1952 gust-tunnel investigation of a delta-wing model with the leading edge swept back 60 degrees

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RESEARCH MEMORANDUM

GUST-TUNNEL NVESTIGATION OF A DELTA-WING MODEL

WITH THE LEADI NG EDGE SWEPT BACK 600

By Harold B. Fierce and Slaton L. Johns

Lamgley Aeronautical LaboratoryLangley Field Va.

NATIONAL ADVISORY COMMITTEE

FOR AERONAUTICSWASHINGTON N A C A

L u 3, WAl* -

p r i l 9,1952 L f Laogkr



1E N C RM L52BOh

i

NATIONAL ADVISORY COMMITTFX FOR AERONAUTICS

RESEAEGH FBMORAIiDUM

GUST-TUNNEL INVESTIGATION OF A DELTA-WING MODEL

WITHTHE LEADING EDGE WEFT BACK 60

By Harold B. Pierce and Sla ton L. Johns

A gust- tunnel inves t iga t ion of a delta-wing model wi th th e leadingedgesweptback 600 has ind ica ted that t he gust load i s grea te r thanwould be predicted by using a s lope of t he l ift curve determined f r o msteady-flow force t es t s . The use of a slope of a lift cmveder ivedfrom s imple aspec t- ra t io cons idera t ions resul ted i n a good estimate ofthe load.r

i INTRODUCTION

Gust-tunnel investigations of th e lo ad s on swept wings (refer-ences 1 o 3 ) have i nd i c a t e d that t he s l ope o f the lift curye determinedfrom s teady-flow fo rc e te s t s i s n o t a p p l i c a b l e i n a gus t bu t r a the rthat one dependent on th e sl op e of t h e l i f t curve of an equiv alents t ra ig ht wing and on th e co si ne of th e an gl e of sweep would be app li-

cable. n addi t ion , he results fo r th e swept wings showed that s t r i ptheory could be used to estimate t h e effect of gr a dua l pe ne t r a t i on i n t oa gust. Since t h e delta wing mightbe considered a s pe c i a l form of a

swept wing it appeared possible that a s lope of t he l i f t curve otherth an th at determined from steady-flow fo rc e tes t s would apply i n a

gust. A simple re la t ionshipforde te rmining the appl icable slope oft h e lift curve however, w a s not nmediatelyapparent. Accordingly, ani nve s t i ga t i on has been ca r r i ed out i n the Langley gust tunnel wi th adelta-wing model having th e leading edge swept back 600. The purposeof the in ve sti ga tio n was t o determine th e magnitude of t he gus t load

and t o determine i f steady-flow aerodynamic co ef fi ci en ts co ul d be useds u c c e s s f u l l y i n i t s predic t ion. This pape r pre sents he re su l t s of theinves t iga t ion .



2

APPARATUS AM TESTS

A l in e drawing.of th e 60° sweptback delta-wing model i s shown i nf igure 1 and a photograph of the model i s shown as f igure 2. The char-a c t e r i s t i c s of t he model and the tes t cond i t ions are g iv en i n t a b l e I.

The a i r fo i l was an NACA 65 006 sec t ion a t t he roo t and was tapered toan NACA 65,-012 sec t ion a t a point 1.5 inches from th e ti p. Thecon-st ru ct io n of th e model was such t h a t it could be considered a r igidbody fo r th e t e s t s . A n accelerometer was mounted under the forwardpar t of t h e f in a t th e ce nt er of gra vit y. Two l i g h t s weremountedonthe model fo r th e measurement of p i tc h in f r ee f l ig ht .

The gus t tun ne l and i t s equipment are desc r ibed in r e f e r e nce 4The gus t prof i les of the sharpedg e gust and 6.5-chord-gradient gustar e shown i n f igure 3 s t h e r a t io of t he l o c a l gus t ve loc i ty to theaverage maximum gust veloci ty as a fun cti on of mean chords of penetration.

The t e s t s c o n s i s t e d of e ig h t fl ig ht s through he sharp-edge gust

and seven f l ights through the gust with the 6.5-chord gradient distance .Measurements of fomardeloci ty ,uste loci ty ,ormal-accelera t ion \

increment, and pitch-an gle ncrem ent were made f o r ea ch f l i g h t .

Force t e s t s were conducted i n the Langley f ree- f l ight tunnel fort he purpose of de ter mi nin g he free-f l ight trim condition. A steady-f l o w slope of t h e l i f t curve was determined from t he da ta and i sincluded i n t a b l e I .

PRECISION

The measured quan t i t ies a re es t i mate d to be accurate wi th in thefollowing limits f o r any t e s t o r run:

. .

Norm al-acce leration ncrem ent, An, g units . . . . . . . . . . . . 0 05

Forward-ve loc i ty , ee tpar second . . . . . . . . .. . . . . . W sGust velocity,eeter second -. .- . i -. +O.l. . . . . . . . . . . .Pitch-anglencrement, 50.1

. . . .-

. . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . .

RESULTS ND DISCUSSION

The records of all f l i g h t s w e r e evaluated t o o b t a i n h i s t o r i e s ofthe normal-acceleration ncrement and pitch-angle ncrement during rav-e r se th rough the gus t . Represen ta t ive t e s t r e su l t s are shown i n fig-.u res ,$(a) and 4( b) . The maximum acceleration ncrement.wasdetermined



NACA RM L52sQ4 3

from the time hi st or y of each tes t f l i gh t . S ince minor v a r i a t i o n s i nforward speed and g ust vel oc ity are obtained f r o m f l i g h t t o f l i g h t , t h e

mhum accelerat ion increments were c or re ct ed to a forward speed of88 f e e t p e r secondand a gust ve loc i ty of 10 f e e t per second on th eassumption th at th e ac ce le ra t io n increment i s d i r ec t ly p ropor t iona l t oforwardspeed and gus t velo ci ty. I n add i t ion , he co r r ec t ed data werefu r th er reduced t o the valu es for zero pi tc hing motion by the approx-imate method of reference 1. The values of the maJdrmzm acce le r a t ionincrement f o r each f l ight as cor rected for forward speed and gust veloc-i t y together with the values reduced t o zero pitching motion are give ni n t a b l e II The averagevalues f p r bothgustshapes were determinedfrom the data and are i nc lu de d i n the t ab le .

Examination of t h e pftch-increm ent c.urv-esof f igure 4 shows thatth e delta-wing model in i t ia l l y pi tc h es upon entering t h e gust and soonafterwardpitches down. The effect of this sequence of pitching motioni s evident when a comparison i s made of th e e ff ec t of pi tc h on th e aver-agemw values of accelera tion increme nt i n each of th e gu st shapes.(See tab le I I ) I n t h e sharp-edge gust, where the maximum acce le r a t ionincrement i s obtained quickly, the initial pitching-up motion increasesthe load a sm a l l amount. In th e gu st wi th th e 6.5-chord gra die nt d i s -

pitches down s o tha t the pi t chi ng motion decreases the load about

f l tance, however, the m a ~ m u m ccelerat ion incrementccurs af ter t h e model

d 5 percent .

The ra pid pit ch ing motion of the model as i t passed through thegusts and the reversal of the e f f e c t of pitching motion on the m a x i m u m

accelerations which occurs for th e change i n gust shape from sh rp edgeto 6.5-chord gra die nt ind ica te tha t the pi t ch ing motion of the del ta -wingmodel is probably qui te sensi t ive to the center -of -gravi ty posi t ion .Fur ther invest igat ion will be necessary, however, bef ore qu an tita tiv epredic t ions can be madeof th e change i n l o a d with center-of-gravity

posi t ion. The i n i t i a l po s i t i ve p i t c h in g motion of t h e model i s believedt o be a result of the gradual penet ra t ion of the del ta wing i n t o t h egusts. The ef fe ct of penet ra t ion on the p i tching motion i n the pre sen tcase, however, doesnotappear as grea t as t h a t on t h e swept wings ofreferences 1 o 3 .

Predic t ion of t he gust load was made with the use of equation (2)

of reference 1. The slope of the l i f t curve was that determined romforce t e s t s and the unsteady - l i f t funct ions were th os e f o r i n f i n i t easpe c t r a t io where the uns t eady- l i f t f unc t ion fo r pene t r a t ion of t he

gust w a s modified by s t r i p th eo ry to account for the gradual penet ra-t i on of the de l ta wing in t o he gus t . The results of this ca lcu la t iona re compared with he experim ental results reduced t o zero pi tching

l i f t curve derived from force-test measurements in th e ca lc ul at io nsresults i n an undere stimation of th e gust lo ad of some 2 0 t o 25 percent.

I motion in a b le III. The comparison shows t h a t use of thelope of th e

-



4 W A RM L52B04

-

In ord er to inv estig ate the disc repa ncy between the calc ulat ed andexpe r tmenta lesul ts ,h reeddi t iona l -ca lcu la t ionso rhee l ta wing -

were made with only the slope of th e lift curve being changed and, f o rcomparison, a cal cu lat ion was made far a s t r a i g h t wing of the same aspectra ti o . The lift-curve slopesu se d i n t h e c a l c u l a t i o n s f o r t h e d e l t a w i n g

were: 1)a slope of 2.61 per radian obta ined f rom if t ing-surface-t he o r y c a l c u l a t i ons f o r a60d e lt a wing, (2 ) a slope of 3.66 per radianpredicted from the work of Jones based on Hunk s a i r s h i p theory (refer-ence s f o r low-aspect-ratiopointed wings and 3 ) a s lope of 3.23 perradianobta inedfrom hes impleaspec t- ra t iore la t ion 6A/(A + 2) whichhas been used successful ly for de termin ing s lopes for the predic t ion of

gust oads on s t r a ig ht wings ( re ference k ) . The slope of the lift curveof 3.23 per radian was a l s o u sed i n t he c a l c u l a t i on f o r t he s t r a i gh twing togeth er with the unmodified un stead y-li f t fun ctio n for pen etrat ionint o he gu st . The results of these four ca lcula t ion s are inc luded i n

t a b l e 111.

e

I t i s apparentfromexamination of table I11 t h a t only two of thecalculationsagreedwellwith heexperimental results. Use of thelif t ing-surface theory un derestimated the experimental results by 15 t o20 percent; whereas use of the s lope f rom airship theory overestimated

them by about 8 percent. The best agreement was obtained when t h e l i f t -curve lope,derived from th e simple ormula 6A/(A + 2) , was usedw i t h e i theruns teady- l i f t unc t ion. If the assumption i s made thatoth er fac to rs such as the choice of the uns teady- l i f t func t ion are cor-r e c t , t he e f f e c t of the gradual penetra t ion of the de l ta wing into thegust i s ind ica ted t a be small. On thebasis of these resul ts , here-fore , it i s impl ied tha t the gust load on a 60° de l ta ying can be pre-

dicted by use of the slop e of the l i f t curve of 3.23 per radian derived

from the ormula 6 A / A + 2 ) even when t h e e f f e c t of thegradual pene-

t r a t io n of th e de l ta wing i n to the gust i s disregarded.

Although th e im pli cat io ns of the preceding paragraph are i n agree-ment w i t h the experiment, much doubt s t i l l e d s t s ' a s t o what t h e r e a ls i t u a t i m might be. The resul ts pres ente d ind ica te d tha t the load s maybe predictedequal lywel l by methods having different concepts . I t is

apparent , herefore , ha t t h e bas ic pr inc ip le s a re no t fully understoodand addition al inform ation will be needed before.extension of t he resultsof t h i s paper can be made for the ca lcu la t ion of t he gust load on deltawings havin g apex angles- other than 60°



NACA RM L52B04

CONCLUDING REMARKS

A gust - tunnel invest igat ion of a delta-wing model with the leadingedge swept back 6 has indicated that the use of th e s lope of the liftcurve, determined by steady-flow f o r c e t e s t s i n gust- load calculat ions,underest imated he gust oad by 20 t o 25 percent.Furtherstudy showedt h a t a good estimate of t he gus t l oad f o r this w i n g was obtained throughthe use of a slope of t h e l i f t curoe .der ived from t h e simple a s p e c G r a t i orelation 6A/(A + 2). Extension of the se results t o o th e r de l t a wingswi th d i f ferent apex angles, however, does not appear warranted a t thisti rne. Ad dit io nal nve st ig at io n w i l l benecessa ry to e s t ab l i s h the

importance of the center-o f-gravity position on the loads induc ed by t h epi tching motion of th e de l t a wing i n a gust.

. Langley AeranauticalLaboratowNational Advisory Committee f o r Aeronautics

Langley Field, Va.

1. Pierce, Harold B.: Tes t s of a 450 Sweptback-WingModel in the LangleyGust T u n n e l . NACA TN 1528, 1948.

2. Reisert, Thomas D.: Gust-Tunnel Investigation of a Wing Model withSemichord Line SweptBack30°. NACA TN 1794, 1949.

3. Pierce, Harold B.: Gust-Tunnel Investigation of a Wing Model withSemichord Line SweptBack 60°. NACA TN 2204, 1950.

4. Donely, Philip: Summary of InformationRela ting t o G u s t LoadsonAirplanes. NACA Rep. 97, 1950. (Formerly NACA TN 1976. )

5. Jones, Robert T.: Proper t i e s of Low-Aspect-Ratio Po in te d Wings a t

Speeds below and above the Speedof Sound. NAGA Rep. 835, 1946(Formerly NACA TN 1032.



6 NACA RM L52B04

TABLE I

CHAFtACTEFUSTICS OF THE MODE& ND TEST CONDITIONS

Weight, l b s . . . . . . . . . . . . . . . . . . . . . . . .Wing area, sq f t . . . . . . . . . . . . . . . . . . . . .W i n g loading, lb/sq f t . . . . . . . . . . . . . . . . . .Mean geom etric chord measured i nS p a n , f t . . . . . . . . . . . . . . . . . ? . . . . .

p l a n e p a r a l l e l t o p l a n e of

symmetry, Area/Span, f t

. . . . . . . . . . . . . . . . .A s p e c t r a t i o , A . . . . . . . . . . . . . . . . . . . . . .Root chord, f t . . . . . . . . . . . . . . . . . . . . . .Slope of t h e l i f t curvedetermined

by s teady-f low fo rc e es ts , per radian . . . . . . . -.Center-of-gravityposition,percent

m e a n geometric hord . . . . . . . . . . . . . . . . . .Gust velocity, fps . . . . . . . . . . . . . . . . . . . .Forward velocity,p s . . . . . . . . . . . . . . . . . .Pitching moment of inert ia , slug-ft' . . . . . . . . . . .

. . . 11.7

. . . 6.92

. . . 1.69

. . . 4.90

. . . 2.4

. . . 0

9 10

. . . 88

. . . .286



Gust ahap

6 . chord

gradient

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

TAJZE I11

COIBARISON OF EXPEEMEXI? ND CA L CU L A T I O N

Calculated

(g w i t s )

Corrected

reduced.

,

experiment l Straight w h qelta ing

to zero pitch

g mite) lift-curveurface-theoryeasured 1Fft- UrsMp theory

of 3.23f 3.23f 3.66

Lift-curveift-curve

curve s lope of s lopelopel i f t - c u r v e2 a 4 slope of elope nA/2) (6A/(A + 2))6A/(A + 2))

2.61

1.27 1.27.21.35.0295

1.07 1.10.06.15

186

=

A

. . . . . . . . .

71. .

'Ir .. . . . .



2E

c

a

9

Figure 1. PLan f o rmof 60delta-wing model.



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

F r. . . . . .

...

- ul

I;

Figure 2.- Photograph of delta-wing model. B

* *. . . . . . . ...

V. . . . . . . . . . . . . . . .



I

-

-2 0 2

c ' i 2

Figure 3. Velocity bistributlm throua gust-tunnel jet.

E



12

?

L

. . . _

.-2 0 2 6 8 / a

~m.zonfa/ sfome h m eo ?g e e of funned meanchords

(b) Gust with 6.>chord gradient d i e t a c e .

Figure 4.- Representative history of events in teat gus t s .



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1952 gust-tunnel investigation of a delta-wing model with the leading edge swept back 60 degrees

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