The DH-4B and DH-4M modifications extended the DH-4’s service life until the mid-1920s, but by then, the model was completely obsolete. However, considering the large number of engines and spare parts for these aircraft in storage, the U.S. Army decided on a “final” extension of the DH-4’s operational life. As part of the approved program, Boeing was tasked with developing a modernized DH-4, designated Boeing Model 42.
This design combined the powerplant, fuselage, and vertical empennage of the DH-4M-1 with new horizontal empennage, wing, and landing gear. The U.S. Army provided Boeing with three DH-4M-1 aircraft for conversion into CO-7 prototypes, which were intended as observation aircraft. One aircraft, the XCO-7, was allocated for static tests.
Development and Prototypes
The other two, the XCO-7A and XCO-7B, were designated for flight tests. The XCO-7B featured a new tail assembly and powerplant. Notably, the XCO-7B differed from the XCO-7A only in its elevators, which included mass balances, and an inverted version of the Liberty 12A engine with a high shaft line.
After assembly, both aircraft, the XCO-7A and XCO-7B, were transported by rail to McCook Field, Ohio. There, on February 6, 1925, the XCO-7A performed its maiden flight. Tests indicated that the aircraft was quite adequate in terms of flight performance and handling, demonstrating better characteristics than the DH-4M-1.
Flight Tests and Final Decision
Despite these positive results, a decision for serial production was not pursued. The U.S. Army ultimately opted to develop an aircraft of an entirely new design. Furthermore, Boeing also created a similar aircraft based on the DH-4M-1 for the Navy, which was designated O2B and produced in O2B-1 and O2B-2 modifications.
Technical Specifications
| Modification | Model 42 (XCO-7A) |
| Wingspan, m | 13.72 |
| Length, m | 8.89 |
| Height, m | 3.25 |
| Wing area, m2 | 40.88 |
| Empty weight | 1409 |
| Maximum takeoff weight | 2116 |
| Engine type | 1 Piston engine Liberty 12A |
| Power, hp | 1 x 420 |
| Maximum speed, km/h | 196 |
| Cruising speed, km/h | 177 |
| Practical range, km | 676 |
| Practical ceiling, m | 3980 |
| Crew, crew members | 2 |
| Armament | two fixed forward-firing 7.62-mm Browning machine guns in the forward fuselage and two turret-mounted 7.62-mm Browning machine guns in the rear cockpit. |
Image and diagram gallery of the Boeing Model 42 (CO-7)
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |
 Boeing Model 42 (CO-7) |