Keystone XLB-3 - United States, 1927
Detailing the development and operational history of the Keystone XLB-3 Prototype Light Bomber Biplane.
Entry last updated on 5/26/2016; Authored by Staff Writer; Content ©www.MilitaryFactory.com
The Keystone XLB-3 was a twin-engine prototype form of the earlier Huff-Daland LB-1 model of 1923.
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.