The Keystone LB-7 was identical to the LB-6 except for the replacement of the Wright Cyclones by Pratt & Whitney R-1690-3 Hornet radials. In those days, the simple act of replacing one engine by another would often call for a new aircraft designation.
Sixteen production LB-7 aircraft were delivered to the USAAC between February and June of 1929. Serials were 28-388/395 and 29-001/010. Additionally, three LB-6s (29-013, 29-014, and 29-016) were converted to LB-7s at France Field in May 1930. The Cyclone-powered LB-6s could be externally distinguished from the Hornet-powered LB-7s by looking at the exhaust collector rings on their engines. The Hornet of the LB-7 had exhaust collector rings BEHIND the cylinders, whereas the Cyclone of the LB-6 had exhaust collector rings AHEAD of the cylinders. (Several references have this backwards). The aircraft were otherwise externally identical.
The LB-7 actually preceded the LB-6 into service. The LB-7 served alongside the LB-6 with the 2nd Bomb Group based in the US. Most of the LB-7s were stationed at Langley Field until being sent to the 40TH School Squadron at Kelly Field in March-June 1931. Three aircraft (28-388, 29-009, and 29-010) spent their careers at Wright Field as conversion experiments until March 1932, when the sole survivor (29-010) was converted to an LB-6 and was also sent to the 40th School Squadron at Kelly Field. Three LB-6 aircraft were re-engined late in their lives to become LB-7s, one LB-7 was modified to become the XLB-8, and yet another became the XLB-9 after an engine change and a final modification resulted in the XLB-12.
Like the LB-6, the LB-7 was known as Panther by Keystone, but this was not an official USAAC name. Like its LB-6 stablemate, the LB-7 rapidly became obsolete and the survivors were all withdrawn from service and scrapped in 1933-1934.
28-388 DELIVERED 2/9/29, CONVERTED TO LB-12 6/27/29, WRECKED 8/30/29. 28-389 DELIVERED 1/31/29, WRECKED 2/6/29. 28-390 DELIVERED 2/20/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 6/15/31, WRECKED 12/23/31. 28-391 DELIVERED 3/4/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 5/26/31, SURVEYED 8/7/34. 28-392 DELIVERED 3/12/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 6/14/31, SURVEYED 6/28/34. 28-393 DELIVERED 3/18/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 6/26/31, SURVEYED 5/23/34. 28-394 DELIVERED 3/16/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 6/25/31, SURVEYED 5/23/34. 28-395 DELIVERED 4/15/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 4/28/31, SURVEYED 8/20/34. 29-001 DELIVERED 3/28/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 4/28/31, SURVEYED MAY 33. 29-002 DELIVERED 4/17/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 3/10/31, SURVEYED 6/28/34. 29-003 DELIVERED 4/11/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 3/29/31, SURVEYED 4/9/34. 29-004 DELIVERED 4/27/29, BURNED 3/1/30. 29-005 DELIVERED 4/26/29, REDESIG. ZLB-7 WITH 40TH SCHOOL SQ. ON 6/25/31, SURVEYED 8/20/34. 29-006 DELIVERED 4/30/29, BURNED 9/17/29. 29-007 DELIVERED 5/1/29, WRECKED 11/22/29. 29-008 DELIVERED 5/10/29, BURNED 1/15/30. 29-009 DELIVERED 11/6/29, CONVERTED TO XLB-8 12/11/29, BURNED 3/18/31. 29-010 DELIVERED 12/27/29, CONVERTED TO XLB-9 3/2/31, CONVERTED TO LB-6 12/4/31, REDESIG. ZLB-6 WITH 40TH SCHOOL SQ. ON 3/16/32, SURVEYED 9/26/33. 29-013 DELIVERED 7/21/29, CONVERTED TO LB-7 5/14/30, WRECKED 6/19/31. 29-014 DELIVERED 7/26/29, CONVERTED TO LB-7 5/14/30, SURVEYED 11/2/33. 29-016 DELIVERED 7/21/29, CONVERTED TO LB-7 5/14/30, WRECKED 6/19/31.
Specification of the Keystone LB-7:
Two 525 hp Pratt & Whitney R-1690-3 Hornet air-cooled radial engines. Maximum speed 114 mph at sea level, 110 mph at 5000 feet. Cruising speed 95 mph. Landing speed 55 mph. Service ceiling 13,325 feet, Absolute ceiling 15,700 feet. Initial climb rate 660 feet per minute An altitude of 5000 feet could be attained in 9.1 minutes. Range 432 miles with 2000 pounds of bombs. Weights: 6556 pounds empty, 12,903 pounds gross. Wingspan 75 feet, length 43 feet 5 inches, height 18 feet 1 inches, wing area 1148 square feet. Two Lewis machine guns in an open gunner's position in the nose, two Lewis machine guns in an open dorsal gunner's position, one Lewis gun firing downward through an opening in the lower fuselage.