MXNSSTRY OF SUPPLY AERONAUTICAL RESEARCH COUNCIL REPORTS AND MEMORANDA. of 7 a Pitot ~ntake the Air Stream. X. PLACE and R.

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1 P~. & M. N A.~.G. Technical Reprt t.i ~ ;2 I!Z:, ' MXNSSTRY OF SUPPLY AERONAUTICAL RESEARCH COUNCIL REPORTS AND MEMORANDA :!' ~ i " ',' ~i~ i''~ 'i j i[;_ " ~', c,-, '....~ "-:~ 7 ):, ~Fhe, Efiqciency t f 7 a Pitt ~ntake the Air Stream ]Tnd[~ned. X. PLACE and R. LECAVALIER Crtn Cpyright Reserved LONDON" HER MAJESTY'S STATIONERY OFFICE 195z PRIc~ zs 6d ~ET

2 The Efficiency f a Pitt tntake Inclined t the Air Stream E. L. PLACE and R. LECAVALIER COMMUNICATED BY THE PRI>:CIPAL DIRECTOR OF SCIENTIFIC RESEARCH (AIR), MINISTR~I~l~.:U~'Fy:-27,-,.'W~... 'i... ~"<:<q -: "--~-:,~ Y?.52 Reprts and Memranda N J ~.~k ]:'~ "~ Y':~ ~ ~ i Oct/~er, 1947 "~... Summary.--In an earlier reprt n intake ducting fr supersnic flight 1, the efficiency f a 'pitt' type intake was discussed and shwn t have a marked effect n the perfrmance f gas turbine engines. The present reprt is supplementary in that it describes the effect f inclining the pitt intake t the main air stream directin in the transnic Mach number range 0-7 t 1.5, an effect which is at present incalculable. Curves are presented shwing the influence f inclinatin n intake adiabatic efficiency and air mass flw int the intake. These experimental results are then illustrated by applicatin t the perfrmance f a typical turbine engine and a prpulsive duct in snic and supersnic flight. At a flight Mach number f 1.5, it is fund that, fr bth turbine engine and prpulsive duct, an inclinatin f 5 deg reduces the net thrust by rughly 2 per cent cmpared with the nrmal flight thrust. Fr inclinatins greater than 5 deg, hwever, thrust fails ff mre rapidly, and at 10 deg inclinatin, it is reduced by rughly 6.5 per cent fr the turbine engine and 7.5 fr the prpulsive duct. 1. Experimental Investigatin.--A sketch f the mdel is shwn in Fig. 1. The pitt intake (a half-scale mdel f that emplyed in the investigati.n f Ref. 1) cnsisted f a straight taper, divergent duct f 7 deg ttal internal angle, the entry internal diameter being 0.5 in. and the area rati fur t ne. The static pressure (P,) at the delivery end f the divergent duct was measured ver a range f air mass flws at apprach Mach numbers 0.7, 0-9, 1-0, 1.3, 1-5, fr a range f inclinatin 0 = q- 15 deg in intervals f 8 deg. The airstream, apprximately 2.5 in. square in crss-sectin, was supplied by Busemann nzzles fr Mach numbers greater than unity, while fr the snic and subsnic streams a nndivergent nzzle was used. 2. Discussin f Results Efficiency:--The variables invlved are verall adiabatic efficiency, Mach number f the apprach stream, air mass flw and angle f inclinatin (0). The intake adiabatic efficiency, ~i, is based n delivery static pressure Pe, n crrectin being made fr any difference between delivery static and ttal head pressures. That is (p,/p~) {~ - 1)/~ _ 1 (p,/p~) {~ -111~ 1 = 1 1) 2 where Pt,~ ttal head pressure f apprac h stream. P~ static In Figs. 2 t 6, this efficiency is shwn pltted against the rati f actual mass flw t the maximum mass flw at zer inclinatin, fr the five apprach Mach numbers, with angle f inclinatin a~s parameter. Each curve is the mean f tw experimental curves, ne fr psitive, the ther fr negative angle f inclinatin. Fig. 7 gives an indicatin f the scatter f the experimental pints. Within the chsen range f inclinatin, that is 4-15 deg, there is n effect f inclinatin n efficiency at zer mass flw, which is perhaps t be expected since the intake is then acting as large pitt tube. 1

3 It will be seen that fr zer inclinatin at supersnic apprach velcities, there is a fairly well defined mass flw belw which the efficiency remains cnstant, and abve which the efficiency rapidly falls t zer. The first regin f the curve crrespnds t the state in which a curved shck surface is lcated ahead f the intake, delivery pressure being cmparatively independent f mass flw. With increasing mass flw, this shck wave appraches the intake and becmes less cncave, until in thery a plane shck wave is lcated acrss the entry, and the mass flw reaches a maximum 'crrect' value equal t the mass f air impinging n the entry. This cnditin crrespnds t the regin in which the curve turns ver sharply. Any further reductin in delivery pressure leads by 'ver-expansin' t higher supersnic velcities in the diffuser, fllwed by a cmplicated system f shck-waves. In practice, the theretical curves are apprached nly at high Mach numbers, and belw an M~ f abut 1.5 the abrupt change in directin f the curves becmes mre gradual. As is t be expected, inclinatin f the intake t the apprach stream directin als gives the curves a gradual sweep, since a plane shck wave can bviusly nt ccur acrss the entry. Subsnically, this tendency is much mre marked Reductin f Mass Flw.--Inclining the intake, t the apprach stream leads t a reductin in the maximum mass flw which can pass int the entry (Fig. 8). As this effect is mst marked at subsnic apprach velcities, sme additinal curves have been added dwn t a Mach number f 0.5. Fr the lwest Mach numbers, the reductin in back pressure was limited by the rifice meter and straightener plate, and curves are given nly fr small angles f inclinatin. It is seen that an angle f inclinatin f 10 deg leads t a mass flw reductin f 1.5 t 3 per cent ver the Mach number range 0-8 t 1-5, but t a much greater reductin at lwer Mach numbers. At zer anal e f inclinatin, the mass flws calculated frm intake cnditins are in reasnable agreement with thse measured by the air-flw meter. Als shwn are pints, indicated by circles and squares, crrespnding t the pssible laws f mass-flw rati varying as cs 0 and cs ~ 0 respectively, where 0 is the angle f inclinatin. 3. Engine Thrust in Supersnic Flight.---By virtue f the influence n intake efficiency, inclinatin f an aircraft with pitt intake t its flight path will affect the engine thrust. In rder t illustrate this effect, calculatins have been carried ut fr a typical gas turbine engine and fr a prpulsive duct in supersnic flight, the fllwing characteristics being assumed at isthermal height. Gas Turbine Engine. Cmpressr temperature rise = 200 deg C Bypass air mass flw/cmpressr air mass flw = 2 Fan temperature rise = 35 deg Engine T... = ll00deg K Augmentr Tm,~ = 1500 deg K Cmpressin efficiency (including cmbustin pressure lss) = 75 per cent Fan efficiency = 80 per cent Turbine efficiency = 84 per cent Augmentr cmbustin pressure lss as fr prpulsive duct belw Pr@ulsive Duct T~,~ = 1500 degk Cmbustin chamber inlet velcity/aircraft velcity = 0.1 Jet efficiency per cent The cmbustin chamber pressure lss is assumed t be made up f an aerdyn~/mic lss f fur inlet velcity heads tgether with the fundamental heating 10ss. That is Cmbustin chamber pressure lss Trt... = +3 Cmbustin chamber inlet velcity head ~F~~ ~ 2

4 In bth cases the assumptin f cnstant vlume flw is made (fr the prpulsive duct the cmbustin chamber inlet velcity is taken cnstant fr a given frward speed), s that it is pssible t find a relatin between intake efficiency and mass flw rati fr each apprach Mach number, prvided that a design mass flw is assumed. Fr the thrust calculatins, this has been taken, fr each apprach velcity, as 95 per cent f the maximum mass flw which can pass thrugh the intake at zer inclinatin. As nted previusly, this value is reasnably well defined fr Ms =1.5, ccurring just befre the abrupt reductin in efficiency. The same value f 95 per cent is used fr lwer apprach velcities, althugh the pint becmes less clearly defined. Thus in Figs 2 t 4, the dashed lines represent perating curves fr bth turbine engine and prpulsive duct, and have been drawn fr design mass flws f 95 per cent and 90 per cent f the maximum mass flw at zer inclinatin. Figs. 9, 10 shw the net thrust and specific fuel cnsumptin fr the turbine engine and prpulsive duct respectively, relative t their values at 100 per cent intake efficiency, this basis being chsen t avid vercrwding the curves, the slpes f which are rughly equal at flight Mach numbers f 1.5 and 1-3 but rather greater in snic flight. Cndusins.--At zer mass flw thrugh a pitt-type intake, angles f inclinatin up t 15 deg have n effect n verall adiabatic efficiency, the intake then acting as a large pitt tube. With increasing thrugh-put a reductin in efficiency appears, but is nt serius fr angles f inclinatin belw 5 deg until the mass flw appraches the crrect value, that is the maximum mass flw at zer inclinatin. It is pssible t plt mass flw-efficiency curves fr which a cnstant vlume f air enters the intake, and these will represent engine perating curves fr given designmass flws. Chsing a design mass flw equal t 95 per cent f the crrect mass flw fr each apprach velcity, it is fund that fr bth turbine engine and prpulsive duct at a flight Mach number f 1.5, an inclinatin f 5 deg reduces the net thrust by rughly 2 per cent cmpared with the nrmal flight thrust. Fr inclinatins greater than 5 deg, hwever, thrust falls ff mre rapidly, being reduced at 10 deg by rughly 6-5 per cent fr the turbine engine and 7-5 per cent fr the prpulsive duct. Under the same cnditins, specific fuel cnsumptin is increased by 3 per cent and 4-5 per cent fr turbine engine and prpulsive duct respectively. Maximum thrugh-put is mderately affected by inclinatin in the transnic Mach number range 0.8 t 1-5, the reductin being f the rder 1.5 per cent t 3 per cent fr 10 deg inclinatin. Fr lwer subsnic velcities hwever, the effect is much greater. REFERENCE N. Authr 1 A.G. Smith, E. L. Place, and S. J. Andrews Title Intake Ducting fr Sfipersnic Flight. Pwer Jets Ltd. Memrandum N. M December, 1945.

5 PITOT INTAKF-. ' BUSEMANN MOZZLE DELIVF..~Y PRES ur P.. ANGLE 0~' [NCLINATIOH (,~'~ P'r'r= FIG. 1. Inclined pitt intake test rig. ~ NOI.L~ INI"I"~NI.,-4.) 0 m it3 D " iv Ill ~ Z Z ~ v U 9 ul... O I1_ ~ >- UU 0 b~ ~ ~ ~ O O 13, 4

6 .IOO ENGINE OPERATINC~ CURVE5 (CONSTANT VOLUME) i5 ENCnlNE OPERATING CURVES ('CONSTANT VOLUME ) % ~0 8O 0 ~ Z I~ ~j % Z.0 z.j LI :Z m ~0 GO ADIABATIC. I EFFICIENCY % O 40 5O ~ I00 MASS FLOW RATIO % I00 MASS FLOW RATIO % I~IG. 3. Variatin f verall adiabatic efficiency with angle f inclinatin. Apprach Mach number = FIG. 4. Variatin f verall adiabatic efficiency with angle f inclinatin. Apprach Mach number = 1-0.

7 IO " ;Z "7 w ta _z B z g Z 3 u 15 z ADIABATIC EFFICIENCY % EFFICIEMCY O EO I00 MASS FLOW RATIO % 2O I00 MASS FLOw RATIO /. FIG. 5. Variatin f verall adiabatic efficiency with angle f inclinatin. Apprach Mach number = 0.9. FIG. 6. Variatin f verall adiabatic efficiency with angle f inclinatin. Apprach Mach number = 0.7.

8 I0 I00 M~Sf= FLOW R~ITIO% 9C 80 & V B X ii.i l 9S 9O j M = 1.0 M, = 1.31 M = I0 IS ADIABATIC EFFICIENCY ".a 60 ~S N = I-0 MASS FLOW R~Tt0% M = M = 0-8 Ma = 0"7 40 8S 3O FIG I00 MASS FLOW RATIO ~ Variatin f verall adiabatic efficiency with angle f inclinatin 0, Apprach Mach number = S IO 1 ANGLE OF inclination ~0 FIG. 8. Variatin f maximum thrugh-put with inclinatin. (Curves crrespnding t mass flws beying cs 0 and cs ~ 0 laws are indicated by circles and squares respectively).

9 I00 I00 a ~O 90 ~r T~UST% NET q'h RUST ~/ BO M~ = I'0 M, = 1"3 Ma = 1"5 "70 GO M = I-3 Ma = I-0 M ='1"5 GO 60 1"3 // M "2 SR VIJEL CONS RATIO I.I f J J M : 1-5 M = 1.0 Ma = 1"3 $P, FUEL. CONS 19, AT] 0 I-2 I.t J I I / //, M = 1.5 M = S I0 IS ANGLE OF INELINATION (~ FIG. 9. Net thrust and specific fuel cnsumptin fr typical turbine engine. (Relative t 100 per cent intake efficiency}. Design mass flw 95 per cent f maximum mass flw at 0 = 0 deg. I,'0 5 1O IS ANGLE OF INCLJNATIOIN 6 FIc. 10. Net thrust and specific fuel cnsumptin fr prpulsive duct. (Relative t 100 per cent intake efficiency). Design mass flw 95 per cent f maximum mass flw at 0 = 0 deg.

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