The Keystone LB series had been characterized by tapered wings, but the XLB 6 of 1927 (converted from the tenth LB 5) introduced constant chord wings with new powerplant (two 525 hp Wright R 1750 1 Cyclone radials) mounted between the wings, and a lengthened fuselage. Thus modified, this became the standard configuration for the remaining Keystone LB types, beginning with 17 production LB 6s and continuing with 18 LB 7s, which were identical except for their 525 hp Pratt & Whitney R 1690 3 Hornet engines.
All Aero 