hlf\c(\ L'lo3 y MR No. L5L05 NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS M'ARTIME REPORT ORIGINALLY ISSUED Fetruary 19^6 as Advance Restricted Eeport L5L05 THE EFFECT OF LATEEIAL AREA ON THE LATERAL STABILITT AND CONTROL CHARACTERISTICS OF AN AIRPLANE AS lETERMINEri BY TESTS OF A MODEL IN THE LANCcLET FREE-FLIGHT TUNNEL By Hubert M. Drake Langley Memorial Aeronautical Laboratory Langley Field, Ya. 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 tech- nically edited. All have been reproduced without change in order to expedite general distribution. -I . DOCUMENTS DEPART, Mr.,f NACA ARR Wo. L5L35 RESTRICTED NATIONAL ADVISORY C0I*.1?.'IITTES FOF AERONAUTICS ADVANCE RESTRICTED REPORT TKS EFFECT OF LATERAL AREA ON THE LATERAL STABILITY AI'ID CONTROL CHARACTERISTICS OF AN AIPPLAI^E AS DETEPJ:I1'IED by TESTS OP A I'ODEL IN THE LANG LEY FF^E- FLIGHT TUNITSL By Hubert M. Drake SUTffilARY The effects of large variations of lateral area on the lateral stability and control characteristics of a free-flying ^.odel vhen ailerons are used as the principal control have been determined by flight tests in the Langley free-flight tunnel. The effects of the lateral- force parameter Cy (r^te of change of lateral-force coefficient with arxgle of sideslip) were investigated for a wide range of values of the directional-stability pararrieter Cj-. (rate of change of yav/ing-xpoment coeffl- cient vdth angle of sideslip) and the rotary-damping-in- yaw ■oaraiTieter Cn (rate of change of yawing-moTnent coef- ficient with yawing angular velocity) . Although large values of C-y were found to increase the lateral stability, a definitely undecirable effect was obtained with large values of this parameter when ailerons were used to raise a low wing or to make a banked turn. "Ith large am.ounts of lateral area the adverse yaw sccom.panying aileron rolls crested adverse side forces of sufficient m.agnitude to interfere with the aileron control. This action was particularly objec- tionable for low values of Cn ^^^'^ Ov, . It is indi- cated that decreasing Cv will im.prove the over-all lateral flight behavior. RESTRICTED Digitized by tine Internet Arclnive in 2011 witln funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/effectoflateralaOOIang NAG A ARR No. L5LO5 Cj lateral-force c oefficlent ^Lateral forc^ S wing area, square feet b wing span, feet q dynamic pressure, pounds per square foot ( ^pV^] & V airspeed, feet per second p mass density of air, slugs per cubic foot P angle of sideslip, degrees ^ angle of yaw, degrees (for force -test data, ^= -p) L rolling moment, about X-axis N yawing moment, about Z-axls T.I pitching iiiomont, about Y-axis 5j, rudder deflection &Q elevator deflection a angle of attack T' /p time for oscillation to damp to one-half amplitude ? period of lateral oscillation, seconds k-j^ radius of gyration about X-axis, feet ky radius of gyration about Y-axis, feet pb/2V helix angle generated by wing tip in roll, radians p rolling angular velocity, radians per second r yawing angular velocity, radians per second I4. MCA ARR No. L5LO5 C; rate of change of rolling-inoraent coefficient v;ith ^P angle of sideslip, per degree ('^Ci/^p) C. directional-stability "parameter, that is, rate of "P change in yawing -moment coefficient with angle of sideslip, per degree \^Cj-|/opj C rotary-dam'ping-in- j'aw para/n?-ter, that is, rate of r change of ya'A'ing-iT.orr^ent coefficient v;ith yawing ana-ular velocity, ner radisn 6C„/6(-r— j •-'■'v y lateral-force par'^.meter, that is, rate of change P of lateral-force coefficient with angle of side- s li o , 3r d egr e e {^6 Cy./d 9) APP ARAaT:S The invastigation wa3 conducted in the Langley free- flight tunnel, a complete description of lA'hich is gi'^'^en in reference 2. A protograph of the test section of the tunnel vvlth the nodel in flight is given as figure 2. Force tests to deterirdne the static stability character- istics of the model were m.ade on the free-flight-tunnel six- component balance (described in reference 5), which measures mioments and forces about the stability axes. The free-oscillation method em.oloyed in reference I}, '."/as used to determine experimentally the values of the rotary-dam-oing-in-ya'-.v parameter C^- . These values were derived from damoing rr.easuremxents of the model mounted on a strut that oerm.itted freedom In ya^-. A three-vie"'.' sketch of the model used in the tests is shovrn as figure 5 ^-^"^'^ ^ photograph of the m.odel is shown as figure [|.. The test model was so designed that vertici.1 tails of different size (fig. J) could be mconted at various locations along the fuselage, both ahead of and behind the center of gravity. Ten vertical tails were used during the tests. Eight of these tails, two each of tails 1 to Ii (fig. 5)> *>/'.'ere geometrically similrr. CI the other two tails, one was extremely large (tail ^) and the other was of lo^^v aspect ratio (tail 6). NACA ARR N'^. L5LO5 A photograph of the model with tail 5 in place is pre- sented as figure 5* '^h® dimensional and mass character- istics of the model used in the tests are given in table I, TESTS Test Conditions The flight tests of the model were made for a v-ide range of values of the lateral-force param.eter Cv-, P over a range of values of the directional-stability parameter C^ 3-"^d the rotary-daTi:ping-in-yav; parameter C^^ . Changes in these parameters were obtained by various com.binations of vertical-surface area and tail lengths so that the lateral-force parameter could be varied while the directional-stability and rotary-dam.ping-in-yaw pararrieters were held constant. The dihedral was zero for most of the tests. The rar.g;e of test conditions covered in the investi- gation is shov:n in figure 6 in the i ormi of slope values obtained from the force tests and the free-oscillation tests of the various configurations. For m.ost of the tests, the values of C-r , Cv, > and Cv, were varied, ip' Hp' np respectively, from -O.OOlJi to -0.0201, from. -O.OOOOi; to 0.00260, and from -0.011 to -O.l^S. The ratio between -Cri and Cr, v^as held at a convenient norm.al value of about 6vO:l for most tests, but no attempt was m.ade to m.aintain an exactly constant value of this ratio. In addition, the m.odel was tested with two configurations having a very high value of G-.r (-O.060O) for two large values of Cr, snd Cv^ • For some tests the vertical tail was removed and Che minimum value of Cv-, r occurred in this condition rather than at the negative value of Cv, because, in order to obtain nea-ative Cn i np - np» a vertical tail had to be added aliead of the center of - Flight tests were arbitrarily made at a lift coef- ficient of 0.5 for each of the conditions represented by the test points shown in figure 6. In order to determine the effect of lift coefficient, some tests were also made NAG A ARR Ho. L5LO5 ■at a lift coefficient of 1.0. Flights v;ere made for each test arrangement hj use of ailerons alone or rudder coordinated with ailerons for control. The total aileron deflection used in. the tests was 50'^', 'Ihis deflection gave a value of pb/2V of about 0.07 as iTieasured in rolls froiii level flight with rudder fixed. For most of the tests the edlerons were rigted up lO'-' in order to minii''ize the adverse ailoron yav,'ing. Flight tests rere macie at approximately 0° effective dihedral angle as indicated by force tests. The vertical tails were added above or below the fuselage in order to maintain the effective dihedral angle as near O*^ as possible. One exception v/as the test with tail 5, which trave approximate! effective dihedral angle. Throughout the tests, the mass characteristics were mai.ntained. constant at the values given in table I. Flight Ratings The model was flown at each of the test conditions reoresented by the parameter values in figure 6. Graduated ratings on stability, control, and general flight char- acteristics v'ere assigned each test condition froi.c pilot's observations of the model in flight. The stability and control ratings used were as follows: ; Rating stability or control 1 i A ! B : C ' D ; E 1 Good Fair Poor Very poor Diverger.it i ! 1 Plus or m.inus ratings v.'ere assigned to indicate slight but perceptible changes in the rating. Ivioti on-pi cture records of some flights were made to permit more careful study of the flight behavior and thereby to aid observers in making more accurate fli.^ht ratings. NAG A ARR Fo . L5L05 7 The stability rating of a free-flying mcdel in a stable condition is generally deter-nnined in the free- flight tunnel from the steadiness of flight in the rather - gusty air of the tunnel. A very stable model returns to its oricina] flight p c.th irore rapidly after receiving a gust disturbance and generally does not tend to move as far frora its original flight path as one v/ith less stability. Greater stability is thus indicated by greater steadiness. For nonstable conditions, hov.-ever, the stability is judged from the rate at which the model deviates from straight and level flight and from the frequency of control appli- cation required to m-aintain steady flight. The control rating is determined from the ease with which straight and level flight is m.aintained and from the response of the model to control applications designed to perform m.aneuvers. Any unnatural lag or m.otion in the v/rong direction Is judged as poor control. The general flight ratings are based on the over-all fl^-ing characteristics of the model. The re tings indicate the ease with which the model can be flown, both for straight and level flight end for performance of the mild maneuvers possible in the Langley free-flight tunnel. Any abnormal characteristics of the model are generally judged as poor general flight behavior, inasmuch as they are disconcerting to the free-flight-tunnel ollots. RESULTS AI:D DISCUS SIC N The results of the investigation are summarized in figure 7> v;hich presents pilot's ratings for the stability, control, and general flight characteristics. The sta- bility and control ratings are substituted for the test point values of figure 6 and are therefore representative of various configurations. It should be rem.embered that these results were obtained at a dihedral angle of 0" (C2, - 0), except for tail 5^ ^^'^ ^--^^ strictly true only for this dihedral angle; however, the qualitative effects of Cy^ are believed to be unaffected by dihedral. The general effects of dihedral have been reported in refer- ences 5 S-^^d 6. Cv 8 NACA ARR No. L5LO5 Effect of Cv , on Stability The stetility ratings of figure 7 show that increasing y- vifhile maintaining Cj^ and C^ constant slightly increased the stability. The results of stability calcu- lations, made by the method of reference 7> ^^e presented in figure 8. The lateral-force parameter is given as a function of the oeriod of the lateral oscillation (P) and as a function of the time required for the oscillation to damp to one-half amplitude ^ T-] /n ) • The results shown in figure 8 show the sane trend noted in the results of figure 7' The increase in stability v.l th increased Cy,, is greatest for the smallest values of Gj-; , and C-^-^ . Tlie calculations also show that Cy has very little effect on the period of the Ister&l oscillation. Effect of G-rr on Gontrol by Use of Ailerons The results of figure 7 show that increasing Gv generally decreased the ease with which the miodel could be controlled with ailerons alone or rudder coordinated with ailerons. The deterioration in control was much greater for the low values of G^, and G^ than for the large values of these derivatives. The reduction in control Vidth increased Cv-^ is explained as follows: VJhen the model received a gust disturbance In yaw causing it to sideslio, the pilot gave cox-rective aileron control to bring the m.odel back on course. As a result of this control application, the miodel rolled but the large side force opoosed the lateral component of lift that tended to bring the model back to its original location in the tunnel. The return to the original flight path v/as thus abnormally slow. As Gy and, hence, the opposing side " P '■ ■ force was increased, the aileron control became less effective in restoring the m.odel to its original lateral position in the tunnel. For another case, if the model was in straight level flight and the pilot applied aileron control to perform a maneuver, the adverse yawing caused by the aileron deflection and rolling introduced NAG A ARR No. L^Wy a side force in such a direction as to opoose the side force produced by the angle of bank. This effect caused the model to hesitate or move first in the wrong direc- tion and was therefore considered undesirable. Effect of Cy^, or: General Flight Characreristics P The pilot's ratings for general flight character- istics are presented in figure 7 together with those for stability and control. These ratings are shown by the separated regions of figure 7(ti) and indicate that the pilot preferred the ease of control obtained with low values of Cyo ^^ '^■-'^- slight increase in stability resulting from increased C,r • Obviously, the ideal configuration v;ould be one that was both very stable and easily controlled. If low stability characteristics necessitated a cor.-proTise , the pilot's rating indicated a preference for ease of control rather than a slight increase in stability. The tests shovced that the qusmti- tative effect of varvine Z^r was dependent u-oon the accora-nanying values of C^ and Cv, • ng n-p Large values of C„ and C^ .-At e.xtreirelv large ■-^ n r^ Li-p values of Cr^ s.nd C^ , such 0s are shown in the flying- bomb region in figure 6, all flights were given an excel- lent rating by the pilot despite the fact thst two of the configurations tested had extremely large -^'alues of Cv- • For conditions in this region, the large a'-iount of directional stability limited to small values the side- slipping due to adverse aileron yaw. .As a result, the side force created by the large values of Cy was net large P enough to affect the aileron control ao:oreciably. Moderate values of Cn and C_ .- v'.hen 0^,.- s>.nd C^ were reduced to values corresponding to those of the ordinary conventional airplane, large variations of Cy appreciably affected the control of the model. ?or values of G,^ Gorresoonding to a conventional airplane with a np - c rather large tail (C^^ = 0.00200), increasing Cy from ip / ' - xp 10 NACA ARR No. L5LO5 srr^all to large values caused a corresponding reduction in general flight ratings from excellent to good. Vi'lth smaller values of C^., and C„ (C = O.OOlLO) in the conventional- aire lane range the change in flight character- istics V'/ith large increases in Cy, '^^^s inore pronounced (excellent to fair) ■p Small values of C^p and Cp^ .- Flights made in the tailless-airplane region (C-^ = O.OOOlii to O.OOO8O) were satisfactory only for the smallest values of Gv • Increasing Cy, to larger values in this region resulted in very poor flight behavior. Plights made at ths lowest value of Cj-^ , (C = O.OOOlM in the tailless region, although very \ -p controllable (control rating, A-) were given a general flight rating of only fair. This rating was given Decause, although the model was stable in this configuration, it had a long-period large -amplitude yawing oscillation that was objectionable to the pilot. The model flew very steadily, however, because of the long period of the oscillation. This flight behavior has been previously reported for other tailless designs (m.odel and full scale) and y\;as similarly objectionable both to free-flight-tunnel and airplane pilots. Increasing Cn-^ to a value of O.OOO8O reduced the yawing oscillation to a great extent and resulted in satisfactory flights. The Model was directionally divergent in flights m.ade mth a negative value of Cv, for values of C,^ ^ no i\- equal to -O.OO5O and -O.OIO5 and thus could not be given a control rating, but was however given a general flight rating of very poor. The directional divergence at both values of Cy v^as vary slow and the pilot felt that the divergence could have been prevented witli independent rudder control had this control been available. In any case, the condition would have been given a general flight rating of very poor because of the unnatural control required. NACA ARR No. L5LO5 11 Effect of lift coefficient ,- Fli^:hts made at a lift coefficient of 1.0 showed a neglifrible change in flight behavior frorr corresponding flights made at a lift coef- ficient of 0.5 and consequently no dota are presented for these tests. CONCLUDING REMAFFS Tn tests, made in the Langley free-flight tunnel, in which ailerons were used as the principal control, it was found that, although large values of the lateral-force oaraimeter C^r (rate of chan;-e of lateral-force coeffi- cient with angle of sideslip) increased the lateral sta- bility, a definitel.y undesirable effect was obtained vhen ailerons were used to raise a lo?; wing or to make a banked t"arn. This effect was particularly objectionable for sinall values of the directional-stability paraineter C^-^ (rate of change of yawing-moment coefficient with angle of sideslip) and the rotary-danrping-in-yaw parameter C^^ (rate of cbange of yawing-momsnt coefficient with yawing angular velocity). For such conditions the adverse yaw accompanying aileron deflection created adverse side forces sufficient to interfere with the aileron control. The over-all flight behavior of the model was considered best with srrall values of Cv • For sny value of Cy the over-all flight character- is ties were imorovad b'y increasing C^ and C-n • ^ "' li g -Lip I , and Cv, l|5 Dp Increasing C^ - ^^^^ C^ _ was mcst effective at the smallest values of C Little change in the fli^:ht characteristics was caused by a change in lift coefficient from O.5 to 1.0. Langley I'em.orial Aeronautical Laboratory National Advisory CoriU:ni ttee for Aeronautics Lang ley Fi eld, V a . 12 NACA ARR No. L5LO5 REFERENCES 1. Bamber, :.:. J.; Effect of Changes in Aspect Ratio, Side Area, Fliglit-Path Angle, and Normal Accelera- tion on Latersl Stability. NACAARR, Dec. 19ii2 . 2. Shortal, Joseph A., and Osterhout, Clayton J.: Pre- lirrinary Stability and Control Tests in the KACA Free-Flight "'ind Tunnel &nd Correlation with Full- Scale :^light Tests. NACA TN No. 81O, I9I1I. 3. Shortal, Joseph A., and Draper, John ?,'.'. Free-Flight- Tunnel Investigation of the Effect of the F'uselage Length and the Aspect Ratio and Size of the Vertical Tail on Lateral Stability and Control. NACA ARR No. 3DI7, 19ij-5. 1;. Cav-robell, John P., and Kathe-A'S , Tard 0.: Experimental Determination of the Ya^A'ing Moment Due to Yavi/ing Contributed by the Ving, Fuselage, and Vertical Tail of a lidwing Airolane ?'odei. NACA ARR No. 3F26, I9I1.5 . 5. Ca'Tiobell, John P., and Seacord, Charles L. , Jr.: The Effect of Mass Distribution on the Lateral Stability axod Control Characteristics of an Airplane as Determined by Tests of a "■."odel in the Free-Flight Tunnel. NACA ARR No. 5H3I, 19^5- 6. Campbell, John P., and Seacord, Charles L. , Jr.; Effect of ^'^'ing Loading end Altitude on Lateral Stability and Control Characteristics of an Airplane as Deter- mined by Tests of a ''Todel in the Free-Flight Tunnel. NACA ARR No. 3F25, 19i4-5 • 7. Zlnirrerman, Charles H. : An Analysis of Lateral Stability in Power-Off Flight vrlth Charts for Use in Design. NACA Fep. No. 589, 195?. NACA ARR ^To. L5LO5 I3 TABLE I ?,1ASS AI^ID DT?/f5N£I0NAL CHARACTERISTICS OF THE "lODEL "/eight, lb 5.03 "Ing; Area, sq ft 2.67 Span, ft k.O Aspect ratio o.O M.A.G. , ft 0.70 Sweepback of 50~ps^cent- chord line, deg Dihedral, deg Taper ratio (ratio of tip chord to root chord) . O.5O Root chord, ft O.90 Tip chord, ft O.Ll5 Loading, lb per sq ft I.89 Radii of gyration: k^, ft 0.625 k^, ft O.i^kh ■ Ailerons: Type Plain Area, percent S 7 Span, percent b .6 '.2 NATIONAL ADVISORY COm:!ITTEE FOR AERONAUTICS NACA ARR No. L5L05 Fig. 1 YJind dbrection Wind dbrecfion Z NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS figure /.- System of s/abt/ity axes. /9rroi/vs jnd/ca/e posifj^e direct ions of monnents ^ forces ^ cmcL control - surface, def/ections . NACA ARR No. L5L05 Fig. 2 Figure 2.- Test section of Langley free-flight tunnel with model in flight. Cy = -0.0160; -0.064; C^ ■= 0.5. /S '"/3 0.00080; r NACA ARR No. L5L0! Fig. 3 Tail Aspect ratio Area (sgtt) Span (ft) 1 Z oze? 073 2 £ O.ZOI 0.63 3 Z 0.134 O.SZ 4 Z 0.067 0.37 S upper US' Z.ZZ 1.67 S/oiver 0.75- 1.333 1.00 6 / 0.086 0.Z9 Q O 2 — 4Q S /\rea added above and be/Oi^ e.g. -/o vary /a/era/ force NATIONAL ADVISORY COMMITTEE FOP AERONAUTICS I Ffaure 3 - Three - view skeich of model used in laiera/- force invesHgaf/on . All d/mens/ons in inches . NACA ARR No. L5L05 Fig, I QJ U l-i O CO (0 D -H OJ M c s tf-l M S-l tlO 0) c +J n3 U. J (0 3 C C3*.H to i-i c c 3 -H -H NACA ARR No. L5L05 Fig. Figure 5.- Side view of model used in lateral -force investigation in Langley free-flight tunnel showinj tail 5 mounted on model. NACA ARR No. L5L05 Fig. 6 -660- ^ I ■300- -.156- -.130- -JOO- -.064- -.02S- -.Oll- -.024- .011 .0/0 .009 .ood Q ^ .007 i I .006 ^ .004 I S 005 -I -^ ooz OOI o ---o lil XL o --e -<>• F/y/ng-bomJb reg/on- Ordinary convGnHonal a/rp/ane region Tai//es5-airplane reg/on NATIONAL ADVISORY COMMITTEE FM AERONAUTICS O -.0/ -OZ -03 -.04- -.OS La^^ Figure &.- Range of vo/ues of Cp^ , C^ and Cy covered in /aMra/ -fonze /m^es/igar/on /n^ the >° Lang/ey free ~f//gn^ i-unne/ ana range of va/ues for different iypes of aircraft. Ci-O.S. NACA ARR No. L5L05 Fig. ^p ' ja/SU/DJCX/ /\i//igOiZ- /DUO/^OQMO § ^ ^O ' jBfaaiDJDd MD/{-u/ -du/dujDp-/^JDioy I I NACA ARR No. L5L05 Fig. 8 'O &) 1 c s 1— » 3 -QOb^ u.uuuac - .OJ5 .ooon \ \ ^ \ \ 1 "^ ■v ^~- — — — — ■ n '0 }' ^ o — - — - c 1 NATK OMMITT 3NAL fi EE FOfi kDVISORY AERONAUTICS 1 O -004 -,008 -0/2 -0/6 LcderoJ -force parornefer^ Cy -.C^O Figure.