The Huff-Daland XLB-3 was the first example of the series of twin-engined Huff-Daland/Keystone bombers.
The Huff-Daland LB-1 three-seat biplane bomber of 1923 had been powered by a single enormous 800 hp Packard 2A-2540 V-12 water-cooled engine instead of the more traditional pair of lower-powered engines. Ten examples had been delivered to the Army. However, the Army soon found the single-engined format to be unsatisfactory, and decided to revert to a more conventional twin-engined format.
In response to this need, the Huff-Daland company submitted the XLB-3. A single example was ordered by the Army. The serial number was 27-333. It was essentially an LB-1 airvrame powered by a pair of experimental air-cooled and inverted Liberty V-1410-1 engines mounted on top of the leading edges of the lower wing, one on each side. The single vertical rudder of the LB-1 was supplemented by a pair of smaller vertical rudders mounted outboard on the horizontal tailplane. A crew of five was carried, with the two additional members being housed in the nose gunner and bombardier positions. The XLB-3 was designed in parallel with the Huff-Daland LB-5, which had the same overall format but was powered by a pair of ordinary water-cooled upright Liberty engines.
By that the time that the XLB-3 appeared in December of 1927, the Huff-Daland company had been reorganized as the Keystone Aircraft Corporation and had moved its headquarters to Bristol, Pennsylvania. The experimental Liberty engine installation in the XLB-3 proved to be unsatisfactory, and before the first flight could take place the Liberty engines were replaced by a pair of 410 hp air-cooled Pratt & Whitney R-1340-1 air-cooled radial engines. The engine change caused a designation change to XLB-3A.
The performance of the XLB-3A was actually poorer than that of the single-engined LB-1 that it was designed to replace, and no production examples were ordered. However, the parallel LB-5 project was to prove more successful, and was the first of Keystone's successful biplane bombers.
Specification of the Huff-Daland XLB-3A:
Two 410 hp Pratt & Whitney R-1340-1 air-cooled radials. Maximum speed 116 mph at sea level, 113 mph at 5000 feet. Cruising speed 93 mph. Landing speed 59 mph. Service ceiling 11,210 feet, Absolute ceiling 13,700 feet. Initial climb rate 550 feet per minute. An altitude of 5000 feet could be attained in 11.3 minutes. Range 544 miles. Weights: 6065 pounds empty, 11,682 pounds gross. Wingspan 67 feet, length 45 feet, height 16 feet 10 inches, wing area 1138.7 square feet.