Document
t It-;'" COpy NO I-W TECHHICAL NOTES NATIONLL ADVISORY COMMITTEE FOR AERONAUTICS No. 813
f
I COOLIlm TESTS OF AN AIRPLAliUi] EQ,urpPED inTH AN NACA COWLING AND A WDTG-DUCT COOLING SYSTEM By L. 1. Turner. Jr •• David .:Biermann t- and 'rf. E. Eo othby Langley - Memorial Aeronautical Lab~ratory
COpy
To be returned to
filss of tho Natitn
Advi ry Comnl
for Aeronautics
W . gton, D. c: Washington June 1941 NATIONAL ADVI SORY COMMITTEE FOR AERONAUTICS T ECHN IC AL NO TE NO. 813 C OOL I NG TESTS OF AN AIRPLANE EQUIPPED WITH AN NA CA COWLI NG AND A WING-DUCT COOLI NG SYSTEM By L. I. Turner, Jr., Da vid Biermann, and W. B. Boothby SU MM ARY Cooling tests w ere made of a N ort h rop A-17A attack airplane successively e q ui pped ' w ith a conve nt io na l NAC A co w li ng and with a wing-duct cooling s ystem . The me t h od o f co ol ing the en g ine by admitting air from the propeller slipstream into wing ducts, passing i t first throu gh the a cces sory co mp art men t and then over t he en gine from rear to front, a pp eared to offer possibilitie s for i mproved engine cooling, increased coolin g of the accessories, and bet ter fai r ing of t he p~w e r - p la nt in stallation .
Th e results showed tha t ground co ol in g for t he wing - duct system . wi t hou t co wl flap was better t han for the NACA · cowling with flap; ground cooling was appre ciably impr o ved by in stal lin g a cowl flap. Satisfactory temper- atures were mainta i ned in bo t h climb and high-speed flight, but, with t h e use of conv ent io nal baffles, a g reater quan - tity of coolin g air app eare d t o be re quir e d for the wing - duct syst em.
I NT RODUCTIO N The increasin g p ower of new designs of air-cooled en g ines w ith little cha ng e in frontal area has mad e it difficult to obtain cool ing at low a irplane speeds with the conventional cowlin g arrangements. Th is d ifficulty is particularly acute for inst allati o ns with large pro- peller s , in w hi ch the o ~en in g of the co w lin g may , be blocked by the propeller hub and the blade shanks. Dif- ' fic ult ies may also a rise in coolin g the accessory com- partment. If no specific provision for cooli ng the ac- cessor y compartment is made, high tempe ratures of the in- ta ke system may decrease the en gine power. I n addition, it appears that the drag of the conventional cowling is often relatively high ' andth~t " a " be"t ' te~ shape might be ob- tained.
The wihg-d~2t cooling system appea~s to offer one solution of . these , l)ro , blell)s. In sU ,c h a system the coolin g air i s admitted int o duct 's through orenin gs neaT the leading edge of the wing in sid e t h e propeller , slipstream, is passed throu gh the a c6es s ory co mp~ rtmen~ and,the en- gine baffles from rear to front, an d is ejected rearward through a suitable exit slot. By proper location of the duct entrances the slipst~ea m can be utilized for low- speed cooling. The nose can be faired with or without a propeller spinner, and the oil radiator and th e carburetor- air int ak e c a ~ be ~nclos~d in the fuselage and suppl ie d with air diverted from the ducts.
In order to test such an arran gemen t on an engine un- der actual conditions, a wing-duct cooling system was in- stalled on a Northrop attack ~irplane ( A ir Corp~ designa- tion A-17A) borrow~d from the Army Air Corps. Tests were made of the airplane with th e ori g inal NA CA cowling and with the w ing-duct system. Whe~ th e airplane was equipped with the w in g -duct system, several incidental improvements in fairing w ere made. B~cause it was impossible to analyze the separate effects of the various modifications on the drag, the results of the tests relate primarily to cooling rather than performance.
APPARATUS Airplane The A-17A airplan e with the original NACA cowling installation is shown in figures I, 2, and 3. The ex- te~nal~rrangement of the c,a rburetor- a ir , intake and the oil ~adiator may be noted. The en g ine exhaust was t h rough a sirigle '- outlet located on the ri gh t side of the fuselage.
The ' ilow of cooling air w as regul a ted by a conventional ' outward-opening cowl-flap installation. With the flaps , closed t~ the limit, the width of the exit slot measured acros 's" the minimum distance was ab ' out 2 inches. ~ Jith fl~ps f~lly o~e~, ' the ~ffecti~e , o ~e ning was large; but it is : diff ' ic " ur't to ' assigri a significant value t 'o the slot ""i :d' th , 'ljec ;' aus~ 'i ' 'Of' the : o'j;>enin 'gs at the flap hinge line and betwe ' en th-e s<e 'c,t ' ions ' of the flap ', wh ich may be seen in
f'i gure 3-. ' : Th 'e-' ,' pr ' lh 'c ipal ch a rac t er i s tie s otf the air prane
are as follows : NACA Technical Note No . 813 Airplane Type - Northrop attack, U.S. Army designation A-17A 47 feet 9 inches Span - - - - - - - - - - - - Wing area ~ - - " - - - - - - - " - - - 362 square feet 31 feet 8 inches Le ng th - - - - - - - - - - - - - 7150 pounds Aver~ge gross weight as tested - - Engine Type - Pratt & Whitney m odel R -15 3 5-l3; l4-cylinder, 2-row radial, rated 750 horsepower at 2500 feet at 2500 rpm.
Compression ratio - - - - - - - - - - - - - - - 6.7 Blower ratio - " ~ - - "- - - - - - - - - - - - - 8.7 Propeller-shaft ratio - - - - - - - - - - - - - 4:3 temperatures: maxi m um c y linder head Recommended C) F (288° F" or in or climb 550
90 seconds ta k e-off -
C) F spee " " d 500 (260°
Continuous hi gh or climb - - -
F C) 455° (235°
Continuous cruisi ng - -
- - - - -
- -
(It should be noted that t he se recommended values are ac- tual head temperatures, whereas the test results are given in terms of temperature above t ha t of free air.)
Propelle r " Type - Three-blade, Ha milton Standard, controllable, two-position; Hamilton Standard drav,ing number 610lA-6.
Diameter - - - - - - - - - - - - - - 9 feet 6 inches Settings at 42-inch station - - ~ - NACA Technical Note No . 813 Wing-Duct Cooling System Diagrams of the wing - duct cooling system are shown in figures 4 and 5. Fi g ures 6 and 7 are photographs of the air p lane with the wing - duct cooling system installed.
The duct entrances were located ahead of the leading ed g e of the wing at t h e retracted position of the wheels, as shown in figure 8, w ith th e mouths at ap p roxi m ately two-thirds the pro~eller radius. The entrance lips of the ducts were well rounded a nd t h e duct housings were faired into the fuselage and t h e wing . The completed duct inst a llation with wheels retracte d is shown in figure 9.
Eac h d uct made one 90 turn, in which guide vanes were place d , just before reaching the accessory co m partment.
The coolin g air was admitted to t h e accessory compartment throu gh a set of diffusin g v a nes designed to minimize e x pan s ion losses accompanyin g the large increase in cross- sectio na l area of the flow at this poi n t. The air passed for w ard over the accessorie s and throu gh the engine baf- fles from rear to front, was reversed in direction at the propeller · spinner, and was ejected rearward through the exit slot at the trailin g ed g e of the s pinner.
Th e pro p eller spinner w as of relatively large diam- eter, covering th e propeller hub and m ost of the portion of the blade shan k s that are of poor airfoil shape. It was closed at the rear by a plate behind the propeller blades. This plate a n d the trailing edge of the spinner formed the forward part of the cooling-air exit slot.
The re a rward part of t h e exit slot was formed by the non- rotatin g section of the oowling to the rear. This sec- tion m oved back a n d forth to vary the width of the exit slot and thus to regul a te the flo w of coolin g air. Such an arr a n g e m ent performs this function without destroying the smooth shape, as outward-openin g cowl flaps do. The slot wi d th, measured across the minimum distance, could be varie d from 0.6 to 2.7 inches. For one of the ground- cooli n g t ests, a stri p of metal wa s attached to the cowl- ing to s i m ulate a cowl fla p at t h e trailin g edge of the spi n ner, as . shown in figure 4.
The internal arrangement of the cooling system and · the acce s sories with t h e wing-duct system was consider- ably d ifferent from that with t h e NACA cowling. The pri- mary modification was the replace m ent of the original engine b a ffles. The baffles installed for the wing-duct tests covered about as much of the cylinders as did the NACA Technica l Note No . 813 5 o riginal ones , but th ey w ere applied to the front of the cyli nd ers instead of to the rear because of the reversal in direction of t h e cooling air flow. They followed the conto u r of the cylinders clo sely and fitted more ti g htly than the ori gi nal set . Particular care was taken to eli mi na te a ~y openings , oth e r than the space between the cooling fins, throu gh which the air mi g ht flow past the cyli nd ers . The inner cowlin g and the partition between the e ngi ne and t ho accessory comp a rt me n t in the original i nstall a tion were removed . The exit slot for the acces- sory compartment was elim i nated.
The ori g inal exhaust system was entire l y removed and was re p laced by a new one with t wo outlets , one on each side of the fuselage . The ori g inal exhaust manifold was rel atively l a r ge because it collected the exhaust from all the c y linders . The manifold was divided into two sep- arate smaller systems i n order that the engi ne cooling air could pass with le ss resi s ta n c e and preheating than was poss ibl e w ith the ori g in a l arrangement . The two modi- fied outlets had about the same total area as the original outl et, but they p rotruded less and probabl y ha d a lower dra g . The manifol d s and the outlets were pa rtly enclosed in met a l shrouds open . to the accessory compartment at the inner ends a n d to the a ir stream at the outer ends. The pres sure i n t h e accessory co mpa rt m ent forced air through the space between the shrou ds and the manifolds and out- lets. This air jac ket was inte nd ed to prevent the cool - in g air from bein g excessively heated in passing over the exha~ st pipe~ b~fore reac h in g the cyl · ind~rs . As the re - sults show , thi~ ar r angement was not com~letely effective, but equippin g the airplane with a · better system for t h ese test s w as not fe~gible because of · the extensive revision re quired . The shroudin g a nd the outlet of the ri ght -hand exhaust s ys tem may be eeen in figure 8.
The ori g inal carburetor - air scoop and i ntake system were removed . In . the wing - duct s ystem , ai r was supplied to the carburetor throu gh a walled - off section of t he left duct. No provision was made for heating t h e air before it reaci h ed t h e carburetor , as had been done in the original i nstallation .
The lower part of the a~cessory co mpa rtment cover was reb uilt to enclose the o il radiator, as shown in figure 9.
The entrance end of . the oil radiator was left open to t he i nterior of the accessor y comp a rtme n t; the exit end op e ned into the air s .t r eam through a s hort du c t , so that the NACA Technical Note No. 813 pressure in the accessory compartment forced cooling air through the radiator.
Instrument Installation Cylinder temperatures were measured by thermocouples at the front and the rear spark-plug bosses and at the front and the rear of the barrels, midway between the head and the flange, on cylinders 4, 5, 11, and 12. The ther- mocouples at the plug bosses were inserted in the metal and those on the barrels wer e weld ed ~o the cylinder walls between the fins. The cyli nd ers were numbered in the di- rection of propeller rotation beginning with the uppermost.
which was in the rear bank . Thus, cylinders 4 and 5 are on the right side of the engine, 11 and 12 on the left side, 4 and 12 in the front bank, and 5 and 11 in the rear bank.
El ectrical resistance thermometers with suitably locat ed bulbs were used to mea sure the temperatures of the accessory compartment, the carburetor-intake air, and the cooling air after passing over the accessories and after passing through the engine baffles. Total-pressure tubes were used to · determine the pressure of the cooling air in t he front and the rear of the engine cylinders and insi de the mouth of each duct just forw~rd of the guide vanes.
In addition to the usual service instruments, a sen- sitive recording statoscope, a recording tachometer, and an NACA air-speed recorder connected to an NACA swiveling pitot-static head were installed for the tests.
ME THODS AND TESTS Ground Cooling Tests Time histories of cylinder and oil temperatures for full-throttle operation of the engine on the ground appear to be the best measures of the ground-cooling characteris- tics. The engine was started when cold and the throttle was fully opened as soon as the engine had idled long enou gh for the oil temperature and pressure to reach the val u e s recommended in service. The ' propeller VIBS kept at the lo w blade-angle settin g (19.5 ) · and the mixture was NACA Technical Not e No . 813 7 held full rich during the runs. Runs were made with th e cowl flaps fully open on the NACA co w lin g and w ith an exit slot width of 2.7 inches on the wing - duct system; an additional run was also made after the in s t a ll a tion of a simulated co wl flap on the wi n g - duct s ys tem.
Climb Cooling Tests Full-throttle cli mbs were made with t h e p ropeller at t h e low blade - angle s e ttin g and with t he a ir speed ap- proximately t h at for best r ate of cli mb to find the climb- c a a lin g c h a r a e t e r i s tic s • Th.e · t h rot tIe wa s filII y 0 pen e d at a p res sure altitude of 2500 fee t, which was the criti- cal al ti tude of the engine . A steady climb w as then es- t a bli shed and re adi n gs we re be gun a t 3000 feet. Th ree sets of temperature values wer~ taken in t he cli mb to de- ter m ine the trend. Th e mixture was kept full ric h through- uut the climb in o r d er that this condi ti on of the test mi ght be reproducible from run to run. Such a procedure is no t rep resent at ive of servic e ope r a t ion , but it would hav e been virtu ally i mpossibl e to make any other ad just- ment repro du cible in various f li g hts . In an effort to i mpose the m ost s e vere oper a tin g conditions on t he w in g - duct system. however. one test ~ as conducted in wh ic h an at t empt was made to adjus t the ~ixtu re con tin uou sly for best p ower operation. In the cli mbs 1d . th the NACA cowl- in g the cowl flaps were fully open , and in those with the wing-duct system the exit slot width was 2 . 7 inc hes. The cowl flap installed on the wing - du ct sys t em for one of t h e g round coolin g tests wa s not · us ed in any flight.
Hi gh-Speed Cooling Tests In order to determine the cooling characteristics in ths hi gh -s p eed condition, data we re taken i n full-t hr ottle, level flight with t h e mixture adjusted for best power .
After steady conditions had been establish ed , recior ds w ere ta k~n . Ru ns were mad e with t he cowl flap s fully closed fo~ the NACA co w lin g and wi th exit - slot wid t h s of 1.3 · and 2 . 7 inch es for t he w ing - du ct system. The reasons for choos ing t h ese t wo values of th e exit - slot width will be discusse d later.
Maxim um - Spee d Tests The maximum speed of the airplane appears to be the 8 NACA Technical Note No. 813 best ' over-all criterion of possible ' chan ges in drag, pro- peller efficiency, and , engine power. In order to deter- mine the speed, a number of full-throttle runs were made at a density altitude of 10,000 feet. ' In these runs the mixture was adjusted for best power, and considerable care was taken to obtain steady conditions and to main- tain level flight. All maximum-speed runs were made on the NACA cowling with the cowl flaps fully closed and on the wing - duct system with exit-slot widths of 1.3 and 2.7 inches.
Reduction of Data In the reduction of the data on cylinder and acces- sory temperatures, the val~es were referred to free-air temperature as the datum. The measured values of impact pressure were converted into true air speed by the u sual method. The observed air speeds and the engine speeds from the maximum-speed tests were adjusted to 10,000 feet on a density-altitude basis, because the runs were not all made at exactly the desired alt itude. Such a proced- ure is believed sufficiently accurate for these tests, although maximum speed is not a function of density alti- tude alone.
The pressure drop across the engine was reduced to coefficient form by the relation 2 D2 pn where t:.p is the pressure drop across the engine; e the air d' en ' si ty; n, the propeller rotational speed; and
'ti, the propeller diameter ' iri any donsistent system of '
units. A similar coefficient Pe/pn D2 .. \Olas set up for Pe' the p ressure insi de the mouth of the ducts, and a 22 1 coefficient t:.PT pn D was , set up for t:.PT' , the tota / pressure drop across the ducts and the engine excluding any loss at the duct entrance.
NAGA Technical Note No. 813 RESULTS AND DISCUSSION Ground Cooling Th e t empe r a ture data obtained in . full-throttle ~round runs are presented in figures 10 and 11 . (Temperature data at some points are missing because of thermocoupl~ failure . ) The time histories of cylinder tem p eratures for the NACA cowling indicate that, after 6 minutes, about half of the temp era tures had become steady while the rest were still increasing. The maximum head temperature was about 455 F above free air . For the wing - duct system with an exit slot of 2.7 inches, a ste ady state was reached in about 8 minutes, with a maximum he~d temperature of 445 F above free air . The inst allat ion of the cowl flap on the w in g -duct system improved the g roun d -cooling charac- teristics . The cylinder te mperatures rose more slowly and became c· ons ta nt at a lower value than with the NACA cowl- ing, reachi~a maximum of about 425 F abov~ free air in appro x imately 9 minutes . The in crease in oil temperature was a lso appreciably less rapid than with t h e NAOA cowling after 4 minutes of oper at ion, as shown in figure 11.
A d irect comparison of the three arran g ements on the basis of time is sli gh tly unfair to the NACA cowling, be- cause the time is plotted from the full opening of the throttle . as zero and the engine was idled somewhat longer previously to that time with t he NACA cowling. This pro- cedure resul~ed in higher temperatures at zero ti~e, as shown in fig~reslO and 11. From the equilibrium tempera- tures, however, it . appears that . the wing-duct system with- out cowl flap is a small im provemen t over the NACA cowling and that the addition of .a cowl flap to the wing-duct sys- tem renders it considerably . better . ~his comp a rison holds for the syste~ as actually tested. The exhaust shielding, however , was not completely successful and the cooling air was appreciably heated before reaching . the cylinders. If this effect could have been eliminated, the cylinder tem- peratures for the wing-duct system would have been reduced as much as 40 F. The wing-duct system would then afford much better ground . cooling than the NACA cowling.
If comparison is made between individual cylinder temperatures for the two cooling systems, the effect of reversin g the direction of coolin g -air flow should , be taken into account; that iS the comparison should be made t between readings of thermocou p les similarly disposed rela- . 10 NAOA Technical ' Note No. · e13 tive to the air flo~ rather than between the readings of the same thermocouple for the two arrangements.
The time histories of the oil temperatures for the ground runs are shown in figure 11. The temperature given was the actual temperature of the oil entering the engine; it w~s ppt referred to free air. The higher ini- the tial temperature at the opsning of the throttle with It NACA cowling · should be noted in considering the data.
thus appea~s, · . from the slopes of . the curves, that the cooling as . shown by the rate of change of temperature with t . ime was abput the same for the NACA cowling as for the wing-duct : system without co~l flap and that the cooling was improved by the addition of ~ cowl flap to the wing- d~ct ~ystem • . · These . results are in agreement with the in- dications of the ' cylinder temperatures.
A particularly valuable characteristic of the wing- duct system with respect to oil cooling is that any reason- able size of oil cooler oould be installed without increas- ing the external drag of the airplane because the oil cooler can be enclosed in the accessory compartment.
Climb and High~Speed Cooling Typical ~esults of the climb-cooling tests and of the high~speed co~l~ng tests are ~hown . in tableS I and II, re- spectively. In ~ t~~le I the trend of any particuiar tem- perature with inc~easing time an~ altitude is~howh by the variation in the readings fro 'm left to right in ' the corre- spond~ng row; the three sets of readings ~or each climb were taken successively during the ~un. After the data in table II had been obtained, it was found that the values
for the NACA cowling were ' from a r11n in \'1hich th 'e' speed
was sever a l miles an hour ress tban the probable ~aximum.
but the temperatures are believed not to have been materi- ally influenced • . The ' climb co . oling was satisfactory. As sho\,lD: in table I. the engine cooling of the two systems in the full-~ich climbs was about the same, with the maximum tem- perature slightly higher for the wing-duct system. The increase ~n . tem.perature for the . best-p .owe.r climb . ",as not lar ge . ., In , : th e wing-duct S. ys t em t · he q· ool lng ai,r was pr . e- heated: in passing over the accessories . : and the exhaust .
system. If . t~~s effect could be obviaied . by a more cpm- plete sh~ . elding or ' by a rearran ' gement ' of t . he exhaus1;. the cooling wit~ wing-duct system would be better than with the NACA cowling.
1 1 · NACA Technical . Nate No • . 813 In full-throttle, level flight (table II) an exit- slot width of 2.7 i n ches ga ve su bsta nt i a lly correct cool- ing for the w ing-duct system in spite of t h~ p reheated air . Closin g the ex it slot to 1.3 inche s rai sed th e max- imum head tem p erature an amount ap~rox i ma tely e~ual to the p reheatin g . Elimination of t~e preheating would re- duce the te mpe rature by that a m ount for the sa me exit- slot w idth~ These two settin gs of the exit slot were therefore chosen as the actua l and the ideal adjustments for satisfactory coo l ing .
Bringing the coolin g air directly into t he accessory com partment considerably lo wered th~ te mpe rature of the c om pa rt me nt , as shown i n the tables . Th e te mpe rature · of t he carbu reto r -in take air was also les s f or the w i n g - d uct system, but this reduction may have been due to the elim- in a tion of the carburet or -air heater r athe r th an to a c hange in accessory coolin g .
T~e pressure d rop a cro ss the engine in high -s peed , level f li gh t (table II) was incre ased f rom 6 . 6 inc hes of wa ter fo r the !ACA cowlin g to 10 . 3 i nches of wa ter for the w in g - duc t system w ith a 1.3-i n c h · exit slot. Although these conditions represent p r acti c a lly equivalent cool- in g , th e difference ~n pr e ssura drop~ is not a measure of t he ch ange in quantity of coolin g air required because the conductivity o f t he engine was reduced by the new baf- fles. Th e fact t ha t t he te mpe rature r ise of t he cooling air through the baffles was less f or the wing - du c·t sys te m t ha n for t he NA CA cowling in di c at e s an i ncre ase i n the qu antity of a . ir for t he wing - duct sys te m. Because the power expended in cooli ng t h e engine i s p ro po rtional to the produ ct of t he rate o f coolin g - a ir flow and the pres-
sure d ro p . it appears that the coolin g p o wer was g reater
for t he wing-duct system. It s ho uld be noted t ha t the nature of t he coolin g p roce ss is dif ferent for t he two sys te ms . Fo r t he NACA cowli ng , the front of t he en g ine is lar g ely coole d by turbulent ai r , par t of whi c h mai flow over the f ront of t he en~ine and then outsi d e t he co w lin g ; that i s , the amou n t ~f air actually use d i n cooling the en g ine may be g re ate r th an tha t pass i ng throu g h the baf - fles . For the wi ng - d uc t system, the cooling was nonturbu- lent and al l the c oo li ng air passed through the baffles.
A diff~rent type of b af fle desi gned for nonturbulent cool- ing would p rob a bly have been more efficient .
NACA Technical Note No. 813 Pressure Coefficients The pre~sure data are summarized in figure 12 in the form ' of the previously derived coefficients. Except for the ground p oints, the pres su res w ill be given in this
discussion in ter ms of the dynamic pressure . q, at '/nD =
1.05 a p p roxi ma tely. Th e coefficient based on Pe' the q
pressure in s ide the duct mouth, wa s about 0 . 67 (or Pe/ =
1.21) in the hig h -speed condition and was not appreciably affected by the exit-slot width ~r by the presence of the cowl flap. Slot width or cowl fl a ps merely regulate the flow of the cooling air through the system, and the accom- panying variation in qua . ntity ap pa rentJ.y \'1as too small to influence appreciably the flow co n ditions at the duct mouth.
The coefficient 6PT of tot a l pressure drop across the ducts and engine (exclusive of any loss at the duct
mouth) decreased . from about 0.60 (or 6P /q = 1 . 09) with
T
a 2.7-inch exit slot to about 0.42 (or 6P /q = 0 . 76)
T with a 1.3-inch exit slot in the range of VlnD for high- speed flight. The effect of the cowl flap on the pressure
for g round operation . V/nD = 0 is shown by the increase
in the coefficient from 0.16 to 0.22 when the flap was added. Both Fe and 6PT are the average values from both ducts, which showed no significant difference.
The coefficient of pressure drop across the engine .
6Pe presents a comparison of various exit-slot arrange- ments for both the NACA co w lin g and the wing-duct system .
In the hi g h-speed range, t h e wing-duct system gave values
of 0.50 (or ~Pe/q = 0.91) and 0.35 (or ~Pe/q = 0.63)
for exit-slot widths of 2.7 and 1.3 inches, respectively, as compared with values for the NACA cowling of 0 . 36 (or
~Pe/q = 0.65) with the cowl flaps open and 0 . 27 (or
~Pe/q = 0.49) with the flaps closed. The effect of the
wing-duct system for the ground condi~ion was marked. The coeff~cient increased from 0 . 02 for the NACA cowling with , the flaps open to 0.11 for the wing-duct system with a 2 . 7- . inch exit slot and to approximately 0 . 15 with the additi on of the cowl flap.
It should be noted . that, in the install a tion of a wing-duct system on an airplane to which it is more easily adapted than to the A-17A, such as a large multiengine airplane, the problem of duct design would be considerably NACA Technical Note No. 813 13 easier. The duct losses could be made substantially smaller than for the A-17A, and greater engine pressure drops would then be available or, if the engine pressure drop were held constant, the cooling power could be ac- cordingly reduced.
Maximum Speed The results of the full-throttle runs are listed in table III. The quantities ~isted in tho column headed 110bserved" are the values actually found in the runs. The quantities tabulated und~r the heading . "Adjusted to 10,000 feet," have been corrected to that altitude, as mentioned in the section on Reduction of Data. The data appear fairly consistent, with the exception of two evidently low values for the NACA cowling. The probable mean values of the speeds are estimated as 203 miles per hour for the NACA cowling, and 210 and 213 miles per hour for the wing-duct system with exit-slot widths of 2 .7 and 1.3 inches, respec- tively. It was not possible to evaluate the effect of the wing-duct system on the drag of the airplane from these data because the maximum speed was affected by a number of other changes whose influences could not be separated. The increase in maximum speed appears to be the combined result of decreased drag , higher propeller efficiency, and possibly greater engine power.
CONCLUDITIG RE M ARK S The ground cooling for th3 wing -duct system without cowl flap was better than for the NACA cowlin g with flap; with a cowl flap added the ground cooling was appreciably improved. Satisfactory temperatures were maintained in both the climb and the high-speed conditions, but a larger quantity of cooling air appeared to be required for the wing-duct system with the conventional type of baffle used.
It was impossible to evaluate the merits of the wing -duct system with respect to drag because of the number of other chan ges whose effects could not be separated.
Langley Memorial Aeronautical Laboratory, National Advisory Committee for Aeronautics, Langley Field. Va., May 22, 1941.
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exit- 2.7
9 IT
32 35 tempera 10,300 -=~ altitude, --- 355
305 405 395 275 345 385 260 --- 325 355 290 245
--- adjusted --"-'56~1 __ OF bF I
to 1 _ I
41°F system power; Vlidth,
---"-1
to 34. 13 11
385 340 380 --- .320 350 --- 340.360 335 235
air! air, 295 .390 --- 270 250 280 ixture ARRANGEMENTS OF slot 3000 free-air 55 M best pressure L..---"5"""O ~s~,_u~:F~~ _ _ I
I
e cooling OF free free ~r~i~ ~'-T-I of of 9 6 5 2.7 Q6 baffles, 60 a.ir --- 300 305 390 380 270 33 375 255 --- 290 310 2 80 .310 235 3() ,"-:4 --- altitude, tho. t that ft; erature, rich;
I I I
Wing-duct -
free COOLING-SYSTEM mp rouM width, - te -6 F ...
36 t h 60 bove Qv~cesso. 57 10 of full 9500 o --- 335 - 320 315 310 405 375 265 0~ .375 255 315 280 235 a above ---
--
4.0 to I
t>reSEure I I I
that rise rise VARIOUS t o ture 39T 57 10 L 57 14 txture 350 32 38 --- 330 350 --- 3.35 235 H ~_38 300 395 250 255 270 ---- eX1t-slot in.; 3000 free-air - 1 5 era - ture WITH tno IJli3.35 above -- I ra te temoerature
__
open 72 90 46 22 ft; tempe 305 --- temperature 3 35 375 3 37 --- 250 180 235 280 265 220 245 190 295 FLIGHT ------1 ::==-- air.
I
I
rich; -- rtment fully - cowling Temperature 72 89 4.3 22 8 5 temperature, p a altitude, 10,000 --- 310 360 310 .3 --- 270 335 185 245 270j m 235 39 0 245 200 295 full ---- ------ I co to 31°F NACA flaps CLHIBING Coolina-air Coolinp;-alr to 55 68 19 ___ 340 340 315 395 310 --- 310 375 205 300 280 240 195
- 3000 ------ ------
'.1i"xture ~owl pressure f'rge-air 36 r;fLE ' t t gh -do- -00-1 -do-l -do- -do- -dO-1 err- ef Carburetor-intake Left; -do-- of Accessory --do- --do- --do- Ri --do- --do-.365 "--do- Side gine Left Ri/1h L RiM - - --- FVLL-TrlRO bank Rear --do --do--- Front --do-- --do- --do---I--do- --do--- --do--- --do--- -do--- --do--- Front --do--- --do--- --do--- AIRPLANE Cylinder Ii'i 4 4 4 4 5 5 5 5 A-17A 11 11 11 11 12 12 12 12 number COOLING ON Cylinder F F - F F R F R F R R I.
, p1ug,~ plug,R plug, plug,R plug,F p1ug,R plug, plug,R of froX't; rear) TABLE Location arre R, (F, Spark Barrel, Barrel, Spark B~rel, Spark Barrel, Barrel, Spark Spark Barrel, Spark Spark B Spark I l-hermocouple ~re.1., ~ >-t ~ ~
= o ~ CD o ~ ~ ..... ~ c+ ~ : • m ..... ~ ~
>-f N
J I
ID
ON 3Io 430 295 ~5 430 270 :370 4.10 315 410 405 260 215 ---,..f 440 T.3
10IiJ3 ~ ----s-
-
TS 10,070 :IJ'
I
I
r
1E I.
OF OF
9-r-
GE 42 ~
0-
N system 395 385 340 395 240 .3.35 365 370 365 2.30 212 F .::ov 265 290 14.3
F ---
air, Wing-duct 0 atr 10,070 -
I ! I
ARRA VF free free 02.7 8 0 of of 48
~gr
360 365 305 340 390 310 360 .320 6.6 192 baffles. 395 266 250 405 235 NACA . l'r2". 9000 ...:::e~a.;;:i.:.r...l.--;'_---":"",,,,_
cowling ======== "
I
accessories.
that tho.t _,
-I
rouAA --~ o.:.f--=-f.;.r...::: t COOLING-SYSTEM over t h t of gh Side FA Left RbQve above engine
~~~~t ~f~!t Ri
th ---do---- ---do--- ---do--- ---do---- ---do---- ---do---- ---do---- ---do--- ---do---- ---do---- ---do--- ---do---- ---do---- I rise rise ---~--J--n5r··~ ture VARIOUS ..
l'a rpture bove
_
H ture ture ank &.
b Front Front Rea r ,'nT ' Cylinder t,enlpe t emoe ----do--- ----do--- ---~o-- ----do--- ---do---- ----do-·-- ----do--- ----do--- ----do--- ----do--- ----do--- ----do--- ---do--- ----do--- ture mpera er t elliPera te
d
lt, ir, -------- Jel·a nd & FLIGHT ..
ir 4 4 4 5 5 5 ltl~r 4 5
--
11 11 11 11 12 12 12 12 fi number Tern - Xt.
Cyli f-.ke IIJ& I nt LEVEL R, olitlfl. -i F F R , R le ,F , , rcQJ o of Coolin~-alr Co -_.--_.- t; F R F ug,F
r:, _ F R F R R
I
_
etor cou on --- j plug, plug,R pl plug plug plug plug plug,R r mo fro ti esso bu rk rrel rrel, Cpr _. AcC'
_
'.-'--
(F, ther Ba Barrel, Spark Spark Barrel, Barrel. Spark rtClrl Spark Spark 5a Barrel) Sparl' Spa Spark TLoca
I
1,-- 1 L ,Barrel, __ I N FULL-THROTTLE °F -~rrel, drop water
-=--J
AIRPLA3E closed.
__
___
-
ft------ h-------
___
itl;------- in.
j"p ture.
J COOLING A-17A fully th, - pressure ine p~ r ",id r eng l~ltude, s.?C:t:;d, tem II.
flaps & r r g-ai oss r ai t-slot e-ai ac TABLE ~Cowl
--
Exi Coolin Density True Fre
_______
/--
F
~ ~
o >oj <D o g .... () e 12: o n- et IZ: o m I-' ~
0-
'I r ~
' I I
--J
apeed, to m) ft 415 ~~I 2230 2250 2390 2370 2360 2360 2;360 2360 2360 2400 2410 2410 2395 2400 2395 2425 2J~35 2435 2430 2425 2 2440 2 2410 2400 2415 2400 2385 2400 24,'30 2430 24.30 2450 2435 2435 2435 2435 2465 (r EM Engin, ! I f I , SYST NG- ~O,OOO apeed, V 4. 0 (moh) 11.0 10.8 COOLI 188.4 190.4 201.1 206.5 204.1 203.7 203.0 203.0 203.2 202.8 209.0 212.1 209.3 208.5 212.5 211.8 2 211.9 208.1 209.8 210.4 211.6 211.9 210.2 208.6 211.7 212.8 211.6 211.8 212.0 21 214.8 212.9 217.2 212,8 213.~ 214.1 2 216,0 Air i f
I
~-.aJUatad VARIOUS ) .peed, lJ 0 Ne 400 (rP 2270 2260 2350 2360 2360 2360 2360 2360 WITH 238 2370 2 2410 2410 2395 2400 2395 2425 2435 2435 2430 2435 24."50 2440 2J~15 2410 2400 2415 2400 2385 2400 24m 2430 24.'50 2450 2435 2435 2435 2440 2465 Engine i RUNS rved ilc .3
Ob ° ° 0
• LEVEL "eed' . .
V 9.2 12.2 CE:.3 12 15.1 19 2 203 193.0 206 20;3.6 203.2 202.9 202.9 203.1 202.7 20 2 212.0 2 209.7 208.8 210.2 210.7 211.8 212.0 211.7 210.0 2 212.7 212.0 211.1 212.9 211.8 212.0 212.0 214.2 2 213,1 217.4 213.0 213.4 214.1 212.3 216.J4- Air I--_~Eh) ! I I
t I f
--
AIRPLANE
- __
e uO 00 itud (ft) ,3 A-17A 7,100 9,000 9,000 9,900 9,800 FULL-'l'P.RO'l'TLE Density 9,950 9,950 9,900 9,850 9,800 9,850 9,950 9,950 9,100 9,100 9 9,900 9,900 5.1,950 9,950 9,900 9,900 9,900 9,850 9,900 9,900 9,950 9,150 9,900 9,800 -r 10 IJ,.3uO 10,300 10,100 10,1 10,100 10,100 10,000 alt 10,000 O:
I
I;f ir
ture
a F)
e-a 8 7 7 7 ( 31 37 59 59 59 56 56 56 56 26 26 26 26 25 25 52 52 52 26 26
25 50 51 26 26 25 26 25 50 51 51 53 '9
Fre
! ~empeb I
np.FORHA~CE ARRANGE&ENTS ; - In.
in.
sed In.
2 2.7 1.:3 III.
clo cowling; t-slot t-slot t-slot ldth, ' 'l'ABLE exl system; exl NACA flaps width, Wlng-duct lI Wing-duct system; exl width,
I
NACA Techn ical Note No. 8 13 Fig. 1 ,
j
I
I I .
~ ..-4
"
H j,':
\
\ ..
\
<
~ ..Q +> ..-4 j,': Q) cd
"
H p., s..
. ....
cd ~ H I ~ ~ ~ Q) . ....
> s..
Q) +> s..
~ C' I Q) ~ I .
H t1 s..
~ .....
~ riga. 2,3 NACA Technical Note No. 813 Figure 2.- Front view of NACA cowling on A-17A airplane.
Figure 3.- Side view of NACA cowling with cowl flaps open on A-17A airplane.
.
.
ei- Z
z » () » ..., .. o ::r ::l .... o II> ~ z o .. o Ol CN '"'1 ~
...
0'1 -l WING --.
/"' /"' /' WHEEL /'
I I I
;...
INTA!(E Uf NG VANES I WALL R-n O R FIRE
-'-~l- DIFFUS GUIDE
URET TANI( r CARB CARBURETO
( ~------ --
-- -- - .... .
--
~
TION C OIL \ .
SE NLET I
tb-.,.-,\::c
AIR (ENGINE, COOLER CARBURETOR) WHITNEY MANIFOLD 1535-13 MOVABLE & R- ST ~.
TO f-
ENGINE Moon EXHAU ER PRATT
PPORT
D YLIN .
C
I
_J. AIRPLANE·.
...
COOLING :.,.:> kl7A
»9U
o.6 ~.i
ON
~
G-DUCT DFWI N - INSTALL ED 20r' AGRAM I DI AS - 4.
EM SPINNER RE ST SY ~ '1<\1 FIGU "'l Ul z o e+- (1) Z 9 ~ V> z > C'l > ., (1) () :;Y' ::l 0' e.
aq ~I I / I ,/ / I / _/ I / J / / /
I OFWING--DUCT
I
J
I
I
/
I
I
I I I I / PLANE..
24£
R DUCTS / AI I " / _/ I / CE I 1'1,f
I I I I I I I
VANES / ,/ A-}7A I J ./
/
ON ./ I
-
/
\ , / GUIDE ENTRAN 'J \ \ \ / \ \ \ VIEW / OF / \
--
) \ / TOP INSTALlED ./ AS DIAGRAM - 5.
SYSTE.M E' ht- ~ 0- !.
F IGUR COOLING ;- 'I- ">
T
I I I I ( /' ---; - I
1/1/
- --
--
" ''-- /-----; / IEW 8.6" V ~r ~ -- \ ;--- \ FRONT 0- -1<0
1"
NACA Technical Note No. 813 11gs. 6,7 Flgure 6.- Front view of wing -duct cooling system on A-17A airplane .
Figure 7.- Slde vlew of wlng-duct coollng system on A-l7A alrplane; exit-slot width, 0.6 lnch.
NACA Technical N ote No. 813 Figs. 8 , 9 Figure 8 .- Installation of wing-duct cooling system; the accessory compartment, the right exhaust cutlet and shrouding, and the right duct, before being faired.
Figur e 9.- Cor.lplete insts . llation of ducts on A-17A airplane with wheels retracted.
Fig .lO NACA Technical Note No. 8 13 600r-~~~ --.--.-.--.-~~~--.-~-.--.-.--.-''-.--r-.--.- o--.-,,-.-, ~ I 0.500 . , w dt , .7 :n 6 m' , W i s st t- 10 j..., g- uc ex , ......
ro ....c> I
4F PR
_x~ ,:l ~ ~ 5 R
-
~100 .-y k -. 5P j..., ~ .... , '.. ,
~ ~ E ~ lot:'
'H
=-
~ !
4B Q) ;; ~
~ ~ ...--'
1 1 ?1 "' ~ 300 '" ~ ! ' !-~ .0 ff
V V -
"' 5 + 1
V/ II R BR
ro ........
Q) ~~
~ ~
..., 1/ I
If ro
So-.
Q)
If i
~100 I Q) E--< 500~+-~-+--~+-~-+~--+-~-+~--+-~-+-4--+-~~-4--~+-~-+--~ W ng du t ys em wi h ow f ap 6 of o 2 4 8 12 o 4 6 8 10 12 6 10 2 Time,min Figure 10 . - Time h istories of engine-cylinder temperatures for full-throttle ground operation of various cooling-system arran gemen ts on A- 17A airplane . Curve numbers correspond to cylinder numbers . P indicates plug; B,barrel; F,front of cylinder; R,rear of cylinder.
f-' f-' f-' l\:l z >- >-3 (l) () ::r- ::s ..... () ~ f-' z o c+ (l) z o CD f-' 0J "':I ..... C/l >- n Otl s Of' s ar d in in in t, t, laJ
1("
1.4 sl ( 0 ( x .7 . 3 .7 sl n .
xi ' , , it in in , it in! , • · 1 3 1.2 ~o l. 2 . 10 + ) --E ow 2i ---E --, .~o ~.
~ x t ~ t t.!lll n A d, t·jI- P""" ~ f-'o x ..
1.0 Ex Ex Ex op NA ~ V: c os ) ps V " propeller ( ( x ) .8 fl of ..
( in , (" in (h in g , ,.
it .6 .7 ap .7 1 .7 i.n~ V/nD ap ap o en f f f , , , co ow .4 ow ow CA ow 10 A ap '1 · ~lo N t t h h h NA ,- .2 x t i Wi ~x Wi -E _. -W -Ex ,Exit .
_. - -- .'
--' -' -- .
- - -f-:: 0 0 o .8 . 4 .2 . 6 . 4 .4 .2 .6 . 2 .6 D2 D2 e D2 __ l>p ~ pn pn2 pn2 ~ any of .
duct of '" 16 cooling- ai fAl of blade- ; entering
uc 10 !ooling
~ '''' ~.
i 14 APT' t. oil airplane.
airplane high ;"'" " ~g- 17 ~r operation mouth >Jy P.ll 2 . ~~ -duct Wi of at , em (excluSlve - - ur ound A-17A A-17A -"'tJ - \Tst wing engine; inside s L gr -- on on - b t era I-- n 10 for engine , , ;u :l.u'c hy ~5° Propeller O.
t em across min , temperature and = wUl ~ pg- fl'IT PF !-.- cowling pressure A.i 68 of Wi -wi IPs ~ur V>-<--~ drop Time, duct V/nD ---- static.
Pe' wl a full-throttle arrangements NACA !era c:-..- ; coefficients for
~ !em]: ~
t for and across lir: r histories pressure
V V
ai , CO\\
;V ,,/ except
; entrance); drop system Time engine Pressure free-stream CA en V
V
/' oJ .- to NJ cooljng-system duct
l/
11.- setting /
:J
cooling-air at pressure
o
60 40 Figure various air loss relative angle Q) 81 ro !-. Q) !fl20 Q) Figure APe, +" +" ~ <S 1=«200 o