The Martin XB-16 was a design for a heavy bomber to satisfy a USAAC specification for a heavy bomber with a range of 5,000 miles.
In 1933 the USAAC began work on ‘Project A’, looking at the possibility of producing very long range bombers with a range of 5,000 miles. In April 1934 Boeing and Martin were both asked to produce designs for aircraft that could carry a 2,000lb payload over a range of 5,000 miles at 200mph. The Boeing project was more successful - their Model 247 eventually reached the prototype stage, as the XB-15, but neither design entered production.
Martin’s first design was the Model 145A, which was given the specification XB-16. This was a four engine heavy bomber, using Allison inline engines in place of the radial engines used in most bomber designs of the period. These were completely enclosed in the thick wings, which drove their propellers via extension shafts. It would have featured very large Fowler type flaps, which were expected to give it a landing speed of 60mph. The thick wings were low mounted, and were half the height of the fuselage. The leading edge was straight in the centre and tapered at the ends, while the trailing edge was straight. It had a twin tail, with the horizontal surfaces mounted towards the end of the vertical surfaces. Although this aircraft had a good top speed, its cruising speed was only 120mph, which was far too slow for the Air Corps.
In 1935 Martin produced a modified Model 145B. This was a far more radical design. It would have been powered by six Allison engines, once again all contained within the thick wings. Four would have powered tractor propellers, and two pusher propellers. The crew and payload would have been carried in a large central nacelle carried below the wings. The inner tractor engines were lined up with long booms that linked to the twin tail. It would have been a much larger and heavier aircraft than the Model 145A, with a wingspan of 173ft, and would have been heavier and larger than the Boeing XB-15, the largest aircraft in the world when it was first completed. It was eventually outclassed by the massive Douglas XB-19 of 1941.
The Model 145B was still too slow for the Air Corps, and neither design reached the prototype stage.
Engine: Four Allison V-1710 liquid cooled engines
Power: 1,000hp each
Height: 19ft 7in
Empty Weight: 31,957lb
Gross Weight: 65,000lb
Cruising Speed: 120mph
Climb rate: 740ft/ min
Range: 5,040 miles
Max Range: 6,200 miles with no payload
Guns: Nose and tail enclosures and retractable dorsal and ventral turrets
Bomb load: 2,500lb to 5,040 miles; 12,180lb to 3,200 miles
Engine: Six Allison V-1710-3 engines
Power: 1,000hp each
Length: 114ft 10in
Empty Weight: 50,660lb
Gross Weight: 104,880lb
Maximum Speed: 256mph
Cruising Speed: 140mph
Range: 3,300 miles with 2,500lb
Bomb load: 2,500lb