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were self-sealing but what set the XA-38 apart from its contemporaries was the innovative design of those cells, which greatly influenced the overall layout of the fuselage and wings. To reduce the fuel system’s vulnerability to damage, specially-designed tanks were installed, and required unusually close cooperation between Beech engineers and subcontractors to achieve the correct configuration.
All of the tanks could be easily and quickly removed and repaired or replaced, and thanks to cooperation by manufacturers of the fuel pumps there were no outlets or fittings in the bottom of the fuel cells. Instead, pumps were mounted in the top of the cells, significantly reducing the time required to change a pump in the field under combat conditions. These advantages meant mechanics would not have to drain fuel to replace components, as was the case with many aircraft of that era.
Four tanks were located in the wings and held 640 gallons of fuel. Two additional tanks behind the cockpit held another 185 gallons. In normal operation, the system fed fuel to each engine from separate tanks and a cross- feed system fed fuel to both engines, or could feed either powerplant if one engine was inoperative.
Considering restraints of the airplane’s overall design, Beech engineers went another step further by designing as much safety as possible into the fuel system. A key aspect of this design approach centered on making battle damage survivability an integral part of the design. For example, if a tank was ruptured by enemy fire any fuel leak would be stopped by the self-sealing capability of the cell, but if damage to pumps or connections between tanks occurred, the airframe structure could be flooded with raw fuel ready to explode, blowing up the airplane. By installing pumps, connections and fittings in the top of the XA-38’s tanks, minor battle damage would contain the leak within the tank, not the airframe.
The XA-38’s wing featured an NACA 2300-series airfoil section designed by the National Advisory Committee for Aeronautics (NACA) that provided good high speed performance yet allowed an acceptable low approach and landing speed to enable the gunship to operate from short airstrips. Total wing area was 625.9 square-feet with a taper ratio from wing root to tip of 3.07 to one. Angle of incidence was established at 4.39 degrees at the wing root decreasing to 1 degree at the wing tip, while aspect ratio was 7.19 with a wing dihedral of 5 degrees determined at the quarter chord point on the airfoil.
If the gunship’s booming 75-mm cannon was the offensive focus of the airplane, then its two Wright Duplex Cyclone engines were its fire-breathing heartbeat. The GR-3350-43 18-cylinder, twin-row, air-cooled static radial engines were equipped with a reduction gearbox and produced a thundering 2,300 brake horsepower each at takeoff. That raw power was created by feeding the thirsty powerplants high-octane avgas through Chandler-Evans Model 58 CPB 4 Hydro-Metering pressure carburetors. The massive engines featured a
two-stage supercharger, but flight testing soon revealed that operation in high-blower mode caused detonation and further operations were limited to low-blower only.
In addition, each engine was fitted with an anti- detonate injection system having a water capacity of 52 gallons. When activated, such as during takeoff with a heavy load requiring maximum available horsepower, the system injected water vapor into the cylinders to prevent detonation. A water injection regulator worked in conjunction with the engine’s auto-boost control to reduce manifold pressure to 54 inches Hg when the water supply was exhausted. The system was deactivated anytime manifold pressure decreased below 54 inches Hg.
Each engine turned a Hamilton Standard Model 33E60 propeller that measured 14 feet in diameter and featured three blades. These constant-speed, full-feathering units proved highly satisfactory during service tests. To keep the Wright engines cool, NACA cowling embraced the engines, and cowl flap position was controlled by an ingenious system created by General Electric that automatically positioned the cowl flaps based on cylinder head and oil temperatures. A manual backup system also was installed.
A second XA-38 was built and both airplanes entered company flight testing during the spring and summer
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KING AIR MAGAZINE • 27