Naca Report 730

5/17/2018 Naca Report 730

1/13

REPORT N o. 730AN INVESTIGATION OF THE DRAG OF W INDSHIELDS IN THE 8-FOOT IDGH-SPEEDWIND TUNNEL

By RUSSELL O. ROBINSON and JAKES B. DELANO

SUMMARYTM drag oj closed-cockpit and transport-type wind-

shields was determined jrom tests made at speeds corre-sponding to a Mach; number range oj approrim ately 0.25to 0.58 in th e NAOA 8-foot high-speed wind tunnel.This s-peed range corresponds to a test Reynolds num berrange oj 2,510,000 to 4~8S0pOO based on th-e m ean aero-dynamic chard o j th e fu ll-spa m. model (17.29 in.). Theshapes oj the windshield proper, the. hood, and the tailjairing wen systematically varied to include commontypes and a refined delfign. Transport types varied froma reproduction oj a current type to a com pletely jairedwindshield.The results show that the drag oj windshields oj th esame frontal area, on airplanes oj small to medium size,m ay account for 15percent oj the airplane drag or may bere du ce d to 1percent. O ptimum values are givenjor wind-shield and tail-fairing lengths; the effect, at carious air-speeds, oj rounding off sharp corners to various radii isshoum, The longitudinal profile oj a windsM eld is show nto be m ost im portant and th e iransterse profik, to be muchle ss impor ta nt . The effects oj retaining. strips, oj stepsjor telescoping hoods, and oj recessed windows are deter-m ined. The results show that the drag oj transpor-typewindshields m ay account for 21 percent oj th e juselagedrag or m ay be reduced to 2 percent.

INTRODUCTIONPrior to the present investigation, no comparativetest results were available for obtaining the drag ofwindshields at high speeds. Most windshield investiga-tions were concerned with the field of view and theadaptability of windshields to bad weather (references

I, 2, and 3). Some comparative wind-tunnel tests(reference 1), however, show the drag of a certain familyof windshields; these tests were made at approximatelyone-fifth scale, at 82 miles per hour, and at angles ofattack corresponding to maximum speed and no lift.Wmd-tUlUlel tests reported in reference 4 show. thereduction in drag obtained by modifying a given for-ward-sloping V-type cabin windshield.In the present investigation, the drags_of windshieldsof the types representative of present trends in design

for private, military, and transport airplanes .weredetermined through a wide speed range. For t h Fclosed-cockpit types, tho following geometric factorswere investigated: nose shape, nose length, tail length;tail shape, transverse profile, discontinuities (retainingstrips and st-eps for telescoping hoods), and radius ofcurvature at juncture of hood with nose and tail sec-tiona, In addition, surface pressures were measured atone point on a short conical nose section and at severalpoints on a streamline nose section of medium length toserve as an .indication of critical speeds and of the airloads to which windshields are subjected. The transport-type windshields included in the investigation werea reproduction of a commonly used windshield; wind-shields with the same glass area. but utilizingfiush flat'panels, flush single-curved glass, and flush double-curved glass; and a design in which the windshield dis-continuity was complet-ely faired out.These tests were conducted in the NACA 8-foothigh-speed wind tunnel (reference 5) at speeds corre-sponding to a Mach number range of approximately0.25 to 0.58 for fuselage angles of attack ranging from

-3.55 to 0.030 giving airplane lift coefficients from toIl.pproxlmat-ely 0.4, respectively. The speed range cor-responds to a Reynolds number range of 2,510,000 t9'4,830,000 based on the mean aerodynamic chord of thefull-span model (17.29 in.).APPARATUS AND TESTS

The basic model is a *,scale model of the wing-fuselage combination of a transport airplane with thewindshield discontinuity completely faired out. Thescale of the model was large to facilitate accurate dragmeasurements of the windshield parts. Engine nacelles,landing gear, tail wheel, and tail surfaces were omittedso that the drag changes relative to the drag of thebasic model might be as large as possible. The wingtips extended through the tunnel walls and were uti-lized as a convenient means of support. The wing isof steel covered with sheet aluminum, and the fuselageismahogany with interchangeable nose sections for thevarious transport-type windshields. .All surfaces weremaintained aerodynamically smooth.

65


2/13

66 REPORT NO. 73Q-NA.TlONAL ADVISORY COMMITTEE FOR AERONAUTICSThe windshields for the closed-cockpit tests weremounted on the basic model (figs. 1 and 2) in t4rC('interchangeable sections lettered N, M, and T thatrepresent, respectively, the nose or windshield proper,the middle or hood, and the tailor hood fairing. Each

Flot'U 1.-Wlndshk>ld combination 3-1-3 ready for te sting In the tunnel.windshield is designated by three numbers correspond-ing to the part numbers for N, ~I, and T shown infigure 3. For example, combination 1-1-3 has nosesection 1, middle section 1, and tail section 3j 0 indi-cates that the middle section has been omitted and thatthe nose and the tail sections butt against each other.Most of the windshields arc easily reproducible becauseof the regular geometric shapes on which they are based;windshield 4-0-3 isone-half the ..streamline body of

'wing arc approximately one-fourth full scale. For thetransport-type windshields, the scale is one-eighth. Theoriginal transport-type windshield, till' modificatlona toit, and the locations of these windshields are shown infigure 4 . ..

RESULTSThe drag results are presented as nondimensionalcoefficients. For the closed-cockpit types, the wind-shield drag coefficients are based on till' windshieldIron tal area. For the transport types, till' drag of thofuselage with various windshields is expressed as nfuselage drag coefficient based on till' fuselage frontalarea because the windshield aroa is not distinct fromthe fuselage frontal area.For the closed-cockpit windshields, tho windshielddrag coefficient is

wheret:.Dw difference in drag between model with windshieldand model without windshieldFw maximum cross-sectional area of windshieldq dynamic pressure of free air stream (*p 1'2)For the transport-type windshields, the fuselage dragcoefficient is C ' _t:.D,,,-qy;wheret:.D, drag of complete model used less drag of wing;U t a . t is, /)']), is drag of fuselage and Includesinterference of Iuselage, windshield, and wingfilletsF, maximum cross-sectional area of fuselage

FIGt:RB 2.-Typlcal c losed-cockplt wlndmleld Installa tlO!l. Combina tion 1-1-3.revolution, NACA form 111, fineness ratio 5, reportedin reference 6. The windshields were all so locatedthat the foremost part of the tail fairing was 39.69inches behind the nose of the fuselage.For the closed-cockpit windshields on onc- and' two-place airplanes, the windshield, the fuselage, and the

The pressure coefficient P is give by the equationp=ll.pqwhere

ilp local static pressure at a point 01 1 windshield lessstatic pressure of free air stream


3/13

L",{VESTIGATIONOF THE DRAG OF WINDSHIELDS IN THE 8-FOOT HIGH:"'SPEED TUNNEL

WindshIeld P--CJper(N)..3};l radius...

I ~ Sp'7ericaf ~

toQonicaf~p-7---'i

Retaining strips

2 c = : J - ~r--14~3 c = : J ~n ~~21.41 - ~

;JX radius30 (J_j l------~'f--2/.41

.3X radius3b ~ L--- - - - -~-2~.3% radius4~~_

~%radius 5~ ~n ~

1>--2~~, 3 _ Y z radius

6 ~ ~ Ca"Jicol1"-7-- - -


4/13

68 REPORT NO. 730-NATION.U ADVISORY COQ1'ITEE Ji'OnAERON~UTWSThe results for the closed-cockpit windshields arepresented as plots of CD of the windshield combination,,,against the fuselage angle of attack aF for a sea-levelspeed of approximately 260 miles per hour (figs. 5 to

15). These plots show the effects of nose shape, noselength, tail length, radius at the juncture of windshieldand hood, radius at the juncture of hood and tail,retaining strips, and steps for telescoping hoods. Thevariations of drag withangle of attack of the fuselagefor the best and tho poorest windshield combinations

The results for the transport-type windshields arc. presented as plots of CD" against a, Cor n sea-levelspeed of 265 miles per hour (fig. 28).

PRECISIONThe accuracy of the tests is best shown by the scatterof the experimental points. For the closed-cockpit

windshields, the error in drag value is estim ated to benot greater than 4 to 7 percent of th o drag of the wind-shield and is smallest for the best windshields andPlan view

Plan View

~--------~----~-------96.68~ ~--~~----~------~------~

/~-'--==- ..--....~.> : - . . : . .= . : - . : . : : : ; . ~ )

(a) FBIrcd IlQSO. . (d). (e) Wlndshlf lds wi th s lo&le-eurved flwh pl lS ll .(h) OrIgInal transport-typo wlndsbleld. (I) WInd:!hJeld with double-oorved gUo(e) Orl glnBl t ransport.type windshield with window recesses made fl usb.

FIQURE ~-TrBllSporttype windshields .

tested are shown in figure 16 for values of a, from _6to 3.5 for 8. sea-level speed of 137miles per hour.Cross plots showing the effects of nose length, taillength, radius at the juncture of windshield and hood,and radius at the juncture of hood and tail are shown infigures 17 to 22 for sea-level speeds of 229 to 381milesper hour. The local pressures on two of the windshieldcombinations are shown as plots of the pressure co-efficient P with Mach number :A i as 'R parameter fora,= -3.55,-1.79, and -0.03 (figs. 23 and 24).The results for a few windshield combinations areplotted against Affor a,= -3.55 and -1.79 to showthe effect of compressibility on the drag (figs. 25 to 27).

largest for the poor windshields. For the transport-type windshields, the error is estimated to be 110greater than 1 percent of the drag of the basic fuselage.It is realized, of course, that thc most importantsource of error in predicting full-scale characteristicsfrom the model results probably is the difference inReynolds number. Some transition effects mny be oimportance in the model tests; whereas the flow overan actual windshield will be affected by the propellerslipstream and by the character of other parts ahead othe windshield. For comparisons under the mostunfavorable conditions, the results may apply at leastqualitatively.


5/13

INVESTIGA.TION OF THE DRAG OF WINDSHIELDS IN THE 8-FOOT HIGH-SPEED TUNNEL 69

I I [ T -[ T 1 1 I I-0 Combination. .. _~ I ::-:..-......S-1-3 ---0-& Ii I - - - - . . . . . . . . 7-3-4 --0 -0 ~ I ---.:.__ 6-1-3 ---.01 - i C b . zl... 1 - - - . 8-4-5 ---v0 LI 1 - - - /-/-3 - - - t> _1-& t: 1 I - - - 5-3-4 - - - - + _0 .....r-r--_ 8c-Ic-2 ---- t:.0 e: I - - - - 4-0-3 --- _-- -.- -8.-. . . - - - -.-, .- --rl -.-I-- "Wl--. l--. ,

-j-;::- p.-=::J--- - - _- _ - ----j:--1----- -- -- -- -- ---

.800

.700

.600

.200

t OO

-4 -3 -2 -/Fuselage angle of alfaclt,a,.peg:rIGUBJ: &.-EJfect of nale shape ol9bort length. M, OM; V, 21) mpb.

o.160 I I I r I( ! I'- .Combinafion -/"1 r --- 2-1-3 --. 0- /1 I --':_I'O-i"-3 --- C o---I I ----"-1-3 --- 0CI I : : : : - - = - . - . . 3";'/ -3 ---- v -CI ____ 4-'0-3 -----I

. . . .A ,/

-* " . ~ -- -I: - - _ ~" - - _ _ , _ . --I1---- 0_- - - :- '''"'i-- ;==-- ."" - - - _ .- -- --I .-!

.140

.1i'0

.040

.'02'0

-4 -3 -i' -IFuselage angle of affack,a,,de9 oP'IGtIU: 7.-Oompsrlson between Mreamlinl tand conical noses . M, 0.34; V, 2IlOmph.

.16I I I I I [ I I0- _. - - _ . _ - - Combination I--(I 1 - - - - 1-1-3 --- e -'--- /" 1 I - - - 2-- /-3 -- 01--c : r = - : : - = - - . . . 2-0-3 0- r I I --....__ 3-/-3 ---- v ' r - -~ I - - - 4-'0-3 ----- CI

V,./V '" _..'

~ . . . .- - . . .. : < _ . .-, _ -~ -3--; I- . . . . . .~ -A . . . . . . - --r--1- ----'I1--- _ _c ~ _ _ f-;---c

.140

.120

.040

.oza

' C 2 0 -4 -3 -2 -I.Fuselage angle ofaltack,a,;:/a9FIGUU: 8.-E1fect at nose length, IItleamIIne shape. M, ~ V, 200 mpb.

'0

./60

./4()- - A - l - + - h o ; ~ ~ a : l ,J 0-- L. I I ___ 3-1-3 --- < > -r I 1 - - - 3-/-2 --- I>'--- -~ I - - - 4-'0-3 ----- ~

;,...-' ,_.8-l . . - - - ' " " " . -!--

e - -- --4 _ - i- - - - - ----- _ -

lEO

.060

.040

.020

-4 -3 -2 -/Fuselage angle of alfaclr,a,peg oFlaum: a.-Effect 0 1 . tan length, streamlInIt shape. M, 0.34; V, 200mph.


6/13

70 REPORT NO. 73Q--NATIONAL ADYISORY COMM'I'M'EE FOR AERONAUTICSr - r I I I I ~. I I I 1-binatiorrI--'~ .. 3 -1- 5 ---C. j- 1-- -3-'-2 -'-r---~. .. "3--): 7 . tj.'~--".,- I 1~'-3~/~8 ~"~- ,- I ---..:... . - -4--0-3 ---- .__,_> . e -l - - -0 1 - - - - I1;------1-----. --1-- --f V~ 8v--I ~- - 'r----- .l! _ ..-

.,I

'I -'.~ .I ..l! . r---- . . . . . . . _ . ~ ~ ~C:E - ~ _ - _ . . , . . 1--c-- --

,/80

.140

120

,060

.040

.020

-4 -3 -z -/ruse/age angle of affoclt,elFpeg oFIIIUKK fi.-ElIl'Ct of IaIlI~ngth, oonlcal shape. M, O.a.; V,200 mph..460r--.-~~--~~~~---r~T--'~~~

-_.

:I :",'"~.....340 - -------Ii----+------+--II--.,-I---I---I--~.~ I r; Combination.~ . t++ 0 .J=r: : :. :: : :t: 9 -r-e ---0!- :: ......-- .-_ 't '/.,ROLI7>. 9a~!a-EO8 ./60- '/2RACT::":--.- 9b-lb-c ----I>,!l'l R~ .9c"lc-.c_ -----0~ -.._.-C f - : :: :. .. -- ., ." 4-0-3 --------

< : : l .120r--+-~-T-_'--r-+-~~-+--'_--r-_'

,D80r-~--+__+--4__4--~--r-~--+__+~ :_ f--_-li--__.-1--';~I-' r-' - ~

.0401-' -+--r-'-1---+-4--+--~-4-_--t-~-;-4---4- - _-- --

-4 -3 -c -tFuseloge angle or a/facle,elp' degFlOUR!!! 1l.-ElIl'CL of radius at wlndshleld-hood Juncture. ..1, 0.35; 1', 2 I J S mph.

o

~ 9-1-2 0 _c= I ---.. ... .... ...-0-3.700I---+-~-t---i_-+_L_'-i-- ~ -----

.6001---+--t---t---t---+-" ..--.-.- ..L I---+--I---+---+-t-.J_-, r- - - - .--+--

"'~ I.." 5OO1--+-+---I--I--t---I--- ~ .~ ~. . . . ' .l -~~ S ! ~p--t....OI---+....-+---j-+=~....q ~ - . .. : :. - . .~ i-. .-,.~IJ : : 4 : : : : : : - = = ~

.~c 5 .3001--4--+-+--~---1I---t--+--i'''~ --''-1-

.-_ -, ...-....-- .200f----+--+--+--+--I~-+--1------'"~

I']()t---~I-- .-.- ._, .--. 1-." -.-_ ..-~.-.

--1--1--+-- f-----' --- r-----+-- ..---- ----- -- -- -- - - ---'~~~--~~--~~--~~~-7--~~~-5 -4 -3 -2 -I 0Fuse/age angle' of allacJr,c!,.pegFIGl'R!!! 10.- ElIl'Ct of tal l If>ngth. M, OM; 1", 200 mph

.~"- ... o'


7/13

INVESTIGATION OF THE DRAG OF WINDSHIELDS IN THE 8-FOOT mGH-8PEED TUNNEL 71

Combinationandretaining strip(1-1-3)eQl . I - - - - - - -A--Q~ (1-1-3)cI ~v----Q1 l . (1-1-3}dI ~.+----.--

1-1-30(I I - - - - - -v"

,/ ". . . . . . - " l_ . , - .P,/ ~ /" - : : : Y :

/~V+e=- -. : : : : ; e- : . : : : - -"/:_.--

- _ . , -..-1

./60

.140

.060

.040

.0cO

-4 -03 -2 -IFuselage angle or attack, d" degFIGUU: 13.-Efb:toC~strlps, comblllat1ou.l-1-3.M, Il.34; i';200mph.

o

'TOIIIISIIIO-4S-1

Combinationandretaining stripe t 1 f I I - - - - . ! ! : :_ 1-3)b(>----QI (1-1-3)e! - - - - . : . . _ _ _~ --_ (1-1-3)0

~ t 1 T 1 1 ---.:.._: .-A--. (I 1-1-3~. ! - - - - - - -~ ~ - (/-I-.3)fI ---.:.._:v--Qc I (3- 1-3)eI --.:.__D--OL: - 3-1-3I I - - - - - - : : . . . . . ._.4---

./l/V Y/ _,~,. ".. ."j~,/

: " / :x : -:,. /~ ,..- ",./,/~ ~,_ " . . . ; ~ ?/7_.,-'~ ~/

".II",...

C- _V v"~- r:F = - - . . . .. . . ! i _ - - - _ .~I-- ,_--1--'

~ Ca nt' strip eI (~-1-3)e-(I-I-3}

l-t-- --- W- - .,-~. . . . ._..,17-f-- ; . . . . _ -


8/13

Mil . ' r - . J - , - . . . _,R ~ I I ~f-- T~-L-+-ZR-+" ---6J2R----~ I--" r ~ r : : r ~ = r = r--Mochnumber V,mph d.F,~1} r - - - - --- ------o.so 381 -1.79 ----- _40 .305 -1_79f-- - .30 229 -1.79._ "-------- .34 260 ;00- _ . " .\,, -.---. .-- . . . . . --~ ~

~ 1',~

- ,-. . . . - ".-- . .-~- --~-- - . . . . . - r_-r - . . . ~. . . . . - ........--.~ ~ --- _ 'L .. ' ~ . - -~ t-,

'. . . . . . .~ ~ ..-.~- .--~- -~

72 REPORT NO. nQ--NATIONAL ADVISORY COMMl'M'EE FOR AERONAUTICS

I I ICombinalion -+---13-1-30 -_3 -1-3b ------0_3-2-3b ---+3-/-3 0_

.240

.ZOO

~~fl60~a.1208 -~.080

.020~_+-~-+-_'--r-+_~--+-+--r-_' .040

~S=-~-_~4~~-_~3~-L--~2~~-_~/-~~O~~Fuse/oge ongle of otfock,dFpeg o I i! .3Nose length,L/R

FIGt'lU: 17.-ElTed of n_lcnlth, streamlineshalll!.

5FIGUlU: l!i.-Effect of steps fo r telescoping boods. M, OM; V, 260 mph.

I I I I I I I.~. Combinofitin9-/-6 --


9/13

L.",(VESTIGATIONOF THE DRAG OF WINDSHIELDS IN THE 8-FOOT !l1GH-SPEED 'rUNNEL 73

1.200t, Mil T-31

~ R -----I I ~ -t~L42RI . -6.1eB-----i[ r I r I 1 II [ ! I, I 1 1 '.1f-- Mach number V,mph ciF'deg- ----- 0.50 381 -1.75-----.40 305 -/.75-r- - .30 229 -1.79------- .3 4 260 .00\{~~\~\~,. '\ "~ . . . : : : : - -

1.000

tJ~800

.200

o 2 .3 4Nose length LIRFIGl1U 18.-Etrect olnose!eDith, conical shape.

5

.320

.2801 : 3 - . 1 I I , _ _J M-I~ - I ; r - - - - - - .s:f~~-I LI Il '---l I I I IIMach number V,mph d,.deg------ 0.50 38/ -1.79- .---- .40 305 -1.7~_..30 229 -1.79------ .3 4 2SO .00

II III\ .II\

~ \\ \~~

.240

.eoo

aBO

.040

o 4 6 8Toil length, LIBFIGUU 3).-Etfect of taU length, conkaI shape.

10

.240IM.I . _ t _

N-37 I _______ '---hR-I--fR~L---:--I T-I " [I ,I I, [. I ! . _,Machnumber Y,mph d,.cIegf--- ----- 0.50 881 -1.79---- AD 30 5 -1.79.30 229 -/.79f--- ------- .84 260 .00

:\~~.~~\'\ ~

.200

.040

a 8 /06Tail lenh~ LIRFtOl!lLB lQ.-Effect of taU length, streamline shape.

2

.800 J _ - I 'T!2, I I/l d ~_l_-~ B ~-2R--4B->!Mach number V,mp h ci,.deg- 0.30 229 -1.75 ------- .40 305 -1.79f-- ------- .50 88/ -1.79 f------------ .35 265 .00. -

I

~\ \II\ \ \~ ~~ - -- ,...- ----- -- --- - -- -

.700

.600

.300

.200

./00

o .2 .4 .6 .8Nose radius, rfBFlGl1U 21.-EJfect of radIus at windshleld-bood juncture.

1.0


10/13

74

.400

~t:i1:'.300.~~~8 .2000>(c S.100

.500REPORT NO. 73O--NATIONAL ADVISORY COMMITI'EE FOR AERONAUTICS

Air speed, m;' h (.stU} level, 53of.)100 COO .300 400 500N-9c{ ~R I , r lL~1 ~R+21l-,j.....2R-~I I t I- Mach number V,mp h dF.deg-- - -- 0.50 ,38/ - 1.79--- 040 305 '---7;79- .30 229 -1.79-------- .35 265 .09--- ---f--- r-r-'-.. . ~ -... "r - - : : . . : : : . . : -~ : : - : : - . . . .",-- - ~ .~ t--,. : : . : : . : ~ - : : : : : : : . - _ -- '~r== f----

.4 .8 ie 1.6Tail radius. rlJr 2.0FIGURE22.- Effcct ofradlus at hood-tall Juncture.

DISCUSSIONEffect of nose shape.-For nose sections with lengths

approximately equal to the height of the windshield, thedrag of combination 9-1-3 With a conical nose (fig. 5) isabout the highest of any windshield tested and is ap-proximately 15percent of the drag of a small- Of medium-

,N-2

-.600 VI--":::~ - '-,,-a"p--1.7S"W:" ~- ; .~ ; :--I- l\' .~ /'" -r;-.03~V:;~~ ~;355~'~j 1 ;7 -//v IMachnumber V,mph~'l/ ---- 0.50 381!-------- .40 305.30 22 8

1 " 1 A .34 260 f---. .~

-size airplane of average proportions. The conicalnose is characterized by an obtuse angle between thenose and the hood that is of constant magnitude andcontinues around the complete transverse periphery ofthe windshield. That the drag depends on the sharp-

.?DOO so 40 60 80 100Distance from I~ading edge,percent nose length LFIQURJ:23.-Pressure distributIon over streamline nose, mcdlum length.

-I.400 - \-- - - - -~---f---ct., p..- -- ---I-- _ '. ,. _ _ .- J . . . .< I; ;-.03". 'i\200 -

~I.~O I-- ,,r-, -,_1/ r- \00 f~-~l ..-!l: V""!3.5~___ p'I t - - - - - - r-000 - .. --- '~- -- .-p .

~

r--- : I-- - .-~-_ .. -.,...., __ .. _ - _ _ .900 ~ I - - - - I-- - - - - - t - - - - - - J.--- I~Combination 9-/-3 1--' .~-.r- ~ ,800 lL 1-"". .-

~-700-.')3" V~~- - '- f---V~....../.7!p . . . . . ............"- /' \500 . . . .-1- ~5~ -- -.-- --V- l \- 1-- - ~ -,~- .75L '" A A , .r-ti~P )-- - - - -'~ 1--1-

400I-V! 1 I - - - - -,~~L ~I-- 'CombinaNon 2-1-33 0 0 - ~ - .'00 .-- t-----1-- ,----. _ - - -, -- ..

100 . ,_ - -. "- f-.- -,--~ --"_ .. - _ ...,_...- --,-I--- f--- --~-0

-I.

-l

-I.

- L

-.5

-.-.2,

.3 .4 .S .6Mach number. M./ .72FIIlIiK :!!.:....Varlatlonor I",.ak ucPu"c I l I 'C I IS lUOwith ~I"".I ru" t~...wln.l>hk-h"-ness of this angle and the amount of windshield periph-cry With all angular break is shown by tho Cud thatcombination 6-1-3 with a cylindrical nose hus abouthalf the drag of combination 9-1-3 aml that combiua-tion 1-1-3 with a spherical nose and no break has stilless drag. Windshidd drag depends largely on thelongitudinal profile and only slightly on the transverseprofile, as is shown by the general agreement in figure 5of the curves for windshields having tilt' same degree oedge sharpness but having semihcxagonal or semioctag-onal transverse profiles instead of semicircular. Thedrag of the streamline windshield 4-0--3 is the lowest oany windshield tested and is approximately 1percent othe drag of a representative airplane. Rounding otTthewindshield corners, as in combination sc-Ic ..2, is thebest means of reducing the drag of a poor windshield,This effect is later discussed quantitatively,


11/13

INVESTIGATION OF THE DRAG OF WINDSHIELDS IN THE 8-FOOT HIGH-SPEED TUNNEL 75Air speed. mph (sealevel.59 OF. )too cOO .300 400 5f)0

.::IVU Conical /1 1 --...:__ 9-1-.3rBOO I I

_ Cylindrical II 1 - - - - . . : . . . . : . . . 6-1-.3.700

V - - - 4-0-.3.6007 , . , 5-1-.3.500 ~/,f.-"V '" VT l-~ ".,-400 -1.79 ~ V-.3.55" lo--

.300~ ~ 5-1-.:3

coo i . - f " : t : : / $ '-1.73...~ ~ V-3.S5 ..100 .

-I. 79~ = 4-0-.30 -.3.55"-- 1./ .2 ..3 .4 .5 .5Mach number, MFIOl'JU: 2li.-Compresslbillty ellret on wlndshIcld drag.

.7

Effect of nose length.- The variation of windshielddrag -with length is somewhat similar for streamlinenoses and for conical noses, as shown by :figures6 a n d 7ithe drag of the windshields progressively decreases asthe length of the nose increases. The cross plots in:figures17and 18 indicate that the optimum nose lengthfor a conical-nose windshield is about 2R for sea-levelspeeds up to 300 miles pe-rhour and is greater than 3Rfor higher speeds, that the length of a streamline-nosewindshield should be greater than 3R, and that thedrag of _astreamline-nose windshield longer than 3Rwill be less than for a conical windshield.Effect of ta.illength.-Figures 8.and 9 and the cross

plots of figures 19 and 20 indicate that the length ofboth strea.mline and conical tail sections should be fourtimes the height of the windshield. The optimum taillength, however, means little if a bad nose section isused, as a comparison of combinations 9-1-6 and 9-1-2in figure 10 shows. There appears to be little choicebetween a long conical tail and a long streamline tail.Effect of radius a.t transverse junctures.-Large

reductions in the drag of a windshield with a shortconical nose can be realized by rounding off the sharpedge at the windshield-hood juncture (fig. 11). Thecross plots given in figure 21indicate that the minimumeffective radius is approximately 25 percent of theheight of the windshield. Rounding off the sharp edge

A;r speed. 11 7 p h (sealevel,53 "F)100 200 300 400 500

.040

~f~ I ,. . . . . . . . . . . . . R01>50-10-2 ITfR-j_ _l _ I CyL il 1 - . . . . . . . _ , -3.55"c Sb-/b-Z 1R-.t J ~I1 : 1 1x sc-re-e 1 II - - I ._- 10+ 4-0- I

! J-1.79'1.. T1

.--1 - _ ~ _ . ) ' J ,:~'r5"II

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Naca Report 730