the springy-tab installationand far the original tab installation, respectively. Thetime history of a take-off with a rearward center-of-gravity position and the springy-tab installation is givenin i’igure 17(c). %’itb.the springy tab, the airplane wassaid to exhibit a tendency to-wardautomatic take-off.Several ‘ofthe pilsts stated that At the start of thetake-off the elevator nmved Aown and then at an airspeedcf about 80 miles aer hour moved up of its own accord andpulled the airplane off the ground. The action of thespringy tab that pr.sduced this tendency may be seen infigures 17(a) and 17(c). At the stbrt cf the take-gffthe s~ringy tab was ut its maximum up deflection, whichproduced a down-el~vator r.~ove.:~ent;at almut 7’3riles perhaur, the sprlna~ tab started to mve down and therebypermitted the elevator to rove up. Comnarisan of theelavator stick forces for the springy-tab installation(fig. 17(a)) with those of the airplane with the originaltab (fig. 17(b)) shows the forces req~~lred for the uir-plane with the springy tah to be less tkan those far theairplane with the original tab. Approxi:lately one-halfas much push force was required with the s~ri~~y tab tolift the tail off the ground although the town-elevatordeflections were greater ;Yith this ?.nstallatlon.

Trim-Porte Changes

All pilots who flew the uirplane witk: the springytab commented on the apparently large trim-force cha~~ewith power. This and other trim-force chunges are com-pared in table 11 with those ror the airplane with theoriginal tab for speeds of’120 and 100 riles per hour.These data were obtained DT trimming tiletiiralune firstin the climbtng condition ad. nakin.s successive changesin configuration and then trimning in the landing conCi-tlon and making successive chun~es in coni”lguration, withrecords taken after Gach chanqe. The pull tortes requiredto mainta~n tri:]ion closing the throttle with the flbpsup were considerably lar~er with the spri.~y tub installed(table IT) . The push forces required, however, on applyingfull power with the flaps down were smaller w~th thesprin~~ tab installed. The smut of trim-tab deflectionfor trim is greater by the amunt required to offset the

NACA ARR NO. L5120 9

effect of the springy tab at trim speed. The minimum,..s“peedat”which the airplane with the springy tab could betrimmed, when the rnaxlnum trim-tab deflection Is used inthe landing condition (fig. n(a)) at either center-of-gravlty position and in the approach condition (Sig. n(b))at the “forward center-of-gravity position, was ratherhigh, particularly in the land~ng condition. As shown infigure n(a), a force of 22 pounds was required for trimin the landing condition at 100 miles per hour, so thetrim forces shown in table II for this condition do natcorrespond to trim-force changes fror. a trirnned condition.The data given for the airplane with the orlglnal tabtrimmed.at 100 miles ~er hour in the landing conditionwere obtained by interpolation frcm unpublished data .t’oran airplane of the sa~.etype as that of this investigationbecause data for the airplane with the original tab werenot available.

Corl~arlson of Springy Tab with Other Ilevices

?raviding Stick-yree Sta”oillty

In a discussj.on of the springy tab, it night beappropriate to cnmqare It ‘Nitii.otner devices used LOinprovo sticic-free static lo~itudinal stabtlity. ~1nedevice l!sedfor this ~ljrp~sdis d S~I?i~& in the COntr.31

s~nteilthat exerts & ~mx:lentwhich tenl~st~ depress theelevator. Although this device, c:dled the bungee, willincrease the stick-free stability, it -S disadvant~ges:A pull i-orct? must be exerted by the pilot to hold thestick back while taxying and ths hi@ push forces thatmay be required in high-speed fli~ht would result inexcessive accelerations if the stick were released in anout-of-trim dive. The same.disadvanta~es ap?ly to a bob-wei.ght except tb-atit produces an additional increase ofstick force with an Increase in ngrmal acceleration, whichwould prevent excessive accelerations in t~lismaneuver.The springy tab will not cause any appreciable pull forcewhile taxying becaus,e the dynamic pressure on the tab attaxying speeds is low. In addition, the sprin~y tab w1llnot cause large push forces at high speed became it willthen be deflected to its neutral position.

Another advantage of the springy tah over the bungeeor bobweight Is that the stick-force characteristics maybe adjusted to obtain almst any desired elevator stick-force variation with speed. This adjustment may be

10 NACA Mifi Nom L5120

I

accomplished by changing the aerodynamic characteristicsof the tab, the spring moment at zero tab deflection, andthe variation of the moment exerted by the spring withtab deflection. A force increment of almost any valuecan be applied at any part of the speed range of the air-plane. The variation of’M.nge mo.nent with deflection farthe Initial springy-tab configuration is shown In fi~ure 18.The static loi~itudlnal stability characterlstica of theairplane with the initial springy-tab configuration befarethe changes indicated on page 4 were made are shown infigure 19. A comparison of .~i~nu’e19 with figure 9(a)shows the wide variation of elevator stick-force churac-terlstlcs ~btained with the sprindy tab for the cha~e inhinge moment Detween that sh~wn in fiSure 1~ ant til~t

shown in ~igure 6. It should be noted tlwita lar~eincrease in stick-free stability in the low-speed range,where adverse effects of power tireusually .gretitest,m-aybe obtained without greatly aff’ectlng the stability athigher speeds b~ the use of a variation uf s~ring momentwith tab deflection in which the snring moment that tendsto move the tab upward ii~creasesffx’ the larger up-tabdeflections .

secause a springy tab may be used to adjust tilecontrol-force variation with speed within wide limits, itcan be used on the rudder cr ailerons to eliminateundesirable trim-force changes with speed.

~Wom flight, tests to determine the effect of asgrlng-loaded Lab on tke lon&ltuc?inal stability charac-teristics of a low-wing scout bomber, the following con-clusions were reached:

1. Compared with the original tab installation thesprir~y tab increased the stic!!c-freestability in :Lllflight conditions as manifested by the lar~er ne~ativeslapes of the curves of elevatar stick force aEtilnst air-speed. In the climbing condition at a rearward. center-of-gravity position - a condition in which the uirplunewith the original tab showed stick-free instabilitythroughout the speed range - the airolane with the suringytab exhibited satisfactory stick-force variation withspeed.

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NACA ARR NO. L5120 11

2. The pilots did not consider the characteristicsof the airplane to be satisfactory for any flight ccndi-tion in which..it-.was-unstable with stick fixed, alth~u~hthey believed that the control characteristics wereimproved by the springy tab.

3. The springy tab reduced the danger of inadvertentstalling because of the definite pull f’orcerequired tostall the airplane with power on.

4..The springy tab may be used to provide almost anydesired variation cf elevator stick force with speed byadjusting the tab hinge-m~ment characteristics and thevariation of spring moment with tab deflection.

5. The springy ttibtended to reach maximum deflectione.ta sneed near the stalling speed for all flight concii-tions ~esplte the variatian of stalling speed with flightcondition.

6. The spri~gy tab reduced the effect OF center-.~f-gravity pa~itian on st~ck-free atatlc stability.

7. The stick-fixed static l~ngitudinal stability wasslightly decreased by the actian af the spri~y tab.

8. The sprl.~y t~b l,a~little ef’feeton the elevutorstick forces in accelerated flig:ht.

9. Pull forces required to :wintai.n trim sn closlngthe throttle with flaps up were co~siderably lsr~cr iviththe sgrlngy tab Installed than with the ori@nal configu-ration. The push forces required, hwever, on applyin~full power with flaps down were smaller with the srringytab installed.

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TABLE I

AIRPLANE CONFIGURATIONS FOR TEST FLIGHT CONDITIONS

Power

Condition Manifold=ressure Landing Front cowlEngine speed

(h60H;tftFlaps

(rpn)gear hood flaps

Climbing 2)+00 38 up I up Closed Closed

Gliding Power off’ Power off up

L

up Closed Closed

Landing Po*weroff Pcwferoff Down Down Open Closed

Approach 2)+00 21 ~ down Down Open Closed

Wave-off ‘ ~oo 38 Down Down Open Open

NATIONAL ADVISORYCOMMITTEE FOR AERONiiUTICS

. .

Powor I~ngine ~pea~ Mtifold Pr-ure l.,andiq

(rpn) (lnnoH:t;t gear

2W313*

I

38 I upWwcr off up

Power off Power off Eown

Power I

~wlne speed Manifold preesure ~ndi~

(rpn) (i;60H:t;t gear

Power off Poweroff D3wn

400 21 D3wn

2400 38 Imwn21+00 38 up

~o”y~ff38 up38 up

Power off up

Flaps

upupupIkwnDownDown.$ dowr

FlaPa

D3wn

~ dowr

DownDownupupup

Fronthood

closedCloeecClosetClosetOp*nOpen

Open

—

Fronthod

Open

Open

OpenOpenopenCloaecCloaoc

TABLE II

TRIM-FORCE CHAN13ES

Stick force, lb

120 mph 100 mph

cowl Airpl~O with Airplane with Airplane with Airplane with

flaps SpriUgy tab original tab springy tab original tab

Trim tab, 10.80; Trim tab, 2.8°; Trim taD, 15°; Trim tab, 5.20;e.g.poeitiora,26.7e.g.poeitlon, 27.0 e.g. pos~~~on, 26.6e.g.Ws;:;on,25.4

(1) (1)

;losedy::: 2J:{E::

;losed 20.0 pull:losed 19.5pullOpen 2.5push

;losedl 9.0pull

to1 .5pull 24.0°Pull ll.o”pulli .0 pull 25.5 PU1l 15.5pull12.5 pUII 20.0 pull9.5pull

9.5 pull21.0 pull 10.0pull

2.0 pull 4.5push 5.0 push

F L20cowl Airplano with

flaps sprln&y tab

‘Trimtab, 15°;C.g. Poa~::on, 26.5

;loaed o;losed .5pull

Open 10.5 ~shOpen 10.5 pushOpen 9.0 pushOpen;loaed 18:; %:

stick force, lb

~1

0 22.0 pull o4.5Push 9.5pull -------------------22.5push 1.0 push 25.5 push22.5push 5:;w;20.5 push

29.0 push26.0push

20.5push 25.0push------------------- i; ;::’ -------------------

zo.

r’mH

No

lTrlm-tabare in

deflections are in direction for ma. up and e.g. positionspercent mean aerodynamic ctmrd.

NATIONAL ADVISORYCOKMITTEE FOR AERONAUTICS

●

Side view of the low-wing scoutbomber

Figure l.-used in the investigation.

o●

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...

.—. — .—. — -—-— -—-

-—. — .—.

/Elevator trim tab ~

——— ___ _

4-.— .— -— .— .— -----

--__-—________.—.—.—.—.

Subtab1 NATIONAL ADVISORY

COMMITTEE F~ AERSWUTICS

Figure 2.- Plan view of the stabilizer, elevator, and tab used in the te6t~,

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zo.

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m.

N

wr.m.“

~E]evator hge he

/rl?emforcmg p/ate

p ~=iiimiw-—---0- — —

Lead mass balance-.---=

L------ Front spy

NATIONAL ADVISORY

COMMITTEE FORAERONAUTICS

Figure 3.- Diagramof the springy-tabtest installation.

z

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rcm

~

Figure 4.- Uncovered springy-tab mechanisminstalled on the elevator.

FP

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rmH

Figure 5.- Springy-tab mechanism as coveredfor’ flight.

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Cn

NACA ARR No. L5120

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u

20

16

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(//2 ~

8 -

4 -NATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

o-

0 4 8 12 6 20up

Springy-tabangle, deg

Figure 6.- Variat ion of springy-tab hinge moment withspringy-tab angle (as measured on the ground).

Fig. 7 NACA ARR No. L5120

.-.nau

8

20

]0-d; /0 /l-lgdho9cd o- “->a)

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/0 /NATIONAL ADVISbRY

cE= COMMITTEEFORAERONAUTICS

E

?0.--

8 4 0 4 12Forward Back

Stick position, in.

Figure 7.- Variation of elevator angle, measured fromthe stabilizer, with stick position for the testairplane.

z>c-l?-

z0.

20 /0 o /0 20Down

30up

Elevator angle, deg

NATIONAL ADVISORY

COMMITTEEFOR

Figure 8.- Elevator stick force required to moveelevator slowly (as measured on the ground).

AERONAUTICS

the

L-

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‘=3Pml.

a

Fig. 9a NACA ARR No. L5120

/(-j~ Max. up deflection, 28°Ma~=a.

w

Sd o -;: C.g-. position Elevator Spot Continuous>~ (percent M.A.C.)trim tabal

runs3

runs+0w

“ /0’32.0 2.9~, nose up o d26.6 6.I. ,nose up ❑ d

a!A6&l

cd

Dd9

-Max” down deflection, 15°

\

NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

G’– 80 /20 /60 200 240 2/%correct~ervice incliczted airspeed, mph

(a) Airplane with springy tab ir,stalled on elevator.Figure 9.- Static longitudinal stability characteristics in

the climbing condition.

NACA ARR No. L5120 Fig. 9b

31.4 1.4~,nose down o (124.5 2-L ,no~e I.Ip 13 d

A .

LMax.

o

20— up deflection, 31

~

g 10-‘a.ul-lMlG:0 -0*

:@ I,+M

10NATIONAL ADVISORY

COMMITTEE FM AERONAUTICSE

~

f

Max. down deflection, 21°

2080 /20 160 200 240 ??80 320

Correct service indicated airspeed, mph

(b) Airplane with original tab on elevator locked.Figure 9.- Concluded. ,

Fig. 10a NACA ARR No. L5120

,+El

o

20

ZOL e.g. position Elevator(Percent M.A.C> trimtab

Spot Continuous Iruns runs

g‘-d

i5.7~,nose UP o ~

m 9.2 ,nose up ❑ n’.

; 70 Max. up deflection, 2~0cd

$*d*

‘or-lEl

Max. down deflection, 15°

.al

/0

o

!I

\ NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

-\

67 80 120 {60 200 240 280Correct se;vice indicated airspeed, mph

(a.) Airplane with springy tab installed on elevator.Figure 10.- Static longitudinal stability characteristics in

the gliding condition.

NACA ARR No. L5120 Fig. 10b

26 ‘“ ““A

P+

Gm

22C

e.g. position Elevator Spot Cent inuous

(

(percent M. A.C.)trim tab runs runs

0.9~, nose up 0 d~::;5.0 ,nose up D d

20 ‘Max. up deflection, 31°

~

g’ 10.alr+ML%:0;*alAC=4

/0NATIONAL ADVISORY

COMMITTEE F~AERONAUT<CS

gMax. down deflection, 21°

’2080 120 /60 26 280 320

Correct service indicated

(b) Airplane with originalFigure 10.- Concluded.

airspeed, mph

tab on elevator 1ocked.

, . .!!. ! .m...l. . . , ,,.., ,. - . . . . . . . . . —-. . ..—. . . . . . . . . . . . . . . . . . . . . . . ,.- .- - -—.

Fig. ha, b NACA ARR No. L5120

; L e.g. position Elevator

’20 (percentM.A.C.)trim tab

k~1.LL 15.0~, nose

2026.2 ls.20, nose

12.$Io,nose~::j15.0,nose

f

Spot Continuousruns runs

I

up @ G’up Elup oUP A

~- 11

i

~ Max. do?in deflection,

/

(a) Landing condition;springy tab installedon elevator.

Figure 11.- Static longitudinal

15°

NATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

60 /m /40indicated airspeed, mph

(b) Approach condition;springy tab installedon elevator.

characteristics.

NACA ARR No, L5120 Fig. llc, d

e.g. position Elevator Spot Continuous

\(Percent M.A.C.)trim tab runs runs

\

26.2 15.0 °,nose up ❑ d25.7 g.7°, nose up A K

20 \‘Max. up deflection, 2~”

8 QUIIm

/0 &

m

c

I NATIONAL ADVISORYCOMMITTEE FO@AERONAUTICS I

60 100 /40Correct service

(c) Landing condition;original tab onelevator locked.

Figure 11.

60 /00 /40indicated airspeed, mph

(d) Approach condition;original tab onelevator locked.

- Concluded.

Fig. 12a NACA ARR No. L5120

Spot Continuous

runs runs

up o 0’up El P

‘2L C.g.position Elevator

(percent M.A.C.) trim tab

‘-d

.al

\q-- Max. up deflection, 28°

Max. down deflection, 150

.-&

g

0“J

‘Go /00 /40

NATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

correct service indicated airspeed, mph

(a) Airplane with springy tab installed on elevator.Figure 12.- Static longitudinal stability characteristics in

the wave-off condition.

NACA ARR No. L5120

‘J2CI~P+

o J#$@& ~ u -

G:’20

e.g. position Elevator(percent M. A.C.)trlm tab “runs runs

SDot Continuous

25.6 4.6°,noseup ❑ d

t

10’0s Max. up deflection, 2g

G

5 ‘Max. down deflection,

= 10 I 1 I I 11

Fig. 12b

NATIONAL ADVISORY

COMMITTEE FOR AERONAUTICS

.5°.—40 80 [20 /60

(b)Figure 12.-

Correct service indicated airspeed, mph

Airplane with original tab on elevator locked.concluded.

Fig. 13 NACA ARR NO, L5120

~ol-l

GPI

o

s VQ (a) Climbing condition .!4

I I

e.g. -position Elevator

(percent M.A.C.> trim tab

Spot Continuou8runs runs

32.031.731.430.9

Q2.9 °)nos.ew : 1 Elevator with springy~.~~,nose up - K tab installed

,nose down ~ 6019°,nose up A 4 1

Elevator with originaltab locked

80 /20 160 200 240 2m 320Correct service indicated airspeed, mph

Figure lj. - Comparison of stick-free static longitudinalstability characteristics of airplane with springy ta-binstalled and of airplane with original tab locked.

NACA ARR No. L5120

3 la

I— — —_ 6 — —

o Static tab angles‘3

o

GB

g 10

I .

0

.6

----— —

.4

NATIONAL ADVISORY

/80CONMITTIE FOO AERDMNJTICS

140- “vtrim.—

0

Figure

8 /6 24 32 40 48 S6

Time, sec

a) Climbing condition; center of gravityat30.3Dercent mean aerodynamic chord; springy tabinstalled on elevator.

4.- Time history of motion following stick releaseat speed S1ightly above trim.

Ill II II 111111Im nmm IIMUI mnmmm, B I I ,,,.,,.8 B , , ,,,.--!. !.,,,,,,—. --! .,,, - .--,, -...! --—,, . . .-- . . ... —---- . —.. I

Fig. 14b

20 /g Statictab angles /

I

/ c I

10 // /- ,’ \\ /

<. - /

o

Eg

o ‘ ---~ y

/ \ .

2

\

/ \ /

\

o

.8 ~

.6 /~ .(

/ 1.J /

,’4

\

\

.2 /NATIONAL ADVISORY

COMMITTEE FOMAERONAUTICS

/80 - ./

—

+--vtrim’\

140——

\

/000 8 16 24 32 40

I

NACA ARR No. L5120

Tih!e, sec

(b) Giiding ccr2dlti0n; center of gravity at 30.2~Prcent mean aer!xlyna!nirchord; sprinq tabInstalled an e:evat or.

Fi~~~~ Ill.- concluded .

NACA ARR No. L5120 Fig. 15

. .—

.

c.g. position Elevator(percent M.A.C.)t.rim tab

30.4 1+.b~, nose up 026.1 6.o ,nose up ~A

50

40 /

/

30 /

//

20 d

)0 /)

NATIONAL ADVISORY

o- COMMITTEE FOQ AERONAUTICSm

o / 2 3 4Normal acceleration, g

Figure 15.-Variationcf elevator.s~ickforceandspringy-tabangleWithnormalaccelerationinturnsat 196 milesper hour. Airplanewithspringyta”oinstalledon elevator.

,.,, , -,,,--—. --.. -! -.....-. ,,-... .l.l... —- .—-—

Fig. 16”

e.g.position Elevator(percentM..4.C.)trimtab

30.0 O.Z’O,nose down 025.7 1.7 °,nose up El

NACA ARR No. L5120

60L

P

50- /

40 /

3C //

o

/

20 /

10 I /

NATIONAL ADVISORY

0.COMMITTEE FOR AERONAUTICS

o I 2 3 4 5Normal acceleration, g

.

Figure 16.- Variation of elevator stick force with

normal acceler~tion in turns ax ?96 ~ilesPerhour. AirplaneWithoriginalta” ‘n ‘levatorlocked.

NACA ARR No. L5120 Fig. 17a

.

20—‘ss

\

10 \

o

/20J

80 /

/ ‘“

f ‘4C ,

NATIONAL ADVISORYCONMITTEE F(H AERONAUTICS

/

o0 8 16 24 32

Time, sec

(a) Center of gravity at 26.9 percenr mean aero-dynan,ic chord ; elevator-trim-tab setting,]1.6° (nose up) ; airplane wi~h springytab installed cn elevat~r.

Figure 17.- Time history of a take-off.

, , , , !! !..,! ! ! ,,-,, . , ,,.,, ,,, ,. ,.. -,, -.,, , . . . . ./

. . . . . . . . . . .-, .-—

Fig. 17b

10

0

NACA ARR No. L5120

\ , k

t

hl I I/l r--i I

I I I I I I I i i

120

80

40

00 8

—

—

—

—

+

—

-1-

NATIONAL ADVISORYCOMMITTEE FOR AERONAUTICS

I

/6 24 32Time, sec

(tJ) Cen;er c? gravity at 27.2 percent mean aerO-

dvnami: chord ; elevator–trim-tab setting,~b airplane with original tab on elevStOr

locked .Figure 17.- Ccntinued.

.

NACA ARR No. L5120 Fig. 17c

D.

/20~ — ‘

—/

80/

/ ‘

/

40 - / ‘NATIONAL ADVISORY

CQMMITTEE FW ASROUAUTKS

c I

-o 8

(c)

Figure 17. -

/6 24 32 40 48 S6Time, sec

Center of gravity at 32.1 percent mean aerO-dyn~mic chord ;e levator-trim-tab setting,8.1 (nose UP) ; airplane with epringy tabinstalled on elevator.

Concluded.

,

Fig. 18 ARR No. L5120

‘o 4 8 /2 /6 20up

Springy-tabangle, deg

Figure 18.- Variation of sptingy-tab hinge moment withspringy-tab angle as measured on the ground for theinitial springy-tab configuration.

NACA ARR” No. L5120 Fig. 19

.al

h0

,.

I I IA

Reportedtrim~ +

o1.

an o

i

~ Max. down deflection, 15°

20 e.g.poaitlonElevator spot Continuous —(percent ~.A.C.)trim tab runs runs

32.1 2.T”,nose up 0 ~ —

t

D 1 I 1 INATIONAL ADVISORY

COMMITTEE F~AEROUAUIKS\

o n n

80 120 240 2aoCorrect service indicated airspeed, mph

Figure 19.-StaticIn theclimbingconfigurateion.

longitudinal stability characteristicscondition with the initial springy-tab

-..

/’.,’

i

I