Martin XB-27 (Model 182)
High-Altitude Medium Bomber Proposal
The Martin XB-27, developed from the B-26 Marauder line, was drawn up as a possible high-altitude medium bomber solution.
Authored By: Staff Writer | Last Edited:
Ground-based air defenses remained a potent threat to aircraft in the lead-up to World War 2 (1939-1945). As such, there remained a focus on acquiring high-altitude bomber types by the major military players of the period, platforms that could fly higher than ground-based defenses could reach and stay out of the grasp of pesky interceptors attempting to knock the bomber out of the sky. "Twins" - twin-engined aircraft forms - became the normal arrangement for medium-class types and the United States had no shortage of stellar twins before the war drew to a close in 1945.
By this time in history, the Glenn L. Martin Company ("Martin") was a storied, long-running established player for the United States military, supplying all manner of aircraft from the World War 1 (1914-1918) period onward. For the latter part of the 1930s, the company was deeply involved in work on a new "twin", a medium bomber of considerable capability which flew for the first time on November 25th, 1940 and was ultimately accepted into service with the United States Army Air Forces (USAAF) in 1941 to become the famous B-26 "Marauder" - the medium bomber seeing action throughout World War 2 and beyond.
Two major developments sprung from the B-26 initiative: the "Model 182" (becoming the "XB-27") and "Model 190" (proposed as a "Super Marauder"). The Model 182, the focus of this article, was proposed to USAAC/USAAF authorities as a high-altitude, medium-class bomber which was slated to retain much of the form and function that made the B-26 such a success in service. The design was aerodynamically refined, as expected, with a glazed-over nosecone section, stepped cockpit, and single-finned tail unit. A modern tricycle undercarriage would aid in ground-running and related actions. Each mainplane would be mounted at shoulder-height along the fuselage sides and carry underslung nacelles, each engine driving multi-bladed propellers in "tractor" / "puller" fashion. The mainplanes were envisioned with a swept-back leading edge and straight-lined trailing edge while sporting rounded tips.
The primary crew workspaces were contained in the nose, tail, cockpit, and midsection - the crew complement numbering seven and including two pilots (seated side-by-side under a framed canopy space), a bombardier, and several dedicated machine gunners. The expected high-altitude operations of this aircraft required it to have pressurized work spaces for the crew - the aircraft called to operate at altitudes in excess of 30,000 feet.
Structural dimensions included a running length of 60.8 feet with a wingspan of 84 feet. Height was 20 feet and loaded weight would have reached around 33,000lb.
The bomber was drawn up with a war load up to 4,000lb, this to be carried mostly internally in a bomb bay section at the belly of the aircraft (also, in keeping with other similar designs of the period, externally-held munitions could / should not be ruled out). Standard armament was to include 3 x 0.30 caliber Browning M1919 air-cooled (medium) machine guns and 1 x 0.50 caliber Browning M2 air-cooled (heavy) machine gun for point self-defense. One 0.30 caliber weapon was to be focused at the nose with another in a rear-facing dorsal position and the final gun found at a rear-facing ventral position. The remaining 0.50 caliber was to be installed at the extreme end of the fuselage to help cover the most vulnerable area of the bomber.
Power for the twin-engined bomber centered on 2 x Pratt & Whitney R-2800-9 "Double Wasp" air-cooled, turbo-supercharged radial piston engines, each delivering 2,000 horsepower and driving four-bladed propeller units. These engines, first run in 1937, became the centerpiece of many-a-classic design of the World War 2 period: the Grumman F6F "Hellcat" naval fighter, the Republic P-47 "Thunderbolt" USAAF fighter, and the Vought F4U "Corsair" naval fighter to name a few.
Estimated performance specs included a maximum speed between 280 and 375 miles-per-hour (sources vary), an operational range out to 2,900 miles, and a service ceiling up to 33,500 feet.
The bomber was being developed around a USAAC specification (Specification XC-214) originating in August of 1939 - just weeks before World War 2 arrived in Europe (September 1st with the German invasion of Poland). Martin was in direct competition with North American (makers of the famous B-25 "Mitchell" medium twin-engined medium bomber) for the requirement but, in any event, neither design proved an outright success. The North American NA-63 was actually ordered and flown as a prototype through the "XB-28" (detailed elsewhere on this site) but the Martin Model 182 was only advanced on paper as the "XB-27" - becoming nothing more than a relatively advanced design study.
The requirement was eventually fulfilled by a collection of other in-service aircraft that could more than meet the demand of different mission types. The changing requirements of war, namely air superiority for the Allies in the march to Rome, Berlin and Tokyo, also played a role in the demise of such aircraft projects.