Subject: Number Ninety in the Series--Lockheed XF-90

From: [email-masked]
Date: 4 Oct 93 16:19:38 GMT

>From [email-masked]

The Lockheed XF-90 experimental long-range penetration fighter of the 
early 1950s always reminded me of the planes flown by the 
*Blackhawks*, who were comic book heroes when I was a wee lad.  
Hawkaaaaaa......!

The USAAF had found by painful experience in World War II that fighter 
escort was absolutely vital for the survival of bombers in enemy 
airspace.  Unfortunately, the first jet aircraft were notorious fuel 
hogs and lacked the range and endurance of their piston-engined 
counterparts, and would be unable to escort long-range bombers such as 
the B-29, B-50, and B-36 all the way to their targets.  In an attempt 
to solve this problem, the USAF considered all sorts of proposals for 
markedly increasing the range of jet fighter escorts, some of which 
bordered on the bizarre.  One proposal for the solution to the escort 
fighter range problem was for the bombers to tow their escorting 
fighters into the combat zone and release them when their protection 
was needed.  Several experiments were made with B-29s or B-36s towing 
P-80 or P-84 jet fighters, none of them being very successful and some 
being downright dangerous.  Other proposals revived the parasite 
fighter concept of the 1930s, this time with jet fighters operating in 
parasite fashion from the bellies of large bombers.  The best known 
example of this idea was the McDonnell XF-85 Goblin.  Other ideas 
included the use of mixed power concepts such as that which produced 
the Convair XP-81.  Others involved the construction of large, bulky 
fighters that were virtually flying fuel tanks, e.g., the Bell XP-83.  

Initial attempts to produce jet-powered fighters with the endurance of 
piston-engined aircraft (e. g. the Bell XP-83 and the Convair XP-81) 
were disappointing, and in early 1946, the USAAF informally requested 
proposals for a "penetration fighter" with a combat radius of at least 
900 miles and a performance capable of meeting all opposing fighters 
on more than equal terms.  In addition, the USAAF wanted to keep the 
gross weight of the aircraft below 15,000 pounds.  The requirements 
were somewhat ill-defined--combat range requirements changed from 900 
miles to 1500 miles and then back to 900 miles, and climbing speed 
requirements were raised from an altitude of 35,000 feet reached in 10 
minutes to 50,000 feet reached in less than 5 minutes.  In addition, 
the aircraft was expected to be able to fly ground-attack missions if 
needed.  

Spurred on by the USAAF request, the Lockheed Aircraft Corporation 
gathered a team under the direction of project engineers Don Palmer 
and Bill Ralston to work on a submission.  In 1946, the Lockheed team 
submitted a design under the company designation of Model 090-32-01, 
which called for a delta-winged aircraft.  The USAAF was sufficiently 
interested that on June 20, 1946, they issued Lockheed a contract for 
two prototypes under the designation XP-90.  Serials were 46-687 and 
46-688.  A month earlier, the McDonnell Aircraft Corporation of 
St.Louis, Missouri had received a Letter of Intent from the USAAF for 
a competing design, the XP-88.  

The XF-90 had originally been a delta-winged design, but wind tunnel 
tests carried out at the California Institute of Technology indicated 
that such a configuration would not work.  Consequently, work on the 
construction of the delta-winged prototype was immediately halted, and 
those parts which had been already completed were scrapped.  The 
Lockheed penetration fighter project was completely redesigned, and 
the design which finally emerged was the Model 90, which featured 
35-degree sweptback wings, a sharply-pointed nose, and two 
Westinghouse J34 axial-flow turbojet engines mounted side-by-side in 
the rear fuselage and fed by side-mounted air intakes.  The wings had 
leading-edge slats, Fowler flaps, and ailerons on the trailing edge.  
The pressurized cockpit was fitted with an ejector seat and a bubble 
canopy.  Proposed armament was 6 20-mm cannon.  The internal fuel 
could be supplemented by wingtip-mounted tanks, bringing total fuel 
capacity to 1665 US gallons.  

The XF-90 was constructed of 75ST aluminum rather than the 
then-standard 24ST aluminum alloy.  The aircraft was built with heavy 
forgings and machined parts.  The result was an extremely 
well-constructed and robust aircraft.  However, these innovations also 
resulted in an aircraft which had an empty weight more than 50 percent 
greater than that of its primary rival, the McDonnell XF-88.  Since 
both aircraft were powered by the same engines, the performance of the 
XF-90 was certain to be much poorer than its rival.  

In late 1947, the XF-90 was to acquire yet another competitor in the 
form of an enlarged version of the North American F-86 Sabre.  In 
December of 1947, the Air Force ordered two examples of this North 
American design under the designation F-86C.  Unlike the XF-88 and the 
XF-90, the North American entry was powered by a single engine, an 
afterburning Pratt & Whitney J48 turbojet.  Since the F-86C design was 
so vastly different from the F-86A day fighter, the aircraft was later 
redesignated YF-93A.  

On June 11, 1948, the designation XP-90 was changed to XF-90 when the 
P designation was replaced by F.  

In the penetration fighter competition, the USAF initially favored the 
North American design because of its commonality with other Sabre 
variants, and in June of 1948 they supplemented the contract for the 
two F-86Cs with a contract for 118 production aircraft.  It would seem 
therefore likely that the F-93 would be assured of a long and fruitful 
career with the USAF, and that the XF-88 and XF-90 would be consigned 
to oblivion.  However, the F-93A production contract contract was 
suddenly cancelled in February of 1949.  Several reasons were given.  
Perhaps the most important reason was a severe reduction in the 
military budget for that year.  With limited funds available, it was 
decided to give priority to interceptors and to strategic bombers.  In 
addition, a Senior Officers' Board felt that no production order for 
any penetrator fighters should be awarded until a competitive flyoff 
between the three contenders could be carried out.  

The XF-90 was ready for flight testing in the spring of 1949.  The 
engines were a pair of 3000 lb.st. Westinghouse XJ34-WE-11 engines.  
The XF-90 was trucked out to Edwards AFB, where it underwent its 
maiden flight on June 3, 1949 with the well-known test pilot Tony 
LeVier at the controls.  Although test flying initially proceeded 
without many problems, the performance of the XF-90 was (as expected) 
rather sluggish because of its excess weight and the low power of its 
non-afterburning J-34 engines.  

In search of more power, Lockheed decided to fit the second prototype 
(46-688) with afterburning Westinghouse XJ34-WE-15 turbojets, each 
offering 3000 lb.st. dry and 4200 lb.st. with afterburning.  These 
engines were also retrofitted to the first prototype.  When powered 
with the afterburning J34s, the aircraft were redesignated XF-90A.  
The XF-90A achieved a maximum speed of 668 mph in level flight at 100 
feet, and reached a maximum speed of Mach 1.12 in a dive.  It was on 
one of these maximum speed dives that one of the XF-90As was almost 
lost when Tony LeVier experienced great difficulty in pulling out of a 
dive.  

Even though the afterburning engines gave the XF-90A a better 
performance, it was still not good enough to be considered acceptable 
to the USAF.  The performance of the XF-90A was actually poorer than 
that of the F-86A Sabre, which was already in service.  In pursuit of 
better performance, Lockheed explored three other developments of the 
XF-90: the Model 190-33-02 powered by a single Allison J33-A-29, the 
Model 290-34-03 powered by a pair of Westinghouse J46-WE-2s, and the 
Model 390-35-02 powered by a single General Electric J47-GE-21 engine.  
None of these projects ever saw the light of day, as they would have 
all required a major redesign of the intakes and fuselage to 
accommodate the larger air-flow requirements and the larger diameters 
of the engines.  

The flyoff between the Lockheed XF-90, the McDonnell XF-88, and the 
North American YF-93A took place between June 30 and July 8 of 1950.  
On August 15, 1950, the Evaluation Board declared the McDonnell XF-88A 
to be the winner of the contest.  

Work on the XF-90 was formally terminated in September of 1950.  In 
1952, the second XF-90A (46-688) was deliberately destroyed on the 
ground during a nuclear test at Frenchman's Flat in Nevada.  The first 
XF-90A (46-687) was shipped to the NACA laboratory in Cleveland, Ohio 
in 1953.  By this time it was no longer flyable, and was used for 
structural testing, exploring the limits of the extremely robust 
structure of the design.  Presumably it was tested to destruction, 
since I am unaware of the existence of any surviving XF-90.  

McDonnell's victory in the penetration fighter contest turned out to 
be rather hollow since no penetration fighters were ever actually 
manufactured or placed in service by the USAF.  At that time, wartime 
pressures mandated that priority be given to the procurement of 
existing types for use in Korea.  In addition, the development of 
long-range, high-speed jet bombers such as the B-47 and the B-52 
eliminated any real need for penetration fighters.  

Specification of the XF-90A: 

Two Westinghouse XJ34-WE-15 axial-flow turbojets, 3000 lb.st. dry and 
4200 lb.st. with afterburning.  Dimensions: wingspan 40 feet 0 
inches, length 56 feet 2 inches, height 15 feet 9 inches, wing area 
345 square feet.  Weights: 18,050 pounds empty, 27,200 pounds loaded, 
31,060 pounds maximum.  Maximum speed: 668 mph at 1000 feet.  climb to 
25,000 feet in 4.5 minutes, service ceiling 39,000 feet, normal range 
1050 miles, maximum range 2300 miles.  The planned armament of 6 20-mm 
cannon was not installed.  

Sources: 

  Lockheed Aircraft Since 1913, Rene J. Francillon, Naval Institute 
  Press, 1987.  

  Fighters of the United States Air Force, Robert F. Dorr and David 
  Donald, Temple Press Aerospace, 1990.  

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.  

Joe Baugher		AT&T Bell Laboratories   	
2000 North Naperville Road      Naperville, Illinois 60566-7033