The Curtiss NBS-4 was an improved version of the Curtiss-Martin NBS-1 Night Bomber that was produced in prototype form before being superseded by the Curtiss B-2 Condor.
The NBS-1 was a three-bay equal span biplane, with a fabric covered wooden framework for the wings and fuselage. It was powered by two Liberty engines mounted on the lower wing, and the wings folded back to reduce the amount of space the aircraft needed. Although the aircraft was designed by Glenn Martin, Curtiss produced the largest batch - 50 aircraft out of a total of 130 produced by four companies.
It was thus Curtiss that received a 1922 contract to produce two improved versions of the aircraft, as the NBS-4. The new aircraft was very similar to the NBS-4, but with a welded steel-tube frame for the fuselage. The wings were changed to use the new thicker Curtiss C-72 aerofoil, replacing the RAF 15 aerofoil of 1915 used on the NBS-1. A bomb-aimer's window was built into the port side of the fuselage, allowing the nose gunner to remain in position during a bombing run. The NBS-4 was also given a biplane tail, with two vertical surfaces linked by horizontal surfaces at top and bottom.
The two prototypes were original armed with nose, aft fuselage and belly positions each capable of carrying one or two Lewis guns. One of the two prototypes was later modified to include gunner's positions at the rear of extended engine nacelles.
The first of the two aircraft was delivered in May 1925 and was still intact in July 1930. The NBS-4 wasn't ordered into production, but it was developed into the B-2 Condor, which was produced in small numbers as a bomber and a transport aircraft.
Engine: Two Liberty 12 engines
Span: 90ft 2in
Length: 46ft 5in
Height: 15ft 9in
Empty weight: 7,864lb
Gross weight: 13,795lb
Max speed: 100.2mph
Climb Rate: 283ft/ min
Service ceiling: 11,100ft
Range: 728 miles
Armament: Five .30in machine guns
Bomb load: 2,100lb bombs