Subject: Number Ninety-Three in the Series--North American YF-93A

From: [email-masked]
Date: 7 Oct 93 13:44:32 GMT

>From [email-masked]

Immediately following the Second World War, the USAAF wanted to acquire 
jet-powered escort fighters capable of meeting enemy interceptors on 
even terms, but most of the early jet fighter designs lacked 
sufficient range to escort bombers all the way to their targets.  
Since 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, they considered all sorts of proposals for markedly 
increasing the range of jet fighter escorts, some of which bordered on 
the bizarre.  Some thought that the range problem could be solved by 
having the bombers tow their escorting fighters into the combat zone, 
and several experiments were made with B-29s or B-36s towing P-80 or 
P-84 jet fighters.  Other proposals involving having jet fighters 
operate in parasite fashion from the bellies of large bombers, the 
best known example of this idea being 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.  They didn't ask for 
much, did they? :-) 

Lockheed submitted the XF-90 and McDonnell entered the XF-88 in 
response to this proposal, and the USAAF ordered prototypes of both 
designs in the spring of 1946.  In late 1947, North American entered 
the penetration fighter fray with a proposal for an extensively 
revised version of the F-86A.  

North American's penetration fighter proposal began life as company 
project NA-157 on December 17, 1947 It retained the swept-wing of the 
F-86A, but almost everything else was different.  For one, it had an 
entirely new engine.  The engine was to have been a Pratt & Whitney 
J48-P-1 centrifugal-flow turbojet rated at 8000 lb.st.  with 
afterburning.  The J48 was an American-built version of the Rolls 
Royce Tay.  Since the J48 was significantly larger than the J47 of the 
F-86A, the fuselage had to be increased both in width and in length.  
Additional fuel was added, bring the total fuel capacity to 1580 
gallons.  Since the NA-157 was a larger and heavier aircraft than the 
F-86A, twin wheels were used on the main landing gear.  

In December of 1947, the USAF ordered two examples of the NA-157 under 
the designation F-86C, reflecting its Sabre ancestry.  Serials were 
48-317 and 48-318.  

Armament of the F-86C was to have been six 20-mm cannon, and an 
SCR-720 search radar was to have been mounted in the nose.  Since the 
radar set now took up the nose, the air intakes for the turbojet had 
to be relocated to the sides of the fuselage.  These side intakes used 
special NACA-designed flush-mounted air scoops in the hopes of 
reducing aerodynamic drag.  The air brakes on the sides of the F-86A 
fuselage were replaced by a single large slab-type brake mounted on 
the fuselage belly.  

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.  At that time, 
it was decided that there were so many differences between the F-86C 
and the production Sabre that the F-86C should be assigned a new 
F-number--it was redesignated YF-93A.  

It would seem that the F-93 would be assured of a long and fruitful 
carreer with the USAF.  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.  

Even though the production contract had been cancelled, work on the 
two YF-93A prototypes (48-317 and 318) continued so that they could be 
entered in the penetration fighter contest.  The YF-93A was actually 
the last of the three penetration fighter competitors to take to the 
air.  The McDonnell XF-88 competitor had flown on October 20, 1948, 
and the Lockheed XF-90 had made its first flight on June 3, 1949.  The 
YF-93A did not roll out of the factory until late 1949, and was 
trucked to Muroc Dry Lake for flight testing.  George Welch took the 
YF-93A (48-317) on its maiden flight on January 24, 1950.  

The YF-93A was powered by a Pratt & Whitney J48-P-6 rated at 6000 
lb.st.  dry and 8750 lb.st.  with afterburner.  Although the YF-93A 
weighed over 26,500 pounds in combat trim, the 8000 lb.st.  
afterburning J48 was able to give the aircraft a top speed of 708 mph 
at sea level.  Maximum speed at 35,000 feet was 622 mph.  Initial 
climb rate was 11,960 feet per minute, rather impressive for the time.  
Service ceiling was 46,800 feet per minute.  Range on internal fuel 
was almost 2000 miles.  Weights were 14,035 pounds empty, 21,610 lbs 
gross, 26,516 lbs maximum takeoff.  Dimensions were wingspan 38 feet 9 
inches, length 44 feet 1 inch, height 15 feet 8 inches, and wing area 
306 square feet.  

The flyoff between the Lockheed XF-90, the McDonnell XF-88, and the 
North American YF-93A took place in the summer of 1950.  On August 15, 
1950, the Evaluation Board declared the McDonnell XF-88 to be the 
winner of the contest.  However, McDonnell's victory was rather hollow 
since no penetration fighters were every actually manufactured or 
placed in service because 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.  In addition, wartime pressures mandated that 
priority be given to the procurement of existing types for use in 
Korea.  

The two YF-93As were eventually handed over to NACA's Ames Laboratory 
at Moffett Field, California for comparison tests of the flush air 
intakes.  Late in their lives, both prototypes were fitted with more 
conventional air intake scoops extending over the NACA flush intakes.  
At one point in their service lives, both planes had their rear 
fuselages modified to accept a production F-86D tailpipe and 
stabilizer housing.  They were used by NACA as flight test and chase 
aircraft well into the mid 1950s.  They were eventually retired and 
scrapped.  

Sources:

  F-86 Sabre in Action, Larry Davis, Squadron/Signal Publications, 1992.

  The North American Sabre, Ray Wagner, MacDonald, 1963.

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

  Flash of the Sabre, Jack Dean, Wings Vol 22, No 5, 1992.

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