C.P. No. 969

MINISTRY OF TECHNOLOGY

AERONAUKAL RESEARCH COUNCIL

CURRENT PAPERS

An Investigation into a Technique for Measuring Jet Interference Effects using Free-flight Models

by G. H. Greenwood

LONDON: HER MAJESTY’S STATIONERY OFFICE

1967

PRICE FOUR SHILLINGS NET

U.D.C. KO. 533.695.: : 533.696.5 : 533.6.055 : 533.6.013.12 : 621.4.55-846

C.P. NO. 969” Nwember 1966

AN INVESTIGATION INTO A TECHHIQUE FOR MJ?u?SURII~ J'ET

INT3RiWdNCE EFFECTS USING FZZ-PLIGHT XODELS

by

G. H. Greenwood

A free-flight no&s?. investigation is described, the majar obJect @f

which was ts gain design and operational ex;,erience in the field of jet inter-

ference studies. Measurements were made of' the effect of a propulsive Jet on

the external drag of a boattailed botiJ of revolution but because of uncertainties

in the Jet performance these measurements 21‘e of si@.ficance only In illustrat-

ing tne experimental technique. A solid-fuel rocket mcjtor was used as the

primary source of the jet flow.

* Redaces R.A.E. Technwal Report Nc. 66364 - A.R.C. 29039.

COhTENTS

1 IhnPRODUCTION

2 DESCRIPTION OF TKE hfODELS

3 MWHOD OF TEST

3.1 Boosting

3.2 Data acquisition

3.3 Data reductmn

4 TEST CONDITIONS

5 RESULTS AND DISCUSSION

5.1 Pk'light

5.2 Inflight

5.2.1 Nozzle static pressure

5.2.2 Jet thrust

5.2.3 Drag

6 CONCLUSIONS

Symbols

References

Jllustrations

Detachable abstract cards

gcL&

3

3

4

4

4

5

5

5

5

5

5

6

6

6

7

8

Figures I-II

3

1 IiQR3DUCTION

Interaction bobTeen the external florr and the boundary of a propulsive

jet may cause pressure changoz on ad;zoent structures leading to a modified

external drag and pozzibly to trim changes on an aircraft or missile, especially

when the Mach number of the externzl flon is in the tranzonic and supersonic

range an3 if the nozzle is under-expanded.

In the expcrimentel study of such interference effects extensive uza has

been made of wind tunnel facilities but zo far the use of rocket-boosted frec-

flight models has been confined to American tests.

The aim of the present test mas therefore to gain some practical design

and. operational exparicr~ce within the R.A.E. in the use of free-flight models

in the field of jet-interference studies. This zim was achieved by measuring

the totai drag and base pressure on trio models of identical external shape

one with and one without a propulzive jet issuing from the base; a quantitative

reference frame for the results iraz provided by uzing an external shape identi-

cal to that used in the N.A.S.A. test of Rcf.1.

The primary source of the jet flow waz a modified solid-fuel rocket motofl.

Model tests over a Hech number range of 1.17 to 1.42 vere made at free-

stream Reynolds numbers from 8 to 10 millions psr foot.

2 DRSC?UPT_IOX OF THE MODFiS

lbio models were used in the test their external shape being identical to

that used in Ref.1 and az illustrated in the photograph of Fig.1 and general

arrangement dra.ving of Fig.&

The models are designated modelz 1 and 2 and are described az. follonz:-

Llodel 1 This model riaz flight tooted without a jet efflux and its primary

purpose was to provide total drag and base prezzurc measurements relhvant td

the "jot-off' condition.

Node1 2 The purpose of this modelnaz to provide total drag and base proazure

measurements relevant to the "jet-on" condition.

t!

A propulsive jet iras provided

by igniting a plastic composite propellen contained in a 5-inch diameter

rocket-motor tube inzide the model. The propellcnt gases were then exhausted

through a double-nozzle assembly incorporating a plenun chzmber to dissipate

*Development of the rocket motor and its associated nozzle assembly vial carried out by Dr. H. Crook of RP.5. Westcott.

Id X.P.E. Yestcott, specification RD.2307.

4

the high combustion pressures to an acceptable level of jet exit total pressuk'e.

Typical design procedures relevant to such a nozzle assembly and to the simula-

tion of full-scale jet flow parameters at model scale are described fully in

Ref.2.

It was in fact hoped that by using the design principles of Ref.2 jet

exit flow parameters comparable with those of Ref.1 would be achieved but it

became apparent that in practice the required nozzle geometry would have to be

evolved through a protracted series of static test firings. Since the ma,~or

object of the present test was an exercise in operational technique the precise

character of the jet flow was considered of no real importance and the test

firings were therefore terminated as soon as a repeatable exit flow had been

established.

Fig.2 illustrates the base region of model 2 and shows the position of

the nozzle static pressure orifice (see section 5.1) and of the base pressure

orifices; the position of the latter being identical for both models. Ri6.3 shows the internal arrangement of model 2 together nith details of the nozzle

assembly.

In Fig.4 a device is illustrated Trhich was used to delay ignition of the

jet motor until the model had sepsrnted completely from its external rocket

booster. This device sas basically a 6.0 volt electrical ignition circuit

interrupted by inertia-type switches which alloired. ignition to occur only after

the model had been subject to the folloming sequence of accelerations. When

an acceleration of at least +lOg was attained during the initial boosting phase

one half of the ignition circuit "as elcctriwlly complete and igniticn'occurred

when the circuit was finally complete at one second in time after the model

acceleration had fallen to +3g.

3 h!ETHOD DR TEST

3.1 Boosting

Each model was launched to its required test velocity using a tnin 5-inch

diameter rocket motor booster as illustrated in Fig.5. At the motor all-burnt

condition the models separated from their boosters under the existing drag and

inertia forces and nent into free fiight.

3.2 Dataacquisition

Each mcdelnas tracked by kinatheodclite cameras sited along the range

boundary thus providing a record of spncc cc-ordinates froan which trajectory

5

and velocity data were obtamed. Velocity nas also obtained by integrating the

response of model-borne longitudinal accelerometers.

A I+65 ?&c/s multi-chancel R.A.E. sub-mininture telemeter was used in

conJunctmn with variable-inductance type transducers to obtain the required

inflight pressure and force measurements.

Atmospheric pressure, temperature and oind velocity at the appropriate

flight altitudes mere obtained using the standard range procedures.

3.3 &ta reduction

The methods used to reduce the recorded telemetered data to variations

of' drag coefficient, Jet nozzle and base pressure ~11th flight Mach number were

basically as described in Ref.3.

4 TEST CONDITIONS

The variation with flight time of free-stream Mach number, altitude and

Reynolds number is shown in Figs.6 and 7 for models 1 and 2 respectively.

5 RESULTS AND DISCUSSION

5.1 Preflight

The performance of the Jet moto r and nozzle assembly was established

prior to flight by ground tests in which the static pressure measured at a

point inside the convergent exit section of the nosele was correlated with the

simultaneously measured thrust. This static pressure point (see Pig.3) ~2s

located as near the Jet exit plane as model space oould allcw.

Fig.S shows the static pressure/thrust relationship obtained from the prc-

flight tests.

5.2 - Infli&

5.2.1 Nozzle static pressure

Inflight values of the nozzle static pressure measured at the same point

as in the preflight tests (5.1) are presented in Pig.9. It will be soen that

the maximum measured inflight static pressure was only about 501bf/in2 ccmpared

with 6: lbf/in2 measured during the preflight tests (Fig.8). This indicates that

either the full Jet performance was not attained in flight or the flight

pressure measwemcnts were themselves in error due perhaps to a fault in the

pressure transducer. Although the latter is thought unlikely there is never-

theless some uncertainty in the nozzle pressure measurements and hence in the

dcduccd inflight performance of the Jet motor.

6

5.2.2 ;et thrust

In Fig.10 values of inflight thrust are presented. These were deduced

from the pressure/thrust relationship of Flg.8 and the flight measurements of

nozzle static pressure of Fig.9 but because of the anomsly associated witn the

flight measurements of nozzle pressure (5.2.1) the possibility of some

uncertainty must not be discounted.

5.2.3 Drafi

Fig.11 shows the variation with Mach number of the total and base drag

coefficients for both models.

The total drag coefficients for the "Jet-off" cordition are seen to

differ by only about 4 per cent between models 1 snd 2 - an smount easily

accountable as experiment& uncertainty. Excellent agreement has been obtained

between the "jet-off" total drag of model 2 and that from Ref.1.

The "jet-on" total drag coefficients were compbted from the equation:-

CD = T.- (Jet-on) J

W (a/g + sin e)/qo S ;

the inclusion of the inflight thrust term, T , thus introduces the possibdity

of some uncertainty in the "Jet-on" total kg coefficients (5.2.1). This

uncertainty coupled with the fact that the jet thrust and hence probably the

jet pressure ratio was varying throughout the test precludes a direct comparison

with the "jet-on" total drag coefficients from Ref.1 which were obtained for a

constant Jet pressure ratio, pj/po, of 3.75. Unfortunately the uncertainty in

the flight performance of the Jet motor did not allow reliable values of jet

pressure ratio to be computed for the present test.

The presence of the jet efflux induced positive pressures on the base

annulus resulting in negative values of "jet-o*" base drag coeffioignts compar-

able in magnitude to those of Ref.1.

6 CONCLUSIONS

An investigation has been described in iihich measurements of the external

drag of a boattailed body of revolution were made in free flight kth and with-

out a simulated propulsive jet issuitig from the base. Despite some uncertainty

about the jet perforclance the investigation has established the validity of the

free-flight model technique in the field of jet interference studies.

.SYMBOLS

a

Aa

Ab

cD total (jet on)

CD tOtd (Jet Off)

cD base (jet on)

cD base (Jet Off)

g

pb

PO

PJ s, s

T.

wJ

e

longitudinal acceleration

area of base amulus = 0.019

area of base = 0.061+5

T 3

- W(a/g + sin e)/qo S

Drag (lW)/qo S

(Pb - po)Aa/qo S

(‘b - po)Ab/qo S

acceleration due to gravity

base pressure

free-stream static pressure

Jet exit static pressure

free-stream dynamic pressure

reference area = maxmum body cross-sectional

area = 0.23

Jet thW3t

instantaneous model weight

flight-path angle

ft/sec'

ft2 /

ft2

ft/seo2

lbf/ft*

lbf/ft'

lbf/ft2

lbf/ft'

ft2

1k.f

lb

degrees

8

& : Author

I B. A. Falanga

Title. etc.

A free-flight investigation of the effects of

smulated sonic turboJet exhaust on the drag or

a boattsil body with various jet sizes from Mach

number 0.87 to 1.50.

NACA Rd L55FOYa; August 1955

2 C. A. de Moraes Dksign and evaluation of a-turbojet exhaust

V. K. Haggmbothom,Jr. simulator, utilizing a solid-propellant rocket

B. A. Falanga motor, for &e-in free-fli&t aerodynamic research

models. I NACA G L54I15, December 1954

3 J. A. Hamilton Free-flight techniques for high-speed aerodynemic

P. A. Huft& reseerch.

Journal of the Boyal Aeronautical Society,

Vol. IX, pp. 151-185, March 1956

.

7 SoSTRAIGHT-TAPERED AFTEREIODY

\ PROPELLENT.

STABILISING FINS

5 in dia ROCKET MOTOR TUBE

I / BALLAST TELEMETRY E NOZZLE/

IGNITION CIRCUITRY PLENUM CHAMBER

--I-- F F1 c!--

0 co

to 97 In

L 650 In

STATIC PRESSURE ORIFICE’ USED FOR DETERMINATION OF IN-FLIGHT THRUST FROM PRE- FLIGHT CALIBRATION

DETAIL OF NOZZLE ASSEMBLY.

FIG 3 GENERAL ARRANGEMENT OF MODEL 2

I I , , , I 1 , , I , , , , , I , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , n 3, v , , , , , , , , , a,, ,s , , , , , , , , , , , , , , ” , , , , , , , , , ,#,, , , , , , , , / , , , , , , , , , , , , ,,z

G, z

BASIC CIRCUIT 2

a FIRING SWITCHES

PARTIALLY CLOSED AT t 8G

FULLY CLOSED (FIRING) ONE

SECOND AFTER ACCELERATION

FALLS TO + 3G

0 ARMING SWITCHES

FULLY CLOSED AT + IOG

TERMINALS FOR

I CIRCUIT CHECKS

d-i-i-m

Qm$I! ‘8’ PLUGS 4 ‘I q E

2 J GREEN

GREEN = ISOLATING 0R SAFETY PLUGS

RED = ARMING PLUGS

‘A’ PLUGS

FIG 4 JET MOTOR lGNiTt0N CIRCUIT (MODEL 2 1

MODEL SEPARATION

0 0 0 0 2 2 4 4 6 6

FLIGHT TIME (set )

600

0 0 2 4 6 8 40

FLIGHT TIME (set)

44 44

40 40

9 9

8 8

7 7 0 2 4 6 8 40

FLIGHT TIME (SK)

FIG. 6 TEST CONDITIONS - MODEL I

MODEL SEPARATION

INITIAL JET ON I _ JET OFF

-BOOSTING c

0 2 4 6 8 IO 12

FLIGHT TIME (XC)

500

400

‘-; 300 22

ii 2

200

5

4 6 6 IO

FLIGHT TIME (set)

2 4 6 8 IO

FLIGHT TIME (set)

FIG.7 TEST CONDITIONS - MODEL 2

600 600 .

30 JET ST% PRE&E AT P6&,n2)

70

FIG. 8 PRE-FLIGHT CALIBRATION OF

60

50

46

30

20

THRUST v JET PRESSURE

p 0*57in

I3

44 4.2 i.3 44 i.5 FREE -STREAM MACH NUMBER

FIG. 9 IN-FLIGHT JET STATIC PRESSURE (MODEL 2)

THRUST

(lb+‘)

550

500

450

400

I*2 I.3

FREE - STREAM MACH

I .4

NUMBER

FIG. IO INFLIGHT THRUST (MODEL 2)

O-2!

0*21

O-i!

ON

O.O!

C

-0.05

5

I

5

JET OFF -.--

Co TOTAL

/

/’

/

I I 1 REFi, 1 MODEL 2

CO BASE JET OFF JET OFF

___---- _--- __--- ._----.

(0 44

I

vii 4.3 4.4

FREE -STREAM MACH NUMBER

JET ON APPROX M = 4 - i4 (PRESENT TEST )

FIG. II TOTAL AND BASE DRAG COEFFICIENTS

Printed in England for Rer Kajesty’s Statbwy Offke by the Royal Aircraft Bstoblishnent, Farnborough. Dd.129528. X.U.

A.R.C. C.P. No. 969 November 1966 creenwocd C.H. AN IN"dCAT1ON INTO A ‘IECHNIQ”E FOR tlUSlRIN0 JET INWWFBXS~WXSUSIffiFR~-FLIGHTTLi

533.695.7 : 533.696.5 : 533.6.055 : 533.6.013.12 : 621.455-846

A free-flight uodel lnvestlgatlon 1s described. Che mjor object or tiloh A IFee-rlight lmdel 1”vestlgaClo” 1s descrlbedS ti lna,or object of WI&,,

~8s to gal” design end operational exrerlenoe 1” the rleld of jet lnter- me to gain design and ~~mtlo”el erpa-lence ln the rleld or jet inter- lerell~e stodles. tkaaopmnts RIP ~8de or th0 erred 01 .9 propli~i~e rerence etudles. neasurenents m-e mde or the errect or B pmplisi~r

jet on the external ~FW or e boattelled body or remlutlo” but because jet on the external drag of e boattailed body or remluClo” but because 0r tm~ertainties in the jet perfonnanca these meestn‘ements am 0r 0r ~n~~rcdntie~ in the jet per(0-e these ma~l~ems nts are or

sigmicanee my in i~ustming chs experiment.31 technique. A solld- Slgnlf 1oe”ce only 1” 1lluscmt1”g the exper1mnta1 teoh”1q”e. A SolId-

ruei moket m~t0r YS~S uSed 8.9 the primary sou-oe 0r ths jet 11011. rm mcket motor ws usd 88 the primry source 0r tha jet flow.

A.R.C. C.P. No. 969 November 1966 Greenwocd G.H AN IN"dGATIb4 IN“0 A TDCHNIWE FOR HUSlRING JET II~RFERFNCEITFECTS"SING FR~-FUG~f+XZLi

533.695.7 I 533.696.5 : 533.6.055 t 533.6.013.12 : 62l.455-ml6

A.R.C. C.P. No. 969 November 1966

Greenwood CA AN RNEhATICN INTO A TEcKNIQ"E FOR tlUK"RINF JET

IlrnRFEWE ETEms IBfNc Frm-FLIGKT mEIs

533.695.7 1

533.696.5 I 533.6.055 t 533.6.013.12 8 62l.455+6

A rme-rllght model lmestlW&,” 1s desmlbed, the mjor object or nhlc,, slt1s co gal” deslg” end opx’ntlonel erperlenoe 1” the field or jet lnteer reren0e studles. neasmements m-3 mde or rh erre0t or a pmmdra jet 0” the external drag or a boattelled body or ~emluClo” bw. baausa 0r ~ncm3intie~ in the jet ~erf0m0e the98 ma-mt.a ark 0f slh?nlllca”ce only 1” 1110strat1ng the experhe”ta1 ceoh”1que. A solld- ruei rc~ket mm lld9 used BS the primly SOWB 0r th8 jet ri0a

C.P. No. 969

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C.P. No. 969

S.0 CODE No. 23-9017-69