Tag Archives: North American Aviation Inc.

14 October 1947

Test pilot George S. Welch, wearing his distinctive orange helmet, in the cockpit of the prototype North American Aviation XP-86. (U.S. Air Force)

14 October 1947: Twenty minutes before Captain Charles E. (“Chuck”) Yeager broke the sound barrier with a Bell X-1 rocketplane, North American Aviation Chief Test Pilot George S. Welch put the swept-wing XP-86 prototype, serial number 45-59597, into a shallow dive from 37,000 feet (11,278 meters) and accelerated. In direct violation of orders from the Secretary of the Air Force to not do so, Welch broke the “sound barrier.”

Witnesses on the ground heard the distinctive “B-BOOM” double-shock as the aircraft exceeded the speed of sound. Welch was the first to observe “Mach jump” as the airspeed indicator momentarily indicated higher due to the compression of air in front of the aircraft.

Estimates are that the XP-86 reached Mach 1.02–1.04 on this flight.

George S. Welch with his MG sports car and the North American XP-86. (Unattributed)
George S. Welch with his MG T-series sports car and North American Aviation  XP-86 45-59597. (Unattributed)

© 2015, Bryan R. Swopes

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12 October 1954

North American Aviation’s Chief Engineering Test Pilot, George S. Welch, with the first prototype YF-100A Super Sabre, 52-5754. (U.S. Air Force)

12 October 1954: North American Aviation Chief Engineering Test Pilot George S. Welch, testing the ninth production F-100A-1-NA Super Sabre, serial number 52-5764, made a planned 7.3 G pullout from a Mach 1.55 dive to verify the aircraft’s design limits.

A Boeing B-47 Stratojet crew flying at 25,000 feet (7,620 meters) reported that Welch’s F-100 winged over and began a rapid descent, passing within four miles (6.4 kilometers) of their position and diving at a very high speed. The aircraft appeared to be under control but then suddenly disintegrated.

The Super Sabre had encountered Inertial Roll Coupling. It went out of control and then disintegrated. Its nose folded over the windshield, crushing Welch in his seat. The vertical fin broke away. The ejection seat fired but because of the supersonic speeds the parachute was shredded.

Welch was still alive when rescue teams arrived. He died while being flown to a hospital by helicopter.

George S. Welch, North American Aviation test pilot, wearing his orange flight helmet. An F-86 Sabre is in the background. (San Diego Air and Space Museum Photo Archives)

Inertial roll coupling led to the death of test pilot Mel Apt when his rocket-powered airplane, the Bell X-2, went out of control at Mach 3.2 It nearly killed Chuck Yeager when he lost control of the Bell X-1B at Mach 2.4. It is a complex phenomenon which I will briefly attempt to explain:

To increase maximum speed of transonic and supersonic airplanes during the late 1940s and early 1950s, their wings and tail surfaces were made smaller in order to decrease aerodynamic drag. At the same time, the fuselage became longer and the placement of engines, armament, landing gear, fuel, etc., within the fuselage concentrated the airplane’s mass near its center. While the gyroscopic effects of the turbojet engine contributed some degree of longitudinal stability, the torque effect made rolls to the left occur more easily, but with a higher rate than a roll to the right. The resistance to a change in attitude—inertia—decreased at the same time that the control surfaces’ ability to control the airplanes’ attitude also decreased. The airplanes became unstable.

This North American Aviation F-100-1-NA Super Sabre, 52-5761, is from the same production black as the aircraft flown by George Welch, 12 October 1954. (U.S. Air Force)
This North American Aviation F-100-1-NA Super Sabre, 52-5761, is from the same production block as the aircraft flown by George Welch, 12 October 1954. This photograph shows FW-761 with the original short vertical fin of the F-100A. (U.S. Air Force)

When George Welch tried to pull the F-100 out of its supersonic dive, the airplane’s speed began to decrease as the angle of attack increased. The wings’ ability to stabilize the natural roll instability of the fuselage’s concentrated mass was lessened, and the ailerons could not provide sufficient control to counteract this rolling tendency. The low vertical fin of the original F-100A did not provide adequate directional stability. The Super Sabre rolled and then yawed, entering a side slip. This caused the Super Sabre to pitch down and it was suddenly out of control in all three axes. The physical forces exceeded the strength of the aircraft structure and it came apart.¹

[Aerodynamicists and Aeronautical Engineers: Your corrective comments are welcome.]

Wreckage of North American Aviation F-100A Super Sabre, 12 October 1954. (U.S. Air Force)
Wreckage of North American Aviation F-100A-1-NA Super Sabre 52-5764, 12 October 1954. (North American Aviation, Inc.)

Following the death of George Welch, NACA High Speed Flight Station research test pilot Albert Scott Crossfield spent three months conducting flight tests of the F-100A, demonstrating its inertial roll coupling characteristics using three different vertical fins. F-100A-5-NA 52-5778 was Crossfield’s test aircraft.

Scott Crossfield flew the F-100A-5-NA, 52-5778, in flight testing at the NACA High Speed Flight Station, October–December 1954. (NASA)
Scott Crossfield flew this F-100A-5-NA, 52-5778, in flight testing at the NACA High Speed Flight Station, October–December 1954. (NASA)

The North American Aviation F-100 Super Sabre was designed as a supersonic day fighter. Initially intended as an improved F-86D and F-86E, it soon developed into an almost completely new airplane. The fuselage incorporated the “area rule,” a narrowing in the fuselage width at the wings to increase transonic performance, similar to the Convair F-102A. The Super Sabre had a 49° 2′ sweep to the leading edges of the wings and horizontal stabilizer. The ailerons were placed inboard on the wings and there were no flaps, resulting in a high stall speed in landing configuration. The horizontal stabilizer was moved to the bottom of the fuselage to keep it out of the turbulence created by the wings at high angles of attack. The F-100A had a distinctively shorter vertical fin than the YF-100A. The upper segment of the vertical fin was swept 49° 43′.

There were two service test prototypes, designated YF-100A, followed by the production F-100A series. The first ten production aircraft (all of the Block 1 variants) were used in the flight testing program.

The F-100A Super Sabre was 47 feet, 1¼ inches (14.357 meters) long with a wingspan of 36 feet, 6 inches (11.125 meters). With the shorter vertical fin, the initial F-100As had an overall height of 13 feet, 4 inches (4.064 meters), 11 inches (27.9 centimeters) less than the YF-100A.

Following Welch's accident, NACA designed a new vertical fin for the F-100A. Ii was taller but also had a longer chord. This resulted in a 10% increase in area. (NASA E-1573)
Following Welch’s accident, the NACA High Speed Flight Station tested the Super Sabre and designed a new vertical fin for the F-100A. The two F-100As in this photograph are both from the second production block (F-100A-5-NA). 52-5778, on the left, has the new fin, while 52-5773 retains the original short fin. The new fin is taller but also has a longer chord. This resulted in a 10% increase in area. (NASA E-1573)

The F-100A had an empty weight of 18,135 pounds (8,226 kilograms), and gross weight of 28,899 pounds (13,108 kilograms). Maximum takeoff weight was 35,600 pounds (16,148 kilograms). It had an internal fuel capacity of 755 gallons (2,858 liters) and could carry two 275 gallon (1,041 liter) external fuel tanks.

The early F-100As were powered by a Pratt & Whitney Turbo Wasp J57-P-7 afterburning turbojet engine. It was rated at  9,700 pounds of thrust (43.148 kilonewtons) for takeoff, and 14,800 pounds (65.834 kilonewtons) with afterburner. Later production aircraft used a J57-P-39 engine. The J57 was a two-spool axial flow turbojet which had a 16-stage compressor, and a 3-stage turbine. (Both had high- and low-pressure stages.) The engine was 15 feet, 3.5 inches (4.661 meters) long, 3 feet, 5.0 inches (1.041 meters) in diameter, and weighed 4,390 pounds (1,991 kilograms).

The Super Sabre was the first U.S. Air Force fighter capable of supersonic speed in level flight. It could reach 760 miles per hour (1,223 kilometers) at Sea Level. (Mach 1 is 761.1 miles per hour, 1,224.9 kilometers per hour, under standard atmospheric conditions.) Its maximum speed was 852 miles per hour (1,371 kilometers per hour) at 35,000 feet (10,668 meters). The service ceiling was 44,900 feet (13,686 meters). Maximum range with external fuel was 1,489 miles (2,396 kilometers).

The F-100 was armed with four M-39 20 mm autocannons, capable of firing at a rate of 1,500 rounds per minute. The ammunition capacity of the F-100 was 200 rounds per gun.

North American Aviation built 199 F-100A Super Sabres at its Inglewood, California, plant before production shifted to the F-100C fighter bomber variant. Approximately 25% of all F-100As were lost in accidents.

his is the fifth production F-100A-1-NA Super Sabre, 52-5760, in flight southeast of San Bernardino, California. This fighter is from the same production block as 52-5764, the fighter being tested by George Welch, 12 October 1954. In this photograph, FW-760 has the taller vertical fin that was designed to improve the Super Sabre's controlability. (U.S. Air Force)
This is the fifth production F-100A-1-NA Super Sabre, 52-5760, in flight southeast of San Bernardino, California. This fighter is from the same production block as 52-5764, the fighter being tested by George Welch, 12 October 1954. In this photograph, FW-760 has the taller vertical fin that was designed by NACA to improve the Super Sabre’s stability. (U.S. Air Force)

George Welch was born George Lewis Schwartz, Jr., in Wilmington, Delaware, 10 May 1918. He was the first of two sons of George Lewis Schwartz, a chemist at the Dupont Experimental Station in Wilmington, and Julia Welch Schwartz. His parents changed his surname to Welch, his mother’s maiden name, so that he would not be effected by the anti-German prejudice that was widespread in America following World War I.

He studied mechanical engineering at Purdue University, Indiana, and enlisted in the Army Air Corps in 1939. Welch graduated from pilot training at Kelly Field, Texas, and on 4 October 1940, was commissioned as a second lieutenant, U.S. Army Air Corps.

Second Lieutenant Kenneth M. Taylor and Second Lieutenant George S. Welch, 47th Pursuit Squadron, 15th Pursuit Group, the two Curtiss P-40B Warhawk pilots who shot down 8 Japanese aircraft during the attack on Pearl Harbor, Hawaii, 7 December 1941. Both officers were awarded the Distinguished Service Cross. (U.S. Air Force)

George S. Welch is best remembered as one of the heroes of Pearl Harbor. He, along with Second Lieutenant Kenneth M. Taylor, were the only two fighter pilots to get airborne from Haleiwa Auxiliary Airfield during the Japanese surprise attack on Hawaii, 7 December 1941. Flying a Curtiss P-40B Warhawk, he shot down three Aichi D3A “Val” dive bombers and one Mitsubishi A6M2 Zero fighter. Taylor also shot down four Japanese airplanes. For this action, Lieutenant General Henry H. “Hap” Arnold recommended the Medal of Honor, but because Lieutenants Welch and Taylor had taken off without orders, an officer in their chain of command refused to endorse the nomination. Both fighter pilots were awarded the Distinguished Service Cross.

During the War, Welch flew the Bell P-39 Airacobra and Lockheed P-38 Lightning on 348 combat missions. He had 16 confirmed aerial victories over Japanese airplanes and rose to the rank of Major. In addition to the Distinguished Service Cross, George Welch was awarded the Silver Star, the Distinguished Flying Cross with two oak leaf clusters (three awards), the Air Medal with one oak leaf cluster (two awards), the Presidential Unit Citation with two oak leaf clusters (three awards), American Defense Service medal with one service star, American Campaign Medal, Asiatic-Pacific Campaign Medal with one silver and one bronze star (six campaigns), and the World War II Victory Medal.

George Welch, circa 1943. (Unattributed)
George Welch, circa 1943. (Unattributed)

Welch received the nickname, “Wheaties,” because he was the first military officer to be featured on a box of Wheaties cereal. (Wheaties, “The Breakfast of Champions,” was a toasted wheat bran cereal produced by General Mills. It normally featured champion athletes on its distinctive orange-colored boxes.)

Suffering from malaria, George Welch was out of combat and recuperating in Australia. There he met Miss Janette Alice Williams and they were soon married. Welch returned to the United States with his new wife. They had a son, Giles, born in October 1947. Their home was in Brentwood, California.

North American Aviation approached General Arnold to recommend a fighter pilot who could bring his combat experience to testing new fighters. Welch was one of two that General Arnold suggested. The general authorized Welch’s release from active duty so that he could join North American. Welch held the rank of major, Air Reserve, from 13 November 1944 to 1 April 1953.

George S. Welch, now a civilian test pilot forNorth American Aviation, Inc., sits on the canopy rail of a P-51H Mustang, circa 1945. (North American Aviation Inc.)
George S. Welch, now a civilian test pilot for North American Aviation, Inc., sits on the canopy rail of a P-51H Mustang, circa 1945. (North American Aviation Inc.)

Welch went on to test fly the North American P-51H Mustang, FJ-1 Fury, F-86 Sabre and F-100 Super Sabre.

George Welch made the first flight of the XP-86 prototype, 1 October 1947. There is some evidence that on that flight, and during a subsequent flight on 14 October, Welch exceeded the speed of sound while in a dive. It has been said that during the Korean War, while teaching U.S. Air Force pilots how to best use the F-86 Sabre, he shot down several enemy MiG-15 jet fighters.

George S. Welch is buried at the Arlington National Cemetery, Section 6, Site 8578-D.

¹ Recommended: Coupling Dynamics in Aircraft: A Historical Perspective, by Richard E. Day, Dryden Flight Research Center, Edwards AFB, California. NASA Special Publications 532, 1997.

© 2016, Bryan R. Swopes

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12 October 1944

Second Lieutenant Charles E. (“Chuck”) Yeager, U.S. Army Air Forces, standing on the wing of his North American Aviation P-51D-5-NA Mustang, 44-13897, Glamorous Glenn II, at Air Station 373, 12 October 1944. (U.S. Air Force)
First Lieutenant Charles E. (“Chuck”) Yeager, U.S. Army Air Corps, standing on the wing of his North American Aviation P-51D-5-NA Mustang, 44-13897, Glamorous Glenn II, at Air Station 373, 12 October 1944. (U.S. Air Force)

12 October 1944: During World War II, First Lieutenant Charles Elwood Yeager, Air Corps, United States Army, was a P-51 Mustang fighter pilot assigned to the 363d Fighter Squadron, 357th Fighter Group, stationed at RAF Leiston (USAAF Station 373), near the village of Theberton, Suffolk, England.

Recently promoted from the warrant rank of Flight Officer, Lieutenant Yeager—as one of the most experienced pilots in the group— was leading the 357th on a bomber escort mission against Bremen, Germany. While the Group’s 362nd and 364th Fighter Squadrons remained with the B-24 bombers, Yeager and the 363d patrolled 50 to 100 miles (80 to 160 kilometers) ahead.

At 25,000 feet (7,620 meters) over Steinhuder Meer, northwest of Hanover, Yeager sighted a group of Messerschmitt Bf 109 fighters (also called the Me 109). He was soon able to count 22. Yeager and his squadron of 16 Mustangs circled and attacked out of the sun.

A flight of three Luftwaffe Messerschmitt Me 109 fighters, 20 July 1944. (Bundsarchive Bild 101l-676-7975-36)
A flight of three Luftwaffe Messerschmitt Me 109 fighters, 20 July 1944. (Bundsarchive Bild 101l-676-7975-36)

As Chuck Yeager maneuvered his P-51D Mustang, named Glamorous Glenn II, to fire at a trailing Bf 109, the German fighter suddenly turned left and collided with his wingman. Both pilots bailed out of their fighters and the two Bf 109s went down.

It was almost comic, scoring two quick victories without firing a shot. . . By now, all the airplanes in the sky had dropped their wing tanks and were spinning and diving in a wild, wide-open dogfight. I blew up a 109 from six hundred yards—my third victory—when I turned to see another angling in behind me. Man I pulled back the throttle so damned hard I nearly stalled, rolled up and over, came in behind and under him, kicking right rudder and simultaneously firing. I was directly underneath the guy, less than fifty feet, and I opened up that 109 as if it were a can of Spam. That made four. A moment later, I waxed a guy’s fanny in a steep dive; I pulled up at about 1,000 feet; he went straight into the ground.

Yeager, An Autobiography, by Chuck Yeager and Leo Janos, Bantam Books, New York, 1985, at Page 57.

Lieutenant Yeager’s official report of the air battle reads (in part):

“H. Five Me. 109s destroyed

“I. I was leading the Group with Cement Squadron and was roving out to the right of the first box of bombers. I was over STEINHUDER LAKE when 22 Me. 109s crossed in front of my Squadron from 11:00 O’Clock to 1:00 O’Clock. I was coming out of the sun and they were about 1½ miles away at the same level of 25,000 feet. I fell in behind the enemy formation and followed them for about 3 minutes, climbing to 30,000 feet. I still had my wing tanks and had close up to around 1,000 yards, coming within firing range and positioning the Squadron behind the entire enemy formation. Two of the Me. 109s were dodging over to the right. One slowed up and before I could start firing, rolled over and bailed out. The other Me. 109, flying his wing, bailed out immediately after as I was ready to line him in my sights. I was the closest to the tail-end of the enemy formation and no one, but myself was in shooting range and no one was firing. I dropped my tanks and then closed up to the last Jerry and opened fire from 600 yards, using the K-14 sight. I observed strikes all over the ship, particularly heavy in the cockpit. He skidded off to the left. I was closing up on another Me. 109 so I did not follow him down. Lt. STERN, flying in Blue Flight reports this E/A on fire as it passed him and went into a spin. I closed up on the next Me. 109 to 100 yards, skidded to the right and took a deflection shot of about 10°. I gave about a 2 second burst and the whole fuselage split open and blew up after we passed. Another Me. 109 to the right had cut his throttle and was trying to get behind. I broke to the right and quickly rolled to the left on his tail. He started pulling it in and I was pulling 6″G”. I got a lead from around 300 yards and gave him a short burst. There were hits on wings and tail section He snapped to the right 3 times and bailed out when he quit snapping at around 18,000 feet. I did not blackout during this engagement due to the efficiency of the “G” suit. Even though I was skidding I hit the second Me. 109 by keeping the bead and range on the E/A. To my estimation the K-14 sight is the biggest improvement to combat equipment for Fighters up to this date. The Me. 109s appeared to have a type of bubble canopy and had purple noses and were a mousey brown all over. I claim five Me 109s destroyed.

“J. Ammunition Expended: 587 rounds .50 cal MG.

“Charles E. Yeager, 1st Lt, AC.”

Lieutenant Yeager had destroyed five enemy fighters during a single battle. He became “an Ace in one day” and was awarded the Silver Star. Of the twenty-two Me 109s, the 363rd had destroyed eight without losing a single Mustang.

Yeager’s Glamorous Glenn II, flown by another pilot, was destroyed six days later when it crashed in bad weather.

North American Aviation P-51D-5-NA 44-13366 on a test flight near the North American plant at Inglewood, California. This is from the same production block as Yeager's Glamorous Glenn II.
North American Aviation P-51D-5-NA 44-13366 on a test flight near the North American plant at Inglewood, California. This is from the same production block as Yeager’s Glamorous Glenn II.

The P-51D was the predominant version of the North American Aviation World War II fighter. It was a single-seat, single-engine fighter, initially designed for the Royal Air Force. The P-51D was 32 feet, 3.5 inches (9.843 meters) long, with a wingspan of 37 feet (11.278 meters). It was 13 feet, 4.5 inches (4.077 meters) high. The fighter had an empty weight of 7,635 pounds (3,463 kilograms) and a maximum takeoff weight of 12,100 pounds (5,489 kilograms).

The P-51D was powered by a right-hand tractor, liquid-cooled, supercharged, 1,649-cubic-inch-displacement (27.04-liter) Packard V-1650-3 or -7 Merlin single overhead cam (SOHC) 60° V-12 engine with Military Power ratings of 1,380 horsepower at Sea Level, turning 3,000 r.p.m with 60 inches of manifold pressure (V-1650-3), or 1,490 horsepower at Sea Level, turning 3,000 r.p.m. with 61 inches of manifold pressure (V-1650-7). These engines were versions of the Rolls-Royce Merlin 63 and 66, built under license by the Packard Motor Car Company of Detroit, Michigan. The engine drove a four-bladed Hamilton Standard Hydromatic constant-speed propeller with a diameter of 11 feet, 2 inches (3.404 meters) through a 0.479:1 gear reduction.

A Packard Motor Car Company V-1650-7 Merlin V-12 aircraft engine at the Smithsonian Institution National Air and Space Museum. This engine weighs 1,715 pounds (778 kilograms) and produces 1,490 horsepower at 3,000 r.p.m. Packard built 55,873 of the V-1650 series engines. Continental built another 897. The cost per engine ranged from $12,548 to $17,185. (NASM)
A Packard Motor Car Company V-1650-7 Merlin V-12 aircraft engine at the Smithsonian Institution National Air and Space Museum. This engine weighs 1,715 pounds (778 kilograms) and produces 1,490 horsepower at 3,000 r.p.m. Packard built 55,873 of the V-1650 series engines. Continental built another 897. The cost per engine ranged from $12,548 to $17,185. (NASM)

The P-51D with a V-1650-7 Merlin had maximum speed at Sea Level of 323 miles per hour (520 kilometers per hour) at the Normal Power setting of 2,700 r.p.m. and 46 inches of manifold pressure, and 375 miles per hour (604 kilometers per hour) at War Emergency Power, 3,000 r.p.m with 67 inches of manifold pressure (5 minute limit). At altitude, using the Military Power setting of 3,000 r.p.m. and 61 inches of manifold pressure (15 minute limit), it had a maximum speed of 439 miles per hour (707 kilometers per hour) at 28,000 feet (8,534 meters). With War Emergency Power the P-51D could reach 442 miles per hour (711 kilometers per hour) at 26,000 feet (7,925 meters).

The P-51D could climb to 20,000 feet (6,096 meters) in 6.4 minutes, and to its service ceiling, 41,600 feet (12,680 meters), in 28 minutes. The airplane’s absolute ceiling was 42,400 feet (12,924 meters).

With 180 gallons (681 liters) internal fuel, the maximum range of the P-51D was 1,108 miles (1,783 kilometers).

Armorers carry AN/M2 Browning .50-caliber machine guns and belts of linked ammunition to a P-51 Mustang. (U.S. Air Force)
Armorers carry Browning AN-M2 .50-caliber machine guns and belts of linked .50-caliber ammunition to a P-51 Mustang. (U.S. Air Force)

The P-51D was armed with six electrically-heated Browning AN-M2 .50-caliber machine guns, with three mounted in each wing. 400 rounds of ammunition were provided for the inner pair of guns, and 270 rounds for each of the other four guns, for a total of 1,880 rounds of ammunition. This was armor piercing, incendiary, and tracer ammunition. The fighter could also carry a 1,000 pound (453.6 kilogram) bomb under each wing in place of drop tanks, or up to ten rockets.

A total of 8,156 P-51Ds were produced by North American at Inglewood, California, and Dallas, Texas, and another 200 by the Commonwealth Aircraft Corporation, Melbourne, Australia.

The North American Aviation P-51D Mustang remained in service with the United States Air Force until 27 January 1957, when the last aircraft were retired from the 167th Fighter Squadron, West Virginia National Guard.

North American Aviation P-51D Mustang. (U.S. Air Force)
North American Aviation P-51D Mustang. (U.S. Air Force)

© 2017, Bryan R. Swopes

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3 October 1967

Major William J. Knight, United States Air Force, with the North American Aviation X-15A-2, 56-6671. (U.S. Air Force)

3 October 1967: The 188th flight of the X-15 Program was the 53rd for the Number 2 aircraft, 56-6671. It had been extensively modified by North American Aviation to an X-15A-2 configuration following a landing accident which had occurred 9 November 1962. The fuselage was lengthened 28 inches (0.711 meters) to accommodate a liquid hydrogen fuel tank for a scramjet engine that would be added to the ventral fin, a new tank for additional hydrogen peroxide to generate steam for the rocket engine turbo pump, and external propellant tanks to allow the rocketplane to reach higher speeds and altitudes. The entire surface of the X-15 was covered with an ablative coating to protect the metal structure from the extreme heat it would encounter on this flight.

Minor issues delayed the takeoff but finally, after they were corrected, and with Pete Knight in the X-15’s cockpit, it was carried aloft under the right wing of Balls 8, a Boeing NB-52B Stratofortress, 52-008.

At 45,000 feet (13,716 meters) over Mud Lake, Nevada, the X-15 was droppeded at 14:31:50.9 local time. Knight fired the Reaction Motors XLR99-RM-1 rocket engine and began to climb and accelerate. After 60 seconds, the ammonia and liquid oxygen propellants in the external tanks was exhausted, so the the tanks were jettisoned to eliminate their weight and aerodynamic drag.

The X-15A-2 climbed to 102,100 feet (31,120 meters) and Pete Knight leveled off, still accelerating. After 140.7 seconds of engine burn, Knight shut the XLR99 down. He noticed that thrust seemed to decrease gradually and the X-15 continued to accelerate to 6,630 feet per second (2,021 meters per second), or Mach 6.72.

North American Aviation X-15A-2 56-6671 is carried to launch altitude under the right wing of the Boeing NB-52B Stratofortress 52-008. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 is carried to launch altitude under the right wing of the Boeing NB-52B Stratofortress 52-008. The scramjet is attached to the ventral fin. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 immediately after being released from the mothership, Boeing NB-52B Stratofortress 52-008, Balls 8, over Mud Lake, Nevada, 3 October 1967. The steam trail is hydrogen peroxide used to power the rocket engine turbopump. (U.S. Air Force)
North American Aviation X-15A-2 56-6671 immediately after being released from the mothership, Boeing NB-52B Stratofortress 52-008, Balls 8, over Mud Lake, Nevada, 3 October 1967. The steam trail is hydrogen peroxide used to power the rocket engine turbopump. (U.S. Air Force) 
The North American Aviation X-15A-2 56-6671 ignites the XLR99 engine after being released from the mothership, Balls 8, 3 October 1967. (U.S. Air Force)
The X-15A-2’s XLR99-RM-1 rocket engine ignites after release from the mothership, Balls 8, 3 October 1967. (U.S. Air Force) 

Shock waves from the dummy scramjet mounted on the ventral fin impinged on the fin’s leading edge and the lower fuselage, raising surface temperatures to 2,700 °F. (1,482 °C.) The Inconel X structure started to melt and burn through.

Pete Knight entered the high key over Rogers Dry Lake at 55,000 feet (16,764 meters) and Mach 2.2, higher and faster than normal. As he circled to line up for Runway One Eight, drag from the scramjet caused the X-15 to descend faster and this set him up for a perfect approach and landing. Because of heat damage, the scramjet broke loose and fell away from the X-15.

Knight touched down after an 8 minute, 17.0 second flight. His 4,520 mile per hour (7,274 kilometers per hour) maximum speed is a record that still stands.

Firefighters cool down the ventral fin of the North American Aviation X-15A-2 56-6671 after its last landing on Rogers Dry Lake, 3 October 1967.(U.S. Air Force)
Firefighters cool down the ventral fin of the North American Aviation X-15A-2 56-6671 after its final landing on Rogers Dry Lake, 3 October 1967.(U.S. Air Force)

The X-15A-2 suffered considerable damage from this hypersonic flight. It was returned to North American for repairs, but before they were completed, the X-15 Program came to an end. This was 56-6671’s last flight. It was sent to the National Museum of the United States Air Force where it is part of the permanent collection.

In a ceremony at the White House, President Lyndon B. Johnson presented the Harmon International Trophy to Major William J. Knight.

The Harmon International Trophy at the Smithsonian Institution National Air and Space Museum. (NASM)
The Harmon International Trophy at the Smithsonian Institution National Air and Space Museum. (NASM)

© 2016, Bryan R. Swopes

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1 October 1947

North American Aviation test pilot George S. Welch, flying the first of three XP-86 prototypes, serial number 45-59597. (North American Aviation, Inc.)

1 October 1947: After three years development in which 801,386 engineering hours and 340,594 drafting hours had been expended, the first prototype North American Aviation XP-86 (company designation NA-140), serial number 45-59597, was ready for its first flight at Muroc Dry Lake in the high desert north of Los Angeles, California.

Completed at North American’s Inglewood plant on 8 August 1947, it was trucked to Muroc in mid-September. It was reassembled, everything was checked out, and after a few taxi tests, company test pilot George S. Welch took off for a initial familiarization flight. Chief Test Pilot Bob Chilton flew chase in an XP-82 Twin Mustang with a company photographer on board. The duration of the first flight was 1 hour, 18 minutes.

Recently completed, the first prototype XP-86, 45-59597, waits inside the North American Aviation plant at Inglewood, California, 14 August 1947. (North American Aviation, Inc.)

During this first flight, George Welch climbed to 35,000 feet (10,668 meters):

“In a little more than ten minutes he had reached 35,000 feet. Leveling out, the test pilot smiled as he watched the indicated airspeed accelerate to 320 knots. He estimated that should be 0.90 Mach number. . . Rolling into a 40 degree dive, he turned west. . . The airspeed indicator seemed to be stuck at about 350 knots. The Sabre was behaving just fine. Then at 29,000 feet, there was a little wing roll. Correcting the roll, George pushed into a steeper dive. The airspeed indicator suddenly jumped to 410 knots and continued to rise. At 25,000 feet, he pulled the Sabre into level flight and reduced power. The wing rocked again and the airspeed jumped back to 390.”

Aces Wild: The Race for Mach 1, by Al Blackburn, Scholarly Resources Inc., Wilmington, Delaware, 1998, at Chapter 5, Pages 144–145.

George Welch was the first to report instrument readings that would be referred to as “Mach jump.” It has been argued that George Welch flew the XP-86 beyond Mach 1 during this flight, breaking the “sound barrier” two weeks before Chuck Yeager did with the Bell X-1 rocketplane. During flight testing, it was firmly established that the XP-86 could reach Mach 1.02–1.04 in a dive, so it is certainly possible that he did so on the Sabre’s first flight.

North American Aviation Model NA-140, the first XP-86 prototype, 45-59597, at Muroc AAF, 1947. (U.S. Air Force)
North American Aviation Model NA-140, the first XP-86 prototype, 45-59597, at Muroc AAF, 1947. (U.S. Air Force)

The XP-86 was unlike any airplane before it. It was the first airplane with a swept wing. After analyzing test data from the Messerschmitt Me 262, North American’s engineers designed a wing with a 35° degree sweep back to its leading edge. The wing tapered toward the tips, and its thickness also decreased from the root to the tip. In order to create a very strong but very thin wing, it was built with a two-layered aluminum skin, instead of ribs and spars, with each layer separated by “hat” sections. The wing sweep allowed high speed shock waves to form without stalling the entire wing. The wing also incorporated leading edge “slats” which were airfoil sections that automatically extended below 290 knots, smoothing the air flow over the wing’s upper surface and creating more lift at slow speeds. Above that speed, aerodynamic forces closed the slats, decreasing drag and allowing for higher speeds. Effectively, the wing could change its shape in flight.

Test pilot George S. Welch, wearing his distinctive orange helmet, in the cockpit of the prototype XP-86. This photograph was taken 14 October 1947. (U.S. Air Force)
This photograph of the XP-86 shows the 35° wing sweep. Test pilot George S. Welch, wearing his distinctive orange helmet, in the cockpit of the prototype XP-86. (North American Aviation, Inc.)

The XP-86 prototypes were 37 feet, 6½ inches (11.443 meters) long with a wingspan of 37 feet, 1–7/16 inches (11.314 meters) and overall height of 14 feet, 9 inches (4.496 meters). The empty weight was 9,730 pounds (4,413.5 kilograms), gross weight, 13,395 pounds (6,075.9 kilograms) and maximum takeoff weight was 16,438 pounds (7,456.2 kilograms).

The XP-86 was initially powered by a General Electric-designed, Chevrolet-built J35-C-3 turbojet which produced 4,000 pounds of thrust. This was soon changed to an Allison J35-A-5. Performance testing was conducted with the Allison engine installed. The J35 was a single-spool, axial-flow turbojet engine with an 11-stage compressor and single-stage turbine. The J35-A-5 was rated at 4,000 pounds of thrust (17.79 kilonewtons) at 7,700 r.p.m. (static thrust, Sea Level). The engine was 14 feet, 0.0 inches (4.267 meters) long, 3 feet, 4.0 inches (1.016 meters) in diameter and weighed 2,400 pounds (1,089 kilograms).

The three North American Aviation XP-86 prototypes. Front to back, 45-59598, 45-59597 and 45-59599. (National Archives and Records Administration)

The maximum speed of the XP-86 at Sea Level was 0.787 Mach (599 miles per hour, 964 kilometers per hour), 0.854 Mach (618 miles per hour, 995 kilometers per hour) at 14,000 feet (4,267 meters) and 575 miles per hour (925 kilometers per hour) at 35,000 feet (10,668 meters)—0.875 Mach.

The prototype fighter was able to take off at 125 miles per hour (201 kilometers per hour) in just 3,020 feet (920.5 meters) of runway. It could climb to 30,000 feet (9,144 meters) in 12.1 minutes and had a service ceiling of 41,300 feet (12,588 meters).

George S. Welch, North American Aviation test pilot, wearing his orange flight helmet. An F-86 Sabre is in the background. (San Diego Air and Space Museum Photo Archives)

George Welch was born George Lewis Schwartz, in Wilmington, Delaware, 10 May 1918. His parents changed his surname to Welch, his mother’s maiden name, so that he would not be effected by the anti-German prejudice that was widespread in America following World War I. He studied mechanical engineering at Purdue, and enlisted in the Army Air Corps in 1939.

George S. Welch is best remembered as one of the heroes of Pearl Harbor. He was one of only two fighter pilots to get airborne during the Japanese surprise attack on Hawaii, 7 December 1941. Flying a Curtiss P-40B Warhawk, he shot down three Aichi D3A “Val” dive bombers and one Mitsubishi A6M2 Zero fighter. For this action, Lieutenant General H.H. “Hap” Arnold recommended the Medal of Honor, but because Lieutenant Welch had taken off without orders, an officer in his chain of command refused to endorse the nomination. He received the Distinguished Service Cross.

During World War II, George Welch flew the Bell P-39 Airacobra and Lockheed P-38 Lightning on 348 combat missions. He had 16 confirmed aerial victories over Japanese airplanes and rose to the rank of Major.

Suffering from malaria, George Welch was out of combat, and when North American Aviation approached him to test the new P-51H Mustang, General Arnold authorized his resignation. Welch test flew the P-51, FJ-1 Fury, F-86 Sabre and F-100 Super Sabre. He was killed 12 October 1954 when his F-100A Super Sabre came apart in a 7 G pull up from a Mach 1.5 dive.

North American Aviation F-86-A-NA Sabre 47-630. (North American Aviation, Inc./Chicago Tribune)
North American Aviation F-86A-1-NA Sabre 47-630. (North American Aviation, Inc./Chicago Tribune)

After testing, the North American Aviation XP-86 was approved for production as the F-86A. It became operational in 1949. The first squadron to fly the F-86 held a naming contest and from 78 suggestions, the name “Sabre” was chosen. The F-86 Sabre was in production until 1955 at North American’s Inglewood, California and Cleveland, Ohio plants. It was also built under license by Canadair, Ltd., Sain-Laurent, Quebec, Canada; the Commonwealth Aircraft Corporation, Port Melbourne, Victoria, Australia; and Mitsubishi Heavy  Industries at Nagoya, Aichi Prefecture, Japan. A total of 9,860 Sabres were built. They served with the United States Air Force until 1970.

XP-86 45-59597 was expended in nuclear weapons tests, Operation Snapper Easy and Snapper Fox, at the Nevada Test Site, Frenchman’s Flat, Nevada, in May 1952. The second and third prototypes, 45-59598 and 45-59599, met similar fates.

© 2017, Bryan R. Swopes

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