Subject: Number Eighty-Six in the Series--North American P-86 Sabre (1 of 22)

From: [email-masked]
Date: 5 Aug 93 01:38:26 GMT

>From [email-masked]

The North American F-86 Sabre is one of the greatest fighter aircraft 
of all time, ranking right up there with such aircraft as the Fokker 
D.VII, the Sopwith Camel, the Supermarine Spitfire, the Focke Wulf Fw 
190, the Mitsubishi Zero, and the North American Mustang.  It entered 
service with the USAAF in 1949, and was instrumental in denying air 
superiority to the Chinese during the Korean War.  After the Korean 
War ended, many Sabres entered service with dozens of foreign air 
arms, becoming the primary fighter equipment of many Allied nations.  
It was built under license in Canada, Japan, Italy, and Australia.  
Its service was so long-lived that the last operational F-86 was not 
withdrawn from service until 1993, which must be some sort of record 
for a combat aircraft.  

The F-86 Sabre began its life as North American Aviation's company 
project NA-134, which was originally intended for the US Navy.  As the 
war in the Pacific edged toward its climax, the US Navy was making 
plans to acquire jet-powered carrier-based aircraft which, it was 
hoped, could be pressed into service in time for Operation 
Olympic-Coronet, the invasion of Japan planned for May 1946.  The Navy 
had planned to acquire four jet fighters, the Vought XF6U-1 Pirate, 
the McDonnell XFD-1 Phantom, the McDonnell XF2D-1 Banshee, and the 
North American XFJ-1 Fury.  

Work on the NA-134 project began in the late autumn of 1944.  The 
NA-134 had a straight, thin-section wing set low on a rather tubby 
fuselage.  It featured a straight-through flow of air from the nose 
intake to the jet exhaust under a straight tailplane.  The Navy 
ordered three prototypes of the NA-134 under the designation XFJ-1 on 
January 1, 1945.  On May 28, 1945, the Navy approved a contract for 
100 production FJ-1s (NA-141).  

At the same time that North American was beginning to design the 
Navy's XFJ-1, the USAAF issued a requirement for a medium-range day 
fighter which could also be used as an escort fighter and a dive 
bomber.  Specifications called for a speed of at least 600 mph, since 
the Republic XP-84 Thunderjet already under construction promised 587 
mph.  On Nov 22, 1944, the company's RD-1265 design study proposed a 
version of the XFJ-1 for the Air Force to meet this requirement.  This 
design was known in company records as NA-140.  The USAAF was 
sufficiently impressed that they issued a Letter Contract on May 18, 
1945 which authorized the acquisition of three NA-140 aircraft under 
the designation XP-86.  

Both the XFJ-1 and the XP-86 were designed around a General Electric 
J-36 axial flow turbojet fed by a nose intake.  Both had a tailpipe 
exhaust in the rear of the aircraft.  It was hoped that this nose 
intake arrangement would be more efficient than the side intakes on 
the P-80.  Both USAAF and Navy designs employed a low-mounted, thin, 
straight wing.  The Navy's design had to contain some compromises to 
support low-speed carrier operations, but the land-based USAAF version 
was not so constrained and had a somewhat thinner wing and a slimmer 
fuselage with a high fineness ratio.  However, the XP-86 retained the 
tail surfaces of the XFJ-1.  

In the XP-86, a ten percent ratio of wing thickness to chord was used 
to extend the critical Mach number to 0.9.  Wingspan was to be 38 feet 
2 1/2 inches, length was 35 feet 6 inches, and height was 13 feet 2 
1/2 inches.  Four speed brakes were to be attached above and below the 
wings.  At a gross weight of 11,500 pounds, the XP-86 was estimated to 
be capable of achieving a top speed of 574 mph at sea level and 582 
mph at 10,000 feet.  Initial climb rate was to be 5850 feet per minute 
and service ceiling was to be 46,000 feet.  Combat radius was 297 
miles with 410 gallons of internal fuel, but could be increased to 750 
miles by adding a 170 gallon drop tank to each wingtip.  

A mock-up of the XP-86 was built and approved on June 20, 1945.  Early 
wind tunnel tests indicated that the airframe of the XP-86 would not 
be able to reach the desired speed of 600 mph.  It is highly likely 
that the XP-86 project would have been cancelled at this time were it 
not for some unusual developments.  

After the surrender of Germany in May of 1945, the USAAF (along with a 
lot of other air forces) was keenly interested in obtaining 
information about the latest German jet fighters and in learning as 
much as they could about secret German wartime research on jet 
propulsion, rocket power, and ballistic missiles.  American teams were 
selected from industry and research institutions and sent into 
occupied Germany to investigate captured weapons research data, 
microfilm it, and ship it back to the USA.  

By the summer of 1945, a lot of German data was pouring in, much of it 
as yet untranslated into English.  As it turned out, German 
aeronautical engineers had wind-tunnel tested just about every 
aerodynamic shape that the human mind could conceive of, even some 
ideas even only remotely promising.  A particular German paper dated 
1940 reported that wind tunnel tests showed that there were 
significant advantages offered by swept wings at speeds of about Mach 
0.9.  A straight-winged aircraft was severely affected by 
compressibility effects as sonic speed was approached, but the use of 
a swept wing delayed the effects of shock waves and permitted better 
control at higher speeds.  Unfortunately, German research also 
indicated that the use of wing sweep introduced some undesireable 
low-speed stability effects.  American researchers had also 
encountered similar problem with the swept-wing Curtiss XP-55 
Ascender, which was so unstable that it flipped over on its back and 
fell out of the sky on one of its test flights.  

In 1940, these German studies were of only theoretical interest, since 
no powerplants were available even remotely capable of reaching such 
speeds.  However, such studies caught the attention of North American 
engineers trying to figure out ways to improve the performance of 
their XP-86.  

It would do no good to build an aircraft capable of high speeds which 
would be so unstable that it would fall out of the sky at low speeds.  
The cure for the low-speed stability problem was to use automatic 
slats fitted to the wing leading edges.  The wing slats were entirely 
automatic, and opened and closed in response to aerodynamic forces.  
When the slats opened, the changed airflow over the upper wing surface 
increased the lift and produced lower stalling speeds.  At high 
speeds, the slats automatically closed to minimize drag.  

In August of 1945, project aerodynamicist L. P. Greene proposed to 
Raymond Rice that a swept-wing configuration for the P-86 be adopted.  
Wind tunnel tests carried out in September of 1945 confirmed the 
reduction in drag at high subsonic speeds as well as the beneficial 
effect of the slats on low speed stability.  The limiting Mach number 
was raised to 0.875.  

Based on these wind-tunnel studies, a new design for a swept-wing P-86 
was submitted to the USAAF in the fall of 1945.  The USAAF was 
impressed, and on November 1, 1945 it readily approved the proposal.  
This was one of the most important decisions ever made by the 
USAAF--had they not agreed to this change, the history of the next 
forty years would undoubtedly have been quite different.  

North American's next step was to choose the aspect ratio of the swept 
wing.  A larger aspect ratio would give better range, a narrower one 
better stability, and the correct choice would obviously have to be a 
tradeoff between the two.  Further tests carried out between late 
October and mid November indicated that a wing aspect ratio of 6 would 
be satisfactory, and such an aspect ratio had been planned for in the 
proposal accepted on November 1.  However, early in 1946 additional 
wind tunnel tests indicated that stability with such a narrow wing 
would be too great a problem, and in March the design reverted to a 
shorter wingform.  An aspect ratio of 4.79, a sweep-back of 35 
degrees, and a thickness/chord ratio of 11% at the root and 10% at the 
tip was finally chosen.  

All of these changes lengthened the timescale of the P-86 development 
in comparison to that of the Navy's XFJ-1.  The XFJ-1 took to the air 
for the first time on November 27, 1946, but the XP-86 still had 
almost a year to go.  

On December 20, 1946, a Letter Contract for 33 production P-86As was 
approved by the USAAF.  

The wing of the P-86 was to be constructed of a double-skin structure 
with hat sections between layers extending from the center section to 
the outboard edges of the outer panel fuel tanks.  This structure 
replaced the conventional rib and stringer construction in that 
region.  This new construction provided additional strength and 
allowed enough space in the wing for fuel tanks.  

The wing-mounted speed brakes originally contemplated for the XP-86 
were considered unsuitable for this type of wing, so they were 
replaced by a hydraulic door-type brake mounted on each side of the 
rear fuselage and one brake mounted on the bottom of the fuselage in a 
dorsal position.  The speed brakes opened frontwards.  These speed 
brakes had the advantage in that they could be opened at any attitude 
and speed, including speeds above Mach One.  

The first of three prototypes, 45-59507, was ready on August 8, 1947.  
Powered by a Chevrolet-built J35-C-3 turbojet of 4000 pounds of static 
thrust The aircraft was unarmed.  Test Pilot George Welch took the 
XP-86 up into the air for the first time on October 1, 1947.  The 
flight went well until it came time to lower the landing gear and come 
in for a landing.  Welch found to his shock that the nosewheel 
wouldn't come down all the way.  After spending forty minutes in 
fruitless attempts to shake the nosewheel down into place, Welch 
finally brought the plane in for landing nose-high.  Fortunately, the 
impact of the main wheels jolted the nosewheel into place, and the 
aircraft rolled safely to a stop.  The Sabre had made its first 
flight.  

With the bubble canopy, the pilot's field of vision was excellent.  
The noise and vibration levels were considerably lower than those of 
other jet-powered aircraft.  

On October 16, 1947, the USAF gave final approval to the Fixed Price 
contract for 33 P-86As, plus they authorized 190 P-86Bs.  

On April 26, 1948, George Welch took the XP-86 through the sound 
barrier for the first time, entering a shallow dive to do so.  It was 
the second American aircraft to exceed the speed of sound, following 
Capt.  Charles Yeager who had attained sonic speeds in the Bell X-1 on 
October 14, 1947.  The XP-86 was the first Western combat aircraft to 
be capable of supersonic speed.  It was found that the XP-86 could go 
supersonic in a dive with only a moderate and manageable tendency to 
nose-up, although below 25,000 feet there was a tendency to roll which 
made it unwise to stay supersonic for very long.  Production Sabres 
were limited to Mach 0.95 below 25,000 feet for safety reasons because 
of this roll tendency.  

XP-86 number 45-59597 was officially delivered to the USAF on November 
30, 1948.  By that time, its designation had been changed to XF-86.  
It was wrecked in a crash in September 1952 after accomplishing 241 
flying hours.  The second and third XP-86 prototypes (45-59598 and 
45-59599) were identical to the first, and remained in the test 
program until they were retired in April of 1953.  

Specifications of the XP-86: 

Dimensions: wingspan 37 feet 1 7/16 inches, length 37 feet 6/1/2 
inches height 14 feet 9 inches.  Weights were 9730 pounds empty, 
13,395 pounds gross, 16,438 pounds maximum takeoff.  An Allison-built 
J35-A-5 rated at 4000 lbs of static thrust was installed for USAF 
tests, and a maximum speed of 599 mph at sea level, 618 mph at 14,000 
feet, and 575 mph at 35,000 feet were attained.  It was 75 mph faster 
than anything else in service at the time.  Initial climb rate was 
4000 feet per minute.  An altitude of 20,000 feet could be attained in 
6.4 minutes, and 30,000 feet in 12.1 minutes.  service ceiling was 
41,300 feet.  Takeoff run was 3030 feet, and the aircraft could clear 
a 50-foot obstacle in 4410 feet.  

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.

  The World Guide to Combat Planes, William Green, MacDonald, 1966.

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

  Fury-The Navy's Sabre, Robert F. Dorr, Air International vol 44 No. 1
  1993.

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