The immortal "Whitey" Powers once vowed that he was going to "lay one right on the flight deck" of a Japanese carrier. His effort stirred the President of the United States to extol his heroism to the Nation over an international radio hookup. Unfortunately, there are no sentimental awards for airplanes, but it might be recorded somewhere that the plane in which Lt Powers flew to fame was a Douglas Dauntless, the SBD dive bomber. In the early days of the war, when few really modern aircraft were carried aboard our flat-tops, the SBD family was the major vector of the air fleet. The fighter planes, efficient as they were, had their hands full protecting the fleet and wresting the air initiative away from the enemy. The old TBD, the Douglas Devastator torpedo plane proved inadequate under fire. Until more modern equipment arrived, the Dauntless had to act as heavy artillery for the air fleet, and its triple-threat record as bomber, scout and fighter has been superb. While recent additions to the fleet's roster of planes have introduced newer and more powerful designs, the old Dauntless still pulls its own weight, and will be serving with the fleet for many months to come,
The Dauntless' record, particularly in the Southwest Pacific theater, proves that the technique of dive bombing should not be condemned on the record of the German Junkers Ju-87 series. This Nazi type failed because its speed, armament and maneuverability were insufficient, and the bomber required constant cover. The Dauntless proved that it could knock down enemy fighters, because few of its fighting features had been surrendered for undue weight-carrying characteristics.
The Dauntless is a two-place low-wing monoplane with a retractable landing gear, single fin and rudder, designed particularly for use from an airplane carrier. As a result, all of its dimensions and many of its operational characteristics are limited and influenced by requirements of carrier operation.
It has a wing span of 41' 6-3/8", an overall length of 33' ¼" and a standing height of 12' 10-13/16". The SBD-5 is powered by one 9-cylinder radial air-cooled Wright Cyclone R-1820-60 engine, rated at 1200 hp at takeoff and 900 hp at 14,000 feet. The engine swings a 10' 10", three-bladed Hamilton Standard hydromatic propeller.
The SBD's wing is a single, full-cantilever, multicellular structure, consisting of a center section built integral with the fuselage, two main outer panels, removable wing tips, ailerons, diving and landing flaps and trim tabs. The center section embraces a series of webs and lengthwise stringers, crossed by bulkheads and covered with Alclad skin. The bulkhead construction has been modified to include reinforced supports for the landing gear. Wheel wells are incorporated into the center section to accommodate the wheels when they are in the fully retracted position. The center section also accommodates two of the main fuel cells and provision is made for the installation of the exposed bomb ejection system.
Like the center section, the outer wing panels are built up of four longitudinal webs and a number of stringers, a series of chordwise bulkheads within the wing, covered by a stressed Alclad skin. The outer panels are attached to the center section by two internal wrenching bolts, one on each side of the airplane, and by a series of ¼" bolts through the attaching angles on the outboard ends of the wing center section, and the inboard end of the outer wing panel. The outer panels are rigged with 8.5° of dihedral. Each outer wing panel carries a fuel cell internally, mounts a set of fixed eyebrow-type slots which overcome the tip-stall, characteristic in highly tapered wings, likely to disqualify a plane from practical carrier operation. The pitot-static tube system, required for the operation of the rate-of-climb, air speed and other pressure instruments is built integrally with the main wing panel. The pitot-static head protrudes from the leading edge at the end of the port main panel, is attached to the outboard bulkhead of the panel. The detachable wing tips are of bulkhead, web and stressed skin construction, secured to the outer panels by means of a series of screws, inserted through the flange in the wing tip closing bulkhead and into nut plates in the outer panel closing bulkhead.
The ailerons are an all metal frame, consisting of a metal spar near the leading edge, connected by channel ribs to a V-channel along the trailing edge. Each aileron is statically and dynamically balanced, and is hinged on three aluminum alloy brackets fitted with three sealed anti-friction bearings. A trailing edge trim tab is installed on the port aileron only. This trim tab is a light, sheet metal unit, hinged to two brackets on the aileron and actuated by means of a push-pull arrangement and a drum assembly. Through this control the lateral trim of the plane can be adjusted from the cockpit either on the ground or in the air.
The landing and diving flap arrangement consists of five perforated sections, built of ribs and stringers and covered with a stressed skin on the outside only. Three of these sections are installed on the lower surfaces of the wing, one in each panel and one in the center section. These three deflect downward and act both as landing and diving flap. Two more of these perforated sections are installed in the upper surface of the outer panel's trailing edge and are deflected up to act as diving flaps in unison with the three lower surfaces. These surfaces are hydraulically motivated.
The Dauntless' fuselage is a reinforced semi-monocoque structure, consisting of channel-type bulkhead frames spaced 18" apart, which are thwarted by extruded alloy stiffeners at 5" intervals. The entire structure is covered with an Alclad skin. The fuselage is built integral with the wing center section, and special stiffeners are used to distribute the concentrated load of the engine mount fittings, the cockpit cutouts, stabilizer and tail-wheel fittings. An overturn structure extends from the top of the cockpit enclosure aft of the pilot's seat to protect the crew in case of an inverted landing.
The cockpit is enclosed by a greenhouse which covers both the pilot's and gunner's cockpits. It is made up of four sections. The transparencies are Plexiglas, supported in steel or aluminum alloy frames. The section over the pilot's cockpit is mounted on sliding rollers, so it can be latched in any of five positions. This section slides back over the fixed enclosure section which is fastened firmly over the overturn structure. In front of the cockpit is the windshield consisting of two curved and two flat pieces of metal-mounted Plexiglas. The curved dome and front shield are fixed, while the two flat side pieces are hinged to provide the pilot with easy emergency access to the fixed front machine guns. The curved Plexiglas acts merely as a streamlining for the 1½" slab of bullet-proof glass set in front of the pilot. The two sections of the enclosure over the gunner's compartment are also mounted on rollers and can be moved forward toward the fixed enclosure and latched in either the open or closed position. The aft enclosure is also movable to allow the gunner to operate the rear flexible guns freely.
The structure of the empennage of the SBD is fairly conventional. The horizontal stabilizer and fixed fin are two-spar units, with ribs and stringers and a stressed skin. The stabilizer is attached to the fuselage in fixed alignment by steel internal wrenching bolts, which are safety-wired to the structure. The vertical stabilizer is integral with the fuselage. The movable surfaces are constructed of box spars at the leading edge and channel-type ribs, terminating in an extrusion trailing edge. These surfaces are fabric covered and statically and dynamically balanced. Each of the movable surfaces, elevators and rudder, are fitted with a built-up aluminum alloy trim tab, hinged with anti-friction bearings to the control surface and actuated by means of a push-pull rod from the cockpit.
The alighting gear consists of the two main wheels and legs, which retract fully toward the centerline, the tail wheel and the arrester hook, used on all carrier-based aircraft to pick up the arrester cables which stop the airplane on the short carrier deck. The landing gear assembly, whose retraction is hydraulically motivated, consists of a single, cantilever Cleveland Pneumatic shock strut and a standard Hayes wheel and brake assembly. The tail wheel is a fixed unit, consisting of the regular fork and swivel and a small Cleveland Pneumatic shock strut. The wheels used are of two types, solid rubber for carrier operation, pneumatic for land operation. The arrester hook assembly is used only for carrier operation. It consists of a hook, a recoil snubbing cylinder, an operating lever, a cable and a cable take-up spring. The arrester hook is attached under the fuselage at one of the strongest bulkheads and, when stowed, rests against a rubber stop under the fuselage. The hook itself is built of welded chrome-molybdenum steel.
Dual rudder, elevator and aileron controls are provided at the pilot's and gunner's stations. The rudder control is the conventional cable system, as are the elevators and trim tabs. The ailerons operate partly by means of a push-pull tube system, and partly by cable and pulley. The flap system, however, is motivated by two torque tubes, connected to the surfaces by a connecting link assembly. These tubes are moved by a hydraulic actuating cylinder, part of the entire main system.
This hydraulic system operates not only the landing and diving flaps, but also the landing gear, engine cowl flaps and the automatic pilot. Although the braking system is not connected to this main system, fluid for its operation is provided by its main reservoir. The main hydraulic system pressure is about 1,000 psi and is controlled by a manually operated engine pump control valve. When all the hydraulic units are at rest, the normal pressure passes to the automatic pilot where its regulator reduces pressure to 120 psi for use in "Elmer," the unpaid crew member.
The Dauntless' armament consists of four guns; two .50-cal Colt-Brownings fixed on the upper forward side of the fuselage, synchronized to fire through the propeller. Each gun extends from the side of the instrument panel to the trailing edge of the engine cowling diaphragm. The guns are controlled by a trigger switch on the forward side of the pilot's control stick. Provision is made for the installation of a 16-mm motion picture camera, focused in line with the guns, on the right side of the fuselage.
The rear cockpit armament consists of two .30-cal Browning machine guns, mounted on a twin adapter. The gun truck rolls on a sector track attached to a circular tilting ring which supports the gunner's seat. Bomb racks are carried either under the fuselage or the wings. For dive-bombing with a single heavy unit (up to 1600 lbs), a sturdy steel yoke, hinged at the forward end, is used to displace the bomb under the propeller arc. The same center-section rack can also be used to carry a chemical smoke container for laying smoke screens. The Dauntless was the first dive bomber adapted as such by the Army. The AAF uses it as a close-support plane under the designation of A-24.
This design analysis article was originally published in the April, 1944, issue of Air Tech magazine, vol 4, no 3, pp 17-23, 71-72.
The original article includes 4 photos, three of the plane and one of the cockpit, 4 drawings of systems and a schematic of the hydraulic system.
Photos credited to Official US Navy (3), Douglas Aircraft Co