— _— —.. J ,. /. ,. ARRNO*3E31 -. — NATIONAL ADVISORY COMMITTEE FOR AERONAUTIC&~sm WAlrmm IUIPORT ORIGINALLY ISSUED May 1943as Advance Restricted Report 3E31 THE USE OF A RETRACTABLE PIANING FLAP INSTEAD OF A FIXEO STEP ~ A SEAPLANE By James M. Benson snd Ltidsay J. Llna LangleyMemorial Aeronautical.Laboratory Langley Field, Va. NACA WARTIME REPORTS are reprints of papers originally issued tv provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but =e now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution, L- 237 / https://ntrs.nasa.gov/search.jsp?R=19930093612 2018-05-20T01:11:54+00:00Z
Transcript
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J,./. ,. ARRNO*3E31
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTIC&~sm
WAlrmm IUIPORTORIGINALLY ISSUED
May 1943asAdvance Restricted Report 3E31
THE USE OF A RETRACTABLE PIANING FLAP
INSTEAD OF A FIXEO STEP ~ A SEAPLANE
By James M. Benson snd Ltidsay J. Llna
Langley Memorial Aeronautical.LaboratoryLangley Field, Va.
NACA WARTIME REPORTS are reprints of papers originally issued tv provide rapid distribution ofadvance research results to an authorized group requiring them for the war effort. They were pre-viously held under a security status but =e now unclassified. Some of these reports were not tech-nically edited. All have been reproduced without change in order to expedite general distribution,
Data are presented and discussed to show the im-provements in both the hydrodynamic and the nerodynamioperformance of a secplano that could be obtained If aretractable Qlanlng flap were used instead of the con-ventional main step. Z%.e improvements in resistancemade poeEible Iy ‘a~e of a planing flap to vary the depthof step (?:arin~and efter take-off are of the order of 8percent in the water raaistance a: the hump speed and&i”DOUt2 or 3 percant in t] e total air drag of a loneraxge fiyin~ 3Gat of c~~..,.:hdesigu at cruising attitude.One ty”~e of retractable flap that could be used is de-scribed [~nd the results of hydrod:~namic stability testsof a maclel fitte~ with the flnp are given. The tests in-dicated that very good stability characteristics could beprovideti with the planing flap for take-off and landing.
IITTROI)UCTIOIJ
In the design of the conventional flying boat, thedepth of the main step la the result of a eories of com-promises. DurinS the take-off, a ehallow step is desir—able for low water resi.stanoe up to and including humpspeed; but a iieepor stop is essential at hi@ sp~ods toa~oid excessive water resiatiance and violenv Instability,While the seaplan6 – partio~larly a long-range seaplane -ie in f~ight, tha step I;ay account for an ihportant frao- “tion of the para~ite drag. Devic~s for retr&ot?.ng orremoving the Gtep in tlidht are frequgntily ccins:dored asa means of. roducir.g .tho ~.ir drag, but the improvement tobe obtained has appareut~y been lnsufflci~nt to warrantthe devGIOpmOnt mud adoption of such dwricos. If a r+tractable device can be made to l~provo the take-off
2
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performance as well as to docreasc the air drag, itsvalue may then become sufficient to warrant installationin the seap?.ane.
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Thk report includes a limited colicot~on of data toindicate the mount of Improvement in air drag and inwater resistance that may be obtaineJ. by the uso of aretractable planiug flap instead cf a fixed step. A flapof the t~’l>erequired is descrioed and the results of testsIE iqACA tank no. 1 of a Lynmlc model cf a flying boatthat had teen fitted with scve~al. arrangements of theflap are preGented to show the effects UPOU stability du~ing tcdse-off and landing.
EI’33!ICT
Water resiotence.–
01”DEPT~ CF STEP
Tank tasts have shown that atspeeds be?.ow aati at hump spee~ a saall depth of step is .desirable for low w~ter resistance, For example, thedata in rofersnce 1 show that the resistance at best trimwill be about 8 pel-cent lower for a step having a depth .cf 1 perco~t of the beam than for ono having a depth of “6 percent of the hem. .4 relatively deep step is requiredat speeds %ctwoen humF speed :~nd gat—away speed hecav.sean irisufficient depth of step nay result in excessivew6tting of the nftgrhod;~ and rapid increase i-a water re-sistance just prior to the ~st-awoy, vhich ca:l entirelypre-.-enttrike-off. (See ::eferences 2 and 5.) In order toavoid thi~ excessive wetting, a depth of step of n~t lessthan 5 percent of the beam is flener-,ljy considered neces-s~ry; and in some hee.vily loaded flyi~g 3oats a &epth of .step of as much as ‘?percent of the beam IS u~eil.
ZWlc St:~k4w.- The data in refer enoe 4 in-dicate ~~l:bt m decrecse i~ depth of thO CII~VO~ti.OIId 13b0preduces the lower trim linit at and near hump speed, wherelow-angle Forpoising is most likely to occur, but that athigh spe~~ds, where the h?.%h—:mgle t~pe of per-poising pr -se~ts a problem, either s relntl?ely deep step or venti-lation of c 3tep oF lea~er depth irJ essential.
Air drag. - Tno effect of the depth of stop on the air
drag of a ful.i-size seai]lene float has been determined byteets in the NACA propeller-research tunnel, but the re-sults h~ve not yet been published. The float was of a
type currently used for +n airplane with a normal gross “load of 5S00 pounds. !Chs form of “the original float ,with the successive ohanges, “is shown In figure 1. Th e“step was reduced from the original depth to one-half th~original depth and to zero by successively filling outthe after body. The magnitudes of the air &rags at zero ..pitch - which are practically the same as the minimumair drags - have been tabulated in figuro 1, and tho ef- -feet of reducing the depth of step is apparent.
Additional data on tk.e oi~oct of the depth OS step~ hulls and floats are given in refer-on the [Lir dr~~ ().
ence 5.
I!XS CRIPg ION Oii’PLAHIKG I’LJP
Nunerous arrangeine~ts hsTe Been suggeetod ~;herebythe air drag of a hull nay be reduced by fairlng the otepin flight. 3’l~ro 3 ehovs one of the eimFlest arrange-ment, which wcs represented by tho .fairing ueed in thefull+ scale tunnel tests referred to provlousl~. Tlle
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transition flzkp shown 16 a surface hinged at about 1 beamlength abaft the step and is defiected in flight to ro-dnce the depth of the step to zero. One advantage of thistype of flap is that the loads imposed by the water reao- .tions occur when the flap is seated against the mainstructure of the hull. In the extended position the onlyloads on the flap ere the smaller loads Imposed by theair flow.
Figures 2 and 4 I?.lustrate a type of flap that of-fers interesting possilllittes in performing functionsother tkan the ~educbion of the air drr.g. This flep muybe used to reduce the we,te? resistance at and near humpspeed end to impaove the stalllit~ characterigtlcs duringtake-o:f and Ian&ing. .4 tan~svarse axis is fielected atov slightly ~.hove the china~ and at a suitntile distance~or:w==~ of tkO s~ep= Zhc ?laF is a movablo section ofthe hull, having a V- ‘:ottom vith ch!aa flare, if desired,ard lfJboun?od on the ufte= cnd b? a c~lindrical surfacahnving as its center li~e the hin~e axis of the flap.OC the forward end the flap is bG~mied by a surfaceformed by rotating a t%ans-rerHe soctiou of the V-h:ttomabout tlze hinge nxis. The oxtont of tk,e c~rved surfacesr.t ths ends t.eponds ‘~pcn the anguler de::lection requiredand upon the etructurai details. Zhe thickness of theflap vould be sonowhP.t great~.r than the vertical distancefrom keel to chiiia. Qhe resulting %oxi?he structurewould te of ebout thg came type as would pro%ably be r~quired in any for:: of planing flap desflgned to withstandthe Tressures derolo:,gc on the fore-~otly in the vicinityof the step. Th~ flap mcy eesily be adapted. to Frovid.Qvcntilction by means of &icts from the sides above thechino of the flap to the after end In Grder to dischnr~eair through the z*iser of tile main step.
Althou@ the present discuss~.on is confined to con-sldermtion of the main step, the type of fl~.p deucribedin the foregoing paragraphs may be used at other ~laco~on ths Tlaning botton. Thifl type of flap offers r.rele.-tivel~ sim?lc salction to the problem of incorporatingchino flare in the flap and of dofleotlng the flnp with-out opening e. gap at the ~eol. Qhe plr.n form of the stepshown in fib%re 4 departs slightly from the straighttransverse form (with a vertical step) that is often used.The departure may, however, be made so small th~t the hy-drody~umic Fropertles wtll not be affeoted a~preciably.For special applications the trailing edge of the flap
may have any of a wide vnriety of shapes and“a-s-tep resembling closely almost any form ‘dfpointed step.
3u5 DIM C~Il?TIOH OM HODEII
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may presentV-step or
A dynamic model of a flying boat waa teOted in NAOAtank no. 1 to investigate the effect on the dynamicstabiltty of fitting flaps of the type shown In figure 2.The model is similn,r to and about one-half as large asthe model used in the tests la the full-scale tunnel,whloh was previously described. The hull of this modelis outlined in figure 2. !lho construction of the modelfollowed tho usual >rnctice at IIACA tank no. 1 aa de-scribed in reference 4.
DimeQ3ic:ns ar,d we?.Ehts of the basic model, which 1Sdenlgnated i?f.GAngd.el 1C4, are as follows:
qhe moment of inertia is a scale valuFJ t.vpicr.l ofcurrent practice in the design of large Ily:ry .~t.~,-:n.Thed-j~t~~ce ~~ tl~a center of &raVity fo~l?:~~ 1? ‘-..”>;.~~ wasatij~sted Cur.‘~g the tests as requi..”e~ L71 Gl:..2li ‘ble. tr~mlimits. q],= gli96s load ooefficicnu is e.~r~s=ed as
CA o = Ao/wb=
6
where “
A. initial load on water, pounds
II maximum beam of moJ.ol, i’eet
w spacific weight o: ‘;atar, pounds .por cubic foct(63.2 lb/cv. ft for tkc water in NACA t~nk no. 1)
—.,——. -. ,--- , -, ,, -,, ,.,, ,,- 11 ■ ,,
... the mo,del ran stably aq.d.of the maximum and minimum trimswhen porpoising occurred. The rune. were re@dat”6d’for ‘-several positions. of the center of gravity to deterr.isethe fore-and-aft range for which porpoicing would notoccur with either full-up or neutral elevator.
~ st~. - Observations of tho behavior of
“ the model on landing were made hy flying the mclol offthe water, decelerating the towing carriage whiio theelevator of the model wae adjusted to obtain the desiredtrim at contact, and. then noting any tendency of themodel to skip or porpolso after landing, The rate ofdeceleration was approximately the same in emch ease.
RESULTS AND D ISCUSS IOIT OF SLAB ILIIT !KSSTS
Qnitins ~csitlons of centt.r ~f f~b~rity.- 11i,..-r.re 11shows the variation of trim with epoed for neutral P.ndfor full-v~ eleTatOr with ths centez’ of ~avity at t.kree “dlfferont loc~tions, Na porpolsing occ”azred vith thecent er of gravity at 36-percent or at 40-fer cect nomaerodynamic chord. With the oenter of grnvity at G> “.percent mean aerodynamic chord, no poryoisin& occurredwith f-~11-up elevator. lflth nWtJ?iLl elevator and withthe center of ~mavity at 34-~orcent maaa nerodynamlcchord, however, the trin o: the model pa~sed below thelower llrait ai about 29 feet per second and $Lo lo-anglet~e of porpolaing followed, Conpariso~ cf figure 11 withfigure 10 chows that with full-up e:.evator and with thecenter of gravity at 40-percent mea~ aeroti~nnmic chord,
e
the trim of the nodel nt a speed of about 40 feet pernecond was near the upper branch of the upper limit andthat porpoising might occur if the model were acceleratedat a nuch lower rate through this unstable region nearget -away. ~he plots indicate that the stable range ofpofiitlons for the center of gravity is frcm about 33to 40 percent of the mce.n aorotlynmic chord if tho stable“ra~~e is defined tiB that ran~o for which porpoising willnot occur with either neut~al or full-up elevator. O&.~~~~fi~~, the) stable ra~lge will be infl.-~enc~d to an im-pcrtant extent by t~le effects that thrust, slipstream,and variations in tho defis”,tion of t.le aerodynamic flapsV:Ill h{~ve on tha tr ia cnd on the wi..g lift, Tho range of7 percept , althsugh smeller CS comFarod with that .--hickIs comnonl~’ prcvidod fo:- in flight , is typical ot’ thevalue obt~ined in test~ of con~snt ional dynamic nodelswithout powered psopeilers.
2he forcgoiug intcrr=etatlon of the datn cbtei.nedduring the accelerated. ‘:r.ns Is b&s Gd OE the criterionsfor str.billty as prop:sed %y Stout (reference 6) to as-sure tb.at a seaplane will hc h~drcd.,-ncinically stable forall :~o~itio~s of the contei’ of gr~vity likely to occurin pr~ct ice. !l%e coccept of a stable rango of the pos3-ticn of tha center of #Jkav!t~ is eesentlal and nust bedenlt wtth ZG practice, but there may be doubt a~ to thetrimmi~.~-aonunt cr iteri ons that should be uced. The cri-terion that bcth tull--up and neutral elevator aucit be~vaii.zlle without caust~g excessi~ e porpoi~ing nay Inso~e caees he uwccessr. rll>- conservative. If it i.S aS–Ewed that the pilct w511 te,ke precautions to avoid por-poisin~} the noJ~2 wi+h tie planing flap will pl*oLablyhcve u saticfactcry r.nnge of stn”~le pocitions of the cen-ter of gravity. in a specific design the lGcatlon of thestep relabivc to the wing Hay differ from that used inthe present tests in order that the hydrodynamicallyctablo ran~ei be within the range for which the seaplanewms d~cigneil to fly.
.is:c~.~~g● - Cbservr.tiouz on the bahavior of the modelafter i~.~di]:{~a~e listed in tabie~ I nnd 11. ‘Mo shortflap t!eflectcd 7= cazced very se~eru skipping after land-ing cnd fo= that reason alone pro babl;r would be i~prac-ticabie. ‘2he tr ia li.zits for the short fla~ ehcw that ahigh pro ba’oiiity of skiFplnG cr some form of instability ‘should be o::pectoi!.when a l~mdiag Is made at tr iao greaterthan abc-at 4° bocuuse cf the unfavorable lowor brnnch of
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t~e UPPer itrn~t. The slnklng speed of most landings wouldk.,-.be “e’ufficSent to provide “an ihpulke-”thdt--wduld”-titilikelyto cause the h~gh-angle type of porpolqing to appear attrims considerable below the upper branch of the tipperL
~n limit.yd When the model with the long flap was landed at some *
of the higher trims, skipping occurred. In general, themodel with the long flap appeared to have a slightlygreater skipping tendency than did the basic model withan equal depth of step. The type of motions involved,however, were much less violent with the long flap thanwith the short flap.
The phenomenon of skippkg nay be considered as in-volvln~ one or more of ~t least three different types ofinstability. The first, and nest Important type, is thatinvolving ‘stlc!cin~’11and is commonly asmoctated with in-sufficient depth of step. If the supply of inflowing air.aft of the step is Inadequate, rather l~ge ~egativepressures occur intermittently OJ the nfter%ody near thestop and cause rapid fluctuations in the draft of the sea-plane. !I%e motions that follow are usunlly violent andthe seaplane may leap clear of the water at epeeds andattitudes unsafe either for flight or for l~ding. Thistype of Instr.bility nay be prevented by fui’nishing annmple suppl,y of air ei.tho-+:~y an iucrense in the depth ofstep or by tl~e use of relubively large ventilation ori-fices at tha step near the keel.
A second type of instability is merely a recoil thatoccurs with no change in trim and has been observed dur-ing tnnk tests of siagle planing surfaces being towedfree to rise at fixed trim. Planing surfaoes have bouncedclear of the water several times after being dropped. intothe water with a light load at high forward speeds.
A third type of instability is the result of a dif-ference betvreea the equilibrium attitude while the sea-plane is I.n fllgh.t and the attitude it assumes after italights oa the w~ter, With the center of gravity wellforward, eontaot with the water may cause an immediatedecrease in trim, which reduces both the lift coefficientof the wing and the plmiag coefficient of the bottom. Areduction in either coefficient will cause the model tonink deeper Into the water. If equilibrium Is approachedasymptotically no bouncing ocicurs. With the center of
1 — —
10.
gravity well aft, an Increase in trim will probably fol-low the landing aEd both the wing and planing bottomwill gtve aa upward inpulse that will be followed by adownward motion as the forward speed decreaties. Thus ,forwa~d positions of the center of gravity add dampingto any ckipping tendency; whereas aft pcsltlons tend toaocen%uc.te this type of instability. This effect of theposition of the centex cf ~rcvity is shown my comparingtke data In table II for the ceatcr of gravity at 28-perceat rnena aerodyaauic ciiord with the results for thecentev of ~rc.vity at 40-per c~nt Eeen aerod~mamio chord.
Phe results cf the sta-iility tests indicate that the~iole~t type6 of instm~ility mar ke avoided If both suf-ficie~t &epth of step :s pvovidod and the planin G bottomo? t>e fo~ebody AL Gtvalght longitudinally for n distcmceforwarc G: the ~tep aqr.al to about 2 been length. 3othconditions aFEe~ to be bati Sfi Od if a ret Yacta31e flap “kavinG a length e ual to tho beam is ‘ased with a &eflec-tlon of ahol-.t 2.2 ? or possibly ne much as 4°.
A retractable plcning flap mar be used Itietead of afixed step to Tary the depth of step during and aftertakeoff in order to iower the resistmce both on thewater and An the air. Such a Zlap may also be used tolmpro~e tho hydrodynamic stability characteristics. 1’ora lon~range flying boat of current deeign, the possiblereduction in wzter ~ecistaace at hump Epeed will be about8 percent. The reduction in air dr~~ of the completeflying boat at cruisi.~g attitude will he of the order of2 percent. The planing flc.~ m~v be uzed to improve sta-bility characte=istica b~ makiag possible ine use of ashallow steT at hump speed and n deep step at high speeds.The shallow step would increase the effectiveness of theafterbod.y r.t low speeds and would thereby Increase thespeed at which low-angle porpoislng could first occuriiurlng tak-off. The deep step at h~Gh speeds would aE-
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11
. . sure aaple olearaqce .of the after body and would therebyremove to a large exteat the probability of ‘sttoklng “andthe associated type of high-augle instability.
P~la Langley Memorial Aeroriaut30al Laboratory, “
National Advisory Oommi.ttee for Aeronautics,Langley Field, Va.
REI’IELEHCES
1. Bell, Joe W.: The Effect of Ilopth of Step on theWater Pcrfor~ance of a Flying-Boat Hull Model -U. A. C.A. iiodel 11-C. T.N. ITO. 535, NACA, 1935.
2. Truscctt, Starr, Parkinson, J. B. , Ebert, John W., Jr. ,art 7al Gntiao, E. Floyd: i<ydrodynaaic and Aerod~—nemic Qestn of Moileli3of 3’lFing-Iloat Eulls Designed”for LOW Ae~o&ynamic ~rcg. ~.~. 2:0. 668, lThCA, 1938.
3. i2iekl, Yal.ter S.: A ~iscuesl~n of Certain ProblemsConnocted with the Deoign of HuIIG of Flying Boatsazd tho Use of General Test Data. Rep. Ho. 625,~7ACA, i93d.
4. Olson, Roland E., and Land, Zorrnan S.: The Longitudi-nal Stcbility of Ylying Bents a~ Determined by Testsof Models in the XACA Tank. I - I1etLods Used forthe Investigation of Longitudinal-Stabilft7 Charac-teristics. HAOA A.T.:::.,MOV. 1942.
5. Hartmaa, Edwin P.: The Aerotiynamio Drag of 3’lyin==Eoat Hull Models as Measured in the XACA 20-YootWind Tunnel - I. T.N. Ho. 525, 1935.
Figure3 .-Profileof model with transition flap behind step.Dotted lines show positionof flap
extended in flight.
I v“ I v
I (d) Transverse section through hingeaxis of flap.
(a) Flap retracted in flight. Here the keel and chine of flapfair into the afterbody.
(b) Flap deflected to form step.
—- .—
A
— Axis of flap
..~ ~ . ~.~ t3a@——— —__. —_ ——___ —___
1 Afterbody keel: I
(e) Plan fom of step. The departure from the—.—_ ————_ ———__ —____ . conventional, straight transverse fom
is small.0.12 beam~
(c) hmngement having larger angle of afterbody keel. Here the keel and chine of theflap when retracted are inclined at an angle between that of the forebody and fAAllONALALNISORY
afte?body. Dotted lines show flap deflected 2° below forebody keel. CUMMITIEEFOR AERONAUTICS
Figure U.- Sketches showing typicalspeeds and a deep step
alteration to conventional lines resulting from use of two arrangements of the flap for providing a shallow step at lowat high planing speeds.
A. I I0115 20 25 30 35 40(a) CAO = 0.87 8peed, fpa
E’lgure 9 (a, b).- b!odel 134PF. Variation of trim limits with epeed.Depth of step = 0.1% beam.
. . . . ...-. —.
,
!;1
-- .— ., . . . . . . A-. -—
I1
I-—-. - . ...— ----
—— .-—
z
10
Short flap, upper bran
8
6
L+
rm--l--r--’t-t-rr”urr””r“Speed, ?ps
Figure 10.- Comparison of the trim limits of stability for the basic model and for the model fitted With threedifferentplaning flaps. CAO = 0,87; depth of step = 0.14 beam; angle of keel of afterbody = 5.5°base line.
NACA Fin. I I
12
8
L+
(l block= 10/40B)~.
Center of gravity,~-percent M.!4.C.
1111111–11
e > f
/n \
1y % I ,
0I
4 -‘ be” 7. J ~~ [ ;
.— ___ L: -+’=0 -~ a
12Keel of planing flap 2.2°
-—
Y
~ ~ percent / y\ Elevator full up
v\,\ jk--
Ml / \% ‘ \ L ----+ f
/ ‘
~- 4 - \
cw ~ ‘ ‘\.+ \ Elevat or neut ral2 =.. ,.
‘ ‘ ‘[---- ,—
-.0 !
-4.—-..4.- 1
I4 ~-1
1- ‘F-i ‘*T1
___! . ...-. : --- .-. .7. i
+
t I+ I
12 _UO per cen t — —-- I
,=. J,
(’ \<I
\ ~ ~—J . ‘ Take-of f
8) —(>
‘\45“ 1 .1 I
—. L . . . . —..- .-— —— ..—\
u, . /~ “\ \ ,—
‘1-’ ~~ -- .1 I \ :1I ! I I I } I I Y. I I ‘i
\ \/0
5 10; 151a 25 I m\35 u5 wSpeed, fps
-u
- Figure 11.- Model 134PF-3. Variation of trim With speed. Step depth = 0.14beam, stabilizer 50 up. CAO . 0.~7. ~le of pl~ing flap .2.20; chord = 1 bean.
