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Martin XB-16 (Model 145)

Long-Range, High-Altitude Heavy Bomber Proposal

United States | 1935

"No prototypes of the proposed multi-engined Martin XB-16 were ever completed - the design failing to impress USAAC authorities."

Authored By: Staff Writer | Last Edited: 04/04/2019 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
The 1930s saw considerable technological growth concerning military aircraft. Losing inventory space were the classic "fabric-over-wood" biplanes debuted during, and after, World War 1 (1914-1918) with these being actively succeeded by more metal-skinned types relying on stronger metal under-structures. While biplanes still existed in various frontline fighting forms, the monoplane was picking up steam as the aircraft-wing-design-of-choice from newer entries.

In 1933, U.S. military personnel at Wright Field undertook work to flesh out a new all- modern bomber - one that could carry a war load of at least 2,500 lb out to distances of 5,000 miles while maintaining a speed of 200 miles per hour. The United States Army Air Corps (USAAC) developed "Project-A" around these specifications and this was presented in 1934 to large-aircraft makers Boeing and Martin. The intent was to develop an bombing platform capable of reaching (and subsequently protecting) American interests in far-off places like Alaska, Hawaii, and Panama.

The Glen L. Martin Company was founded in 1912 and contributed to the American aircraft effort of World War 1 - its biggest success being the MB-1 biplane bomber of 1918. From there came the MB-2 of the 1920s and culminated with the B-10 of 1932. The B-10s entry was of particular note as it marked the first mass-produced bomber that could outrun "pursuit" fighters of the period. Nearly 350 of this Martin product were produced.

Martin's submission to the project was known internally as "Model 145". To contend with the requested range and performance, a four-engined layout was selected - power stemming from 4 x Allison V-1710 liquid-cooled inline piston engines of 1,000 horsepower each. This proved something of a departure for the USAAC as its contemporary stock of large aircraft relied heavily on trusty air-cooled radial piston engines. Liquid-cooled inline engines aided high-altitude performance and could be fitted within more streamlined nacelles, therefore inherently improving aerodynamic efficiency. The trade off in selecting an inline engine, however, was in the increased vulnerability to enemy fire due to the internally fragile nature of such an engine.

For the USAAC program, the Model 145 was designated the "XB-16" and a prototype was commissioned (Boeing's entry became the "XB-15" and is detailed elsewhere on this site). A twin-boom form was achieved in which the crew sections, bomb load, and other primary mission components were held in a centralized nacelle. The wide-spanning wing elements (showcasing a combined 140 foot span) were affixed to this structure and high-mounted. Each wing was to hold a pair of engine nacelles that were well-contoured into the general shape of the wing elements themselves. The cockpit was stepped (the pilot's overlooking the aircraft's nose section) and window panes accompanied the bombardier's position at the nose. The tail booms emanated from the wing trailing edges and were capped at their absolute ends by vertical tail fins. The booms were joined to one another by a shared horizontal plane that also protruded from the vertical fin sides outboard. A tricycle undercarriage (wholly retractable) was envisioned for the final design and the standard operating crew would number ten.

Initially, the XB-16 design was roughly equivalent in dimension to the Boeing submission but it was decided by Martin to increase its bomber's size to meet the intended bomb load and range requirements (an increase to internal space allowed for greater fuel loads to be carried and lifting and strength properties could be spread out over the larger aircraft as a result. The wing span now measured 173 feet - even greater than the World War 2-era Boeing B-29 "Superfortress" still to come - and these changes called for a new company model designator to be used, the "Model 145B".

The larger aircraft required more power so an additional pair of engines was added. As the original set faced forward at each wing leading edge, the two additional engines were positioned to face aft at each wing trailing edge. In all each wing would hold three engines apiece with the new engine installs added directly behind the existing outboard fits.

In the end, it was decided by USAAC authorities that the Martin bomber could not meet the intended requirements, particularly in the category of speed. It was estimated that the XB-16 was to have a maximum speed of 237 miles per hour, reach out to 5,000 miles (3,200 mile mission range), and reach an altitude of 22,500 feet. Its rated bomb load was 12,180lb of internally-held drop ordnance. As such, the XB-16 was cancelled before any tangible work on a prototype was ever completed.

Boeing's XB-15 held greater promise and a single, flyable prototype was completed which evolved to become the developmental "Y1B-20". Boeing's large bomber work eventually produced two classics of the period - the B-17 "Flying Fortress" and the aforementioned B-29 - both proving their mettle over Europe and the Pacific theaters during World War 2.

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Power & Performance
Those special qualities that separate one aircraft design from another. Performance specifications presented assume optimal operating conditions for the Martin XB-16 (Model 145) Long-Range, High-Altitude Heavy Bomber Proposal.
Model 145A: 4 x Allison V-1710-3 V12 liquid-cooled inline piston engines developing 1,000 horsepower each and driving three-bladed propeller units (inboard engines "puller"; outboard engines "pusher").
236 mph
380 kph | 205 kts
Max Speed
22,507 ft
6,860 m | 4 miles
Service Ceiling
5,002 miles
8,050 km | 4,347 nm
Operational Range
740 ft/min
226 m/min
City-to-City Ranges
Operational range when compared to distances between major cities (in KM).
The nose-to-tail, wingtip-to-wingtip physical qualities of the Martin XB-16 (Model 145) Long-Range, High-Altitude Heavy Bomber Proposal.
114.8 ft
35.00 m
O/A Length
141.1 ft
(43.00 m)
O/A Width
18.0 ft
(5.50 m)
O/A Height
31,967 lb
(14,500 kg)
Empty Weight
104,940 lb
(47,600 kg)
Design Balance
The three qualities reflected below are altitude, speed, and range. The more full the box, the more balanced the design.
Available supported armament and special-mission equipment featured in the design of the Martin XB-16 (Model 145) Long-Range, High-Altitude Heavy Bomber Proposal .
2 x 0.30 caliber machine guns in dorsal turret.
2 x 0.30 caliber machine guns in port side engine nacelle (inboard engine).
2 x 0.30 caliber machine guns in starboard side engine nacelle (inboard engine).
2 x 0.30 caliber machine guns in rear fuselage emplacement.
2 x 0.30 caliber machine guns in port side tail boom section.
2 x 0.30 caliber machine guns in starboard side tail boom section.

An internal bomb load of up to 12,180 lb (conventional drop ordnance / drop bombs).
Notable series variants as part of the Martin XB-16 (Model 145) family line.
XB-16 - Base Prototype Designation; none completed.
Model 145 / Model 145A - Original design with 140-foot wingspan and four-engine configuration.
Model 145B - Revised product with 173-foot wingspan and six-engine configuration.
Global customers who have evaluated and/or operated the Martin XB-16 (Model 145). Nations are displayed by flag, each linked to their respective national aircraft listing.

Total Production: 0 Units

Contractor(s): Glen L. Martin Company - USA
National flag of the United States

[ United States (cancelled) ]
Relative Max Speed
Hi: 300mph
Lo: 150mph
Aircraft Max Listed Speed (236mph).

Graph Average of 225 MPH.
Era Crossover
Pie graph section
Showcasing Aircraft Era Crossover (if any)
Max Alt Visualization
Small airplane graphic
MACH Regime (Sonic)
RANGES (MPH) Subsonic: <614mph | Transonic: 614-921 | Supersonic: 921-3836 | Hypersonic: 3836-7673 | Hi-Hypersonic: 7673-19180 | Reentry: >19030
Aviation Timeline
1 / 1
Image of the Martin XB-16 (Model 145)
Image copyright www.MilitaryFactory.com; No Reproduction Permitted.

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to airborne requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
The Martin XB-16 (Model 145) Long-Range, High-Altitude Heavy Bomber Proposal appears in the following collections:
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