As promising as the performance jump from the Martin MB-2 to the Huff-Daland LB-1 series was, Army authorities were not convinced of the merits of a single-engine bomber form. Instead, they elected to pursue a twin-engine variant of the design from Huff-Daland as the "XLB-3". With a twin-engine layout, the crew nacelle was now cleared of complex operating systems which allowed engineers to introduce additional storage and crew operating space - adding a whole new crewmember to the original staff of four. The biplane wing arrangement was retained and each engine drove a two-bladed propeller. All other functions of the aircraft were largely carried over from the preceding design.
The original XLB-3 was outfitted with 2 x Allison VG-1410 (a variant of the "Liberty 12") air-cooled inverted V12 engines of 400 horsepower (each) and it was this prototype form that was handed to the United States Army Air Corps for formal testing in 1927. The crew included two pilots, a bombardier, and two dedicated machine gunners. The defensive gun network included five trainable .303 Lewis machine guns while the offensive bombload carried reached 2,205 lb.
However, performance of the original prototype was less than that of the preceding single-engine LB-1 design which forced a revision of the XLB-3 to become the XLB-3A. This mark was modified through the installation of a pair of Pratt & Whitney R-1340 radial piston engines of 410 horsepower. Beyond that, the design stayed largely faithful to the original offering.
Despite the engine change, the required performance was still lacking and USAAC interest waned as it moved on the related LB-5 instead. The LB-5 found a bit more success in that it was procured in 36 examples from Keystone. Keystone Aircraft Corporation was formed from the purchase of Huff-Daland by Hayden, Stone & Company. Keystone then fell under the Curtiss-Wright brand label from 1929 onwards until its services were terminated in 1932.
Only a single XLB-3 aircraft was ever completed.
[ 1 Units ] : Keystone Aircraft Corporation . Huff-Daland Aero Corporation - USA
- Ground Attack
- X-Plane / Developmental
45.01 ft (13.72 m)
66.99 ft (20.42 m)
16.83 ft (5.13 m)
(Showcased structural dimension values pertain to the Keystone XLB-3 production model)
6,074 lb (2,755 kg)
11,718 lb (5,315 kg)
(Showcased weight values pertain to the Keystone XLB-3 production model)
(Showcased powerplant information pertains to the Keystone XLB-3 production model)
116 mph (186 kph; 100 kts)
11,155 feet (3,400 m; 2.11 miles)
541 miles (870 km; 470 nm)
550 ft/min (168 m/min)
(Showcased performance values pertain to the Keystone XLB-3 production model; Compare this aircraft entry against any other in our database)
2 x .303 Lewis machine guns in nose on trainable mounting
2 x .303 Lewis machine guns in dorsal cockpit position on trainable mounting.
1 x .303 Lewis machine gun in ventral position on trainable mounting.
Up to 2,205 lb of conventional drop bombs.
(Showcased armament details pertain to the Keystone XLB-3 production model)
XLB-3 - Base Series Designation; original designation when fitted with 2 x Allison VG-1410 air-cooled inverted V12 engines.
XLB-3A - Re-engined with 2 x Pratt & Whitney R-1340 radial piston engines.
* Ribbons not necessarily indicative of actual historical campaign ribbons. Ribbons are clickable to their respective campaigns/operations.
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