an investigation into a technique for measuring jet...
TRANSCRIPT
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
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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 [email protected] 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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S.0 CODE No. 23-9017-69