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North American B-25 Mitchell
The North American B-25 Mitchell is an American medium bomber that was introduced in 1941 and named in honor of Brigadier General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theater of World War II, and after the war ended, many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 B-25s were built. It was the most-produced American medium bomber and the third-most-produced American bomber overall. These included several limited models such as the F-10 reconnaissance aircraft, the AT-24 crew trainer, and the United States Marine Corps' PBJ-1 patrol bomber.
On 11 March 1939, the US Army Air Corps issued Proposal No. 39-640 specifying a medium bomber capable of carrying a 3,000 lb (1,400 kg) bombload over a range of 2,000 miles (3,200 km) at top speed in excess of 300 mph (480 km/h). North American Aviation (NAA) used its NA-40B design to develop the NA-62 proposal. More state of the art compared to the competing Martin No. 179 proposal, the North American team included easy field maintenance and repair features, and according to Avery, "It promised to be an easy airplane to fly and placed no special requirements on pilot training programs." On 20 September. the Air Corps issued North American contract No. W353-ac-13258 for 184 B-25s powered by the Wright R-2600. The plane used the NACA 23017 airfoil at the wing root changing to a NACA 4409-R at the wingtip. On 19 August 1940, Vance Breese and NAA test engineer Roy Ferren flew the first flight test, when Ferren noted a severe roll-yaw condition.
Preliminary flights by the Air Corps noted the Dutch roll characteristic, accentuated by wind and gusts and demanded a fix. NAA's first nine aircraft had a constant-dihedral, the wing having a consistent upward angle from the fuselage to the wingtip. "Flattening", or changing the outer wing panels dihedral to zero degrees, was a simple solution that solved the aerodynamic problem. This gave the B-25 its gull wing configuration. The 25 February 1941 flight test confirmed the change resulted in optimum flight characteristics. The vertical tail also went through five variations before being finalized. By the time of the Attack on Pearl Harbor, 130 B-25s had been delivered.
Special variations were made to accommodate photo reconnaissance, armament, long range ferry, anti-submarine patrol, winterizing, and use in a desert environment. By February 1941, the first 24 B-25s were configured with three .30 cal guns and a single .50 cal tail gun. The B-25A had self-sealing fuel cells. The B-25B had top and bottom turrets with twin .50 cal guns each, though the tail gun was removed. By December 1941, the B-25C had additional self-sealing fuel cells outboard the wing center section. By February 1942, the first B-25D, and then in May 1943, the 75mm cannon-armed B-25G series were accepted by the Air Corps. By August 1943, the B-25H had a lighter 75mm cannon, 4 nose guns instead of 2, two waist guns. two in the tail turret, four blister gun packs, and eliminated the co-pilot after Jimmy Doolittle questioned the need. In December 1943, the B-25J was introduced, the final variant and the most produced, reincorporated the co-pilot position and included a bombardier.
NAA manufactured the greatest number of aircraft in World War II, the first time a company had produced trainers, bombers, and fighters simultaneously (the AT-6/SNJ Texan/Harvard, B-25 Mitchell, and the P-51 Mustang). It produced B-25s at both its Inglewood main plant and an additional 6,608 aircraft at its Kansas City, Kansas, plant at Fairfax Airport.
After the war, the USAF placed a contract for the TB-25L trainer in 1952. This was a modification program by Hayes of Birmingham, Alabama. Its primary role was reciprocating engine pilot training.
A development of the B-25 was the North American XB-28 Dragon, designed as a high-altitude bomber. Two prototypes were built with the second prototype, the XB-28A, evaluated as a photo-reconnaissance platform, but the aircraft did not enter production.
The B-25 was a safe and forgiving aircraft to fly. With one engine out, 60° banking turns into the dead engine were possible, and control could be easily maintained down to 145 mph (230 km/h). The pilot had to remember to maintain engine-out directional control at low speeds after takeoff with rudder; if this maneuver were attempted with ailerons, the aircraft could snap out of control. The tricycle landing gear made for excellent visibility while taxiing. The only significant complaint about the B-25 was its extremely noisy engines; as a result, many pilots eventually suffered from some degree of hearing loss. A Clayton S stack, introduced to quench the exhaust flame, was introduced in the B-25C series. These stacks protruded through the cowling, and though they weighed less than the replaced collector ring, they reduced aircraft speed by 9 mph due to the required aircraft fairings. According to Avery, "The increase in noise as compared to collector rings ported on the outboard side of the nacelles was a general crew complaint."
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North American B-25 Mitchell
The North American B-25 Mitchell is an American medium bomber that was introduced in 1941 and named in honor of Brigadier General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in every theater of World War II, and after the war ended, many remained in service, operating across four decades. Produced in numerous variants, nearly 10,000 B-25s were built. It was the most-produced American medium bomber and the third-most-produced American bomber overall. These included several limited models such as the F-10 reconnaissance aircraft, the AT-24 crew trainer, and the United States Marine Corps' PBJ-1 patrol bomber.
On 11 March 1939, the US Army Air Corps issued Proposal No. 39-640 specifying a medium bomber capable of carrying a 3,000 lb (1,400 kg) bombload over a range of 2,000 miles (3,200 km) at top speed in excess of 300 mph (480 km/h). North American Aviation (NAA) used its NA-40B design to develop the NA-62 proposal. More state of the art compared to the competing Martin No. 179 proposal, the North American team included easy field maintenance and repair features, and according to Avery, "It promised to be an easy airplane to fly and placed no special requirements on pilot training programs." On 20 September. the Air Corps issued North American contract No. W353-ac-13258 for 184 B-25s powered by the Wright R-2600. The plane used the NACA 23017 airfoil at the wing root changing to a NACA 4409-R at the wingtip. On 19 August 1940, Vance Breese and NAA test engineer Roy Ferren flew the first flight test, when Ferren noted a severe roll-yaw condition.
Preliminary flights by the Air Corps noted the Dutch roll characteristic, accentuated by wind and gusts and demanded a fix. NAA's first nine aircraft had a constant-dihedral, the wing having a consistent upward angle from the fuselage to the wingtip. "Flattening", or changing the outer wing panels dihedral to zero degrees, was a simple solution that solved the aerodynamic problem. This gave the B-25 its gull wing configuration. The 25 February 1941 flight test confirmed the change resulted in optimum flight characteristics. The vertical tail also went through five variations before being finalized. By the time of the Attack on Pearl Harbor, 130 B-25s had been delivered.
Special variations were made to accommodate photo reconnaissance, armament, long range ferry, anti-submarine patrol, winterizing, and use in a desert environment. By February 1941, the first 24 B-25s were configured with three .30 cal guns and a single .50 cal tail gun. The B-25A had self-sealing fuel cells. The B-25B had top and bottom turrets with twin .50 cal guns each, though the tail gun was removed. By December 1941, the B-25C had additional self-sealing fuel cells outboard the wing center section. By February 1942, the first B-25D, and then in May 1943, the 75mm cannon-armed B-25G series were accepted by the Air Corps. By August 1943, the B-25H had a lighter 75mm cannon, 4 nose guns instead of 2, two waist guns. two in the tail turret, four blister gun packs, and eliminated the co-pilot after Jimmy Doolittle questioned the need. In December 1943, the B-25J was introduced, the final variant and the most produced, reincorporated the co-pilot position and included a bombardier.
NAA manufactured the greatest number of aircraft in World War II, the first time a company had produced trainers, bombers, and fighters simultaneously (the AT-6/SNJ Texan/Harvard, B-25 Mitchell, and the P-51 Mustang). It produced B-25s at both its Inglewood main plant and an additional 6,608 aircraft at its Kansas City, Kansas, plant at Fairfax Airport.
After the war, the USAF placed a contract for the TB-25L trainer in 1952. This was a modification program by Hayes of Birmingham, Alabama. Its primary role was reciprocating engine pilot training.
A development of the B-25 was the North American XB-28 Dragon, designed as a high-altitude bomber. Two prototypes were built with the second prototype, the XB-28A, evaluated as a photo-reconnaissance platform, but the aircraft did not enter production.
The B-25 was a safe and forgiving aircraft to fly. With one engine out, 60° banking turns into the dead engine were possible, and control could be easily maintained down to 145 mph (230 km/h). The pilot had to remember to maintain engine-out directional control at low speeds after takeoff with rudder; if this maneuver were attempted with ailerons, the aircraft could snap out of control. The tricycle landing gear made for excellent visibility while taxiing. The only significant complaint about the B-25 was its extremely noisy engines; as a result, many pilots eventually suffered from some degree of hearing loss. A Clayton S stack, introduced to quench the exhaust flame, was introduced in the B-25C series. These stacks protruded through the cowling, and though they weighed less than the replaced collector ring, they reduced aircraft speed by 9 mph due to the required aircraft fairings. According to Avery, "The increase in noise as compared to collector rings ported on the outboard side of the nacelles was a general crew complaint."