1、REPORT No.273WIND TUNNEL TESTS ON AUTOROTATIONAND THE “FLAT SPIN”By MONTGOMERY KNIGHTLaey Memorial Aeronautical Laboratory341Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without
2、license from IHS-,-,-REPORT No. 273WIN) TUNNEL TESTS ON AlJ!170ROTATION NND THE “ FLAT SPIN “By MONTGOMERY KNIGHTSUMMARYTle following report desk w“th the autorotational characteristics oj certain diering wingsystems as determined from wind tunnel tests made at the Langley Uemorial Aeronautical Labo
3、ra-tory. The incestigaiion was con$ned to autorotation about a jixed axis in the plane of symmetryand paralleZ to tfie wind direction. Analysis of the tests leads to the follom”ng conclusions:Auiorotation below 30 angle of attack is gcmerned chiejly by wing profle, and abore that angleby wing arrang
4、ement.me strip method of autorotation anak gie$uncetiain Tesuh%beheen rfla-rfiurfi = and 85”.The polar eurce of u wing system, and to a lower degree of accuracy the polar oj a completeairplane model are wj%ient for direct determinatwn of the limits of rotary instability, subject tostrip method limit
5、ations.2%e results of the instigation indicate that in free jlight a monoplane is incapable of jlatspinning, whereas an un.staggered biplane has hherent $at-spinning endencies.The dificuliy of maintaining equilibrium in stalled $igiit is due primarily to rotary instability,a rapid change from stabil
6、ity to instability occurring as the angle of maximum lift h exceeded.INTRODUCTIONAutorotation may be explained by a consideration of t-he torques brought into pIay by therotation of a wing or combination of wings about an axis in the plane of symmetry and paralklto the wind direction. This phenomeno
7、n k recognized as a vital factor in the “spin” of anairplane -The so-called “flat spin” may be defined as a spin in -which tihe Iongitudirwil axis of theairpIane is more nearIy horizontal than vertical in contradistinction to the “ normaI spin” inwhich the reverse is true. The flat spin is a charact
8、eristic of certain unstaggered biplane-s,notabIy the British B. A. T. Bantam and Short Springbol, and the American Boeing ATB-I.This type of spin is considered dangerous owing to the difEcuIty of retmmi.ng to nornxd flight,and means of insuring against its occurrence are being soughk.4utorotation ha
9、s been studied for severaI years with the aid of wind tunnel r.otationaIexperiments and mathematical analys= b=ed on force tests. Spinning tests of airplanes tifree flight have a3so been made, and these have been supplemented by tests upon Iight modelsdropped from a height.The present investigation
10、was instituted for a further study of autorotation with emphasisIaid upon the flai spin. Three airfoik of wideIy tiering characteristics -were tested as mono-panes, and tests were also made on an unst.aggered biplane cell.The experiments, -which consisted of both force and rotation tests from zero l
11、ift to 90angle of attack, were conducted in the 5-foot, circular-throat, atmospheric wind tunnel (Ref er-ence 1) of the Langley Memorial Aeronautical Laboratory.343Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-344 REPORT NATIONAL ADVISORY COMMITTEE
12、 FOR AERONAV-TICSIn this report three terms are used with reference to rotation about a fixed axis in the planeof symmetry and parallel to the wind direction. They are defined as follows:1. “Stable autorotation” signifies a state of equilibrium in autorotat,ion to which theIW. I.Biplanemountedon aut
13、orotationapparatusmodel returns whenever disturbedtherefrom.2. “Unstable autorotat.ion”signifies a state of equilibrium hautorotation such that a smalldisturbance aiding the rotationcauses stable autorotation, whilean opposing disturbance brigsthe model to rest.3 “Rotary instability” sig-nifies a st
14、ate of equilibrium inrectilinear motion such tlmt asmall rot ary disturb ante causesstaMe autorotation.APPARATUS AND TESTSThree airfoil profiles wereused in the tests. These wereGottingen 3871B (flat bottom),R. A. F. 15, and N. A. C. A.-hfl.Rectangular wings, 5 by 30 inchmin plan, having these profi
15、les weretested as monoplanes. An unstag-gered biplane cell of Gottingen 387FB profile was also tested.The autorotation. apparatus, illustrated in Figures 1 and 2, consisted of a barrel containingball bearings supporting-a-shaftupon which the models weremounted as shown. A simplescrew adjustment perm
16、ittedlocking of the modd at anyde.sired angle of attack. Areduction gear and electricalcontact at the down-wind endof the barrel operated a lightoutside the tunnel for deter-mining rates of rotation.The a-erage rates of rota-tion in opposite directions fora given mean angle of attack gave the result
17、s presentedbelow. The limits of rotary in-stability were obtained merelyby noting the angles of attackbetween which stable autoro-iation was induced when themode was disturbed slightlyfrom rest. ,The force tests were madeFIG.2.JIonoplanemountedon fwtorotstionapparfituson the regular wire balance of
18、the tnel (Reference 1). Lift and drag were measured fromapproximately zero lift to 90 ,Reynolds h;o. = 152,f310(i by 30 inches), f=23,2 kg/mZ,. ReoIds XO.=M3,CWDISCUSSION OF RESULTSAUTOROTATION TESTSThe test resuIts shown in Figure 7 furnish a striking demonstration of the possible variationin autor
19、otational characteristics of common types of airfoiIs and airfoil combinations, Anoutstanding feature is the wide difference, both in range and in magnitude, between monoplaneand biplane resutsl illustrating the already recognized effect of multilane interference.Provided by IHSNot for ResaleNo repr
20、oduction or networking permitted without license from IHS-,-,-WIND TUN-ELL TESTS ON AUTOROT.4TION AND TEE c FLLkT SP” “ “ 347The ditlering rates and res of autorotat.ion up to 45 furnish a means of comparing theeffects of cMerent airfoiI profiles upon autorotation.Another and unanticipated fedmre is
21、 the well-defined autorotation of the symmetrical Mlairfoil, for which strip method calculations predicted but a slight degree of instability.The experimental autorotation cumw are merely interpolated for unstable autorot ation(shown by dotted Iines in Figures 3,4, and 5) since the apparatus did not
22、 permit of obtainingthese values experimenhlIy. In I?re 3 is included also a ca.kdated curve of the vaIuesof tan at which unstable autorotation occurs for the biphme. These zdditions are intendedonIy as a rough indication of existing conditions.FORCE TESTS AXD AUTOROTATIOX CALC?JLATIOXSThe polar dia
23、grams in Figure 12 afford another illustration of the marked difference betweenthe charactetitics of the monopIane and the unstaggered biplane. This difference has previ-ously been attributed to the shielding of the upper wing of a biplane by the Iower (References 6I$i/2Lo.8Ton * GEffingen387-FB b a
24、s obtainedfrom tests recentIy made at this labora-tory at the request of the Army AirCorps. Calculated ranges of rotaryins tabilit y are shown on these curves.E.speriment al ranges for the XO2 aregi-ren in Fibwre 14.The criterion for rotary instability.r.-.c.FIG. 12.Force kts on four modelsis deveJo
25、ped from the strip method analysis of wing systems only. Therefore the presencein the complete model polars of the forces upon body, tail, and landing gear may be expectedto introduce errors in determining the limits of rotary instability. EoKever, in spite of thwespurious M ectsz flat-spinning tend
26、encies are distinctly indicated for the modek in Figures 13and 14, and in the latter figure the caIcuIakd ranges of instability are in fair agreement withexperiment.d(C*)In Figure 15 are shown curves of the compIete criterion for rotary instability, !agat angIe of attack. (See .Appendk for derivatio
27、n.) This criterion indicates not only thestate of equilibrium, but also the degree of stability or instabiliy. The pobts shown are -vaIuesof cos cw ) and are included to show that the simpler expression may be used with gooddaaccuracy. The following deductions may be made from these curves:Maximum d
28、amping (stable) tendencies occur at or near zero angIe of attack and are ofpractically the same magnitude for all the models tested.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-350 “REPORT NATIONAL ADVISORY C.OMXCLTEE FOR. AERONAU.TIC!SMaximum aut
29、orotationai (unstable) tende.ncies occur in each case just beyond maximumlift, and vary wideIy in magnitude for the diflerent models.Beyond 35 the characteristics of the monoplanes are practically identicaI, with small stabletendencies between 45 and 75, and practically neutral equilibrium at 45 and
30、 between 75and 90.6!II!620” %, and SIMMONDS,O. E. Rolling and Yawing Moments Due to Rollof Model AWO Wings with Standard and Interpkme Ailerons, and Rudder Moments for Standardand Special Large Rudder. B. A. C. A. Reports and-Memoranda Xo. 848, November, 1922.7. TONNEND, H. C. H., and KIRKW, T. A. S
31、ome Experiments on a Modelof a B. A. T.Bantam Aeroplane with SpeciaI Reference to Spinning Accidents. B. A. C. A. REports andMemoranda No. 976. November, 1925.8. IRWI, H. B., and BATSO, A. S. Preliminary Note on the Effect of Stagger andDecalage on the Autorotation of a R. A. F. 15 BipIane. B. A. C?
32、. A. Reports and MemorandaNo. 733. September, 1920.9. AERONAUTICS STAFF. Air Force and Moment for NB1 Airplane. ConstructionDepartment, Washington Navy Yard. Aeronautical Report No. 282. June, 1925.10. THONMON,G. P. Calculations on the Spinning of an Aeroplane. B. A. C. A. Reportsand Memoranda No. 2
33、11. November, 1915.11. LINDEtiN, F. A., GLAUERT, H., and HARRIS, R. G. The Experimental andMathematical Investigation of Spinning. B. A. C A, Reports and Memoranda No. 411.March, 1918.12. RELF, E. F., and LAVENDER, T. The Autorotation of StalIed Aerofoils and ItsR-elation to the Spinning Speed of Ae
34、roplanes. B. A. C. A. Reports and lMemoranda No. 549.October, 1918.13. RELF, E. F., and LAVENDER, T. A Continuous Rotation Balance for the lMeasure-ment of L at SmaIl Rates of RoIL B. A. C. A. Reports and Memoranda No. 828.August, 1922.14. BRADFIELD,F. B., and COOBES, L. P. Autorotation Measurements
35、 on a Model Aero-plane with Zero Stagger. B. A, C. A. Reports and Memoranda No. 9?5, April, 1925,15. OFSTIE, RALPH A. The Flat Spin of the _Boeing N, B, Training Airplane. Bureauof Aeronautics, hTavy Department Technical ote No. 164. May, 1926.16. LACHMANN,G. “StalI-Proof AirpIanes. N. A. C. A. Tech
36、nical Memorandum No. 393.1927. (Translation from the Yearbook of the “ WissenschaftIichen GeselIschaft fiir Luf t-fahrt,” 1925.)17. BRYANT, L. W., and GATES, S. B. The Spinning of .4eroplanes. “The Journal ofthe RoyaI Aeronautical Society.” July, 1927.Provided by IHSNot for ResaleNo reproduction or
37、networking permitted without license from IHS-,-,-APl?m”mxSTRIP METHOD KN.ALYSISFollowing is the strip method derivation of the expressions for torque and force coefficientsin rotation, and also the development of a criterinfor rotary instability.The symboIs used are illustrated in Figure 16. CRis t
38、he resdt,ant force coefficient (absolute) for the angleOf attack C, retie CA and CA are its components, re-spectively, along and rLormal to the axis of rotation.The angle of the wing chord to this axis is a Theeffective wind velocity VE is the vector sum of the veloc-ity V along the axis and the ten
39、tiaI velocity VE.The wing chord and span are represented bye and 6, re-spectively, and, in this derivation, c is a constant.Therefore the hrque increment due to a given wingelement of -width Ay at a distance y from the atis ofrotation may be writtenM= Cgc (Ay) (1)where=;pv.z p(V see Aa)2=.= q (see A
40、a)FIG. 16.WW element in.auto.mtatiort(2)Accbeing the aIgebraic sum of the angIe of attack of the element in question and CY. The totaltorque for the wing is thereforeJwA=qc (?.y (see Au) dg (3)-CAy (see Aa) dye -+,2 (4)where CA is the eoefbient of autorotational moment.axis) isThe lift coeficientt (
41、force nornd tody “ (4a)353Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-354 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICSThe corresponding equationnormaI to that of autorotation iswhiIe the drag c.oeficient-infor moment about an axis in the pl
42、ane of symmef,ry tindsimilarlyu J-vYrotation is(4b)(see Aa) dy (4C)If we now consider wmy srnaIl angular velocities we may determine the criterion of rotaryinstability for the model at rest. Th; angular velocity is to be taken .sui%ciently small thatvariations in (7A aIong the span may be considered
43、 linear. For this condition equation (1)shows that, for a gien wing element, the increment of torqueAA= KCAwherelZ= gyc (Ag).lf we consider two wing-tip eements (1, 2) such that 1 is on the up-going or sroall-angle-of-attack tip, and 2 the down-going or arge-angIe tip, we have from Figure 16(?hl= (?
44、e:”1 $cc. degrees17.1 0.319 ! 0.458/ 2519.5 .376 30 .503I20.2 .389 33.513722. .5 .429 J: HTABLE III.4wtorotation TestR. A. F. 15 monoplane (5 by 30 inches)q=20.2 kgmReynolds Number= 152,000amdegrees tan+ i a. degress tall+15 0.152 Si 0.30815.4 .161 32 .21417 228 32:5 .19620.2 :307 ;:.: .16125 .338 .
45、1473Q .341. .T-4BLE mAutorotation TestN. A. C. A.-Ml monoplane (5 by 30 inches)q=20.2 kglmReynolds Number= 1.!i3,000_. .! a-de=ees I *+ f :de:;-” : “- - - :-+, _ _ =.,- i-r . . ,;. . . =,. -=Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-WIND TUNZEL
46、 TESTS ON .4UTOEOTATION AND TEE “ FLAT SPIN Y 357TABLE VForce Test.G5ttingen 3W-FB biplane (5 by 30 inches)Gc= 1, stagger= Oq= 2,0.2 kmReynolds Number= 156,000a degrees I CL1 0.006: +. 1003 .262z degrees1.51s225O. 046 ! 0: ;: 0.509.030i:; 59s02s 40 .734 :676:037 45 -669 730.051 50 .596 “:769- 1 : -:
47、 , . :s:$: if6.126 Ii ;160-,9s .75 %J 72s.244 I 80 . 12s.344 S5 .072. 450 90 .014TABLE VIForce TestG5ttingen 3S7FB raonopkne (5 by 30 inchesq=20.2 IrnzReynolds Number= 155,000CLo. 005+. 127.323.534.7449*Si 1361. 2s5L 3771. 41sL 37SL 2601.075. S360.052.030.029.036.050.070.095.124- 6.217.283.331.39.5.
48、461.a degees30323540655055606570.75so8590CL0.840. S76. S92.851. Sll751:700.631.544.452.347+: %. 009o. 53Z.602. ;$016. S-54i L 124L 195L 270L 32SL 3S61.390L 389.,. -.=.2. ., = :-_:. . .-,- 5- .-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-358 REPORT NATIONAL ADVISORY COMFIJTTEE FOR AERONAUTICSa degrees2+1:1315;:232527a71TABLE VIIForce TestR. A.F, 15monoplrme (5 by30 inches)q= 20.2 kg/ln2Revnolds Number= 155.
