Lateral stability and control.pdf

8/14/2019 Lateral stability and control.pdf

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NATIONAL ADVISORY COMMI~ E _FOR AERONAUTICS .-~ ~ : -= ; ._

+. ..... . . ,-- ---- . ...-TECHNICAL NOTE

No, 1094 . -

. ...EXPERI1iENTAL DET271:LNATION OF TEEEUFH2TS OF l ~D~AL - -VERTIC AL.TAIL AR2A, AND LIFT COEZFICIENT (2NLAT?ARAL - , .

. STABILITY AND CONE?(XL GEARX7YZRISTICS -.i, -.-.+_By Marion 0-KcKimey, Jr.


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NATION& ADVISORY COMM7XTElZ FOR AERC)NAUTICS

TECHNICAL NOTE NO. 1. 094EXPERIMEWM.L BETERMINATICN OF T:EE EE??TCTS OF DIECS12ML,VERTICAI,=TAIL ARKA , A:f:)IF~CCzF~IC IEl~T0-:7JJAT~iUL

STABILITY AN i)CONTROL CH MUG TZR1STICSBy Marion O. McKfnney, Jr.

The effects of wifle variations of dihed?al, verticslstail area, and lift coofficlent on lateral stability andcontrol and on general flying characteristics kave beendetermined by fli~ht tests of a model in the Langley ---free-flight tunnel. In order to vary the effective dihe-dral and directional stability of the model, the ~eo-metric dihedral angle was varied from .20 to 18 andthe vertical-tail area, from O to ~~ psrcent of tli~ wing ares. The tests were made over a rang9 of liyt coefli-cient from 0.5 to 1.8.


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. .

2 NACA TN NO 1094rolling and yawing radii. of gyr~tion not exceeding 0.2and.O.5 of the wing spanz respectively, will have the ----best general flying characteristics if th6 effectivedihedral is ~reater than zero hut not so great that thevalue of the effective-dihedral perar~eter -Cz exceedsPone-h..lf the valu6 of the directional-stsbilityparameter CnP providing the valuG of Cn? is greaterthan 0.0020.

Tests of modern military airplanes have indic~tedthat large changes in effecbive dihe2ral xay.occtu?overthe speed range of an airplane o~erating under variouspower conditions. Wfs chang6 In @ff6ctive dihedral maycause an airplane that has n normal armunt of positiveeffectfve dihedre,lin the [email protected] condition to hav~large ncgatlve effective dihedral M a flaps-down, low-speed, high-power condition (wave-off or ls.ndin~-ap,proachcondition), If an ~tte?npt is Kade to satisf~ the require-ments of r6ference 1 that the-airplane have pasftfveaffecti.v6 dihedral at all speGd,s~ it msy have excessive


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NACA TN NO 1094 3free-flight tunnel. ~G objects of this,investig*ionwere to determine t~~eoptimul~lcombinations of dihedraland,directional stability over a wi~e range of liftcoefficient and.to provtds fiatathat wo-~ld aid in theselection of the proper dihedral angles for airplanesthat must experience large changes of sffective dihedralover the speed and power ran~e, The results of theinvestigation are presented ~herein. Some of these re9ul.ts(negative dihedral at hiEh lift coef~icients ) are reportedin rsference 5.

The present investigatlan consisted in power-offflight tests of a mod61 on which changes in effective .dihedral were obtained by varying the .geomtric dihe-drs.1angle. The tests w6re m=de over a range of~eo-metric dihedral angle from -20 to 18 for vertical-tailares.sfrom O to ~~ percent of the wfn.garea and for liftcoefficients of O.~ and 1.0 with flaps up and 1.O.11.4,and 1.8 with flaps down. Sufficitint combinations ofdihedral angle and vertical-tail area were testefl ateach of the lift cosfficimts to determine the effect offiihedral, vertical-tail .crba,8*3 lift coefficient onlaterel stability and ccmtrol and general fl~in& ch&ac-tsristics over the rm.gc of the vmiables. .


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i$MA TN Xo 1094mass of model, slugswing area, square feetvertical-tail area, square feetwing span, feetfree-stream velcmity, feet per seconddynamic pressure, pounds per square foot & @time to damp to o~le-naltamplitude, seconds; nega-tive values indicate tzime to increase to doubleamplitude ,period of lateral oscillation, seconds radius of gyration of model about longitudinalaxis, feet -. Jradius of gyration of model about vertical axis,feet- . .


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6 NM A TITNOs 1094

tests to determine the static lateral-stability deriva-tives o.tthe model were made on the Langley free-fliXt-tunnel six-component bal&nce, which is described inreference 8. This balance rotates in yaw so that-allforces and moments are measured with respect to the sta-bility axes. Free-oscillation tests were made to deter-mine the rotary-damping derivative Cnr by the methoddescribed in reference ~.

The control used on--free-flight-tunnel models Is a.~flickerttfull-on or full-off) system. During any oneparticular flight the control deflections in the full-onposition are constant and the amount of control appliedto the model is regulated by the length of tiriethe con-trols are held on rather than by the magnitude of thedeflections used.A tliree-view drawing-of themodel used in the testsis shown as figure 2.and a photograph of the model is

presented as figure 3. Figure 4 is a photograph of themodel, with flaps down and a geometric dihedral oi-15,flying in the test section of the tunnel. Although themodel used in the tests was nota scsle model of anyparticul= .airplane, it approximately represented a


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~~~A TN ~T~ . 1o94 - .. : 7

The relative-density I_actorand radii of g-yrationfor the model varied during the test yrogra. between tb..e _following limits :8.10 to 8.?2: :::::::::::: :::::: 6.161 to O.IC I

kZ/b . . . . . . . . . . . . . . . . [email protected] data presented in references 4, 5, and l~indi~atethat changes- in w6iglht and moment 02 inertia of themagnitude invelved in the -present investigation wouldmake no pronounced difference in the stability or flyingcharacteristics of the rtodel.

TESTSScope of Tests

Flight tests of.the model were made with the combi-nations of dihedral .ar@e and vertica-tail areaand atthe liftcoefficient shown in table I. The-values of


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8 NM~ TN No. 1094that used for coordinated rudder ~d aileron control atthe same test condition, For the tail-off condition theailerons were rigged up 12 In order to eliminate the- adverse yawing due ta aileron deflection. The stabilityand general flying characteristics of the modelwerenoted by the pilot from visual observation and eachtest condition was assigned graduated ratings for spiralstability, oscillatory stability, and general flight-behav~or. Motion-picture records for later study weremade to supplement the pilot s observations.

The spiral stability ofthe model was determined bythe pilot from the rate at which the model, with controlsfixed, sideslipped ~d rolled from level flight. Anincreasing rate of ro~l~ng and inward sideslip was judgedas spiral instability.The general oscillatory-stability characteristics

were judged by the pilot from the damping ofthe lateraloscillations of the model after a disturbance. A modelcould never be allowed to fly with controls fixed forsufficient time to allow measurement of the period anddamping from the motion-picture records.


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NACA TN No. 1094 . 9Lines of constant damping of the spiral mode were

also calculated for the model by determining tb.eroot ofthe stability quartic h that wouid give the desiredvalue of damping by the following formula (reference 6):

A= -o.693~Tand determining various values of CZ~ and Cnp thatwould give tkis root h by substitution of the root inthe stability quartic. The calculated lines of constantdamping are shown In figures ~ ,to12.

Lines of constant period and damping uf the oscil-latory mode were calculated from the following appraxi-mate relations given in reference 6:,=_?

D.-

and


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10 NACA TN NO . 1094RESULTS AND DISCUSSION

The variations of effective-dihedral parameter CtPand di.recta~nal-stability parameter CnG were obtainedin the present investigation by changin~ the geometricdihedral .a?@e and the vertical-tail area. Flying char-acteristics, however, depend onthe values or the sta-bility derivatives, not on the method by which they areobtained; hence, the flying characteristics of the modelmay be applied to conditions in which changes in thestability derivatives were obtained by some other means,such as power.

The principal re~ults or the present investigationare g~ven..infigures b to 14 tn the form of ratings ofthe general flight behavior ofthe model. All flightratings not h parentheses were obtqinsd with. a totalaileran deflection of;00; tlioj=~in par~ntheses wereobtained with a total aileron deflection of 500. Themaximum values of pb/2V corresponding to aileron defl6c-tions-oT 30U.and 50 were determined to be about 0.08


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NACA TN No. 1094 11

.

Theseresults are in qualitative agreement with thecalculated spiral-stability characteristics of the modelpresented in figures 8 to 12 as lines of constant dampingnf the spiral mode . These theoretical results, likethe test results, show that reducing the effective-dihedral parameter -Czp or increasing the lift coeffi- ,cient caused an increase in the time for the spiral modeto damp to one-half amplitude or a decrease in the timeto increase to double amplitude over the range of condi-tions tested. Similarlyl the theoretical and experi-mental results show that Increasing the d$rectional-stability parameter CnP caused a slight reduction inspiral stability for positive ef~eotive dihedral anglesand a slight increase in spiral stability for negativeeffective dihedral angles with very little effect ofvarying the directional stability for effective dihedralangles near zero.

No quantitative check of theory with tests could beobtained inasmuch as a spiral ejvergence could not beallowed to developfar enough in the confines of thetunnel to permit measurement of the rate of spiral con-vergence. A reasonably good check of the calculatedspiral-stability boundary (E = O) was obtained, how-


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12 NAC~ TN No. 1~94

Rating

ABcDE

Qualitative rating

StableSlightly stableNeutralSlightly unstableDangerouslyunstable

Approximate quantit&tiveequivalentDwps to one-half smplitudein less than 2 cyclesDanps to one-haif amplitudein more than 2 cyclesZero dampingBuilds up ta double ~plitudein more than 1 cycleBuilds up to double smplitudein less than 1 cycle

The ratings in figures ~.to 1.2..sho.what-,.althoughincreasing the lift coefficient reduced the oscillatorystability for virtually dll model configurations having-positive effective dihedral, the magnitude of the reduc-tion varied for the different combinations of effectivedihedral and directional stability. lilgeneral, theeffects oflift coefficien.ton the osclllatary dsmpingwere more pronounced with high effective dihedral and


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13Lateral Control

Increasing the effective dihe@al caused a reduc-tion in the effectiveness of the ailerons for roll-of~sfrom a zero-bank condition and an incre&se in the effec- -tiveness of the ailerons for recoveries because ofthesideslips involved in these maneuvers when the controlswere coordinated in a normal manner. No measurements of _-this effect of dihedral on rolling velocity were madebut the pilotts comments indicated that recoveries were __more rapid than roll-offs at l&rge positive effectivedihedral angles,whereas the roll-offs were r.uchmorerapid than recoveries at all neg~tive effec


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14 NACA TN ~~o 1094dihedral angle greater than 10 (-C tp > 0. 002 ) . ~~nthe effective dihedral angle was less.-than 10butgreater than Oo, it was possible to pick up a low wingby means of rudder alone although control by rudder alonewas not satisfactory.

General .FlightmBehavlorThe results of the tests are best summarized by thegeneral flight-behavior ratings. Spiral stability,oscillatory stability, and controllability are all con-sidered desirable but a proper ba la nce of ~e.s? f.actors~..with consideration of their relative tiPort&n.ce~ isnecessary to give satisfactory flying characteristics.The general flight-behavior r~tings~ for which the over-all flying characteristics have been considered, aretherefore thought to be the most significant results of

the tests.Effect of dihedral,- The general effectofvariationsof effective dihedral on the genera flight behavior 1s


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.

NAC A TN NO 1094 . 15.

.The oscillatory-stability cha~acteristics, however,were not the only factcrs affecting the general ~lightbehavior in th positive effective-dihedral. ragfcn. - -Increasing the etfective dihedral angle cmmed the flyingcharacter~sti.cs to become worse because of the abrupt -rolling ad lateral oscillations that followed each *tdisturbance in the normally rou&h afii uf the tunnel &nd-because of the adverse ef~ects of higln dihedral anglescn the lateral cor.trol. The rOlling oscillationsresulting from ~sts were particularly object~onable at

high airspeeds, whereas the contiaolcharacteristics werethe more predominant CaU38 or the poor flyin~ ohWacter-istics at low spseds. ,.,-- -.:-...-The rate of spiral divergence for the test condi-tions at wh].chthe r&odel had positive effectfve- dikedzzalwas observed to be s~, allfoi~the ran~e or lit% coeffi-cient cuvorod in the present invest igation,- ~d--tl=controls-~ixed Iatersl motion wtis characterized by aslow gentle roll-off aridsidesl.ipironthe steady Statea

The di.vei-gencecould be controlled readily by occ~si~nalapplication ofa total aileiondeflection .of 30- Undorthese conditions, the nodel.was as easy to -fly Qsif Lthadbeen spirslly stable and because oi the gusty _Qiy i-n


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16 NACA TN ITos 2.094The controls had to be applied almost immediately afterthe divergence was noticed because, when there was onlya slight lag in t~ application of corrective controlfollowing a disturbance, the unstable moments resultingfrom spiral instability becsm.e sufficiently large tooverpower the moments of the controls so that return tostraight flight was impossible.

It was generally found impossible to fly the modelwith negative effective dihedral angles greater thanabout -10 (-c~p z -0.002 ) with a total aileron deflec-tion of 300. The rate of-spiral divergence apparentlyhad become great enough by the time the pilot appliedopposite control to make recovery Impossible. Aileronapplication retarded but did not-stop the divergence.

In order to obtain data for the whole test range,the total aileron deflection was increased from 300 to~0 for almost all test conditions far whichCLP < -0.002. It was therefore possible to control thespiral divergence over the complete range of negativedihedral angle. Flight was difficult, however, when-CZ* < -0.002, because constant attention to the con-


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ITAOATN NO. 1094 17

.

of the model due to gust disturbances appeared to be tl+ecause of the trouble. llhen the model yawed around dueto a wst disturb~ce the leading wing dropped very wt---apld y, because of the high airspeed, and the roll haddeveloped so f&r by the time the controls were appliedthat no recovery was possible. .. .-.

The general flight-behavior ratings in figures 8to 12 were given when the rudder was coordinated withthe ailerons in the normal manner (right rudder withright ailer?n). The flight tests, however, showed thatwhen the ailerons alone were used cm even when the rudder. control was crossed the flying characteristics of themodel were improved throughout the negative dihedralrange and the model was slightly easier to fly. Thisimprovement evidently occurred because the sideslipresulting from adverse yawing opposed the inward angleof sideslip caused by the spiral divergence and, in spiteofthe adverse effect of rolling due to yawing, .reduc_e.d___the rolling divergence. This reduction of inward side-slip improved the response to the controls. The largeamplftude of the yawing motions causad by crossing therudder control, however, was objectionable to the free-flight-tunnel pilots. Application of opposite rudder..:.....with ailerons would probably be objectionable to the


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18 NACA TITNo. 1094that af the model, where N is.the scale of the modelas 1/10, 1/15, a nd- so forth. Nb.information is available,however, concerning the relative reaction time and thetime to deflect the.controls for.free-flightand airplanepilots , Because no correlation has been made of time todamp with the boundaries of the regionin which flight i.simpossible in the Langleyfree-flight tunnel, an exten-sion of the results to more negative dihedral angles i-s -difficult. Inasmuch as the rate af..spiral divergence offull-scale airplanes 1sslower tian that o~the model,however, it is believed that the amount of negative effec-tive dihedral that-would constitute a dangerous conditionwould be greater for airplanes than for the model.

The results of the tests have-bgen summarized infigure ljas boundaries of the region within which goodgeneral flight behavior of ths model was obtained. Theseresults, as shown in figure 15, are believed to bedirectly applicable to airplanes having mass character-istics similar to the model. This criterion, hewever,should be modified to take into consideration differencesin the mass characteristics ofairplanes from those ofthe model. The data of-references 3, ~ , and 10 may beused to interpret the present data f~r tb~eeffectsof


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NA~A TN NO 1094 19with low directional stability. The rates of spir8.1divergence within the positive effective dihedral rangewere, as previously discussed, quite slow even with ahigh degree or directional stability. . .

For higher positive values of effective dihedral,at which the oscillatory stability is sm importantfactor =fecting the general fllght behavior, increasingthe directional stability caused a great improvement inthe general flight behavior by increasing the.oscillatorystability as well as reducing the rolli~ and yawing due ~to gusts and improving the control characteristic as--waspreviously discussed. The detrimental effect on generalflight behavior of the slight decrease in spiral stabilitywith increasing directional stability was thus F.eavilyoverbalanced by the tiprovemen$ of tineoscillatory char-acteristics and lateral cunii.rol,When the effective dihedral was negative, increasingthe directional stability caused a slight reduction in

the spiral instability as well as a reduction in theyawing due to gusts and aileron control and resulted inan improvement in the general flight behavior.The motions of the model with tails off,geometric


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20 NM A TN ?0. lc>~Effect of lit% coefficient.- Figure 16 was preparedby interpolation from figu~es 8 to 12 to show the effectsof lift coefficient on the general flight behavior inas-much as the effect of lift coefficient w&s slight andcol~ldnot readily be ascertained from an inspection Ofthe separate figures Figure lb shows that increasingthe lift coefficient caused the general flight--behaviorof the model to become slightly worse for the range ofeffective dihedral angle presented exceptfor the con-dition of negative effective dihedral and low directional

stability, which h&s previously been discussed. Theeffect of lift coefficient was slightly greater at lowvalues of the directional-stability parameter Cn..f

Thedetrimental effect af increasing the lift -coefficentwas greater when the ailerons were used as the sole meansof control, as may be determined from figures 13 to 16,because of the increase in adverse yawing due to rolling,and ailerons at the higher lift coefficient-s.

CONCLUSIONS

Tests were made in the Langley free-flight tunnel to


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k.ACATN No 1094 21

.

These criterions are believed to be applicable to air-planes having tiass characteristics siruil&r to those oftne model tested.

2. The model w&s found to be flyable over the rangeof posltlve effective dihedral angle tested, profilded itwas directionally stable. As the effective dihedral wasincreased from an optimum value of &pproximately 2, however, the flying characteristics b9came worse andmore critically dependent upon the aseof the correctamount of rudder control in conjunction with the ailerons.At high speeds the use of large rudder travels causedunnaturally rapid rolling, and at Zow speeds the use oftoo little rudder caused serious adverse yawing with -accompanying reduction in rolling.

3. The mcdel was found to be ~lyable for effectivedihedral angles as low as -l~ for lift coefficients of ___1.0 or greater. As the effective dihedral was decreasedfrom 0~ to -15, h,owevmr, the model became increasinglydifficult to fly.( ~;ith an effective dihedral or

_150)-Czp< 0,003 the flying ch&racteristics were considered~o be dangerofisbecause when there was only a slight lagin the application of corrective control following a


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22 NAcA TN No o 1C54.control because the adverse yawing due to rolling andailerons was Increesed by an increase in lift coefficient.

Langley Memorial Aeronautical LaboratoryNational AdVi90ry Committee IorAeronauticsLangley Field~ Vs., Jaum?y 18, 1946

... . , . .


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1. Gilruth, R. R.: Requirements for Satisfactory, ~lying@alities of Airplanes. NACA ACR, April 1941.(Classification changed to Restricted Ott.. 1943. )2. Weick, Fred E., Soule~ Hartley A., and Gough,Melvin N. : A Fli@t Investigation of the LateralControl Characteristics of Short wide Ailerons and -Various Spoilers with Different .Amounts of \Ving

Dihedral. NACA Rep. No. 45 , 1?34.3. Campbell, John P. , and Seacord, Charles L., Jr.:Effect of Wing Loading and .A1.titudeon Lateralstability and Control Characteristics ofariAir--plane as Determined by Tests of a Nodel in theFree-Flight Tunnel. NACA ARR NO. 3F25, 19/ +3.~. Campbell, John P., and Seacord, Charles L., Jr.: TheEffect of Mass Distribution on the Lateral Stability

amd Control Characteristics of an Airplane asDetermined by Tests of a Model in the Free-Flight~~ne 1. NACA ARR No. 3H31, 19~3 .


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9. Canpbell, John P. , and Mathews, Ward O.: Experi-mental Determination of the Yawing Moment Due t-oYawing Contributed by the iving,Fuselage, andVertical Tail of a Midwirig Airplane Model. NACAkFiR NO. 3F28 1943.

10. Bryant, L. W., and pugsley, A. G.: The Lateral Sta-bilit of Highly Loaded ~e~oplanes .5 R. i? M,No. 1 40, British A.R.C,, 1938.11. Pearson, Henry A.j and Jones, Robert T. : Theoretlca~Stability and Control Characteristics of Wingswith Various Amounts ofTaper and Twist. NACARep. No. 635, 1938.12. Bsmber, tiillard J.: Effect of Some Present=l)ay Air-plae Design Trends on Requirements for LateralStability. NACA TN NO. 814, 19@.


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NACA TN No. 1094

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Fig. 1


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Fig. 2 NACA TN No. 1094

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NACA TN No. 1094 Fig. 4


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NACA TN NQ.t1094 Fig. 5a,b.

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Fig. 6a-c NACA TN No. 1094

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Fig. 8 0Mg NACA TN No. 1(+Pid..029 1 I7=-2 s--

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.a - T;5/ D ~ // A. ax /\ D DAD I- -c ~ /I /.a2 +, A=. .

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w


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NACA TN No. 10941Fig.

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Lmsofcomtuntdamp}q of theqvro/ mode andspmldabdityrwtmgsA tWb/eB Slightly stubieC A4tutr01D Sltght& umtt2tYeE Duqen@ wshz~e

Lfnes of constuntjwwiano duzq.p)njof the ~Jtory mwi?osclliQtwy-stabl@YratingsA StableB Shghf@ StUbbC NeutrufD Shghtfy unsfuble


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Fig. 10 NACA TN No. 1094mr I I I I I I I I I 1 I 11117-=? 1117=-211111

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Lines of constuntdamping ~f theqvrul mod? undspwa)-dalvhtyrzz?n~A St abl eB SJf9htjyStOL eC NeutrulD S1/ghz7yunstableE &zgera@ U.ZMJ4( ) Wz71akrofl z%ukelkrease~ 30~0 60Lmas of constuntperlodunddompmgof the asciltutoryma+?andoscWzory&ob/dyYiatlflffsA Stob~e: SJ:MI){ stableD .Wghtly umtableE Dangerouslyomifubk


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. --77H 111 [17.1 -Al. I Illk I I I I I t %1 I c1 I I

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Lines of constantperiod and dampmgof the Osu/lutorym&eandOsclllatiwyatabihtyruiwgsA StobleB SIIght~ S2t7b/.4C NeutralR Sllght~ unsfableE Donj7efvkIsiyxtff~e


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Lines of constantoumpq of theSplruln?oo e andspJlw/-stoblhtyrotwgsA StablG6 Sllghtly Sfm$leC NeutralD Sllght/y unst.obkE LWgmavjtuz?shble() T&/a&ton Z%nd//-zn7?@& J@& &j~Lines of Cons.tuntpeflod Ond Ompmgof z%eoscdlatwjmcdeandoscd)atory-stob}htyratln~A0c


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6enera/ flight-behwwratingsA (booB. FuIrc PcwD Flight lmposslb)e


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Fig. 16a-c NACA TN No. 1094

Geflerul flighf-behuvzw ruh gsA GoodB /%Q/r POOPD F/IgM mpossdle

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DI VI S I ON: Aerodynamics 2)I s E C T I O N : StabilityndControl 1)I C R O S SEFEBENCES.Lateralstability 5li5^9-7);planes -Controlharacteristics 06393) Air-

MeKinney, M .0. O B I G .A G E N CT N -109i|

A U T H O a ( S ) REVISExperimentaldeterminationofheeffectsofdihedral,vertical-tailarandli tcoefficientnateral stabilityndontrolharacteristicaF O B G N .T I T L E i

ORIGINATINGA G E N C Y : NationalAdvisoryCommitteeorAeronautics,Washington,TR ANSLATI ON: D C.

L A N G U A G EFO BG N.CL ASS| U S X X A S S .Eng. F E A T U R E S diagra, graphOUNTRYu.. Unclass. T E JulI j6 P A G ES L L U Si|06 photos,

Anairplanemodelw asested inLangleyree-flightunnelverangeofliftcients from.5o1.3- Geometricalihedralan leariedrom20o18n dvtailrea from o ofwingarea. Best resultswerebtainedwitheffectiveangleboutE. Withangle above, flyingcharacteristics becameworse. Withdecreased to -15,model became increasinglydifficultoly. Increasing liftcient ha detrimentaleffectnlyingharacteristics.

.NOTEi Hequests foropiesfhis reportmust beddressodo:Washington, D .C . N.A.C.A.,T-2.HQ,A IRM T E R I E LC O M M A N D lRDKHNICAINDEX W R I G H T IELD,O H I O .USAAt o-JI

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