Document
NATIONAL ADVISORY COMMITTEE
FOR AERONAUTICS
REPORT No. 522
THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS
AND LANDING GEARS-III
By WILLIAM H. HERRNSTEIN, JR., and DAVID BIERMANN I HIS CC~UMCIT Clj La .. :! . ,.~'. ThE rilES ~ For sale by the Superintendent oC Documents, Washington, D. C. • • • • • • • • • • • • • • • • • • • • • Price 10 cents Subscription price, $3.00 pcr year AERONAUTIC SYMBOLS 1. FUNDAMENTAL AND DERIVED UNITS Metric English Symbol Abbrevia - Abbrevia- Unit Unit tion tion meter ______ ____________ Length _______ foot (or mile) _________ l m ft. (or mi.)
Time ____ _____ second _________________ (or hour) _______ t s se cond sec. (or hr.)
Force _________ weight of 1 kilogram _____ weight of 1 pound _____ F kg lb.
- P owcr ________ horsepower ___________ horsepower ( metric ) ______ P hp.
--------- - miles per hOUL _______ {kilomet ers per hOUL _____ k.p.h.
m.p.h .
Speed _________ V f eet per second ________ meters per second _______ m.p.s. Lp.s.
2. GENERAL SYMBOLS v, Kinematic viscosity
w, Weight=mg
p, Density (mass per unit volume) g, Standard acceleration of gravity=9.80665 2 2 Standard density of dry air, 0.12497 kg-m-~-s2 at m/s or 32.1740 ft./sec.
15 C . and 760 mm; or 0.002378lb.-ft.-4 sec.
W m, Mass = - s g Specific weight of "standard" air, 1.2255 kg/m or I, Moment of inertia = mk • (Indicate axis of 0.07 65 1 lb./eu.ft.
radius of gyration k by proper subscript.)
Coefficient of viscosity f.L, 3. AERODYNAMIC SYMBOLS S, .Area tID, Angle of setting of WIngS (relative to thrust .Area of wing line) SID' Gap Angle of stabilizer setting G, (relative to thrust '1."
b, Span line) c, Chord Q, Resultant moment b 11, Resultan t angular velocity Aspect ratio S' Vl p -, Reynolds K umber, where l is a linear dimension True air speed V, f.L (e.g., for l1 model airfoil 3 in. chord, 100 m.p.h. normal pressure at 15 C., the cor- q, Dynamic pressure - ~P VZ responding number is 234,000; or for a model L, Lift, absolute coefficient OL=:S of 10 cm chord, 40 m.p.s. the corresponding number is 274,000)
D, Drag, absolute coefficient OD~ ~
Center-oI-pressure coefficient (ratio of distance of c.p. from leading edge to chord length)
Profile drag, absolute coefficient aD. ~~s Angle of attack
Angle of downwash
Induced drag, absolute coefficient ODI=~S
Angle of attack, infinite aspect ratio Angle of attack , induced
Parasite drag, absolute coefficient aD - DSp
Angle of attack, absolute (measured from zero- • q lift p os ition) 0, Cross-wind force, absolute coefficient Oc= q~ Flight-path angle R, Resultant force
REPORT No. 522
THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS
AND LANDING GEARS-III
By WILLIAM H. HERRNSTEIN, JR., and DAVID BIERMANN Langley Memorial Aeronautical Laboratory 116679-35 NATIONAL ADVIS ORY COMMITTEE FOR AERO NAUTICS H EADQUARTERS, NAVY B ILOI G. WASHI GTO • D. C.
LABORATO I UES, LANGLEY FIELD, VA.
Created by act of Congre s approvcd Man'h 3, H115 , for tllC su pervision ~\I1d direction of the scientific study of the problems of flight . Its membership was increased to 15 by act approved Ma rch 2, 1929. The members are appointed by the President, and serve as such without compensation.
CHARLES A. LINDBERGH, LL. D., JOSEPH S. AMES, Ph . D., Chairman, ew York City.
Pr esid ent , Johns Hopkins University, Baltimore, Md.
WILLIAM P. MA CRA KEN, Jr., Ph. B., DAVID W. T AYLOR, D . Eng., Vice Chairman.
Washington, D. C.
Wa sh ingt on, D. C.
AUGUSTINE W. ROBINS, Brig. Gen., Un it ed States Army, CHARLES G. ABBOT, Sc. D., Chief, Materiel Divi ion, Air Corp s, Wright Field, Da~ 'to n, Secretary, Smithsonian In stitution .
Ohio.
LYMAN J. BRIGGS, Ph . D., EUGENE L. VIDAL, C. E., Dir ector, National Bur ea u of Standards.
Director of Air Commerce, Department of Commerce.
BENJAMIN D. FOULOIS, Major General, United States Army, EDWARD P. W ARNER, M. S., C hief of Air C orps , War Department.
Editor of Aviation, New York Cit y.
WILLIS RAY GREGG, B. A., R. D. WEYERBACHER, Commander, United tates avy, Chief, United States Weath er Bureau.
Bureau of Aeronautics, avy Department.
HARRY F. GUGGENHEIM, M . A., ORVILLE WRIGHT, Sc. D., P ort Washington, Long I s land, . Y.
Dayton, Ohio.
ERNEST J. KING, R ear Admiral, Un it ed Stat es Navy, Chi ef, Bur eau of Aeronautics, Navy Department.
GEORGE W. LEWI , Dir ec tor of Aeronautical R ese arch JOHN F . VICTORY, ec retary HENRY J. E. R EID, Engineer in Charge, Langley l'vlemorial Aeronautical Laboratory, Langley Field, Va.
JOHN J. IDE, T ec hnical Assistant in Europe, Paris, France TECHNICAL COMMI TTE ES PROBLEMS OF AIR NAVIGATION AERODYNAMICS AIRCRAFT ACCIDENTS POWER PLANTS FOR AIRCRAFT I VENTIO S AND DESIG S MATERIALS FOR AIRCRAFT Coordination of Research Needs of Military and Cwil Aviation Preparation of Research Programs Allocation of Problems Prevention of Duplication Con ideration of J nventions OFFICE OF AERONAUTICAL INTELLIGENCE LA GLEY MEMORIAL AERONAUTICAL LABORATORY W ASmNGTON. D. C.
LANGLEY FIELD. VA.
Collection, cIa 'ification, compilation, Uni fi ed conduct, for all agencies, of and disse mination of scient ifi c and tech- scientific re sea rch on the fundamental nical information on aeronautics.
p ro bl em' of flight.
REPORT No. 522
THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS, AND LANDING GEARS-III By WILLIAM H. HERRNS'I.'EIN, JR., and DAVID BIEHMA N SUMMARY Data were obtained concerning five general subjects: l. Drag measurements of several landing gears each The tests reported in this paper conclude the investiga- equipped with 21-inch and 24-inch streamline wheels tion oj landing- gear drag that has been carried out in the in addition to the 27-inch streamline and 8.50-10 N. A. C. A. 20100t wind tunnel. They supplement low-pressure wheels previou ly tested. Since the pub- ear lier tests (reported in Technical Report No. 485) made lication of reference 1 the load-carrying capacity of with jull-scale dummy wheels, wheel jairings, and landing the streamline wheels has been changed, the 21-inch gears intendedjor airplanes of 3,000 pounds gross weight and 24-inch now overlapping at about 3,000 pounds and include tests oj tail wheels and tail skids.
and the 27-inch being used on heavier airplanes.
For airplanes oj this weight classijication the results 2. Development and tests of landing gears combining indicate that the drag of a landing gear having slight the best features of the cantilever and tripod types.
wh eel -stl'ut interjerence will be materially less when 3. Tests of additional fairings, particularly about the equipped wi th the proper size oj streamline wheels than wheel-strut intersections.
when Jurnished with low-pressure wheels . The drag oj 4. Measurement of the mutual interference between a cantilever landing gear is as low when equipped with a wing and attached landing gear.
the proper size oj streamline wheels as when equipped 5. Measurement of the drag of a tail-wheel unit and wi th low-pressure wheels and the best type oj wheel that of several tail skids.
Jairing.
Two oj the landing gears tested combine, to a high APPARATUS degree, the structural advantages oj the tripod types with The tests were made in the N. A. O. A. 20-foot the low drag oj the full cantilever typ es.
tunnel which with its test equipment is fully described The drag oj a conventional tripod landing gear with in reference 3. The method of supporting the test streamline wheels can be reduced about 39 percent by models on the balance is shown by figure 1.
careJul Jairing oj all strut intersections.
All the test models were designed for an airplane of Expanding fillets are useJul in reducing landing-gear 3,000 pounds gross weight. The fuselage, engine, drag, especially on landing gears that are attached to wing, and most of the landing gears used for these tests wings.
were the ones used for the tests reported in reference The drags oj tail-wheel units and tail skids are, even I, differing only in the strut fairings and size of the in the worst case, almost negligible.
wheels. The fuselage dimensions as well as the land- ing gear, wing, and engine locations are shown in INTRODU CTION figure 2.
Th e suggestions and queries that followed the publi- Wheels, -In addition to the 8.50-10 low-pressure cation of reference 1 resulted in a considerable exten- wheel and the 27-inch streamline wheel used for the sion of the original program of the investigation of tests of reference 1, new 21-inch and 24 -inch stream- landing-gear drag. Th e first part of the extended pro- line wheels were added because they are commonly gr am was reported in reference 2 and deals with tests used on airplanes of about 3,000 pounds gross weight of landing gears for low-wing monoplanes having a in place of the 27-inch wheels, which are now being gross weight of about 16,000 pounds. The second used on heavier airplanes. The wooden models of part of the extended program is herein reported and the wheels (see fig. 3) were made to a tolerance of contains information on the drag of nonretractable ± Ya2 inch. All tire had smooth treads.
landing gears for airplanes of about 3,000 pounds Landing gears. -All the landing gears were designed gross weight.
to comply with the requirements of the BW'eau of 2 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Air Commerce, Department of Commerce, and the in the rear. Tail skid 2 consisted of two struts in tandem, one of which was an oleo unit. Tail skid 3 design outside dimensions were strictly adhered to in the fabrication of the various parts. Landing gears la, was of the cantilever spring-leaf type; tail skid 4 la, 11b, 15a, 15b, 15c, and 16 (see figs. 4, 5, 6,7,8, 9, was of cantilever construction with the shock-absorber and 10, respectively) were attached directly to the unit inside the fuselage.
fuselage. Landing gear 13 (fig. 12) was attached to TESTS the wing. Landing gears la, 11 a, 11b, and 13 were of the same basic types as those reported in reference 1; Drag and all· speed were measured for all tests and additional lift measurements were taken in conjunction landing gears 15a, 15b, 15c, and 16 were types not FIGURE I.-Fu se lage witllianding gear 15c mounted on balance.
previously tested. Dimensions for the wheel fairings with the tests of landing gears 13 and 16. Landing used on landing gears 11a, 11b, and 13 may be obtained gear 13 was the only landing gear whose drag was from reference 1. measured in the presence of the wing. Landing gears Tail skids and tail-wheel unit.-The tail-wheel unit 11a and 13 were tested in conjunction with a radial used in the tests was taken from service and consisted air-cooled engine located in the nose of the fuselage but in the absence of propeller slipstream.
of an Air Corps tail-wheel fork and a 10 by 3-4 wheel.
Landing gears equipped with four different wheels.- The principal dimensions of the unit may be obtained from reference 4. Figure 14 shows the location of Landing gears la, 11a, 11b, 15a, 15b, and 15c were this unit with reference to the test fuselage and also tested when equipped with 8.50-10 low-pressure.wheels, shows the details of tail skids 1, 2, 3, and 4. Tail and with 21-inch, 24-inch, and 27-inch streamline .wheels.
skid 1 was of tripod construction with an oleo unit It was thought that such a variety of landing gears DRAG OF AIRPLANE WHEELS, WHEEL FAIRI GS AND LANDING GEARS A r - - - - - - - - - - '-----x
, , I
I , I I ::: Clark Y , C) section ---
, -
I C!::J
: I
L ________ _ r-3' O!'
______ ,, __ -l---Y.
+ :1.
:.r-+
C\i ~ ~ ::-- '\t
l +
I ~ \ Radial_ ) 18 'O'c.' ------.>1 engine -6'6"-~ I
I Standard wheel
r
+ + <---- -locations) oleos
col/opsed --- ....
r------------r L _______ -._ .... / I Fuse/age mounted in '" , 51 J:6"-\."
.... __ .....
inverted post/on FIGURE 2.-Sketch oC Cuselage showing locations oC wing, wheels, and engine.
NOTE.-For gears designed Cor a 6- by IS-Coot wing Oow-wing monoplane), the wheelloeatioDS are 13~' inches to the rear of the standard locations.
" k-------------- 25~"-------------~ 8.50--10 low-pressure wbeel and tire 27-incb streamHne wheel and tire 3'· 6" o 9" 12" 15" 18" 2/" 24" , J I I I 24-inch streamline wbeel and tire 21-inch streamline wbeel and tire FIGURE 3.-Dimensions oC wheels.
4 REPOR'l' NATIO AL ADVISORY COMMI'ITEE FOR AERO AUTICS due to differences III the set-ups made at the two would give an indication of the relative merits of these wheels on almost any type of nonretractable landing different times.
gear for a 3,000-pound airplane.
RESULTS A D DISCUSSION Landing gears combining the advantages of the cantilever and tripod types.-Because the tests re- All drag and lift value presented in this report were ported in reference 1 had indicated that the drag of taken from fau'ed curve of drag and lift plotted conventional tripod landing gears was large because against dynamic pressure. In all cases, excepting of the high interference and fitting drag, it was thought those where the forces are presented plotted against that if this part of the drag of a tripod landing gear angle of pitch or lift coefficient, the values are given were eliminated it would be possible to combine the for 0° angle of pitch.
light structure of such a landing gear with the low-drag Landing gears equipped with four different features of the cantilever types. With this idea in wheels.-The results of the tests of several landing mind, landing gears 15a, 15b, and 15c (figs. 7, 8, and 9) genrs equipped with different wheels are given in the were designed and tested. figures showing tbe landing gears and, for convenience, Landing gears with various fairings and modifica- are summarized in table 1. Some of the results tions.-Landing gear la was tested with a long-tailed obtained during the original tests presented in reference fairing at the wheel- trut intersection and then with 1 are included for comparative purposes.
additional fairings at the axle cross and the intersection The results of tests of landing gear la (fig, 4) of the landing gear and the fuselage. The drag of the equipped with the 8.50-10 low-pressure wheel and the landing gear was later measured with the additional 24-inch and 27 -inch streamline wheels confirm those fairings on but with blunt-tailed fairings replacing the of reference 1 in showing that the streamline wheel long-tailed fairings at the wheel-strut intersection has no aerQdynamic advantage over the low-pressure (fig. 4). Landing gear 13 was tested with modifications wheel llnle the interference a t the wheel-strut 1,2,3,4,5, and 6, which are shown in figure 12. Land- intersection is small. Unless this wheel-strut inter- ing gears 15a, 15b, and 15c were tested with fairing ference is small the low-pressure wheel is slightly .
at the wheel-strut intersections and then landing gears superior.
15a and 15c were tested without the fairing (figs. 7, The 8.50-10 wheel a.nd the 21-inch, 24-inch, and 8, and 9, respectively). The drag and lift of landing 27 -inch streamline wheels were u ed on landing gear gear 16 was measured with and without an expanding lIa. (See fig. 5.) Since the landing gear had very fillet at the intersection of the fuselage and landing small interference and total dng the streamline wheels gear (fig. 10).
were better than the low-pressure wbeel. The drag Mutual effect of wing and landing gear on landing- ,vjth the 21-inch wheel was reduced to 20.0 pounds, gear drag.-Lift and drag measurements were obtained 6.5 pounds less than that of the low-pressure wheel for a set-up composed of the fuselage, wing et at 0°, under the same conditions and only slightly greater and landing gear 13 for various angles of pitch from than tbe drag ,vjth the low-pressuro wheel and the _5° to 6°. Similar measurements were obtained for be t wheel fairing (wheel fairing C).
the fuselage and wing combination with the landing When the same wheels were used with landing gear gear removed. From these data the landing-gear 11 b as were used with lla the superiority of the stream- drag with respect to the total lift was determined, line wheels wa even more pronounced. (ee fig. 6.)
thereby taking into account any changes in induced The usc of the 24-inch treamline wheel resulted in a drag due to the presence of the landing gear. landing-gear drag equal to that ·with the 8.50-10 low- Tail-wheel unit and several tail skids.-The drag of pressure wheel and wheel fairing A. "When the 21- the tail-wheel unit in its original form and with modi- inch wheel was used tho landing-gear drag dropped fications 1 and 2 was measured with the landing gear from 17.5 to 13.5 pounds. In addition to the low removed. The drag of tail skids 1, 2, 3, and 4 was also drag that can be obtained ,vjth the proper size of obtained. (ee fig. 14.)
streamline wheels without wheel fairings, further advantages are presented in that the installation is ACCURACY lighter, less costly, and more accessible for repairs.
Tests of landing gears 15a, 15b, and 15c again Te ts made in conjunction with the fuselage alone demonstrate that the streamline wheel i effective in are estimated to be accurate to within ±0.5 pound; reducing the landing-gear drag, e pecially when the tests made in conjunction with the fuselage, wing, and wheel-strut interference is reduced. (See figs. 7, 8, engine at various angles of pitch are believed to be and 9.) As might be expected, the smallest stream- accurate to within ± 1.0 pound. The faired lift curve drn.g the most.
are considered correct within ± 1 percent at 0° angle line wheel reduces the Landing gears combining the advantages of the of pitch. The discrepancies between the results cantilever and tripod types.-Landing gears 15a, 15b, obtained in this investigation and those reported in and 15c were designed and tested in an effort to reference 1 for similar conditions are believed to be DRAG OF AIRPLANE WHEELS, WHEEL FAIR I NGS A D LANDING GEARS 5 28%·'----- F;ttings streamlined_ -',"";---r-----+- ----;..,-r-I -6' W, Olea extended X , Staggered 37J1J" Y, Oleo co/lapsed Z, 1J1J" x 2~s" streaml i ne tube _.8 .5 0'10 low'pressure wheel ----- 39 ~·------~ ---25r,s'----- FIGU~E 4.-Drag and dimensions of landing gear la.
Pound8 Drag oClanding gear at 100 m. p. h. (oleos extended): 8.50-10 low· pressure wheels, st rut intersections n ot faired (tests of reference 1)_ •..........•. _ .• _ .............•..•.....•.•••..... _ •••....•••......••••••••.•• 42.5 24·inch streamline wheels, st rut intersections n ot faired .........•............. •............................... _ ... _ .......... __ ...................... _ .•.•... • 44.0 24·inch streamline wheels, long· tailed fairings at wheel·strut intersections only •.......... _ •..•....... _ .. __ .....•..... _ .••..... ___ .•..... . ............... .• 31.0 24-inch streamline wheels, all st rut intersections streamlined, including axle cross ..........••.........•.. _ ...........•••..•..•...... _ •••......... _ ... _ ........• 27.0 30.0 27-inch streamline wheels, all st rut intersections streamlined, including axle cross .... .... _._ ... _._ ... _._. __ •...............•................ _ .......... . ..... • 8.50-10 low·pressure wheels, all st rut intersections streamlined, including axle cross .......... _._ ..... _._.......... _. . .. "_' •. _._._ ..... _. __ ......... ..• 32.5 35.5 .50- 10 low·pressure wheelsbblunt-tailed fairings at wheel· strut intersections, otbers unchanged ... _ •. _ ........ _ ..•. _. ... . ._ •.•.... __ ._ .............•.. • 34.5 24-inch streamline wheels, lunt-tailed fairings at wbeel·strut intersections, otbers unchanged .... _ .. __ ._ ....•......••.•..•................. __ ..... ....... ....... • Y, Strut section Z , Airfoil section Ai rfoil section---. __ (or strut 5Betion not 5hown) r-ll)'f'-i Sect i on A'A Wheel fairings D - --_, 37}6" C ., '" B .. \ ~ \ " f I 1 i ,-l----tt--, : ~-7}Zu-~ <_~ __ ~+14"_:_~ . ~.--1...-+ - 1_.1 ____ 1. __ 1 A A ~ ------3 9 '---- -1-- -~ FIGURE 5.-Drag and dimensions of landing gear 11a.
Drag of landing gear at 100 m. p. h.: Pound • . 50-10 low·pressure wheels, wheel fairings D, no engine in fuselage (tests of reference 1} •••••••••••••••••• - •••••• - ••••• - •••••••••••••••••••••••..•.•••• ••••••••••• 20.5 .50- 10 low·pressure wheels, wheel fairings C, no engine in fuselage (tests of reference 1) .••.....................•.. . ... _ .••.....•........•.......•.. __ ._...... .... 18.5 .50-10 low·pressure wbeels, wheel fairings C, engine in fuselage_ ••.........•.•...................... ___ ............•............................................ 18. 0 .50 - 10 low·pressure wheels, wheel f ai rin gs D, (modification D, ), no engine in fuselage (tests of reference 1) ..... ......•....•.. _._...................... ........... 19.5 .50- 10 low·pressure wbeels, airfoil section alongside wheel, no engine in fuselage ........• _ •••..•...... . ........•.........•••...............•••.............. _ •... 26.5 21-incb st reamline wbeels, airfoil section alongside wheel, no engine in fuselage ••..•............••... _ .... ......... _ ......... _ ...................... ............• 20 . 0 24-inch streamline wbeels, airfoil section alongside wheel, no engine in fuselage •.. .• .........•..•............. _ ..... _ ....................... _................... 22.5 27-incb streamline wbeels, airfoil section alongside wheel, no engine in fuselage ..... ••.•••.•... .•..... ......•........... _ ••......•.................... _ ... _...... . 24.5 27-inch streamline wbeels, airfoil section alongside wheel, no engine in (uselage (tests o(relerence 1) .... _ ......•.....• _ •...•.•.•.•.•.•...•.•.....•.•.•...•.•...•. . 22.0 6 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Y, Wheel fairing A Z, 27" streaml in e wheel
T
, 8~ H ~ ---¥~.:. - ----- --,; ---+-- "'----,," k------41Io/t6 .. -----~ FIGURE G.-Drag and dimensions of landing gear !lb.
Drag of landing gear at 100 m. p. b.: Pound8 8.5G-I0 low·pressure wbeels .• • ..... _ ........ _ ....• ..... .. ..... .... _. '" __ ' .•.. _ .... """ __ . ___ .......•.....•••••. __ ._ .................. _. _...... .•........... . 24.0 8.50-10 low·pressure wheels (tests of reference 1) ....... _ ..•.• _ ... _.. . _ ...• _ .. __ . __ ..... _ ..•....... ___ ._ .•...............••... ... 23.5 8.5G- 10 low·pressure wheels, wheel fairings A (tests of r efe rence I) ... . ___ ...... _ ... _ .. _ •. _ .• _.... ... . ........ _._. _____ ..........•.. __ .......... 17.5 21·inch streamline wheels .... . ... • ................•....•......... .• _. . ........... _________ ._ .. _ .......... _. ____ .................. _ ............... .••. 13.5 24·inch st reamline wheels._ .....•......... .. ...... _............. .._ ••.•..........•••.••• __ ...........•..•..• _._ .. __ ..............• ____ .•..•......•.... _ 17.5 27·inch streamline wheels .•....•.•................. . __ ._ .....••....•..... _' __ ....•........... _ ..•.•••.•.............•••.. _ -.. .••.......•.•.. ..•• .•.. .... .. ... • 20.5 27·inch streamline wheels (tests of reference 1) ... ...............•• - _ .•............ " ........................... _ ........................................•.. _ ... 21. 5 X ,a/eo extended Y, Infersecfion fairing Z, 24' streamline wheel 1"' -- 21 ,4"- ' 8!{i I 12
r.- "-1
-Y./, II ~/Z I
15:d '
,
I
I
--z k------ 39"------~>' FIGURE 7 .- Drag and dimensions Of landing gear 15a.
Drag of landing gear at 100 m. p. h. (oleos extended): Pounda 21·inch streamline wheels, wheel·strut intersections faired •.•......... _. _. _ ...•. ..... .. _ .. _., __ . _ ... _. __________ • __ .. ________ ... __________________________ __ . 23.0 24·inch streamline wheels, wheel·strut intersections (aired .... _____ ........... ____________ ....... - ...... ______ ... ___ ..... ________________ .... __________ .. __ . 27.0 :~~I~ l¥::iri:~r:~:I~~:~:l~~r~~~n~i~;~~~~t~~~ ~~·~~~~::~~~~:~:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ ~~~~~~~~~~~:~:~::::~~~::::: ~ ~: g 24- inch streamline wheels, wheel·strut fairings removed ...... __ .... __ ...... __ ........ ____ .. __ .. ____ ........ ____ ...... __ ............ __ . __________ ...... __ . ____ .... 28. 5 DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS 7 X, Oleo extended Y, collapsed.
-/5%"- -8WLl
r- %"l
I}f'
-L I r.- "-1
3" ......51...- Lr---""'" s}{," - 37J& " 24" Streamline wheel i<>----- , 39"-------<>l FIGURE 8 .- Drag andldimensions:of landing gear :1 5b.
Drag of landing gear at 100 m. p. h. (o l eos extended): Pound8 24·inch streamline wheels, all intersections 1llIeted . . .. .......................................................................................................... . 22 .0 8.50-10 low·pressure wheels, all intersections ftlleted ..... ...................................................................................... .. ........ .. ... ... 25.0 X, Oleo extended Y, collopsed
r- %"--1
IC
r- "=1 I
5}{," - X. __ _ 24" Streamline wheel 1<----- --3 9 " -----.......;:>\ FIGURE 9.-Drag and dimensions of landing gear 15c.
Drag of landing gear at 100 m. p. h. (o l eos extended): Pound8 21·inch st reamline wheels, all intersections faired .. .................. _ .. _ .......... .............................. ............................................ . 17.5 24·inch st reamline wheels, all intersections faired .... ...... ............ . ........................................................ ...... .. ...................... .. 22.0 27·incb st reamline wheels, all intersections faired . ......... ................................................ .................................................... .. 25.0 8.50-10 streamline wheels, all intersections faired . ........... ....... ....................................................... .. ................................... . 25.5 8.50-10 streamline wheels, wbeel· strut fillet removed .......................................................................................................... ... 27.0 24·inch streamline wheels, wheel·strut ftllet removed . . .......................................................................................................... 23 . 0 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS eliminate the high interference and fitting drag of was only about 4.0 pounds greater than that of canti- conventional tripod landing gears and bring uch lever landing gear lIb; the additional drag represents landing gears into the same drag range as the canti- that due to the strut. (Of. figs. 6 and 9.)
Ex panding ' il l e f , , , , \
-- --- --- - ~-~ ~:: - =; ~ ~ ---. "T---:=-"""
"- " / " " 36 " ---- 4Z "--- - - >
I
14 "
I
,<- ,. 8 . 50 - 10 low -
~ - .39 "---+- >1
pre s s ur e wh e e l V((a.' R~ I O. - lJ imcnsions of land ing gear 16.
Landing gears with various fairings and modifica- level' types. It is apparent from figures 7, ,and 9 tions.- Figure 4 shows the effects of two different fair- that landing gear 15a with the oleo-axle intersection ings at the wheel-strut intersection of landing gear la.
ne xt to the wheel is not the equal of landing gears 15b One fairing had a long tail and the other was blunt at I .1 the rear. The long-tailed fairing was appreciably Drag -' I :~ more effective in reducing the drag, as may be seen by Wifhoul expanding Tillels w, With " " an examination of the drag values. This fairing when .20 used in conjunction with the 24-inch streamline wheel ~ tt, reduced the landing-gear drag from 44.0 pounds to
e
31.0 pounds thereby eiIecting a saving in drag of 30 <::) percent. Fairing all strut intersections at the fuselage and also the axle cro s accounted for a further decrease of 4.0 pounds.
--: Q. 0 The negligible eiIect of an engine on the drag of Lift, wilh and without expanding rilleTs ~ I ,,- landing gear lla with 8.50- 10 low-pressure wheels and C) ( , C) wheel fairing C is shown in figure 5.
--
f-Y
1; 4 0 The effects of various modifications to landing gear
------
~ 13 are shown by figure 13 (b). At a lift coefficient of V 0.2 the drag of the original landing gear is shown to be
------
/'
0 12.5 pounds at 100 miles per hour. The addit ion of ~ .....
V
expanding fillets (modification 1) reduced the drag ~- / to 11.0 pound s. "When the engine was placed in the -...J V / nose of the fu elage '(modification 6), the drag of the -40 landing gear dropped to 10 .5 pounds. These drag
I I
values are the lowest recorded for any nonretractable -4 -2 6 o 2 4 Anq l e of p i tch , degrees landing gear tested during the investigation. When F IGURE n .- L i ft a nd drag o( l anding gear 1 6.
modification 2 (wheel fairing extended to wing) wa made to th e original landing gear, the drag was in- or 15c on which the int erference has been reduced by having the intersection placed a considerable distance creased from 12 .5 to 21.0 pounds. The addition of modification 3 and 4 (expanding fillets of different up the axle. Landing gears 15b and 15c had practically the same drag when tested under similar conditions. size) to the lauding gear in this condition reduced the Both had very low drags for tripod landing gears. drag from 21.0 pounds to 17.0 and 15.0 pounds for the With streamline wheels the drag of landing gear 15c small and large fillets, respectively. When streamline DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS 9 side brace struts were added (modification 5) to modi- Mutual effect of wing and landing gear on landing- fications 2 and 3 and to modifications 2 and 4, the drag gear drag.-Figure 13 shows how the mutual effect of was increased to 25.0 and 23.0 pounds, respectively. a wing and landing gear may affect the drag credited U, ModificaTion 1, expandinq fillef. loY, Mod. 3, expanding r-ill(!:t(ma)(.rad. S oo ) Y, Mod. 5, streamline tube, /-fr6 "X 03'/ttJ· V, Mod. 2., wheel roiring exiendedfo wing. X, "4, .. .. (.. .. S ") Z,8.S0-/0 low-pressure wheel.
Nofe:-Mod iTic ofion 6, radial eng in e in nOSe of' ruse/age 6' x 18' C''Fr .'< Y wing """ Y -"r-------'-----n+-------'----X-----,--,---l , , , I , v u ------"-,,,/ " y Wheel fairing A-- - , /< -----42" ----- ' >:JI
~-3S .. --+-->i
FIGURE l2.-Dimensions of landing gear 13 witb various modifications.
Modification 6 (engine in fuselage) in combination with to the landing gear, depending upon the manner of modifications 2 and 4 resulted in a drag of 13.0 pounds, presenting the results. Landing gear 13 (fig. 12) was just 2.5 pounds greater than for the landing gear in its used for this illustration. The curves in figure 13(a) best condition (modifications 1 and 6). In all tests where the engine was used it was in the uncowled con- ~ , dition. Results reported in reference 1 showed, how- ~ -1:':' .Ongmal ever, that there was little difference in the effect of the c::::: /
---
ti...20
---
-
engine on landing-gear drag when the engine was r:: :.::: ~
LU- I---
uncowled and when it was equipped with N. A. C. A.
............
~ 'y .,' Modification ,
-
~ cowling.
'0 The effect of adding a wheel-strut fairing to 1m ding
--- I--
15' ~ gear 15a is shown in figure 7. The fairing decr('ased , -.........
cS (a) the drag bu t not nearly as much as did a similar fairing M07ificftio~ 2 a on landing gear la (fig. 4). The reason for this differ- -4 -2 0 2 4 Angle of pitch, de9rees ence is not clear for the fairings were very much alike and so were the intersections at the wheel and struts.
Figure 9 shows how a fillet at the wheel- trut inter- ----- . --- ---- .
2,3,5 section affected the drag of landing gear 15c, The ~---- ------ - --- - 2,4,5 ~ .......-
- ~-
,../ ,'- 2 fillet reduced the drag 1.5 and 1.0 pounds when used '-----
----
.---- :g
r-=::::: .----- ----- -~ .,' 2.3_ with the 8.50-10 low-pressure and 24-inch streamline I-q- i20 ----.
.---- ----- .l> 2,4 .;::
-
~ wheels, respectively. Although the reduction was not .-::
---~
/V
~ Original' "~I- ~- great, it is probably sufficient to warrant the use of .~ ~ ?,4,6 ~
-
~
~ ~
0 '. 1,6
such fillets.
'010 f-- The results of drag and lift tests made with landing 15' gear 16 (fig. 10) are presented in figure 11. Inasmuch
---
cS (b) as this landing gear had a large lifting surface, it was o .1 .2 .3 .4 .5 thought advisable to take lift daia in conjunction wiih Lift coeffiCient, C L the drag measurement. The landing gE'ar wa (a) Drag uncorrected for induced drag (curves from reference 1) (b) Drag co rr ected for induced drag (present tests) tested with and without an expanding fillet at the FIGURE l3.-Drag of landing gear 13 witb various modifications.
fuselage junction. The fillet had practically no effect were taken from those presented in reference 1 and are on the lift and little effect on the drag, The drag was based on the assumption that the landing-gear drag higher than expected, being about 28.0 pounds at 100 miles per hour. was the difference in drags of the set-ups, with and
10 REPORT NATIO AL ADVISORY CO IMITTEE FOR AERONAUTlCS
without landing gear, at the same angle of pitch. Thi Tail-wheel unit and several tail skids.-Figure 14 method did not take into account any change in in- gives the drag of a tail-wheel unit and several tail skids duced drag that might be caused by the presence of when measured with no landing gear on the fuselage.
the landing gear. Figure 13 (b), which presents the Th 'e addition of a wheel fairing to the tail wheel did results of the present investigation, does take into not decrease the drag of the unit. Adding a stream- account cha.nges in induced drag because the landing- line fairing to the fork did decrease the drag a small amount (0.5 pound). Tail skid 1, which was built of gear drag was obtained by taking the dillerence between the drags of the set-ups, with and wHhout round tubing, had slightly less drag than the tail- landing gear, at equal lifts. wheel unit in its best condition, 3.0 pounds as com- pared with 3.5 pounds at 100 miles per hour. Tail skid A comparison of the two sets of curves shows that 3 had the highest drag, being equal to that of the tail- the change in induced drag should be considered, es- pecially after modification 2 (wheel fairing extended wheel unit in the unfairecl condition (4.0 pounds).
to the wing) has been made. At a lift coefficient of Tail skid 2 had but 1.5 pounds drag and tail skid 4 1011 Po.st of fuselage Modlficat/~n 2-Navy I Fuselage strut section ..
6W Tail·wheel unit-Drag at 100 m. p. h.: Tail skid 1-Drag at 100 m. p. h ..................... .... pound._ 3.0 Tail·wheel unit with no fairing ................... pound .• 4.0 Tail·wheel unit with modification L.......... .. .. do •... 4.0 'rail·wheel unit with modifications 1 and 2...... ... .. .do .... 3.5 Toil pos,t of fuselage
/}t, "IJ. round 4
strut +1' .
~~
Tail skid 2-Drag at 100 m. p. h .. pound . I. 5 Tail skid 3 Ural( at 100m. p. h .... pound .• 4.0 Tail skid 4-Drag at 100 m. p. h. pound .. 1. 0 FIGURE l4.-Drag and dim ensions of lail·wheel unit and various tail skids.
0.2, which is a reasonable assumption for the high-speed only 1.0 pound. These results indicate that the drag of tail-wheel or skid units, even in the worst cases, is condition, the angle of pitch for the set-up without almost negligible.
landing gear was -0.75°. If no induced-drag change Effect of landing gears on high speed. -Figure 46 of due to the presence of the landing gear be assumed, the reference 1 may be found convenient in computing the drag of the landing gear with modification 1 would be effects of the various types of landing gear on the high 14.5 pounds. By the present method the drag is shown speed of an airplane.
to be 11.0 pounds. The difference is not large for this case. A similar comparison of the landing gear with CONCLUSIONS modification 2 shows that drag varies from 14.5 pounds, The results of this investigation indicate the follow- assuming no induced-drag change, to 21.0 pounds. The ing to be true for airplanes of 3,000 pounds gro s weight: results also definitely show that modification 1 is supe- 1. The drag of a landing gear, for which the inter- rior to modification 2, a fact not indicated in reference ference between wheels and struts is small, is appreci- 1. Check tests have pro'Ved that other results reported ably less with streamline wheels than with low-pre - in reference 1 where landing gears were tested in con- sure wheels of equal load-carrying capac-ity. When junction with the wing are not subject to any appre- the wheel-strut interference is high the drag of a ciable induced-drag correction. landing gear with streamline wheels is greater.
DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS 11 2. A low-drag cantilever lfl.nding gear has about the Langley Memorial Aeronautical Laboratory, same drag when equipped with the correct size of National Advisory Committee for Aeronautics, streamline wheel as when equipped with the low- Langley Field, Va., November 21,1934.
pressure wheel and the best type of wheel fairing.
REFERENCES 3. By careful design to eliminate acute angles between the members and b V fauing the fittings, the l. Hcrrnstein, William H., Jr., and Biermann, David: The drag of a tripod landing gear can be made to approach Drag of Airplane Wheels, Wheel Fairings, and Landing Gears-I. T. R. No.4 5, N. A. C. A., 1934.
that of a cantilever landing ~ear without any marked 2. Bi erma nn, David, and Herrnstein, William H., Jr.: Drag of increase in weight.
Airplane Wh eels, Wheel Fairings, and Landing Gears.
4. The drag of a conventional tripod landing gear II- onretractable and Partly Retractable Landing with streamline wheels may be reduced as much as 39 Gears. T. R . No. 518, N. A. C. A., 1935.
percent by carefully fau'ing the strut intersections.
3. Weick, Fred E., and Wood, Donald H.: The Twenty-Foot Propeller Rese arch Tunnel of the National Advisory 5. Expanding fillets are useful in reducing landing- Committee for Aeronautics. T. R. o. 300, N. A. C. A., gear drag, especially on landing gears that are attached 1928.
to wings.
4. U. S. Army Air Corps, M ate riel Division: Handbook of 6. The drag of tail-wheel units and tail skids IS, Instructions for Airplane Designers, vol. I, seventh even in the worst cases, Almost negligible. edition, November 1932.
TABLF. I. -T IlE DRAG AT 100 M. P. H. OF VARIOUS LANDING-GEAR AND 'YHEEL ARRANGEMENTS [8 .50- 10 lo\y· p r essure wheels; 2Hnch, 24-inch, and 27-inch streamline wheels] Landing·gear and wheel arrangement Drag Landing-gear and wheel ar r angement Drag Gear la with wheel-strut interse ctions unfaired: Pounds Gear 15 a unmodified: Pounds 24-inch wheels ________ ______ __ ________________________ . __ 24-inch wbeels ____ ____________________ ____ _ .. _________________ _ 4-1.0 28.5 8.50-10 wheels __ __________ .. ____________ _ .. _____________ _ 8.5(}-10 wheels, tests of reference L _______________________ _ 42.5 29.0 Gear la with long-tailed f air in gs at wheel- s trut int ersec tion s: Gear 15a wilh fairin gs at wheel-s trut intersection s : 21-inch wbeels ______ .. ______ __ _________________________ _ 24-inch wheel s________________________________ ___ __ _ ______ _ 31. 0 23.0 24-inch wheels ____ _______________________________ _ (lear la with long·tailed fairings at wheel-strut inter sec tions and fairings 27.0 27-incb wheels__ ____ _ _ ___ _ _ .. __ ... __________ _ at all other st rut intersections, including axle cross: 30.0 24-incb wheels ________ _____________________ _ .50-10 wheels ___ . __ .. _______ .. ____________________________ _ 27.0 31. 0 27-inch wbeels ______ _____________________ _ 30.5 Gear 15b with fairings at wheel· s trut intersections and nil other st rut 8.50-10 wheels____ __________________ _ _ _ _ _ _ __ _ ...
32.5 intersections: 24-inch wheels ____ ... ____________________________ _ ______________ _ 22.0 Gear la with blunt-tailed fairin gs at wheel-strut int e rsection s a nd fairin gs .50-10 wheels ______ .. _ _ _ _ _ _ _ _ __ ________________ _ 25.0 at all otber st rut intersections, including a\le cross: 24-inch wheels________ ____________ __ __ - 34.5 Gear 15c with fairings at all intersections except the wheel-strut inter- .50-10 wheels__________ ________ _ __ _ - 35.5 section : 24-inch wheels __ .. ______________________________________ _ 23.0 Gear 11" with 14-inch chord airfoil along the s ide of \\ heel;: 8.50-10 wheeb _________ .. ______________________ ____________ _____ _ 21-inch wheels ____________ _______ _ 27.0 20.0 24-incb wbeels ________ ________ .. ______________ _ 22.5 Gear 150 with fairin gs at wbeel-strut intersections and all other struL 27-inch wbeels __ ___________________________________ __ 24 . 5 intersections: 21·inch wheels .. __ .. __________________________ .. _ ... __ 27-inch wheels, tests of reference L _ _. ___ .. __________ _ 22.0 17. 5 24-inch wheel s _________________ .__ __ _____ - 8.50-10 wbeels______________ ______ _ __ . _ - _ - 26.5 22.0 27-incb wheels _________ .. ____________________ .. __________ _ 25.0 Gear llb unmodified: 8.50-10 wheel s__ _ ______ .... _ .. _ ____ _ _____________ _ 21-inch wbeels ____ ____ ________ ___________________ .. _ - ----- - - 13.5 25.5 24-inch wheels ____ __ ________ _______ ..... ________________ _ 17.5 27-inch wheels________ __ ____ _____ ... _. ___ - - ___________ .. __ _ 20.5 27-inch wbeels, tests of reference L .. ________ ... _________ - 21.5 .50-10 wbeels ______ _ .. __ ______ _ __ .... - .... _____________ --- 24.0 8.50-10 wheels, tests of reference L _________ .. _____________ .. _____ _ 23.5
o
/ y - - ~----
~.~ .... ----
./
"-
"
Z Positive directions of axes and angles (for ces and llloments) are shown by arrows Axis Moment about axi s Angle Velocities Force (parallel Linear to axis) Sym- Sym- Positive Designa- Sym- (compo- Designation Designation symbol Angular bol bol direction tion bol nent along axis) Rolling _____ LongitudinaL __ Roll ______ X X L Y--+Z u p cf> LateraL _______ y Pitching ____ Pitch ____ Y M Z--+X 8 q NormaL _______ yawing _____ Z yaw _____
" Z N X--+Y
w r
'"
Absolute coefficients of moment Angle of set of control surface (relative to neutral
L M N
position), 5. (Indicate surface by proper subscript.)
1 m n G = qbS G = qcS G = qbS (rolling) (pitching) (yawing) 4. PROPELLER SYMBOLS Diameter D, P, Power, absolute coefficient G p = ~nr.
p, Geometric pitch pnLF Pitch ratio p/D, Speed-power coefficient = ~ ~~: G" Inflow velocity V', Slipstream velocity Efficiency '1/, V" n, Revolutions per second, r.p.s.
T,
Thrust, absolute coefficient G = ;D4
T pn
Effective helix angle = tan-l (2!n)
Q, Torque, absolute coefficient G = ~D5
Q pn 5. NUMERICAL RELATIONS 1 hp. = 76.04 kg-m/s = 550 ft-Ib./sec.
1 lb. = 0.4536 kg.
1 metric horsepower = 1.0132 hp. 1 kg=2.2046 lb.
1 m.p.h. =0.4470 m.p.s. 1 mi. = 1,609.35 m = 5,280 ft.
1 m.p.s. = 2.2369 m.p.h 1 m = 3.2808 ft.