www.aerostories.org___________________________________________The heart of the SR-71 "Blackbird" :The mighty J-58 engine
by Philippe Ricco
Translation : Graham Warrener & Marc Binazzi

NASA

Part one :GenesisPh. Ricco

1.1 : Development

page A-1

1.2 : Evolutions

page A-4

1.2 : Ground and flight tests

page A-6

1.4 : Improvements

page A-11

1.5 : Projects and variants

page A-12

1.6 : Note about designations

page A-14

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Genesis : 1.1 : Development

The Blackbird was the only aircraft ever to be designed around
the J-58 (JT-11). This turbojet engine had been developed for a
USN project, by Pratt & Whitney, at their West Palm Beach R &D center in Florida. Eventhough its existence remained a secretuntil revealed on 28th February 1964 by US President Lyndon B.
Johnson, that of the JT-11 engine was already known to specialists.
The very first Mach-3 jet engine, designed by Pratt & Whitney for the
North-American XB-70, was the J-91
(aka JT-9). In spite of a hazy future forthat six-engined bomber, the design
studies for the propulsion units proved
fruitful when a somewhat smaller but
also Mach-3 engine had to be designed for the US Navy, named JT-11
and known later as J-58. The initialdesign-studies for this turbojet werelaunched in 1956.
At the outbreak the project was company-funded, but soon the
U.S. Navy, which was developing a Mach 3 strike aircraft, started sponsoring its development. The U.S. Navy requirement
called for an engine with sufficient thrust for sustained flight in
the environs of Mach 2.5, however able to reach short-burst
peak speeds exceeding Mach 3.

Pratt & Whitney 304-hydrogenengine prototype planned to equip
the project Lockheed "Suntan".
© Pratt & Whitney

Initially it was to be fitted on an upgraded version of the North
American A3J-1, from which the RA-5C "Vigilante" would later
emerge. As part of this program, two projects by Vought designated V-418 and V-419 also came into being, better known under their generic designation of F-8U-3 ”Crusader III". The first
was fitted with a J-75, the second received a J-58.
The engine would implement the ramjet principle to supplement
the low compression rate from the axial compressor. It was designed to supply 26,000 lbs (11,800 kg) of thrust, with afterburning, at sea-level. The first official aid, amounting to $ 11.2
million (55 M Francs) was received in August 1959, with an order for 30 prototypes. In the meantime, the YJ-58 was undergoing ground running trials (in 1957). The 50 hours running acceptance trials were completed in August 1958, thus evidencing thefast pace at which the development of the new engine progressed.
Alas, due to sky-rocketing costs, the US Navy eventually dropped the project. Only the Vought V-418 project succeeded inbringing forth the two XF-8U-3 prototypes, but once again thisproject was abandoned after the roll-out of the first F-8U-3, thepre-series of the McDonnell Douglas F-4H-1 ”Phantom II”.

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Over that period, trials were successfully performed in the specialized facilities at Wilgoos. On theirtest benches, flight conditions ofMach 3.2 up to 30,000 meters(100,000 ft) could be simulated. The
wind tunnel was capable of supplying air at high-pressure (2 at.) with a flow-rate of 750 lbs/sec.
(340 kg/sec.). Pratt & Whitney contemplated two possible developments of their ”super jet”; a military version capable of powering an aircraft at stratospheric altitudes at Mach 3 speeds and acivil version, capable of great thrust (to the order of 20 tons) overan extended flight duration – presented in typical 50’s jargon as”all supersonic”.

One of the first version of the J-58
without after burner as it appearedin the sixties in Pratt & Whitney
advertisements. It is probably a YJ58.
© Pratt & Whitney

Parallel to all this, Pratt & Whitney successfully accomplishedtrials of their model 304 liquid-hydrogen turbojet-engine which,although it had been officially rejected, was successfully tested
in October 1958. The final duration run on the test bench atWest Palm Beach lasted 25 hours 30 minute. As regretful as it
may be, the 304 turbojet remained only a prototype and the‘Suntan’ project, for which it was intended, was closed at the endof 1958 with a bill reaching 250 million dollars. Furthermore,since the General Electric J-93 had officially been selected on
6th November 1957 for the B-70, the development budget for the
J-91 was cancelled.
By then Lockheed had commenced working in the greatest
possible secrecy on a series of high-performance aircraft projects aimed at replacing the U2, numbered from A-1 through A12. Numerous engine installations were envisaged, among
which some featuring the high-thrust Pratt & Whitney J-58,
which had only recently completed
700 running hours. Thanks to the influence of Kelly Johnson and Pratt &Whitney’s chief-engineer William H.
Brown, Lockheed obtained an advance order on 29th August 1959 fortheir project designated A-12, fittedwith two J-58s, and allocated a development budget of $ 600 million. The
program, maliciously entitled ‘Oxcart’,
was officially approved on 30th January, 1960, and included the manufacturing of twelve aircraft for the CIA.
The project propulsion team had a staff of 27 engineers for the
initial stages of design-studies and development, including Don
Pascal, Norm Cotter, Dick Coar and Ed Esmeier, who would bejoined by William Gordon (who had been in charge of Pratt &Whitney’s Florida facilities) under the leadership of Brown. Gordon enjoyed a flattering reputation which helped promoting the
project as well as fostering at the time a good relationship with
Lockheed and the ‘silent’ partners.

This full-scale model of a J-58-P2
was made by Pratt & Whitney inHartford in July 1961 to study the
global size of the engine.
© Pratt & Whitney

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Furthermore the team was reduced and carefully selected. They
worked (like everything at the ”Skunk Works”) using a minimumof documentation and written contracts; instructions mostly took
the form of personal memos from engineer to engineer. The
privileged relations proved to be most enduring between Lockheed and Pratt & Whitney.
At that time, Pratt & Whitney had one of
the most powerful industrial computersat their disposal, an IBM-710. Its calculation capacities were at best equal tothat of some pocket calculators of the
1980’s. So with all things considered,
the J-58 globally still was another offspring of the good old slide-rule. Despite
all the performance graphs and benchruns most of power-unit integration problems would only be resolved by flight trials. The Lockheed – Pratt & Whitney duet enjoyed much from the understanding of government officials incharge of that specific file. They let the companies deal withproblems in their own way, and refrained too much from interfering in the course of the development phase of modifications
which might have operational or major budgetary aftermaths. It
is a consequence of this fast reaction to encountered technicaldifficulties, that project progress was accelerated and this wasrecouped in substantial financial savings.

The J-58 was later equipped with anafter burner. This model was usuallypresented as a J-58-P2 destined toequip the F8U-3 and A3J of the US
Navy.
© Pratt & Whitney

When project Oxcart was born, various codenames were employed for each sub-assembly of the propulsion units. So, theforward bypass was baptized ‘onion slicer’, whereas the aft one
was named ‘cabbage slicer’ whilst the trailing edge flaps were
given the most classic term ‘tail feathers’. But soon the codenames were dropped, an instruction soon being passed aroundinforming that standard terms should be used.

© Aérostories 2002

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Genesis : 1.2 : Evolutions
Resolution of the difficult flight conditions which the A-12 was toencounter, being at that period relatively unexplored, proved to
be a complex matter. Sustained flight above Mach 3 at high altitudes – demanded extended trials in the supersonic envelope(initially conducted with the J-75) as well as the study of new
fuels and lubricants. Moreover, due to the influence temperatures would have upon the function of the engine, every component would have to be manufactured from specialized alloys(stainless steel, Hasteloy X, titanium) which to up that time had
only been used for such smaller components as turbine-blades.
The trials being carried out at the period with the experimental”X” planes were of little help, as these were mainly rocket propelled and their flights of short duration.
At the outset variable geometry jetpipes were to be an integral part of theengine. It was decided, jointly with
Lockheed, that these would be incorporated in the compression chamber,so as to keep dimensions within acceptable limits. Pratt & Whitney was
accountable for the nozzle and postcombustion chamber. On top of this Pratt & Whitney was busy
designing the control mechanisms because the engineers at
Lockheed had absolutely no experience of material requirements for gears, bearings and welding able to withstand suchtemperatures. Pratt & Whitney had hardly any more experience,
but were compelled to acquire it so as to see the program
through.

This Pratt & Whitney J-58-P2 engine was introduced to the French
public at the 1963 Le Bourget air
show.
© Pratt & Whitney via Jane's

The J-58 went through numerous modifications which, by 1960,
included changes to the bypass ducts, increasing the compressor stages from 8 to 9, so augmenting the rather low compression rate, and adopting an afterburner – intended for continuous
operation throughout a mission. The J58-P4 thus conceived for the A-12,
had few common parts with the initial
J-58-P2 studied for the US Navy. Only
the overall dimensions, the aerodynamics of the compressor blades andthe turbine unit were retained for thetime-being. Some time later eventhese would also be modified.
The result of the tests carried out in conjunction with Lockheed
evidenced, from the start, that at the intended higher Mach
numbers the new engine would be unable to cope with the volume of air coming through the air-intakes. This would result incompressor stalling with accompanying loss of efficiency andthrust at high speeds. Pratt & Whitney therefore modified their
JT-11 by installing a series of fixed flow-vanes downstream of
the 4th compressor stage, which directed the surplus airflow
along six longitudinal jet pipes running along the engine casing.

Another variant with after burnerof the JT11. This model was not
yet equipped with the six discharge veinswitch are the characteristics of the J-58-P4 on the
SR-71.
© Pratt & Whitney

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www.aerostories.org___________________________________________The surplus was then carried straight to the afterburner chamber
serving to cool the burners, whilst enriching the mixture; so enabling higher combustion temperatures or increased thrust.
This principle, innovative at that time, figured largely in the future
development of other engines called ”bypass jets". The J-58
cannot be properly referred to as being bypass jet, an unknown
principle at that time, as that did not derive from flow-vanes with
an irregular cooling affect, so serving to relieve the compressor
at certain stages of flight, which was obtained by a bypass flow
constantly shifting air from within the compressor towards theturbine outlet. Nevertheless the chosen formula allowed an effective limitation of the phenomenon of unstarts and compressor
fall-off due to variations in inlet temperature, on top reducing
specific consumption from 10 to 15%. This is the system which
Ben R Rich (Kelly Johnson’s successor as head of the ”Skunk
Works”) qualified as being a ”bypass jet engine by air withdrawal”.

© Aérostories 2002

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Genesis : 1.3 : Ground and flight tests
Despite the major difficulties inherent
to such an ambitious program, the first
prototype of the A-12 was ready to flyin less than two years. Concurrently
improving the JT-11 was a muchslower process, and the initial flights of
the A-12, in 1962, were carried out
with the Pratt & Whitney J-75, only half
as powerful but already proven. The
maiden flight of the A-12 took place on
April 26th, 1962, three months aheadof preliminary flight trials of the newengines, 3 years, 4 months after thegovernmental go ahead was given.
Numerous tests were carried out on the prototypes and preproduction engines before flight testing in an A-12 was undertaken. One of the problems which had to be overcome was thatso far no engine had explored these performance ranges, so no
regulatory documentation existed. Pratt & Whitney would not
only have to prove their new motor, but also simultaneously establish validation procedures. Featuring amongst large numberof tests were prolonged endurance tests of engine-functioning
over a duration of 150 hours.

To adequately conduct the "hightemperatures" tests of the J-58, a
special test bench was ni stalled at
Wilgoos to send the hot exhaust airof a J-75 engine directly into a J-58.
© Lockheed

As no test bench would possibly simulate the overheating likely
to be encountered in service, it proved necessary to build one
for that specific purpose. The adopted solution included the exhaust flow from a J-75 engine to supply hot air to the intake andcasing of a J-58 during a course ofexperimentation. Furthermore, available instrumentation did not make itpossible to obtain the required results
in real time.
As soon as Pratt & Whitney developed
more robust measuring instruments
and adapted calibration techniques tosuit, much more precise results wereregistered. Lockheed was kept informed on how things were progressing and on the analysis of acquireddata.
In the course of July 1963 the final pre-flight engine tests weresuccessfully carried out. It was not until January 1963, ninemonths after the maiden flight of the A-12 that 60-6924 received
the first J-58 installed in the starboard nacelle, so that at last thefirst flight tests could be undertaken.

The J-58 was an engine conceived
to operate continuously at Mach 3
with the after burner on for theduration of the flight, providing
spectacular results: seen here is a
J-58-P2 at the test bench, at night,
with red hot after burner exhaust"Diamond" shock waves can beseen in the burning discharge.
©Pratt & Whitney

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From the outset the J-58 proved to be tricky. Due to theunique nacelle geometry and the considerable gluttonyof the JT-11, the compressor suffered from air deficiency. The wind-tunnel models had not establishedwell enough the mass of airflow which was demandedby the engines. At first, this problem forced Lockheed
to start up the engine with certain access flaps open,
and, in any case, to alter the aerodynamics of the fairings and to install two extra air-ducts downstream of
the compressor to eliminate the trouble when it occurred. The first A-12 flew for some months with one
J.75 and one J-58, almost up to the final stage of testing.
But the greatest difficulties were to appear during in-flight trials.
The J-58 proved to be extremely vulnerable to ingested debris.
The great thrust, its immoderate thirst for air and the tortuous
intake system over the complex nacelle structure, meant that thesmallest nut, bolt or fragment of metal forgotten at the factory
was subsequently ingested – with disastrous consequences.
The smallest piece of gravel or asphalt on the taxiways or runway would cause catastrophic damage.
Many unfortunate events marred thefirst trials, caused by ingestion ofgravel or other foreign bodies such as
the manufacturer's logo which had tobe moved to another location to prevent it to be ingested in the future.
One day an inspector, assigned to theremoval of foreign objects from theintakes, forgot his flashlight in one ofthese. This was duly ni gested whilst
running-up the compressor.
The resultant bill for damages came to $ 250,000. An intensive
campaign against foreign objects of all kind was introduced at allstages of manufacture and operational trials. The tests andchecks were practical in nature and accompanied the nacelles
throughout manufacture. Blanking covers were fitted everywhere, warning signs were positioned visible to all workshop
personnel, the runway and its environs were systematicallyswept twice with the greatest care along the route taken by theengines. By these means the problem was reduced to a morereasonable proportion.

J-58 metal insignia almost intact
after being ingested by its compressor. After that, the factory marking
was engraved directly on the engine
case.
© Lockheed

Some examples of foreign objects
absorbed by a J-58 during taxi
tests: parts of a screwdriver, gravel,
chunks of asphalt…
© Lockheed

The rather complex system of the air-intake made an even supply of air to the compressor difficult to achieve. It was subject tosudden drops in airflow, provoked by numerous flight maneuversof the aircraft which caused compressor unstarts. This chronic
Blackbird problem was not really solved until computers had
been perfected which allowed compensating the slightest fluctuations in supply to prevent untimely unstarts.

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This forced Lockheed to replace the pneumatic air-intake control
system with a more efficient electronic system, despite related
complications caused by heat and vibration. Nonetheless thiscritical aspect of flight at low altitude would remain, making thehandling of the SR71 always a difficult task.
Many other problems to be solved cropped up during
the in-flight testing. Kelly Johnson told that during oneof the first flights, as a result of a sudden unstart, an A12 had to make an emergency landing, but the engine
casing had cooled down faster than the inner body; thecompressor blades made contact with the ‘shrinking’casing inner wall. This provoked ”one of the most im pressive firework displays on earth” to use the description given by the Skunk Works chief-engineer. To avoid
re-occurrence of such an incident, pilots had to maintain power during the descent, so as to hinder too quick
cooling during deceleration. In emergencies the pilots
had to cut the fuel supply completely so as to recoversafely.
The very high temperatures encountered during flight-testing
compelled the engineers to develop adequate new measuring
instruments, or alternatively to adapt instruments available to thedifficult ambient conditions encountered by the J-58 in operation,and for which they had not originally been designed. Therefore
the trial units were cooled using a water system, specially fitted
only for that purpose, so as to acquire the data necessary at thatstage of testing. Many thousands of measuring points were plotted during this stage of testing, particularly to study airflow at the
air-intake and jet-nozzle.

J-58 air inlet after the ingestion of
an inspector’s flashlight in charge ofchecking for foreign objects…Total
damages: $ 250,000.
© Lockheed

Later a second J-58 was installed in
the port nacelle, replacing the J-75
which had been fitted. If the initial difficult testing tended to confirm fears
that performance would be below that
expected, these were subsequently,
little by little, relieved thanks to thejoint efforts of Pratt & Whitney and
Lockheed.
Test pilot Bill Parks, who conducted
the first Mach 3 flights for Lockheed,stated that he had at his disposal a
propulsive thrust more than twice thatprovided by the combined engines ofthe ”Queen Mary”.

First stage turbine blade of the same J-58 after impact by a flashlight.
© Lockheed

Serious wear and cracks which appeared the long drive shaft
between the engine and its gearbox, also posed several key
problems related to the torque and fatigue on the shaft support
bearings. The propulsion engineers had to provide data, although they were incapable of knowing exactly the relative positions of the control box to the motor during operating tests, at thetime calculations were not sufficient.

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Measurements had therefore to betaken during flight. These evidenced,
amazingly, a displacement of about 4
inches (12 cm) of the gearbox from theengine during high speed flight. The
gearbox was then unable to support
the shaft, which not surprisingly wasoften found to be twisted. The problem
was solved by providing a new shaft
containing a double universal joint.
The fuel system, upstream of the engines also showed signs of fatigue
and distortion. Measurements takenusing a fast recorder indicated that thefuel supply pressure to the engine wasgoing off scale.
This over-pressure was fouling theengine hydraulics system. The phenomenon did not show up either during rig testing nor during engine
ground testing, because of the minimal
quantities of fuel involved. To solve
the problem Lockheed designed a”high-temperature sponge”, (promptly
nicknamed ”football”) which was installed in an accumulator ahead of theengine. By this means pressure spikes
were reduced to acceptable levels.

Above: This superb view of the SR-71s assembly plant depicts some ofthe precautionary measures taken following the problems encountered by
the powerful J-58s during the first tests.
© Lockheed
Below: Specifically, Lockheed instituted an awareness campaign for the
personnel working on the SR-71s, especially displaying large warning
signs alerting them to be on the lookout for "FOD": foreign objects damage.
© Lockheed

The major difficulties encounteredduring flight trials appeared in thephases of transonic flight. Under certain conditions, the outer half of thenacelle would rotate into the engine
and crush the engine plumping andanything else in the way.
Pratt & Whitney had to totally redesign the attachment points at therear of the engine. The initial stiff rails
located above the engine, reinforced
by a bracing strut between the motor
and the casing were replaced by tangential links between the lower engine
casing and the external nacelle. This
maintained a finite distance between
the nacelle and engine under all conditions.

The J-58 final version: the J-58-P4, alias JT-11-D20B, with its typical sixvein bypass.
© Pratt & Whitney

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It is strange to think that, although Pratt & Whitney had reacheda paranoid level with the high-temperatures and the almost impossible cooling requirements, their engineers had neglected toconsider that, during certain stages of flight, the fuel would becold whilst the ambient environment was hot – and vice-versa.
When these conditions occurred the fuel supply and ignition systems would malfunction. To remedy this it proved necessary to
install heating for the main controller and to tweak servo responses.

© Aérostories 2002

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Genesis : 1.4 : Improvements
Testing and proving the complex propulsion system of theBlackbird would continue for several years after the SR-71 was
accepted into operational service, especially to overcome theviolent eddies blocking airflow at the air-intake, accompanied by
loud bangs (rumbling) which wastraced to popping of the inlet shock.
Trials were conducted until the start ofthe 1970s by NASA on the YF-12A
and YF-12C. Specifically the introduction of SAS (stability augmentation
system) and digital aircraft flight andinlets control systems (DAFICS) forthe propulsion units allowed for improvement in engine functioning andthus aircraft handling…
According to NASA the analyses confirmed that an integrated
flight and engine control system would, from then on, have amajor influence on the flight characteristics of advancedtechnology aircraft flying at high supersonic speeds. Tests carried out in 1978 showed that in-flight regulation of air-inlet andnozzle exhaust flow brought with it a reduction in the intake air
withdrawal effect, and also permitted extension of operating
range and shortening the time needed for crew training.

A J-58-P4 engine was presented to
the news media at Ewards in 1964,
at the same time as the YF-12. Up
until then, only two photos had been
revealed by President Johnson.
© Aviation Week

Shortly after development commenced, a wager was opened
between Kelly Johnson and Bill Brown, over which of the twocompanies would succeed in producing the best fuel-injection
system for the aircraft. It was settled that the loser would have tocarry the costs for use of the wind-tunnel, which Brown estimated would be about 12,000 $. Pratt & Whitney won and true
to his promise, Kelly Johnson sent a check of sufficient value.
The event was used to play a prank. Bill Brown acquired a complete naval sailor’s uniform, with cap and blue jacket, and thus
attired had himself photographed in front of the 12.5 meters long
private yacht of Bill Gordon. He sent the photograph to Johnsonwith the comment "thanks for the check". The photograph hungfor many years afterwards on the wall of Lockheed’s staff reunion room.

© Aérostories 2002

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Genesis : 1.5 : Projects and variants
An initial batch of 50 motors was delivered to Lockheed in 1963
for fitting in the A-12 and the YF-12s. A second batch of one
hundred examples was dispatched in 1964 to equip the SR-71s.
Pratt & Whitney had great plans fortheir JT-11 super engine. They saw
the prototype and the those as JT-58s
destined for the Blackbirds unfolding
into a production series. Adaptationsof this motor were proposed for all thedesign studies of the period for hypersonic programs, much treasured in the 1950s – 1960s, such as
the SST or the Convair BJ-58. This latter four-engine design,
also known as the B-58C, was contemplated as a supersonictransport flying at Mach 2.5 and cruising at more than 70,000 ft(21,300 m), powered by four J-58s (without after-burning) of 23,
000 lbs thrust (10.400 kgp) mounted in two wing-tip nacelles.
A military version of this Convairmodel 58-9 was also announced under the name of model 62. It would
have had the capability to transport 52
troops. Twin-engine interceptor variants called B-58D (for Air Defense
Command) and B-58S (for the Tactical
Air Force) were also proposed fittedwith J-58s capable of propelling a loadof more than 30,000 lbs (13.600 kg). It
is likely that the Pentagon encouraged
this profusion of projects using theseengines so as not to draw attention to
the A-12.Much later development of adouble-flux version of the J-58 using
compressors of greater size was contemplated.
At the same time Pratt & Whitney proposed a nuclear version of
the J-58 using an indirect propulsion cycle, fuelled by a solid-fuelreactor cooled by a twin line system? The USAF intended being
equipped with a guided missile capable of low-altitude penetration. The program, named CAMAL was cancelled in 1960, but it
had demanded of Convair, involved with the project – in competition with Pratt & Whitney and General Electric, construction of
two subsonic NX-2 aircraft to experiment with the mode of propulsion.

The Convair B-58C bomber
project was to be equipped with 4
J-58 engines without after burner.
© Convair

In its civilian version, theConvair 62 was to beequipped with the same engines.
© Convair

These studies mainly permitted a comparison of the two classesof nuclear flux engines, those envisaged by General-Electric (thesimplest but dirtier system as the radioactive material was sent
directly into the combustion chambers) or those using the indirect cycle proposed by Pratt & Whitney which utilized liquid sodium as a high-temperature conductor between the nuclear reactor and the combustion chambers of the J-58 propulsion unit.

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www.aerostories.org___________________________________________The planes would fly in 1965 under
the designation of WS-125A/L, but
had been registered in 1961 as a
back-up for the WS-110A ”Weapon
System” which gave birth to the North
American XB-70 Valkyrie. Certain
Pratt & Whitney nuclear reactors wereadopted a little later by the commission for nuclear energy in its ”System
for Nuclear Auxiliary Power” (SNAP)
However, despite some trial n
i stallations of a nuclear reactor aboard a
giant B-36 bomber (alias the X-6) no
atomic propulsion unit would ever be
air-tested. Not even the General Electric system, design of which had progressed further than that of Pratt &Whitney’s system.
The description of another project derived from the J-58, namely the
SNECMA M-35 is of equal interest. In
1959 the French SNECMA company
signed a partnership agreement with
Pratt & Whitney which offered enviable
prospects. Not least because, at thestart of the nineteen-sixties, France
decided to conquer the challenge ofsupersonic-transport, SNECMA thus
had to design a propulsion system forthe future aircraft. That led to negotiations concerning the possibility of
manufacturing under license the JT11B3, a civil variant which was being
proposed at the then stage of J-58
development.
The
Franco-British
agreement of 1961, brought an end to
this project, with the decision to equip
the future "Concorde" with a turbojet ofBritish origin. However, one sometimes finds reference to the M-35 engine among the many Mach-3 aircraft
projects fashionable in France at that
time.

This strange experimental aircraft, the Convair NX-2 was to be built (two ofthem) to test the General Electric and Pratt & Whitney nuclear engines.
Effectively, an atomic version of the J-58 was seriously considered.
© Convair

The SNECMA Company considered building the M35, which was theequivalent of the JT11B built under license for the supersonic transport
airplane project (future Concorde). It is without doubts the reason that Pratt& Whitney introduced this J-58-P2 at the 1963 Le Bourget air show,
whereas the "Blackbird" the only airplane equipped with this engine wasstill totally unknown. Its existence was indeed not revealed until February
29, 1964.
© coll. Bodemer© Aérostories 2002

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Genesis : 1.6 : Note about designations
The military designation for this engine is J-58, but that given byits constructor is JT-11. The test-bench testing conducted in
1958 was with the YJ-58 prototypes. The turbofan version envisaged in the 1960s for the American SST (”Super Sonic Transport”) projects carried the designation of JT-11-F4. A JT-11-B4
variant with increased thrust was envisaged during the same erasame era for studying Mach 3 flight. It
seems that the designation J-58-P4
corresponds to the JT-11-D20B series
as the J-58-P2 is the version developed for the US Navy, without bypass,with only a 4 stage compressor (eightstages in all) against five in the J-58P4. The letter ”B” at the end of a Pratt& Whitney engine designation signifies
that it is modified for high-altitude flight(for example with burners adapted forJP-7 fuel).
The American system of engine designation is almost identicalto that used for aircraft; a letter indicates the type of engine (forexample R –”radial” ) followed by a distinguishing number. Withjet motors, their designation commences with ”J” (for jet engine),e.g. J-58 or J-75. double-flux engines, which appeared muchlater, are designated by a letter ”F” (for fan), e.g. The Pratt &Whitney F-100, which equipped the F-15 and F-16 fighters.
These letter-number combinations continue with one or two letters indicating the factory of manufacture, (”GE” for General
Electric, ”P” for Pratt & Whitney) and a ”batch number” indicatinga particular production batch. For example the J-79-GE15 which
equipped the McDonnell F-4D Phantom II, or the J-57-P55
which equipped the McDonnell F-101 Voodoo whereas the
Lockheed U-2 is fitted with the J-57-P31. The entire designation
can also be preceded by a special letter, for example ”X” for an
experimental unit, or ”Y” for a pre-series unit, or even ”R” (for aramjet).

The maneuvering dolly specially
adapted for the J-58-P4 equipping
the SR-71 "Blackbird".
© Pratt & Whitney© Aérostories 2002

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