Bombers
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Multiplace Bomber (MB)
(1918-1921) |
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| Martin | MB-1 | Glenn Martin Bomber |
| Martin | MB-2 | |
Day Bombardment (DB)
(Type XI - 1921 to 1923) |
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| Gallaudet | DB-1 | |
| Gallaudet | DB-1B | |
Night Bombardment - Short Range (NBS)
(Type XII - 1921 to 1924) |
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| Martin | NBS-1 | |
| LWF | XNBS-2 | |
| Elias | XNBS-3 | |
| Curtiss | XNBS-4 | |
Night Bombardment - Long Range (NBL)
(Type XIII - 1920 to 1923) |
|---|
| Witteman-Lewis | XNBL-1 | Barling Bomber |
| Martin | XNBL-2 | |
Light Bombardment (LB)
(1923 to 1930) |
|---|
| Huff-Daland | LB-1 | |
| Atlantic | LB-2 | |
| Huff-Daland | XLB-3 | |
| Martin | XLB-4 | |
| Keystone | LB-5 | |
| Keystone | LB-6 | |
| Keystone | LB-7 | |
| Keystone | LB-8 | |
| Keystone | LB-9 | |
| Keystone | LB-10 | |
| Keystone | LB-11 | |
| Keystone | XLB-12 | |
| Keystone | LB-13 | |
| Keystone | LB-14 | |
Heavy Bombardment (HB)
(1926 to 1927) |
|---|
| Huff-Daland | XHB-1 | |
| Atlantic | XHB-2 | |
| Huff-Daland | XHB-3 | |
Bombardment Aircraft (B)
(starting 1926) |
|---|
| Huff-Daland | XB-1 | |
| Curtiss | B-2 | |
| Keystone | B-3 | |
| Keystone | B-4 | |
| Keystone | B-5 | |
| Keystone | B-6 | |
| Douglas | Y1B-7 | |
| Fokker | XB-8 | |
| Boeing | Y1B-9 | Model 215 |
|
1933 Project A
1933 Project B
193? Project C
1935 Project D
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| Long-Range Bomber
|
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| Boeing | | Model 306 |
| Boeing | XBLR-1 | Model 294 |
| Douglas | XBLR-2 | |
| Sikorsky | XBLR-3 | |
Bombardment Aircraft (B)
(starting 1926) |
|---|
| Martin | B-10 | Martin 139 |
| Douglas | YB-11 | |
| Martin | B-12 | |
| Martin | XB-13 | |
| Martin | XB-14 | |
| Boeing | XB-15 | Model 294 |
| Martin | XB-16 | Model 145 |
| Boeing | B-17 | Flying Fortress |
| Douglas | B-18 | Bolo |
| Douglas | B-19 | Flying Behemoth |
| Boeing | XB-20 | Model 316 |
| North American | XB-21 | Dragon |
| Douglas | XB-22 | Bolo |
| Douglas | B-23 | Dragon |
| Consolidated | B-24 | Liberator |
| North American | B-25 | Mitchell |
| Martin | B-26 | Marauder |
| Douglas | B-26 (A-26) | Invader |
| Martin | XB-27 | |
| North American | XB-28 | |
| Boeing | B-29 | Superfortress |
| Lockheed | XB-30 | Constellation |
| Douglas | XB-31 | |
| Consolidated | B-32 | Dominator |
| Martin | XB-33 | Super Marauder |
| Lockheed | B-34 | Ventura |
| Northrop | XB-35 | Flying Wing |
| Convair | XB-36 | Peacemaker |
| Lockheed | B-37 | Lexington |
| Boeing | XB-38 | Flying Fortress |
| Boeing | XB-39 | Spirit of Lincoln |
| Boeing | YB-40 | Flying Fortress |
| Consolidated-Vultee | XB-41 | |
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Douglas YB-11
The Douglas YB-11 was based on the U.S. Navy XP3D-1 seaplane. The Air Corps ordered a scaled-down version of the aircraft incorporating design changes for amphibious operation (on land and sea). The aircraft was redesignated as an observation plane (YO-44) before construction was completed. The plane was again redesignated as an observation amphibian (YOA-5) when the Air Corps accepted it.
The YB-11 was the only amphibian ever to carry an Army Air Corps bomber designation.
Type Number built/
converted Remarks
YB-11 1 Became YO-44 then YOA-5
Armament: Three .30-cal. machine guns
Engine: Two Wright R-1820-45 Cyclone radials of 800 hp each
Maximum speed: 169 mph
Span: 89 ft. 9 in.
Length: 69 ft. 9 in.
Height: 22 ft. 0 in.
Weight: Approx. 20,000 lbs. loaded
Serial number: 33-17
In the spring of 1939, General Hap Arnold chartered a special board to take a hard look at U.S. aircraft development and the Air Corps' aircraft needs. Arnold appointed Brigadier General W.G. Kilner to convene and chair the board, with members including Colonels Tooey Spaatz and Earl Naiden and Major Al Lyon, as well as Charles Lindbergh (Coop 1980). On May 5, 1939, the board began to study the military characteristics of all types of aircraft under consideration in the Air Corps' 5-year program. By June of 1939, their recommendations were on the desk of the Chief of the Army Air Corps. A major recommendation was the development and production of a 5,000-mile "super bomber" that had greater bomb capacity than the existing B-17 and B-24 aircraft entering production
The origin of the B-29 can be traced to the Boeing Model 316 project, which was essentially a presurrised version of the XB-15 designed in March of 1934. It differed from the XB-15 primarily in the relocation of the wing from a low to a high position and by the installation of a nose wheel undercarriage. Also the proposed Model 316 was to have been powered by four yet to be designed 2000 hp Wright R-3350 Duplex Cyclone eighteen-cylinder air-cooled radials.
In March of 1938, the design of the Model 316 was completed by Boeing. It was quickly followed by the Model 322 design, a pressurized cabin version of the B-17. A review of the design specifications highlights the pressurized cabins and tricycle landing gear. Although the projected ranges of these designs were good, Boeing engineers felt they could improve the numbers.
The story of the development of the B-29 proper began in the winter of 1938. At that time Air Corps staff officers requested Boeing to suggest ideas for a major modification of the B-17 to feature greater altitude, range, speed, and carrying capacity. The company engineers and aerodynamicists rejected the plan as impractical and instead suggested Boeing Model 316, an extended development of the XB-17 Although no definite commitment was made by the W ar Department, Boeing pushed new designs ahead on paper and in December 1939 started construction of a full-scale wooden mockup of Model 341 at company expense.
In January 1940, after England and France had been at war with Germany for three months, the War Department issued "Request for Data R-40B.” which set forth general specifications for an experimental, four-engined bomber. The aircraft industry was requested to submit bids. Sikorsky, Martin, Douglas, Consolidated, Lockheed, and Boeing submitted designs, Boeing submitting Model 341 as its entry. By the time the War Department had received all entries, European war experience had pointed out the need for greater bomb load, longer range, and heavier armament than had been contemplated previously
The Boeing Y1B-20 (Model 316) was a development of the XB-15 design proposed by Boeing as a long-range heavy bomber. About the same size as the XB-15, the Y1B-20 design was primarily done to increase the performance of the large bomber by using more powerful engines. The design was presented to the Army in early 1938 and two aircraft were ordered later that year. The Army leadership reversed its decision and canceled the order before construction began.
Although the Army General Staff remained skeptical of the four-engine bomber into the late 1930s, the experience gained by Boeing engineers designing the XB-15 and Y1B-20 led directly to the development of the B-29 -- one of the premiere U.S. bombers of World War II.
The Boeing XB-15 experimental four-engined long-range bomber of 1937 proved to be seriously underpowered and was never ordered into production. In March of 1938, in an attempt to remedy some of the deficiencies of the basic design, the Boeing company offered a more advanced version of the XB-15. It was known by the company as the Model 316, and was approximately the same size as the XB-15. However, in an attempt to provide more power, the Model 316 was to have been powered by four 1400 hp Pratt & Whitney R-2180 Twin Hornet air cooled radials.
The Model 316 was offered to the Army in several different forms. The Model 316D version, which featured a high-winged design with an 80,000 pound gross weight, 152-foot wingspan, seven machine guns, and a pressurized canopy, attracted sufficient attention so that two examples were ordered by the Army in June of 1938 under the designation Y1B-20.
Leading up to its famous stable of World War 2 heavy bombers, Boeing undertook a variety of projects to further existing technologies and enhance qualities for long endurance flight of heavy airframes. One such program became the Y1B-20 (Boeing Model 316), an offshoot of the experimental XB-15. The original XB-15 was born of a 1933 United States Army Air Corps (USAAC) initiative seeking a bomber capable of 5,000 mile endurance reaching speeds of 200 miles per hour with a 2,000lb bomb load. The Y1B-20 was essentially an evolved, dimensionally larger version designed around use of more powerful engines - 4 x Wright GR-2600-A73 rated at 1,350 horsepower being the intended type. While presented to the Army (and accepted through two prototype orders), the product was cancelled before manufacture of either airframe had begun. As such, no examples were ever completed by Boeing and the project was lost to aviation history.
The four-engine arrangement and general aerodynamic design of the Y1B-20 was estimated to allow for a maximum speed of 258 miles per hour with a cruising speed of 242 miles per hour. Operational range was listed at 4,000 miles. Comparatively, the YB-15 - which saw considerably more interest and usage by the US Army - exhibited a maximum speed of 200 miles per hour and cruising at 150 miles per hour. Range was 5,130 miles while its service ceiling was 18,900 feet. The famous B-17 (G-model) allowed for a maximum speed of 290 miles per hour, cruising at 180 miles per hour, a range of 2,000 miles and a service ceiling of 35,600 feet.
Shortly after the order, the Army concluded that the Y1B-20 was simply too expensive and that they really did not require bombers with range or carrying capability beyond those of the B-17. Consequently, both Y1B-20 prototypes were cancelled before anything could be built.
In March 1936, a team lead by Lysle Wood began work on an updated XB-15, the Model 316. This plane featured the all-glass nose that would make the B-29 distinctive. Designated the Y1B-20, it was 17 percent heavier than the eventual B-29. The Army was not interested. Boeing continued heavy bomber development in 1938 and 1939 with Models 330, 333, 333A, 333B, 334, and 334A. In August 1939 they began work on the Model 341, featuring a much improved wing: the Boeing Model 115 airfoil.
The design challenges stemming from the great size of the XB-15 were difficult to master, but the lessons learned by Boeing were later applied to the Model 314 flying boat. In 1938, the USAAC proposed to update the XB-15 to make the slightly larger Y1B-20, using more powerful engines, but the Secretary of War, Harry Hines Woodring, canceled the project before construction began, in favor of the expensive Douglas XB-19. Boeing went ahead with an internal redesign of the XB-15 called Model 316, a very heavy bomber with a high wing, a pressurized cabin and tricycle gear. The Model 316 was not built. The progression of design work starting with the XB-15 finally bore fruit with the Model 345 presented to the USAAC in May 1940; the very heavy bomber which resulted in the Boeing B-29 Superfortress.
Boeing had begun the process that would result in the B-29 as early as with the Y1B-20 series (Model 316, 316A/B/C/D), a paressurized cabin version of the XB-15.
TECHNICAL NOTES (as designed):
Armament: Four .50-cal. and three .30-cal. machine guns and 17,600 lbs. of bombs (max)
Engines: Four Wright GR-2600-A73 geared radials of 1,350 hp each or four Pratt & Whitney R-2180-5 radials of 1,400 hp each
Maximum speed: 258 mph @ 15,000 feet
Cruising speed: 242 mph
Range: 4,000 miles with 4,000 lbs. of bombs
Span: 157 ft. 0 in.
Wing area: ft² (m²)
wing loading : 34 lbs / ft2
Length: 109 ft. 2 in.
Height: 23 ft. 4 in.
Weight: 87,500 lbs.(39,700 kg) gross weight
Maximum Gross weight 89,900 lbs
Loaded weight: 91,500 lb (41,500 kg)
Max. takeoff weight: 105,100 lb (47,700 kg)
Crew: 9 - 10
3 x .50 caliber Browning M2 heavy machine guns
3 x .30 caliber Browning M1919 machine guns
or
7 x .50 caliber machine guns
Bomb load:
19,400 lbs maximum
Consolidated made a huge jump with the B-24 and its inexperience with building big bombers showed in many ways.
Martin XB-27
The XB-27 was proposed by Martin to fill an Army Air Corps requirement for a high altitude medium bomber. The Martin Model 182 was loosely based on the B-26 with design changes necessary for high altitude operation. The aircraft never progressed past the design phase of its development and no prototype aircraft were ever built.
Type Number built/
converted Remarks
XB-27 0 Proposed high-altitude medium bomber
TECHNICAL NOTES (as designed):
Armament: Three .30-cal. and one .50-cal. machine gun and 4,000+ lbs. of bombs
Engines: Two Pratt & Whitney R-2800-9 Double Wasp radials of 2,000 hp each (takeoff power)
Maximum speed: 276 mph
Range: 2,900 miles with 4,000 lbs. bomb load
Service ceiling: 33,500 ft.
Span: 84 ft. 0 in.
Length: 60 ft. 9 in.
Height: 20 ft. 0 in.
Weight: 32,970 lbs. (gross)
Crew: Seven
Martin XB-33 (Model 190)
The Martin XB-33 (Model 190) was conceived as a high-altitude version of the Martin B-26 Marauder. The aircraft design featured a pressurized crew compartment and a twin-tail. Armament would have been six to eight .50-cal. machine guns and a 4,000+ pound maximum bomb load. Martin engineers originally designed the aircraft with two Wright R-3350 radial engines, but the project was soon modified to a four-engine design. The Four-engine design was designated XB-33A.
Type Number built/
converted Remarks
XB-33 0 High-altitude twin-engine medium bomber
TECHNICAL NOTES (as designed):
Engines: Two Wright R-3350 radials of 1,800 hp each
Span: 100 ft. 0 in.
Length: 71 ft. 0 in.
Height: 22 ft. 6 in.
The Martin XB-33 (Model 190) was initially designed as a high altitude twin engine aircraft to potentially replace the Martin B-26 Marauder. The initial design was begun in late 1940, and as it progressed, it became obvious a two-engine aircraft would not be capable of achieving the performance required in the Army specification.
Rather than continue refining the XB-33, Martin engineers decided to radically alter the original design by adding two more engines. The entire project was scaled up to the approximate size of the Boeing B-29. The Army was sufficiently impressed with the new design, so two prototypes were ordered (S/N 41-28407 and 41-28408) and designated XB-33A.
The XB-33A was to be powered by four Wright R-2600-15 engines instead of the more powerful R-3350, in part, because the 3350s were in great demand for B-29 construction. An order for 400 production B-33A Super Marauders was placed by the Army; however, before the prototypes were complete, the entire order was canceled. Instead of building B-33As, Martin was awarded a contract to assemble 400 B-29s at its Omaha, Neb., plant.
In 1939, the service put forth a requirement for a new medium-class bomber to fill the void resulting in two competing submissions being entertained - the North American XB-28 "Dragon" (based on its B-25 "Mitchell" design) and the Martin XB-33. The designs were given prototypes contracts in 1940 (America did not officially enter the war until December of 1941).
The XB-33 was based on a reworked Martin B-26 "Marauder" and therefore came to be known under the name of "Super Marauder". The initial approach - XB-33 - saw a more slightly-refined B-26 form used that relied on a standard twin-engine approach (2 x Wright R-3350 "Duplex-Cyclone" radial engines). Two prototypes of this standard were ordered but never built. Realizing the capabilities needed for high-altitude performance, Martin returned with a four-engined approach (4 x Wright R-2600-15 radial engines - the original Wright R-3350 stock now redirected to Boeing B-29 "Superfortress" production) superseding the twin-engine model and this became the XB-33A. Beyond its four engines (two nacelles per wing), the B-26 airframe and wings were completely enlarged for the role. Before the end, the medium bomber looked - and would function - more the part of heavy bomber as its qualities grew more in line with other high altitude performers of the day, namely the Boeing B-29 Superfortress.
Again the Army ordered two prototypes of this design and a further 400 production models to carry the B-33A designation (to be built at a Martin plant in Nebraska) in January of 1942. However, progress on the B-29 product was of the utmost importance that Martin was given a contract to help in its manufacture, thus derailing the B-33 initiative in whole. The production contract for 400 was rescinded on November 25th, 1942 and neither of the prototypes were completed. The B-29, meanwhile, went down in wartime lore as the aircraft to drop the two atomic bombs on Japan, helping to bring about the end of World War 2.
The four engine configuration was set to provide a maximum speed of 345 miles per hour for the bomber. The crew numbered seven and would have operated in pressurized cabin spaces. The general arrangement of the aircraft was conventional with a stepped cockpit at front, shoulder-mounted wing mainplanes near midships, and a tapered empennage. The tail unit carried a twin-rudder arrangement. Various defensive positions (nose, dorsal turret, ventral turret, and tail) would be armed by way of 8 x 0.50 caliber heavy machine guns (two guns to a position). The projected bomb load (all ordnance to be held internally) was 10,000 lb.
With the cancellation of its own proposed super-bomber, the XB-33, in 1942, Martin sent part of its workforce to work on Northrop’s ambitious XB-35 at the Northrop factory at Hawthorne, California.
Type Number built/
converted Remarks
XB-33A 0 Two prototypes canceled
B-33A 0 400 canceled
TECHNICAL NOTES (as designed/estimated):
Armament: Eight .50-cal. machine guns plus 10,000 lbs. of bombs
Engines: Four Wright R-2600-15 radials of 1,800 hp each
Maximum speed: 345 mph
Cruising speed: 242 mph
Range: 2,000 miles
Service ceiling: 39,000 ft.
Span: 134 ft. 0 in.
Length: 79 ft. 10 in.
Height: 24 ft. 0 in.
Weight: 95,000 lbs. (design gross weight)
Crew: Seven
Serial numbers: 41-28407, 41-28408
1939 - Four-Engine Medium Bomber
In 1939, the USAAC issued a requirement for a new medium bomber which could operate at high-altitude to avoid attack from ground fire. The significant factor in medium bombardment operations, it might be noted, was the size of the bomb load and not the range. The medium bomber, considered to be a "pure bombardment type," was initially intended to operate at medium altitudes of 8,000 to 14,000 feet and primarily against depots, fortified positions, railroad yards, and other such targets along or behind the battle line. Carrying a heavier bomb load and enjoying the advantage of greater range, the mediums could supplement the work of light bombers and might assist the long-range heavy bombers against the nearer targets in a strategic bombardment effort.
With six-man crews, served as the AAF's medium bombers during the greater part of World War II. North American had initiated design on the B-25 in February 1938 and production began in February 1 94 1, without benefit of an experimental prototype plane. Similarly, the Air Corps bought the B-26 from the Glenn L. Martin Company right off the drawing board in 1939: a production contract was signed in September of that year, the first plane flew in November 1940, and manufacture got under way at approximately the same time as that of the B-25.
Both planes were twin-engine all-metal midwing monoplanes. In 1941 the Mitchell's two R-2600 engines gave it a maximum take-off power rating of 3,400 horsepower as compared with the Marauder's 3,700. In 1945 the rating for the Mitchell had not been increased, but that of the Marauder had been stepped up to 4,000. During the same period the airframe weight of the B-25 was increased from 11,600 pounds to 13,000 pounds and the maximum weight from 25,000 to 35,000 pounds. The Marauder, a larger plane to begin with, grew from an original airframe weight of 14,100 pounds to almost 17,000 pounds, while its maximum went from 33,000 pounds to more than 38,000.
Preliminary designs for new four-engine medium bomber were submitted by Martin and North American. The Martin XB-33 was redesigned from the B-26 Marauder, and North American XB-28 was based from the B-25 Mitchell. In 1940, both designs were awarded prototype contracts. The full-scale development of the XB-33 was begun in late 1940, and as it progressed, the Martin engineers found that a two-engine aircraft would not be capable of achieving the performance required in the Army specification. It was decided to radically alter the original design by adding two more engines. The entire project was scaled up to the approximate size of the Boeing B-29. The Army was sufficiently impressed with the new design; the two prototypes were redesignated XB-33A and an order for 400 production B-33A Super Marauders was placed. In 1944, Martin was awarded a contract to assemble B-29s which were urgently needed to enter Pacific theater. As B-29s had top priority to use the inventory, the entire B-33A order was cancelled before the prototypes were completed.
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