7/25/2019 FI - Primeiro Kfir 1975 - 1254

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8

FLIGHTInternational 7 July

975

IAI Kf i r

M i r a g e

successor

B y Y E H U D A B O R O V I K

O

UTWARDLY

the Kfir i s markedly

similar to the Mira ge family , espec

ial ly the 5J60 del ta wing, central

fin, twin semi-circular air intakes with

variable-geometry spikes , unders lung

pi tot tube and ventral fuel tank pro

t ruding from the rear fuselage.

A m ajo r d rawback o f Mi rage I l l s

and 5s , however, i s thei r Sn ecma A tar

9 eng ine, which develop s relativ ely low

thrust and has a high specific fuel

consumption (s . f .c) .

Is rael i A ir Force M irage IIIBs and

IIICs are engined with the A tar 9B,

whereas later models such as the HIE

and the 5 have the more advanced

A tar 9C. Both develop the same maxi

mu m thr ust b ut the 9C ha s a s l ight ly

lower s.f.c. , an improved compressor

being used.

T he Kfir engine is practic ally iden

tical to the J79-17 which powers the

F-4E, possibly with minor modifica

tions.

T he J79 's s .f .c . i s bet ter tha n the

A tar 's and is about half-way to tha t

of a mo dern en gin e: A tar 9C, 1-01;

J79 , 0-84; F100, 0-70. T he A tar 's s .f .c .

i s 17 per cent h igher than the J79 's in

dry thrust and 3 per cent h igher in

afterburning.

Kfir has the 6 delta wing of the Mirage

SJwhich would have been Israel s ground-

attack aircraft had France not embargoe d its

sale

and employs no leading-edge high-lift

devices

T he Gen eral Electr ic engine therer

fore burns 17 per cent less fuel on a

pound-for-pound basis . T he J79 is

more efficient for a number of

r e a s o n s :

M ass flow is abou t 11 per cen t

higher, necess i tat ing a redesign of

the in t ake duc t s .

Com press ion ra tio is significantly

higher, 12-4:1 compared with only

5-4 :1 on th e A ta r 9 .

T u rb ine in l e t t em pera tu re on th e

J79 is h igher at 954C, thanks to the

use of bet ter heat-res is t ing al loys and

more efficient cooling.

T he increased tu rb ine in l e t t em

perature manifes ts i t sel f in a much

h igher ex te rna l wal l t empera tu re (up

to 700C against 350C for the A ta r) ,

and this posed one of the major prob

lems which the Kfir developers had to

overcome.

T he J79 exha ust sys tem and after

burner, wi th a variable nozzle, are

mo re eff icient than thos e of the A tar .

T he in take flow rate in both th e

Mirage and the Kfir i s varied by

means of a spike moving forwards and

backwards wi th in the duc t , t hereby

chang ing the th roa t a rea and the

Shockwave pat t ern . A s noted above,

the J79 requires a f low rate about

11 per cen t h igher tha n tha t of th e

A tar 9, bu t apar t f rom the increased

inlet area, which obviously entai ls a

modified spike displacement ruleno

other changes in the Kfir in take duct

can be discovered from an outs ide

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inspect ion. To increase the f low rate

during take-off the Kfir, l ike all Mir

ages, is fi t ted with auxiliary blow-in

doors behind the in let .

T he J79 is about 64cm shorter tha n

the A tar 9C, i t self so me 30cm s horte r

than the A ta r 9B. S ince the var i ab le

exhaust nozzle must protrude from

the fuselage to provide operat ing

clearance the Kfir af terbody had to be

shortened and modified.

T he a f te rbody mu s t be des igned

for minimum drag as wel l as to pre

ven t in t e r fe rence be tween the j e t

efflux and the flow passing over the

afterbody and the wing control sur

faces . To reduce base d rag the c l ear

ance between the port ion of exhaust

nozzle enclosed within the fuselage

and inner fuse lage wal l mus t be kep t

to a min imum . A t the sam e t ime t he

afterbody contours must not vary

dras t ical ly , s ince th is would resul t in

increased d rag .

The J79 's ex te rna l wal l t empera tu re

is about 300-350C higher than for

the A ta r . T he A ta r is p rov ided wi th

a thermal shield fit ted directly on the

engine but the-J79 is not . In other

J79-powered aircraft such as the F-104

and the F-4 the fuselage port ion en

clos ing the engines is bui l t of mater

ials such as s teel superal loys and t i

t an ium. T he Mi rage , however , i s bu i lt

ent i rely of aluminium al loys , which

are l iable to develop creep at such

h igh t empera tu res .

Viewed from the outs ide, the Kfir

fuselage appears to consis t ent i rely of

aluminium. I t can therefore be as

sumed that some other type of solu

t ion has been found for engine cool ing

and /o r thermal in su la t ion o f the fuse

lagethe f i t t ing of an extra thermal

shield around the J79 and provis ion of

external cool ing ai r . In the Mirage,

engine cool ing ai r i s suppl ied through

the boundary-layer separat ion ducts

wedged be tween the a i r i n t akes and

the fuselage w al l . T he quan t i ty of ai r

thus provided was adequate for cool

ing th e A tar , bu t insufficient for the

J79. A n exam inat ion of the Kfir re-

Instal lat ion

of a General Electric J79 turbojet

in place of the Mirage s Snecma Atar saves

64cm in engine length and has resulted in a

new design of afterbody being adopted for Kfir