History of Douglas XB-31 (Raidmaster) (Model 332)

The Douglas XB-31 "Raidmaster" became one of four applications submitted to the United States Army Air Forces (USAAF) during World War II (1939-1945) in response to a request for a new long-range high-altitude aircraft encounter height "Super Heavy" bomber". The Boeing B-29 "Superfortress" eventually fulfilled this requirement, and United's XB-32 was selected as the insurance measure (which became the B-32 "Ruler").

Before a decision was made, the XB-31 and Lockheed entries (the XB-30 detailed elsewhere on this site) competed with Boeing's entry -- both of which dropped out in time.

The origins of the XB-31 can be traced back to the late 1930s, when U.S. authorities realized that European (especially German) military aircraft had advanced more than anything in the current inventory. The Army formed a committee to seek guidance, and the consensus was to develop a new platform for the super-heavy long-range bomb.

The outbreak of war in Europe in September 1939 simply focused on getting big planes into the skies for a short period of time.

Requires excellent range and excellent operating altitude, the latter helping to keep the system as far as possible from enemy interceptors and ground fire. Speed ??is as important as a competent bomb load to make a product worth the investment.

So far, the standard heavy bombers in American stables are the Boeing B-17 "Flying Fortress" (introduced in 1938) and the Joint B-24 "Liberator" (introduced in 1941) - both classics, but eventually Obsolete through the progressiveness of warfare.

So continue the search for a successor - Boeing got a head start on its XB-29 product and eventually won the order. In 1940, Douglas prepared their aircraft through the "Type 332" program, for which the U.S. Army designated the "XB-31".

On paper, the Douglas submission has surpassed the other three submissions in size and operational weight -- a massive design, to be sure.

Douglas engineers opted for a traditional arrangement with the flight deck attached above the nose, the monoplane wings slightly forward and a rudder aft. The main-wing aircraft are shoulder-mounted, each with a pair of suspended engine nacelles. The fuselage has a very streamlined appearance, with a very pointed nose and a tapered tail that promotes excellent aerodynamics.

As usual, two bomb bays are in the abdomen. The tail unit contains a large area fin. The tricycle landing gear is present and fully retractable into the fuselage. The crew station was under pressure in anticipation of the high-altitude engagement of the large bomber. The standard operating staff is eight.

There is a dorsal and ventral turret, each remotely controlled by the operator and armed with 2 x .50 caliber heavy machine guns. The empennage carries a set of trainable 37mm cannons to protect the rear of the aircraft from interceptors. Internal bomb load is 25,000 lbs.

Dimensions are 207 feet wingspan, 117.2 feet long and 42.6 feet high.

Power for the design was originally intended to come from 4 Wright R-3350-13 Duplex Cyclone radial piston engines, 2,200 hp each. Later changed (through redesign) to 4 x Pratt & Whitney R-4360 "Wasp Major" radial piston engines, 3,000 hp each.

Estimated performance specifications for the bomber include a top speed of 360 mph, a range of up to 3,000 miles, and a service ceiling of 35,000 feet.

While Douglas' entry was promising, Boeing's progress with its XB-29 (and merging with their XB-32) knocked out the Douglas and Lockheed entries. Therefore, the XB-31 exists only as a design study, nothing more.

Douglas XB-31 (Raidmaster) (Model 332) Specification

Basic

Year:
1944
Staff:
8

Production

[0 units]:
Douglas's Plane - America

Roles

- Ground Attack

- X-Plane / Development

Dimensions

Length:

117.13 ft (35.7 m)

Width:

207.02 ft (63.1 m)

Height:

42.62 ft (12.99 m)

Weight

Curb Weight:

109,195 lb (49,530 kg)

MTOW:

89,800 kg

(Difference: +88.780lb)

Performance

ORIGINAL: Wright R-3350-13 "Twin Cyclone" radial piston engines, 2,200 hp each; Late: 4 Pratt & Whitney R-4360 "Wasp Major" radial piston engines, 3,000 hp each.

Performance

Maximum Speed:

357 mph (575 km/h; 310 knots)

Service Limit:

35,023 ft (10,675 m; 6.63 mi)

Maximum range:

3,001 miles (4,830 km; 2,608 nautical miles)

Armor

Default:

2 x .50 caliber heavy machine guns mounted in the dorsal remote-controlled turret.

2 x .50 caliber heavy machine guns, mounted in the ventral remote-controlled turret.

2 x 37mm automatic cannons in a trainable rear position.

Optional:

Up to 25,000 lbs of conventional temporary storage space in the two ventral bomb bays.

Changes

XB-31 - Base Project Name

Model 332 - Company Model Name

B-31 - Assumed Production Designation

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