The Franklin 12 series of 12-cylinder air-cooled horizontally opposed aircraft engines produced in the 1940s and 50s, (US military designation O-805 was applied to the 12AC-806, 12ACG-806 and 12ACGSA-806).
The Franklin O-805 was to be used in radio-controlled pilotless drones that were to be guided from an accompanying control plane. Due to project requirement changes and cancellations the engine was not produced.
Apparently the engine had no civil application and only a limited military use, as the O-805 in Interstate XBQ-5/XTD2R.
Variants:
12AC-596 / O-595
1941
12-cylinder Horizontally opposed air-cooled
300 hp (224 kW) @ 2,600 rpm.
806.4ci
12ACG-596
350 hp (261 kW) @ 3,500 rpm.
12AC-806 / O-805
1942
12-cylinder Horizontally opposed air-cooled
450 hp (336 kW)
806.4ci
12ACG-806
456 hp (340 kW) @ 3,200 rpm, geared to 0.632:1, (XO-805-1).
12ACGSA-806
500 hp (373 kW) @ 3,200 rpm, supercharged and geared to 0.632:1 (XO-805-3), or to 0.587:1 (O-805-5).
O-805
Military designation of the 12AC-806, 12ACG-806 and 12ACGSA-806.
Applications (intended):
Interstate XBQ-5
Interstate XTD2R-1
Specifications
O-805-2
Type: 12-cylinder air-cooled horizontally opposed aircraft piston engine
Displacement: 805 cu. in.
Cooling system: Air-cooled
Power output: 450 hp
All Aero 