REPORT NO. 720

PRESSURE AVAIIX13LE FOR COOLING WITH COWLING FLAPS

By GEORGEW. STICKLE, IRVEN NAHMN, and JUEX L. CRK+LER

SUMMARY

~ full-scale investigation has been conducted in theNACA. 20-foot tunnel to determine the pressure dif-ference auailable for cooling m“th cowling $aps. 27wJaps uxre applied to an exit s[ot of smoo~h contour at 0°Jap angle. Hap angles of 0°, 16°, and SOOwere tested.TW propellers were used; propeller C has conventionalround blade shanks and propeller F has airfm”l sectionsextending closer to the hub.

The pressure arailab~e for cooling is shown to be adirect function of the thrust disk-loading coe$icn”mt ofthe propeller. l%e maximum suction obtained with acowling Jap set at 30°1 locat~d in a region where the staticpressure for the 0° $ap position is equal to that of thefree air stream, is shown to be equul to approximately one-Mj the arerage total pressure oj the air dream; the totalpressure ti giwn by the sum oj the dynamic pressure andthe thrust loading. The total pressure in front oj thecowling ti crdicaily dependent on the ratio of the jrontopening to the propeller dtimeterfor propeller G? Propel-ler F gate a higher total pressure in jront of the cowling.

For the take-off cond

28-4 REPORT NO. 72&NATIONAL ADVISORY COMMITTEE J?ORAERONAUTICS

ANALYSIS OF THE PROBLEM

The pumping action of the cowling + dependent onthe pressure difference between the entrance and theexit of the cowling. For the condition of high-speedflight, the forward velocity of the airplane producesmost of this pressure difference; the cooling problem istherefore usud.ly easy and interest is centered largely

FKWBEl.–Tsd sst+p In tunnel (NIM slot wai CIOWIfor tbess tests.)

on the efficiency of the cooling. For the static-thrustcondition, the propeller produces all the pressure differ-ence. The most difficult cooling conditions are in takeo-ff and climb. As an aid to the analysis of the coolingproblem under these conditions, it is desirable to con-sider the pressure s.produced by the propelkr and theforward velocity.

If the distribution of the thrust is assumed to be uni-form over the propeller disk area S and the rotation ofthe slipstream is neglected, the total pressure in the airstream behind the propeller is

H~=po+q+;

where p. and g are measured in the undisturbed air.The increase in total pressure due to the propeller isgiven by

m

If both sides are divided by q,

HT~=@Z=-T,=qP,

For a constant vaIue of P,, changes in thrust distri-bution und n with blade-angle setting being neglected,the average value of ~/q gives tie pressure producedby the propeller in terms of the dynamic pressure ofthe air stream. Becrmse the pumping action of thecowling is dependent on the pressures and the veloci-ties in the propeller slipstream, the pressure increasefor the difTerent conditions of propeller operation mustbe known.

A few feet behind the propeller, the pressure increasehas been almost completely converted into velocity. The

static pressure in the region of the cowling exit is thenalmost .~qual to that of the free air stream. If a flapis extanded into the slipstream, the resultant increaseof velocity will cause a drop in the static pressure atthe exiti - -Asuction at the exit will thereby be produced.

The pressure at the cowling entrance is approxi-mately the dynamic pressure of the air stream, beingmore m less than this value depending upon the shapeof thq. inner sections of the propeller. The over-ailpressure difference AP is then the difference betweenthe a-tramce and the exit pressures. Ills thus evi-dent that, by proper design of the inner section of thepropeller and of the cowling exit, for the take-off andthe climb conditions, over-all pressure dtierences sev-eral times the, dynamic pressure of the air stream areobtainable.

The flow equation of the air through tho cmvling,given in reference 1, maybe put in the following form:

AP/Ap= 1+ (K/KJ2 (1)

This equation specifies the ratio of engine to exit con-ductance necessary to secure the de&red cooling-pres-sure drop Ap when AP is available as over-all prmsureWlermce. ‘

.

-—-—--

..:. -,

-.

.- =

FIGUEE2.—Line drawing of the td msngoulenM.

In reference 11 the pump efficiency of a cowling wascletied as the ratio of the useful cooling power to theincreased power required to propel the airplane,

Alternately, this pump efficiency may be exTressed interms of the net efficiency of the propeller, the engineconductance, and the power disk-loading coefficient as

-.. APPARATUS AND TESTS..

The investigation was” conducted in tho NACA 20-foot V’ind tunnel, which with its stanckdequipmcnt isdescribed in reference 4. The test set-up was tho sameas that used in reference 5. Figure 1 shows the generalarra~e”ment of the se~up on the tunnel balance. Thenose slot was closed for these tests. The skirt wasopened at the point shown in the line drawing of thetest arrangements (~. 2). - The skirt for the 0° flap

PRESSURE AVAILABLE FOR COOLING WITH COWLING FLAPS 285 ,

was made of a circular cylinder that could .be movedm.ially to vary the exit area in order to cover the rangeof cooling pressures for all conditions of flight. The 15Cand the 30° flaps were made of conical pieces of metalwith 6-inch chords. These flaps were test ed in only oneposition. The nacelle diameter was 52 inches.

A baflle plate, constructed as a shutter with four stopsand controlled from the balance house, simulated engineconductanceei of O, 0.039, 0.079, and 0.118. The pro-peller was driven by a 150-horsepower, three-phase,

FIOCM 3.–Blades of propdkm uM.

wound-rotor induction motor mounted in the nacelIe.The speed and the power output of the motor were con-trolled by resistance in the rotor circuit. Pressures in-side and outside the exit slot and across the engine bafflewere photographically recorded on a multiple-tubemanometer.

The propellers used for this investigation are shownin figure 3. Propeller C, with conventional round bladeshanks, is Bureau of Aeronautics drawing No. 5868–9;propeller F, with airfoil sections extending closer to the

hub,’is Bureau of Aeronautics drawing No. 4893. Both -.‘propelkrs are three-blade, adjustable propellers of 10-foot diameter. Details of these propeIIer b~ades aregiven in reference 5. All tests were made with a blade-angle &tting of 20° at 0.75 radius.

RESULTS

Table I presents FIsummary of the results obtainedwith both propellers. The table is divided into foursections repmsrmting conductance of O, 0.039, 0.079,and 0.118. Each section is further diyided into columns

for values of ll~~C of 0.5, 0.6, 1.0, &d, 1.6. 13rtch ofthese columns gives the pressure drop across the baffleAp and the rear pressure p, as fractions of the dynamicpressure q; each column also gives the net efficiency.The pump efficiency is given in the high-speed condi-

tion, l~~~d= 1.6, for the 0° flap and is given in the

climb condition, 11~~.= 1.0, for the 15° and the 30°flaps. The pump efficiency is omitted for the otherslot openings and operating conditions bemuse theexperimental accuracy did not justify such comput a-t.ions.

The drag coefficient -with the propeller removed isgiven in the last column. The drag valum for opentit slots wwe obtained in the following manner: Thebasic drag values for the coding with exit slot cIosedat zero conductance were obt@ed by separate dragtests. The basic drag was deducted from the dragof the same cowling-propeller combination at. zero powerto give the drag of the free--wheeling propeller. The “drag of the free-wheeling propeller was then deductedfrom the drag of the open-exit cowling-propeller corn-binations at zero power to obtain the values givenin table I.

Figures 4, 5, and 6 give. the pressure distributions _ ___for the 0°, the 15°, and the 30° flaps, respectively,showing the efIect of two values of engine conduct ~cemd of propeller operating conditions.

The pressure drop for zero conductance is taken asthe available pressure dfierence AP. The value ofthis available pressure difference as a fraction of theiiynamic pressure of the air stream is given in figure 7M a function of the flap angle for several disk loadings.

F~ure 8 ghres a graphical solution of the flow equa-tion of the air through the cowling (equation (l)).I’he experimental points for the 0° flap and the high-

lpeed condition of l/~= 1.6 are plotted on the graph,tvhere K~AS/F, for comparison -with the th~reticalmrve. Figure 9 presents similar re+lts for the tests]f tie 15° and the 30° flaps for the take-off condition,

lj~=O.5 and 0.6.A comparison of the. cooling-drag coefficient titl+ the

?ressure drop in the cruising condition is given in figure10. The drag increase due to cooling was computedkom

ACD= (T?O-%)pC;

286 REPORT NO. 720—NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS--

! \T _—.-_-A. -==-l=-—-”----\ \-

(a)‘Y

—;.— /.:----—–IL

/ p/q =/— .-

‘% -g” ‘/i--..J5-. Is f::

,— - - .98 -. /4 1.6

,

/——

—~

------ .07 .85 /.0—-— .04 .80 1.6

(a) K-o.(b) .K-O.liS.

FIOURE4.—Presmre dbtrlbution for the 0° flap. 6@irrg, ~ Inch; prop?ller C.

At li~a = 1.6 for a 10-foot propeller on a 52-inchnacelle, this equation becomes

AC~=l.305(qo–q.)

From the definition for pump efficiency,

()@J3~

AC~= ~p

The curve for 100-percent p~inip efficiency is includedfor comparative purposes. The section below the baseline in the figure indicates the additional form drag forthe open nose over the closed streamline nose, as givenby unpublished data.

Figure 11 shows the distribution of total-pressureincre~e behind propeller C, which has rouncl bladeehanks, for the diflerent conditions of propelIer opera-tion. Figure 12 shows the strea.dines around the frontof the cowling for high and low slipstream contractions).which correspond to the take-off condition and to the

.-—

high-speed condition, respectively. Figures 11 and 12 -were plotted from unpublished test data.

EFFECT OF FRONT OPENING ON THE AVAILABLEPRESSURE

A study of figure 11 shows that the increme in totalpressure behind propeller C varies considerably withpropeller operating condition and propeller radius.A blocking effect occurs over the inner two-tenths ofthe propeller radius but, outside this radius, the totalpressure increases rapidly with radius, about 80 per-cent of the maximum value realized being obtained atz = 0..3. Inasmuch as the maximum diameter of (hofront opening of the test arrangement, z =0.29, islocated in the region of this steep pressure gradient, thepressui% obtained from the propeller slipstream is VCIYcritical to small changes in the front opening. If morecooling at low airspeed is the determining considerutiwit is advantageous to block off the hub and the innerportions of the propeller with a spinner rmd to incrcascthe diameter of the cowling opening in order to utilizethe available front pressure.

/———

Ap/q p./~3.88 -2.40

—— 3.17 -1.77

7//

.6

%

---—- --- -

(b)

—— .

—-— .77 .25 1.6

(a) K-o.(b) K-o,lls.

lhamm6.—Pm39ure distrlbut!on far the 16° flap. Propeller C.

~— ———

___ —-- -

.—-—

/

(a)

------ jsg -/.(2? /.0—-— . -.72 /.6

+—— _

-— _____-—. —

/

w

(a) K-O.(h) K-o.m.

FIGUREO.—Prwmre df.gtrlbution for the 30° flap. Propeller C.

qoEd

288 REPORT NO. 72&NATIONAL ADVISORY cOtiITTEE FOR AERONAUTICS

FlcIp mgle, O+

(a) Pro@ler F. (b) Repeller C.FI13uuE7.—Aveflable presmre difference.

/.o *.-,. }

.8 ;o Propeller F

\

x“-s

cf I

%

ii ~ ‘,

.4 0 I I I$

\c

.2x I I i I I I—

I I 19I 10 f 2 3 4 5 6

K/K,

a.,FIGURE8.—QraphiceJ solutfm of the Sow equation. The W flap,at the high-epeed

condition, l/m- 1.6.

For l/~~=0,5, propeller C is ’47 percent efficient,giving an average increase in total pressuro in the $ip-strea.m of 3.76 times tlm dynamic pressue in the mainair stream, (The average values of H/q* T, corre-sponding to the given values of l/~~ may be obtainedfrom reference 5.) Reference tQ table I for the oper-ating condition of l/$~ = 0.5. and K= O shows thatthe average front pressure obtained for propeller G is1.25 times the dynamic premure of the main ahstream, an increase in total pressure of O.25q over thedynamic pressure of the air stream. The average in-

.+

—

—

1.0

.8

\D v&

i “

ii-’ \

.4 *Propeller ~~

0;:v L-

-0 c .5x c .6

.2

0 2 .4 .8 .8 /.0X/K,

FIGURE9.—&aphicel eolutkn of the ilow equation, The 15”and the W-.flaps at the taka-ofleond[tfon, –

crease ~ total pressure in” the slipstream being 3.76q,only one-fifteenth of this average pressure increase. isseen to be available for front preesure on the testset-up.

The average front pressure obtained for propeller Funder conditions simihw to those for propeller C is2.67g, or an increase in total pressure of 1.67g over thedynamic pressure of the air stream. When air is flow-ing through the. cowling, the front pressure becomesstall greater. For the condition of l/~ =0.6, thepressure added by propelIer C increased from 0.26q

PRESSURE AVAILABLE FOR COOLING WITH COWLING FLAPS 289

for zero air flow to 1.33q for a conductance of 0.118with the 30° flap; under the same conditions, thepressure added by propeller 1? increased from 1.67gto 2.93g. This large change in front pressure withair flow at low speed is largely an effect of the changein the effective diameter of the opening as a result of

.24

.20

./6

.08

I I I I.04

—

.$ mse w. citucd alrwmlheruse. QO@.

./6

. /.2

AC=

.08

.04

.;

./6

./2

.08

.04

I I 1A I I I I I I I Im

~s=w,- ch~ .f~~~l.h fWSW.ao .2 .4 .6. .8 /!0 L2 /.4

Apfq

(a) If=o.ow (b) lr-rLo79. (o) K-O.HS.FImrm 10.—Ve.riationof cmlfngdrag m?~cknt with prmnre drop at 1/-& 1.6.

changing the streamlines in front of the cowling. Ifthe cowling opening were not located in such a criticalpressure region, the change in pressure with air flowwould be nearly n@gible. For the high-speed con-dition, l/~ = 1.6, the pressure remains approximatelyconstant with radius.

The effect of larger propellem, say 17 feet in diameter,

on this same 52-inch nacelle is interesting. Propellerdiatieters of 10 and 17 feet on this nacelle representthe maximum and the minimum ratios of F/i3 encoun-tered in present-day design. With the 17-foot propellerthe maximum diameter of the front opening wiIl havea value of z of 0.17 as compared with 0.29 for the1O-foot propeller. It should be realized that, althoughthe available front pressure rapidly decreases for eitherpropeller with a decrease in size of the front opening,the pressure decrease occurs at a smaller value of zwith propeller F than with propeller C because of thebetter blade sections. Although on the test set-uppropeller F produced much higher front pressure thrmpropeller C, this large difference in the increase in front

56

&A 7

4.8 T

/

4.0 t

.6

a2 \/ \

HF

.724 \

/ / ‘ -

\

.8

M / ~ \

/ / “ \

I/ / ~

i.o\

.8 .L3

—

L6

o .2 .4 .s .8 Loz

FIGG’PJI11.—Dfstrfbut&mof pressure inmass. Propelhx C; L?,XI”.

pressure would not tist for geometrically similar pro-pellers 17 feet in diameter on the test nacelle. Bothpropellers would probably give some blocking effect forsuch an arrangemmt.

A poiut of further interest is the front pressureavailable for ground operation. The manner in whichthe available front pressure varies with the propellerradius for ground operation is shown in figure 4 ofreference 6. For a front opening of z= O.29, correspcmd-ing to the test arrangemmt, the available front-pressure

coefficient ~S’ “ “ - ““ ‘B equal to 0.25 for a blade-angle

.—

290 RJIPORT NO. 720-NATIONAL- ADVISORY COMMITTEE FOR AERONAUTICS

setting of 20° for prcpeller C. For a value of z=O. 17,corresponding to the larger propeller, the front pressureco&cient is only 0.01. In tither words, the 17-footpropeller would give essentially zero front pressure forground cooling. This remdt illustrates the desirabilityof airfoil sections on the inner portion of the propeller.

EFFECT OF EXIT SLOT ON THE AVAILABLEPRESSURE

Two effects result from changing the area of theexit slot of a smooth-contour exit design by means offlaps: (1) The increase in the cowling-exit mea in-creases the conductance of the exit slot md, conse-quently, the pressure drop across the engine; (2) thechange in the contour of the cgwling in the region ofthe exit changes the pressure distribution over thecowling and thereby affects the over-all available pres-sure. These two eflects are separately illustrated bythe test resulte and will be separately discussed,

EFFECTOF CHANGING THE EXIT CONDUCTANCE

The effect of cht-mging the exit conductance is il.hls-tratecl by the tests on the 0° flap for various exit-slotareas. Table I shows the ratio of the pressure behindthe baffle plati to the dymnnic pressure of the airstream pJg to be nearly constant for all..conditions ofthe 0° flap at K=O, regardless of the slot opening orthe propeller operating conditicm. h examination ofthe pressure distribution for the 0° flap with %inchexit slot (fig, 4) shows the same redt for several con-ditions of propeller operation, For K=O, the staticpressure at the slot was nearly zero for all conditionsof propeller operation, indicating that the total pres-

sure added by the propeller has been almost entirelyconverted inta dynamic pressure in this region. hychmge in the cooling-pressure drop for the 0° flapmay therefore be attributed almost eritirely to a changein exit conductance. A small secondary chti.nge occursthat is due to the change in front pressure,

The solution of the flow equation (equation (1))given in figure 8 shows Wut, for large values of K[Kz(corresponding to small exit openings), the agreementof the points and the theoretical curve is very good;but, for small values of K/Kz, the experimental pointsfalI below the curve. The discrepancy is largely dueto the fact that Az/F=Kz is not a good measure of t,hoconductance for large exit openings.

It m~y be repeatid that the use of Az/F=Kz in thoflow equation will give a fkstr approximation of thechange_in cooling pressure drop with exit conductance.If the test set-up is reproduced, a closer approxima-tion may be obtained by fairing n curve through theexperimental points.

EFFECTS OF CHANGING THE COWLING CONTOUR AT THE EXIT SLOT

The effect of changing the cowling contour at theexit slot is illustrated by the tests of the 15° and the30° flaps. Table 1, K= O, shows that p,/cf undergoesa great change when the flap is extended into theslipstream. Thk change in pJg is evideptly a resultof the deflection of the slipstream, which gives anincrease in the local velocity over the exit. This il~-crease in local vdocity produces a negative pressurebehind the flap. The magnitude of p,/q is a functionof the propeller loading, as is cleurly shown by the ._

Lliiiiii”i”i iii.(a)1 I 1

0 “.2 .4 .6 ““ .8 Lo t.2 o>.

.4 .6 .8 Lo L2z

(a) Take-off mnditfon. 00 H@-epeed mnd[tion.FIGURE12.-Streamllme around front of cowllng. Propeller O.

PRESSURE AVAIL4BLJI FOR COOLING WITH COWLING FLAPS 291

pressure distributions of figures 5 and 6. The decr6asein static pressure for 1{=0 and .l/-$~=o.5 behindpropeIler C is 2.25q for the 15° flap and 2.75g for the30° flap; that is, the 15° fhip produced a negativepressure of 47 percent and the 30° flap produced anegative pressure of 58 percent of the average dynamicpressure in the slipstream, 4.76q.

Emuninat ion of all the results for zero conductanceshows that approximately 55 percent of the averagetotal pressure in the slipstream is avdable as decreasedpressure at the exit sIot with the 30° flap. Other un-published measurements ako show that approximatelythe same decrease in static pressure mn~ be obtaineclfor the static condition, where the average dynamicpressure in the slipstream is given by T/13.

Table I shows that the values of the negative pres-sures for propeller F are somewhat larger than thosefor propeller C. This increase in negative prcswu-e forpropeller F is due to a change in the distribution ofthe total-pressure increase behind the propeller, whichconcentrates more of the thrust over the ironer sectionsof the propeller.

The effect of air flow through the slot for both the15° and the 30° flaps is shown in figure 9. Althoughthe scatter of the test points is explained by the in-ability accurately to determine K2, the points above thetheoretical curve are due in part to the increase infront pressure with air flow.

1% data are available concerning the effect on thepressure at the exit obtained by varying the propellercliameter with respect to the nacelle diameter, but it isbelieved that a study of the test results will give a goodindication of what pressures might be expected withother ratios of propeller to nacelle diameter. Forexample, consider the 17-foot geometrically similarpropeller on the same nacelle. The exit slot in thiicase is located at a value of z of 0.255. Inasmuch asthe flap produces a pressure drop equivalent to 55percent of the dynamic pressure in the slipstream forthe case tested, ib maybe estimated that only 45 percentof the 4.76g, or 2. lq, should be available as suction atthe exit with the 30° flap. Inasmuch as the efit slotwould be located in such a critical pressure region forthis test combination, opening the flaps might result inR further increase in available pressure for cooling.

EFFICIENCY OF THE EXIT SLOT

For the hiih-speed fllght condition, with a properlydesigned writ slot, the drag increase caused by thepassage of the cooling air is approximately that asso-c.iat+d with 100-percent pumping eficiency (fig. 10).The exit must fair smootldy into the nacelle and theair leaving the exit slot must be in the same directionand of approximately the same velocity as that in the

mteide air stream. If the air from the exit is not inthe same direction as that in the air stream, it wilIcause an upset of the main air flow with a resultantdrag increase. Jrery low efficiencies usually indicateimproper exit conditions. The low efficacies shownin table I associated with the small etits, such as the%-inch slot, do not necessarily indicate poor exit-slotdesigns but me probably due to inaccuracies inmeasurements.

For the low-speed-flight condition, the pumpingefficiency is of secondary importmce; the primaryrequisite is large available pressure for cooling. It hasalready been shown that the extended flap k a veryellective means of producing large available pressuredifference.

T~e extended flap causes a break in the air flow,which in turn causes the pumping efficiency to falfbelow 100 percent. For the take-off condition, thedifference in net eficiency is ho small to permit thepump efficiency to be accurately computed. Thepumping efficiencies are included for the 15° and the30° flaps at l/J~= 1.0, corresponding to the climbcondition. For K= 0.118, the value of TPfalls from 0.76for the 15° flrbp to 0.39 for the 30° flap for propelhF and from 0.59 for “the 15° flap to 032 for the 30°flap for propeller C. Part of this huge decrease in 7Pfor the 30° flap is, of coume, due to the disturbance ofthe air flow, but a part of it is due to the fact that the30° flap does not contract the cooling air all the ~vay tothe exit. This condition may be seen in figure 6, wherethe maximum velocity, that is, the lowest pressure, isobserved forvwd of the exit.

DESIGN COMPUTATIONS

It has been shown how the pressure available forcooling with cowling flaps is dependent on the condi-tions in the propeller slipstream; that is, how the total,the static, and the velocity pressures vary with thepropeller operating condition. In order to illustratethe application of thwe results, two typical design com-putations are giwm. Case 1 simulates the test set-upand case 2 applies the results to a different ratio ofcoding diameter to propeller diameter correspondingto a more modem design of sngine-propeller installation.

The specifications for thi two cases me given intable II.

The coding specifications must now be determined forthe various conditions of operation. The diameter istaken as 52 inches for cnse 1 nnd as 60 inches for case 2.The estimates for both cases are for propetiers similnrto propeller C. A propeller with better nirfoil sectionson the inner portion will produce greater pressuredifferences.

292 REPORT NO. 72&NATIONAL ADVISORY CiCiidMIITEE FOR AERONAUTICS

TABI,E 11

DATA FOR DESIGN: COMPUTATIONS

EnKina: Cam I

Powaroutprrt. hp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WIIndlmti Www, hp . . . . . . . . . . . . . . . . . . . .._ . . . . . ---------- MOAltitude mtti, ft---------------------------------------- ~lo, fWTake-off Mwer, hp.. -.. - . . . . . . . ..-.. -.. —-------------- ..OWAp required for oxdfng at raked power and altitude,

lb/q ft ---------------------------------------------- . ...25Indkated pawer at one-balrretid md errd mfnfnmm

bfade-asrglesetting, hp---------------------------------- lMAP raqu!rd for wolhrg at oP&halfretaf spai rmd mtnbnnm

blade-angle eattfng, lb/sqft ------------------------------ LOMexfmnmengInodiameter,in. . . . . .. ------------------ 62Enafne4efflemnduetsnce, K . . . . . . . . . . .. . . . . . . . . . . . . . . . . ..06

Ck#e8

2,OIYI2, 3(YJ

0-15coo2,2CSI

..@

310

L200

.15A1rpfe&

TopsPaed atretcd eltltud%mph. .- . . . . -------------------Dynamicpressureat top speed and reted eftitude, lb/sqft...Crule!ngspeed,mph . .. . . . . . . . . . . . . -------------------Bestslirnbfngsped, mph .-. . . ---------------------------Dynam!epra!sureforWmbbg speedat w lerel, Ib/sqft...

Propeller~timntrol .. . . . . . . . . -------------------------------IWrnberofbfedes. . . . . . . . . ..-.. -. . . ..-... -..--...-.——8@at relcd englnespsed,ram . . . . . ..–-. - . . . . . ..-–.-Dfametar, ft . . . . . ..- . . ..-_... -... _.—--_—–_._Blad~ngIe wtting at top spood and rated eltltade, deg. ----Bfedwmqlesetting for full-wwer cllrnb at kt dtibhg

SWOd, do&-------------------- ——---- ---. —Mhrlmumblade-angle eottlng, do . . . ---------------------Power eeborbad at ons-haff rated spwd and minimum bleds-

anglo eattb, hp---------------------------------------

2W.Wlco 146

.229 _ 270

.Il!l– ..- la31 b4

.%-- .2916 16

bO la

10onetantspeed.

Top speed,—The computation for the top-speedcondition is quite straightforward.

CMC1 care BAP(fer AP/w-1), lb/eq ft ---------------------------------------- MO 145AP/AP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..- .400 .3.03

~fi=I/ti/AP-l----------------------------------L-------~-.i: .L73 .1.02. . . . . .. .

K1-A/F ---------------------------------------------- o-we .aWvWidth ofesft slot (% diem.XAi/F), h ----------------------------- H 1%

Full-power climb,-For the full-power climb, AP/gmust first be known. For case 1, this value is easilyobtained from figure 7 (b). For case 2, the estimate maybe made in the following manner:

In a climb d 145 miles per hour with 2000 horsepowerbeing absorbed by a 17-foot propeller, l/~c = 1.33, orPe =. 0.425. With an efficiency of 80 percent, T== 0.34;that is, the increase in total pressure behind the pro-peller is 0.34q. For this combination, 45 percent of thetotal pressure of the slipstream may be developed bythe 30° flap; 46 pereent of 1.34-is 0.60. Now, becauseof the large propeller hub, rm allowance must be madefor blocking, and a front pressure of only 0.7q may beassumed. The over-all available pressure differenceis thus 1.3?

Cttae1 Caae5~,fi . . . . . ..-. ------------. ---. --—--—-------- --------------- 1,09 L32AP/q..- . . . . . ..-. --- . . . . . . ..------ ..-.. ----_ ----. -y.. ------- ~7 LaAP, lb/sqft----------------------------- —------ -. . . . . . . . . . 43 ITAP\AP------------------------------------------------------ 2JJ L 76K/Kz.- . . ..--- . . . . . . . ..----——–-—--— —. -- —------- -- Lob 0.S7K*... -------------- —--—..--——- — --------- ----------- 0,0b7 p!1?8Width ofmltslok h--------------------------------------------- % %

Take-off.-Probably the condition of greatest interestis the take-off or immediatdy thereafter. Computa-tions similar to the precading ones. indicate that, forcase 1, satisfactory cooling &.-obtained with a 2%-inchflap opening at l/~. = 0.5 tit an airspeed of 50 milespe~hour. The conditions for ease 2 are more severe, a

6%-inch opening being required for l/$Z=l.O at109 miles per hour. For this case, an efficiency of 72percent and, because of the greater thrust coefficient,FLfront pressure of 0.8g were assumed.\ Caee1 tie #Um .-:------------------------------------------------ 0.5 LO. .iP/g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L 20 L .57iP, lb/eq ft.-. - . . . . . ..-... - . . . . . . . . . . . ..---—.--––---—. 27,3 4!3,9~[AP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -l.@ L 16K/KI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30 a 40

I@. . . . . . . . . . . . . . . . ---_ — - — ------------- ----------- . -. —.- am 0.975

Width o! exit slot, h .. . . . . . . . . . ..-. - . . ..-.. -.-.-–-.—..--—--- . . 2% 5%

Ground operation,—The cooling estimate for groundoperation is made for the static-thrust condition at one- .half engine speed and minimum blade-angle setting,A conservative estimate will bc made by assuming thefront pressuro to be zero. If the flap setting is tllosame m for the take-off condition, AP/Ap will rdso bethe same.

Ctleef Cb4e#CT {ah-ti6)------------------------------------------------- @13 0. 12bH= T/& lbleq fL... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L16 L64AP=+; lb/sq ft... -------------------------------------------- 3.38 2.$9&P/AP.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..m. . . . . . . . . . . . ..L09 L 10dp produced,lb/sq ft ------------------------------------------- Al 2.0 ‘-&prequired, Ib/eq fL-------------------------------------- .LQ .f..2

Thusj the engine should be adequately cooled underordinary ground operating conditions.

CONCLUSIONS

1. The pressure available for cooling is shown to bea direct function of the thrust disk-loading coetlicicntof the propeller.

2. .The maximum suction obtained with a 30° COW1- .ing flap located in a region where the static pressure forthe 0° flap is equal to that of the free air stream is shownto bfi equal to approximately one-half the aver~gctotal pressure of the propeller Slipstream, which isgiven by the sum of the dynamic pressure and thethrust loading.

3. .The total pressure in front of the cowling iscritically dependent on the ratio of the front opening tothe propeller diameter for round-shank propeller C.Propeller F, with airfoil sections closer tQ Lho hub, gavea higher total pressure in front of the cowling.

4. For the take-off condition with the 0° flap, pro-peller C produced ogly one-half as much nvailrtblccooling pressure as propeller F.

5. I!’or this same operating condition. with thti 30°flap, propeller C!produced an available cooling pressurethree times .as large as was obtained with the 0° flapand propeller F produced a pressure difference twice- . .that obtained with the O“ flap,

—

6. For the take-off ‘condition, the 30° flap j and aconductance of 0.118, the pressure drop across thothe baffle plate with propeller C was 3.17 and withpropeller F was 4.85 times the dynamic pressure ofthe air stream,

LANGLEY MEMORIAL AERONAUTICAL LABORATORY,

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS,

LANGLEY FIELD, VA., I&y 9, llLjO.

PRESSURE AVAILABLE FOR COOLING WITH COWLING FLAPS 293

REFERENCES N.A.C.A..Nose-Slot Cowling. Rep. No. 695, NACA, 1937.

1. Theodorsen, Theodore, Brevoort, M. J., and Stickle, Geo~e4. lf’eick, Fred E., and Wood, Donald H.: The Twenty-Foot

TV.: Full-scale Teata of N. LC.A. Cowlings. Rep. No.I%opeller Research Tunnel of the National Advisory Com~

692, NACA, 1937.mittee for Aeronautics. Rep. No. 300, NACA, 192S.

5. Stickle, George W., Crigler, John L., and h’aiman, Irven:2. Theodorsen, Theodore, Brevoort, M. J., and Sticklq George Effect of Body Nose Shape on the Propulsive Efficiency of

‘W.: Cooling of Airplane Engines at Low Air Speeds. a Propeller. Rep. No. 725, NACA, 1941.Rep. No. 593, NACA, 1937. 6. StickIe, George W., and Joyner, Umhur T.: The pressure

3. Theodoraen, Theodore, Brevoort, M. J., i3tick1e,George W., Avatiable f~r Ground &ling. in ‘Front of the Chmlfng of ._and Gough, M. N.: Full-scale Tats of a New Type Air-Cooled AirpIane Engines. T. N. No. f373,NACA, 193S.

TABLE I– CONDENSED EXPERIMENTAL RESULTS

Lh!’’E=l.o I IM-%-L8

-----

.—--CONDUCTANCE-O

0.753 . . . . . ..- a ml. 7s -...... - .0s4;;: -------- .085

------- . . cm5.754 -------- .m.751 . . . . . . . .(W.6s0 -------- .165.541 -------- .323770 . . . . . . . . --------

:773 -------- --------.771 . . . . ..-. --------.n3 . . . . . . . . . . . . . . . ..767 . ..- ..- --------.768 -------- --------.;% -....: -- .005

. -------:571 -::::-- . -------

. ....2.s2il. 052.s02.79!4.76

t%

--...-.-CLfl—.—.m

::-2 M–8. M

------ -. ....- . 0:g$ -------- . . . ..-2.23 -0. g 1.34 -0.16278 .560 L 37 –. 162. S9 ::25 ..548 : if2.46 –. 12 .556 W2.43 .5444.01 ––i % A&l :&

–. g

L43 –2. 29 2.30 -- u. . . . . . . .. -. -.. . :M!J ..rii.- . . . . . .L20 –. 15L43 :$ L09

–. 14 %% L 11 :.:i: . –. 16 .&w L 10 –. 141.17 –. 04 L06 –. 11

:% LOi –. 14H –;%’ .568 L 793.82 –2. ls . 51s 1. w -–i H

1 m -------- -------.714 -------- L 09.716 . . . . . . . . L 10.714 -------- L 10.ilz -------- 1.3a.719 -------- 1.W.687 -------- 1.64.6M -------- L77.721 -------- --------.723 -------- 1.m.712 -------- .99.71’4 -.... -.. 1.60.i18 -------- 1.00.721 .-.- . . . . .99.721 - ------- L 01.m . . . . . . . . L03.853 . ------- L57

--------a M-.16–. g

z 14—. 70—. S2,------–. 16–. 15—. 16–. 16–. M–. 17—. 66—. 72

.. ——”-----

L 24L52

i:L07L 373.ssLa

.—

. ..–2. 40–a 96

.. -—

I I [ I

CONDUCTANCE-O.039

1----O.wo; 00)0

.116

.124

.222

.422

. . . . . . .

.. ..------- -------. 0.552L 17 L301.47 .09 :EL@2 .5s .5481.26 .441.97 :E3.69 –1:: .5m4.2a –L 72 .514

. . . . . . . -------- .542.= A&l .540.M .542

.41 . us:% .545.ea :: .M2

.545M –i; .5362.94 –L54 .514

------- ..-----:;; ::

1:E %L 14 .131.35 –. 59z 12 –. 76

I. m ---------------.n6 .-..--:-O.z.716 -------- .45.718 -------- .6s. n8 -------- .s2.7Q3 -------- .Sa.631 0.52 1.42

:% .-.x- .-:-;-.725 . ..--...

-------- .%2: M -------- .67.713 -------- .70.711 -..- . . . . :Q.712 ---:X-.

:&o .19 Hi

F

:FFFF

:c0cccccc

—

—

FFF:

1?FFc!

:cc0

:c

—

------L 44

H!!L 24240;.

-----.3s.64.84

L 00.92

H&70

-------L641.20.73.59

–i Z-2 %. -----

.W

.70

.47

:%.15

-L 66-2.18

......0.70.53.23.16.09

%------

.63

.51

.27

.17

.11

.02—. 32-. a

------0. alL50L 67L 11.s2.4.4.21

------.

l%.93.70.78.39.15

.

...... .-....-:% :3.n ::.i3.20 .13.95 .05

—. 48its –. 69

--------..-.---------1-------.132

t...... I.......——

CONDUCTAN-CE-0.079

: ;lJ ------- .-i.ti..-------

; ;;; .-...--- .l!a------- .40

.714 -------- .6.I

.710 --------

.676 0.76 i;!

.610

.721 .-:?-. l!!-.

.m -------- .05

.718 -------- .18

.716 -------- .23

.7US ------- .49

.713 . . . . . ..- .63--------

:% .47 :kl.620 .23 L 14

..... .. --------0.$5 O.@5.14L 53 :%!1: g . lm

.135.58 .247.29 .5m

------a 75L121.67

kg4. 1s625

------.18.42.a3.71.71

kx3.M

------L 91L 74L221.10.%

~i 67------1.18L02.s3

::.48

~i E

-------1.57L 361.05.*.70

-Y :-----1.00.69.75.65.55.37

—.—. :

-. ..-.0.!2s

.34

:KL2fJ

?;.. . . . . .

.11

.19

.38

.:

:Sa123L46

--....0.97

::.52.40

—.—.E. ....

.s5

.76

:Z.35

-: ?$—. 34

-------:g.60

:$!—.-.B------

.7s

.73

.m

.43

.30

.:

:15

... ... .. -.-.. ..68 --------.62 . . . . . . . ..64 --------

L15 --------.84 -.:iti...74.42 --------.21 -------

..CONDUCJTANCE-O.118

------0.33.54

i:;

i%3.58

------.12.14.40.39.72.s9

L702.32

------0. 1s

:3.64

i~L 67

.- .-. .

:%

:2.57

i;L29

—

F .-.. -.F a 019F . (USF .0i5F .1812’ .228

: :%c --, -.

.019E . 1ssc .175

. la; .228

.s35: .142c .259

1716 -------- -------- .-&-m-..713 -------- ao6.719 -------- .14 .86

--------: M -------- :: ::.708 - .ii6-- .62 .&o.673 .97 2J.56a.721 .-.:! !..-:;.- . . ..m...719 ..-. -....718 .-.- . . . . .07 .78.717 -------- .19 .70. n4 -- ----- .26 .66.709 . . . . . . . . .52 .4s.709 .-.:;6.. .65 .85.&z .25.520 .32 :~ .04

: ;5J .-i.%..752 i37.743 L(S.m l.g.704

.71:% . al.770 . . . . . . ..758 .86.764 .!M.761. 75s &.731 .87.ioo.642 ::.324 .21

......0.83.U

i%

k:4.s3

. . . . . ..13.14.46.36.73.49

;H

.. ....-221203L78L 48L26

–: ti.. -----

1.22L 161.06.97.51.7’4

—. m—. 84

.. . ..-L 75L 5$L 36L 16.97.09

-. 6s--- . .

::

.84

.75

–: z-. 48

-------L04.95.s7

:G.16

–. 17-- —---

.87

.83

.76

.E-4

:E.m

—.6s

--------O.aw.0s8.097.111.141.228.540

.-. ..-. .

.-. . . . . .

.-. ..-. .------- ..-- . . . .--------

.179-- . .. . .

—.. —430174’4”-$2-21)