NATIONAL ADVISORY COMMITTEE FOR A€RO~A~TICS/67531/metadc62408/m... · NATIONAL ADVISORY COMMITTEE FOR A€RO~A~TICS ORIGINALLY ISSUED February 1946 a8 Memorandun Report ~6~08 CALIBRATIONS

NATIONAL ADVISORY COMMITTEE FOR A€RO~A~TICS

ORIGINALLY ISSUED February 1946 a8

Memorandun Report ~ 6 ~ 0 8

CALIBRATIONS OF SERVICE PITOT TUBES IN 'l.!EC

LANGLEY 24-INCH RIGH-SPEED TIBuI6n

By W. F e Lindsey

Langley Memoraal Aeronautical Laboratory Langley Field, Va.

WASHINGTON

MACA WARTIME REPORTS are reprints of papers originally issued to 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 are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution.

L - 580

* NACA LANGLEY EEBIOKIAL AEROlYAUTI'JkL LABORATOXY ?v!~EMORABJIIL~"~ RE PORT

f o r the Air Techr,fcal Service Corn-manci, Army A i r Forces

and the

Bureau oi' Aeronautics, &IVY Department

' xi?. NO. ~ 6 ~ 0 8

CALIBRATIONS OF SEZVfCE P I T W T L ? E S 1% THE

Bg W e F, Lindsey

i: '1 I T 9 r a L Ton t e s t s have Seen madte i n the Lanzley 21~-%ich hlzh-speed tunnel on a I~olls~?;1,y1 t>-pe G - 1 and an 3J.W No, 1 p i t 2 t tube a t an angle o f a t t a c k o f 0' over a Mach number range f rom S , ~ O t o 0.87. A d d - f t i o n a l c a l i b r a t i o n t e s t s were made on the XAF No. 1 p f t c t tube a t v a ~ f o i i s an;;les

\ o f a t t a c k over a h c h nwriber range f r m 0,23 t3 0,53 .

1' iLie ef'Psct o f c.rsin holes on t k e flow xi . thin Q servlcs p i t o t t i i ~ e _ a t 0' m S l e of' a t t a c k was analyzed and a ye1ai;foi-i B ~ S derived wk--.13reb.- t'Le e r r o r i n t o t a l pressure

be estimated. T-Es aiialysis was extended t o include the e2fects of z m - r e s s f b i l i t y 011 t h s e r r o r s o t h a t an e s t izmtsd valuc 3r ar, experimentally 62 t e rmined va1v.e could Sc exkrayola ted t o l-iL$?er s;seeds The c a l i b r a t i o n t e s t s m d i c a t e t h a t the accurnc;~ o f the extrapolated and estimatcrl values are wi th in reasanatole l f r n i k s .

Cal-LkratIon t e s t s have been ms,d.e on one serv ice p i t o t tube (Xollsman type 0-1) su?nlfed by the A r n y A i r Forces, end DE eae p i t o t tube suppi2ed by the Kavy and d3s igmd frsr serv ice i n s t a l l a t i o n s . The t e s t s wzre con- ducted i n the Langley 2 f _ ~ - i n c h Mgh-speed tuilqel,

' Tests o f the K o l l s m a n t:rbe G-1 p i t o t tuSe were requested b y the Amy because of reported erroneous

2 !.E3 No. L6A08

to ta l -pressure ind ica t ions encountered i n f l i g h t during dives , and because a high-speecl c a l i b r a t i o n of the tns t r iment had not been made, Data previously obtained on s i x i l a r instruner , ts ( re ference 1) show t h a t the e r r m i n t o t a l gressure ( i n percent of the d i f fe rence between t o t a l 2nd s t a t i c pressures) i s not apyreciably a f f ec t ed by ETach. number.

If the nressure indicated by the p i t o t tube i n s t a l l e d on am a l rp lane i s i n e r r o r under dfve conditions, i t i s most -,?rcba5le t h a t t h i s e r r o r i s a r e s u l t o f exzeeding i-he usefu l angular range of the instrument, The angular range o f aecepta5le accu.rac;y wovld. be g r e a t l y reeucec? i f the nose of the instrujnant is lo.-ated t o o c lose t o tho leading edge o f the wing, because i n t h a t region changes f n d i r e c t i o n of a l r flow ara rruch g r e a t e r t??m changes i n angle o f a t t a c k of wingSo Instruments have been i n s t a l l e d wfth the nose 10 inches ahead o f the leading edge o f the wing.

Po:? the s t a t e ci c onu i t i ons , wtn? - % uzm 1 ca l ib r a t i olrl t e s t s of the fnstrus-ent alone, even t h o ~ g h made over a wide angular range, could not b4 expectec', t o provi2.e a corrqlete s o l u t i o n t o the problex, which could be b e t t e r s tudied 'cy zomparing in f l i g h t the reacling of the serv ice p i t o t tube with t h a t of an i n s t r u m n t capaSle of de t e r - mining tke cor rec t t o t a l pressure over a la rge angular range, (See re feyeme 2 . )

A S r q t chan:;es i n tl,e inciicated atrspeed under landi rq c o n d i t i c m had beer?. qeported for sozie instrument

. i n s t a l l a t i o n s on ?Java1 r l f rc raf t . This t rouble was belteved- t o be d i r e c t l y r e l a t e d t o the v a r i a t i o n i n the e r r o r o r the meascred t o t a l gressure with angle of a t t ack , The 6avg th s re fc re designed the ITAT No. 1 p i t o t tube lnccr rora t fng a Rfel ty-ye nose whfch was expected t o measure the t o t a l 2ressure t o an accuracy of 1 mile per hour over an extended angular range, The K i g l type instr-uiient; ( re ference 2 ) i s a p i t o t take enclosed within a tij-buular shfe ld , the purpose o f which i s t o maintain allriemant between the p i t o t tube a d the f l o w tkrough the sh i e ld . Tne ins t ruqent I s thus ca2able o f rngasuring t o t a l p v s s u r e without e r r o r over a la rge a igu la r range. The use of a Kie l t y p e nose on the l JAF TJo. 1 p i t o t tu3e without allowing flow tlvough' the instrument except as provided by the d r a i n holes should not be expected to increase i t s angular range f o r zero e r r o r over that o f a simple to t a l - ? re s sure tube , xhich i s approximately "14' ( reference 3 ) .

3

1- method 2s gfveil Pn t h f s rstport wherel;,? the error caused bs: t he drai-n holes i r l a pFtot tu'se a t Oo angle o f a t t a c k can be estimates. The ana lys i s r a s extendeci t o Include the e f f e c t s of ccnz-,?:7essif:,ilit:T on the error so

value could. be ex t rapola ted t o %i$xr speeds . 0 t h a t an e s t t r a t e d value CT an e X y ? i > h 3 n ' k a l l g determined 02 Ln A

&4 t e s t 9rogran was de temined i n a conperenae attended. by P l r . G , A . Rardfng o f the FWlade3,phia N a T q Yard, L t . R e Munnikkugsen of 'Wight Ffe ld , arid aemkers o f the Lang1e.g Lfaborat;ory s t a f f . In accordance w l t l t h i s program, t e s t s Rere inade cm the Iiollsnar, type G-1 arid the KAF No, L ('iv'eigand manufactured) p f t o t tiXrJes a t Oo anglf: o f abtacl: over '1 Each nmbcr ra ige extending f r o m t1,20 t o 0,3'7. ~dditi.ona!- t e s t s ir~are then made on the HA2 ?To. 1 pI t0- t tu3e a t v r r io iw axgles of a t t a c k over a range of Mach n w b e r s from 6'20 t o O,",.

Tke s tp . t ic p e s s u r t : i n the :;(-st s e c t i o n was d-eter- mined bp calfbratctd static-?ressu.i*e orifices in bhe tunnel wall Upstream from the t e s t s ec t fon , The stream Xach niu?ibers and the c o r r e c t t o t a l rressure fn the t e s t s ec t ion were then computed f r o m i:1easured values of the atmos2heric pressure a&. t he pressure a t the cal lbrabed s t a t f c - p r ~ : s sure o r i f' i c e s

Tne two p f t o t txbes c a l i b r a t e d and rep2rted he re in are :

I I 7-

( 2 ) Airspeed tube type '3-1 Spec l r l ca t ion NO. 74-27378 Kollsmanr s ? a r t 30. 7&-02

These in s t ruxen t s a re shown 5% f ig iwes l ( a ) and l(b ), r e spec t fve l y

The p i t o t tu3es were mounted Tor the c a l f b r s t i o n t e s t s on a long support tube lcca ted apyroximately i n the ceii ter o f the tunne l . "lie supnor t 'cube, having an outs ide diameter equal -to that I of the p i t c t -tube sdaptgr shown 112 f i g u r e 1, forned a Tearward extension t o the adapter, and was suncor-bed - _ by two s e t s bf wires which were fr;staned t o the tunnel ~ ~ a l l s ~ Each s e t consis ted of th ree wires sr?accd 12~' apart. Cne s e t o f wires was a t tached to the support t u b e 5 inches downstrekx from the adapter, and ths okher s e t was c inches f a r t h e r do:vn- s t re am Figu.re 2 illus t r a t e s this I;yye of moi.rnt fng .

Changes fn the angle cf a t t a c k xere made by r o t a t i n g the suT3nort tube fn a plane \uhl.ch yassed through the ax i s cf' &.e instrument aad the d ra fn holes , The rotatfon was nads s o that tho nose of the p.'itot tube re"s1ned i t s locat ioir aymroximately a t the center of the tunnel.

s-lwem static pressure

s t r e a n t o t a l p r e s s w e

t o t a l pres sure ind ica ted by instrument

angle of instrument with respec t t o a i r f low

apea of to ta l -pressure duct i n region of pres- Bare Hr

area o f one d r a i n hole i n tube h a v h g N equal- diameter d ra fn holes ( E A 2 i s t o t a l d r a i n a rea )

5

l o c a l s t a k i c pressure at d r a l n hole p2 v e l o c i t y at area Ax

ve loc i ty through r 2 a i n hole 0 a u'\ JTz A

P stream mass d e n s i t y (at a static, pressi tre equal

p I3

to P >

equal to s> s tagnat ion n ihss uens i tg ( a t a static pressure

The e r r o r in t,he ;neasu~~?ien-t ; of total vressure for a p i t o t tube at (3" anele of attack r e s u l t i n g f rom the pi-essi?z.= of drafn hclss can b e a s t i n a t e d by using the eql.iation of contiizufty ad 3srnoullil s equat ion f o r an inco-mpe s sih1e flow 8ernoul l i l s equati-on is

Fr OM w hi. c h

and

assw.iri5 an o r i f i c e coePftcfent of G.8 t h e equation o f con t inu i ty i s

e l imina t ing V

6

Thus

The pressure c o e f f i c i e n t for incompressible flow i s

Pz - P €I - p P =

T1 i'nis r e l a t i o n shows t h a t t32 e f f e c t o f l oca t ing the dra-in ?>ole f n a loff-pressure or nfch-vs loc i ty region wo:ilci be t c increase the e r r o r i n the reading. For pitot t?i3es having d r a i n kales loca ted one o r mere tube dian,e t e r s behind the nose however the -;-nduced. v e l o c i t i e s a t t h e < r e i n holes would be m a l l . The resrr l t ln$ value o f the ; > r e s s - ~ r e c o e f f i c i e n t P w ~ u l ? be between 9 and C.02, 3 s indicated by r e s u l t s Srqm an unpublishcr?, p f t o t - s t a t i c tube inves t iga t ion , snd thus the assuxption t h a t P equals zeyo wolilci i_ntrod-.:ce n~=glig;ible error e

Zqiltation (1) then becomes

The estf;-cii.ted e r r o r i n the masured t o t a l pressure a t 0' angle of a t t a c k for the t;rv.o yftoJC tubes based on rneasw5d d imns fons 2nd equat ion ( 3 ) are : O,oCi06 and 0,0009 f o r the KAF No. 1- a_rd tke Xollsman'type G - 1 p i t o t 'cuke, resnec t ive lg . A coxpnrfson with :he r e s u l t s presented. t n figure 3 shows t h a t i;>e ex2erimantal values

t h e s e estimated values. ch nu-nber o f 0,2 are iin exce l l en t agreement with

Previous experimental resu,l ts ( re ference 1) have shown t h a t the magnitude o f tke s m o r i n the t o t a l - pressure measurem5nt s decre 853 s s l i g h t l y v ~ f t h increas ing Mach number, It can be seen I n f igu re 3 that the e f f e c t of comni-esciuil i ty on the to t a l rp rz s su re e r r o r of these p i t o t tu'zes Is i n agreement x i t h the r e s u l t s of r e fe r - ence 1.

MR NO, ~ 6 ~ 0 8 7 . .

1- * * . ne the f a c t o r s 7 ~ ~ h i c ~ ~ p r o d . u c e

a reduct ion i n the magnituCe of the to ta l -pressure errox' w i t h inoreasin$ ?da&*mhber; W-.S -3rocess whareb

no Losses' we

the, i n c o q r e s s i b i e and cornpre s s5ble f orrns, respec t ive ly ,

a , .. , I . - , . *

Sfiice the last two terns or equat ton ( 5 I decrease with increasing Xach n u m 3 ~ ~ 9 t k a r e l a t i o n shows that the to ta l -pressure e r r o ~ ~ h o u l c ? Gecrsase with increasfng Nach . numbel-, 2Ix3'%k3?T9 the. l a r g e s t cTntrfbuting t h i s decrease F s the chanGe ir? cens$ty. .The -e f f ec t o f c o m ~ r a s z i b l l i t g on 'this e r r o r as determined by equation ( 5 ) i s s h o ~ m In f i g u r e IC.

The r e s u l t s of' the ca l iS ra t fon t e s t s on the NAF KO. 1 p f t o t tube a t various angles o f a t t a c k a re ?resented i n f i p m 5. It can be s e s n t h a t the angular range wherein the e r r o r i s essentFd .1 equal t o the value

o f change o f e r r o r with m g l e o f a t t a c k bc : ro~d loo i s ~ o t l a rge coinpared t o t h a t for a s5;tiple p i t o t tube, ( % e reference 3 . )

A comparison of the Pesul t s for t h e pos i t i ve and negative conditions a t a given angle o f a t t a c k shows t h a t

a t 0' i s l imi t ed t o apnroximately ?LO 8 , although the r a t e

the d i f fe rences a re gene ra l ly within the sca'kter of the te s t points.*

* An examination of the t e s t results and the curve . .

giving the l imft i r lg error fop a reduct ion i n ve loc i ty of I mile p e r Qour under standard oondi'tions shows t h a t the angular range f o r t h i s lzmi t ing e r r o r itecreases f rom f2k0 a t a Mach nqnber of 0,2 t o 2210 a t a Mach number ofI'O,?.

It can be seen t h a t the e f f e c t of compress ib i l i ty on the e r r o r , evea a t the higher angles o f a t t ack , i s

reference 1,. T'ne change i n the magnitude a t these bzgher angle,s- of attaqk- Is such t h a t the e r r o r a t a'llach number 02 0.5 i s approximately 80 percent of the e r r o r a t a Xach number of 0 ,2 , ' It i s i n t e r e s t i n g t o note t h a t a change o f 86 percent would have been predicted by equat ion ( 5 ) o r f i gu re 4 althou5h no Q f f e c t o f angle a f ' a t t a c k wzs considsmd .in the de r iva t ion of'. equatfon ( 7 ) I

- . 1 * .

b

i n agreement. . t y i $ h . , $ F . e . , ~ ( t 3 ~ u l Q s shown in' f i g u r e 3 dn . . .

CONCLUDING REMlLRXS 1 . , . . ., . . .. . _._ ., . . . ~ . I a

The eyror i n $o.tal--preaSu.re i!'2diegtefd by a p i to t . . " tube wi.th d r a i n holes a t small m ~ l e s o f a t tack can be estimated, and. t h i s ostLmuted value o r an experimentally determined value can be extrapolated t o hfgher speeds These c a l i b r a t i o n t e s t ndfoate t h a t the accuracy of the estimated value's w be within reasbna%Ie l i m i t s ,

, .

Langley hlernorfal Aeronautical Lzbaratory ,

Rational Advisory Com-Lttee- $or Aeronautics .

Lansley FPe'ld, V a ,

9

1. HensLey, Weece V,: Calibrations of P i t o t - S t a t i c Tubes

2 , Kiel, 0.: Total-Read Meter with Small S e n s i t i v i t y t o

3 . Hmphreys, Milton j l . : Effects of CompressiSility and

3 a t High Speeds. XACA ACR, Ju ly 1942. 2 Yaw. XACA ‘rhl No, 775, 193’5.

Large Angles of Yaw on Pressure Inaiicated T o t a l - P r e s sure Tube . 8ACk HB No, 15230,

MR No. L6A08

rn a, P 5 4

4 0 .+ .cl a

I

d

a, $4

5 ho .+-I r k

MR No. L6A08

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

MR No. L6A08

MR No. L6A08

MR No. L6A08 0 co In c: