The Martin Model 146 was an unsuccessful American bomber design that lost a 1934-35 bomber design competition to the prototype for the B-17. Before strategic bombing doctrine took form in 1939, the Army Air Corps anticipated a need to explore its ideas for long-range military aircraft. The first recommendation for the Air Corps to develop heavy bombardment aircraft surfaced in 1933, and, in July 1934, the Air Corps defined the specifications for the bomber it envisioned to replace the aging Martin B-10. The Air Corps required this next production bomber to carry a “2,000 lb bomb load at a speed of 200-250 mph over a distance of 1,020-2,000 miles.” Boeing submitted its four-engine Model 299 against the twin-engine Martin 146 and Douglas DB-1.
The Martin 146 was designed for a USAAC competition, announced on August 6, 1934, to find a modern replacement for the assorted twin-engine Keystone biplane bombers. The requirement was for a multi-engine bomber, to be used mostly for coastal-defense. The Martin 146 competed against the Douglas DB-1 (B-18) and Boeing Model 299 (B-17 Flying Fortress).
At the time, the Martin B-10 was the latest bomber in service and the US Army Air Corps was generally satisfied with the plane. However, they were now looking for a longer range aircraft. The Martin 146 was not much of an improvement over the Martin B-10. The Martin 146 was an enlarged B-10 with two Wright R-1820 engines. It had the same configuration of turrets and engines. With a widened fuselage, one difference was that the cockpit had side-by-side seating for the pilots.
The Martin 146 was the first large airplane to use Fowler flaps. Aircraft designers had for many years recognized the need for variable-geometry wings to provide good performance at both upper and lower portions of the aircraft speed range. In high-speed cruising flight, a small-area low-drag wing was needed for optimum performance and ride comfort. A highly loaded cruise-optimized wing of this type, however, was inconsistent with the need for production of high lift for safe operation at low speed during takeoff and landing. Designers accordingly provided aircraft with wings of variable area and contour for good low-speed short-field performance, while still being capable of achieving the desired characteristics during cruising flight.
Variable wing geometry was commonly achieved by providing hinged or otherwise movable flaps at the wing trailing edge. Plain or split flaps sometimes used on small aircraft in effect provide a variable-camber wing for improved low-speed operation. Flaps are a “high lift / high drag” device. Not only do they improve the lifting ability of the wing at slower speeds by changing the camber, or curvature of the wing, but when extended fully they also create more drag. This means an aircraft can descend (or lose altitude) faster, without gaining airspeed in the process. In the 1930s, most airplanes, because of their high wing loadings and cleanness of aerodynamic design, employed some form of lift-increasing and drag-increasing device to assist in landing them in a field of restricted size. Also, increases in lift without increases in drag were desirable in the take-uff and in the climbing conditions of flight.
The use of flaps on high performance airplanes as a device for reducing space required in landing had become common. Thus far split flaps had been most generally used, probably because of their simplicity of application and their superiority in giving steep gliding approaches and short landing runs: the features of flaps with which designers had been most concerned. In order to retain satisfactory operation from normal flying fields with fast airplanes, however, the use of high-lift devices that improve take-off as well as landing was desirable. Since drag is unfavorable to take-off, the comparatively large drag of split flaps places them among the least promising of high-lift devices in this respect.
There are many trailing-edge devices employed today, but the most common are the plain flap, slotted flap, and Fowler flap. Glenn Martin in Baltimore hired Fowler to design flaps for several new Martin airplanes, including the Martin 146 bomber in 1935. The fowler flaps were designed to physically increase the overall surface area of the wing, literally making the wing bigger. A Fowler flap which is hinged such that it can move back and increase the airplane wing area. Also, it may be rotated down to increase the camber. A very large increase in maximum lift coefficient is realized. This extension in wing area increases the airfoil's lift curve slope, generating more lift without a significant increase in drag. However, Fowler action also produces an increase in the nose-down pitching moment which makes the aircraft more difficult to trim.
A Fowler flap is a movable part of the undersurface of the wing trailing or aft portion, and the flap typically extends spanwise from the aircraft fuselage to roughly the midpoint of the wing length. When fully retracted, the flap smoothly completes the contour of a highly loaded wing which is optimized for efficient and comfortable high-speed flight. The flap is extended by being moved rearwardly and downwardly away from the trailing edge of the fixed wing to provide high lift and increased wing area during low-speed flight.
While the Fowler flap is a popular and effective way of achieving variable wing geometry, it has several deficiencies in conventional application. Each Fowler flap is typically provided with two or more fixed supporting and guiding tracks which extend aft from the wing, causing increased aerodynamic drag during cruising flight when the flap is retracted. Flap actuating mechanisms are expensive and complex in that Fowler flaps are usually driven by actuators at inboard and outboard positions, and sometimes by additional actuators at intermediate positions. Multiple synchronized actuators are needed to insure smooth flap deployment without binding arising from construction tolerances, air loads, and temperature changes.
The Fowler flap appeared to offer a better compromise between these conflicting requirements. For equal sizes it would give higher maximum lift with no higher profile drag than most other flap arrangements and its comparatively low drag at high lifts is favorable to take-off and steep climb.
|engines||two 800 hp Wright R-1820-G5 Cyclone|
|wing span||75 ft. 1 in. (22.9 m)|
|length||52 ft. 0 in. (15.5 m)|
|top speed was||234 mph (377 km/h)|
|service ceiling||28,500 ft. (8,687 m).|
|Armament||three 0.30 caliber machine guns bomb load of 2,260 lbs. (1,030 kg).|
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