In 1945, Beech Aircraft Corporation built the most powerful ground attack aircraft of World War II – the mighty XA-38 Grizzly. Armed with a 75-mm cannon and six machine guns, the twin-engine gunship was large, powerful and fast, but the war ended before the enemy could feel its offensive punch.
In 1944, Beech Aircraft Corporation answered a U.S. Army requirement for a multi-purpose attack aircraft capable of destroying tanks, entrenched fortifications and support vehicles, as well as carrying heavy loads of ordnance across long distances to the targets. Dubbed the Grizzly by company officials and “XA-38” by the Army, the aircraft traded its namesake’s deadly claws for a 75-mm fully-automatic cannon, six 0.50-caliber machine guns and a tough hide capable of absorbing battle damage and keep on flying.
In addition to its formidable weaponry, the XA-38 was capable of speeds up to 375 mph at a gross takeoff weight of 32,000 pounds (it may surprise King Air owners/operators to know that the Grizzly remained the largest and heaviest airplane designed and built by the Beech Aircraft Corporation). When it first flew in 1944, Beechcraft’s “flying cannon” clearly outclassed every other ground attack aircraft in the world. Its speed, firepower and load carrying abilities were unmatched. If the airplane had been developed a few years earlier, it would have played an important role in the U.S. Navy’s island-hopping campaigns across the Central Pacific.
Designing the XA-38 was no easy task for company engineers. They had to create an airplane that could deliver a devastating offensive punch, absorb damage, be reasonably maneuverable for its size, and possess a passive defensive system that was effective against attacking fighters. One fact was inescapable – speed and structural integrity were high on the list of design imperatives. No effort would be spared to reduce drag and build a lightweight, but strong, aluminum alloy airframe. The decision was made to use flush riveting and butt-join all exterior surfaces wherever possible.
As the design process progressed during 1943, the Army exchanged the name Grizzly for Destroyer. After the first prototype was completed and tested on the ground, veteran company test pilot Vern Carstens took the big Beechcraft aloft for the first time May 7, 1944. An employee who witnessed the event remembered that when Carstens attempted to land the Destroyer after a successful flight, he flared about 10 feet above the runway and the airplane stalled. It hit the pavement with a resounding “thud” and bounced back into the air. Instinctively, Carstens gunned the two 18-cylinder Wright radial engines and went around the field for another approach. Vern skillfully rolled the XA-38 onto the runway.
At the heart of Beechcraft’s gunship was a Type T15E1, 75-mm cannon fitted with a Type T-13 feed mechanism. Mounted in the nose section, the weapon featured a circular magazine holding 20 rounds. When the pilot pressed a button on the control wheel, the cannon would automatically fire, reload and continue firing at a rate of one round every 1.2 seconds. To expedite rearming, the front streamlined housing surrounding the weapon was hinged on a set of counterbalanced springs and opened to expose the installation. Designed as a package, the cannon could be removed and replaced with various armament assemblies to deal with combat situations in the field. The cannon worked well during testing, and noise level in the cockpit was deemed acceptable by Army pilots conducting the tests.
To ensure that a pilot could hit the enemy with those hard-hitting shells the airplane was equipped with a Type N-6 reflector sight. Because the cannon was designed and mounted as an extension of the airplane’s longitudinal axis, the pilot simply aimed the XA-38 at the target and fired. The Type N-6 reflector, however, did assist in acquiring a reasonably accurate sight picture. As for the Destroyer’s six 0.50-caliber M-2 machine guns, two were installed on either side of the cannon in the nose section, and the other four were mounted in two remotely-controlled turrets, one above and the other below the fuselage. Each gun had 500 rounds of ammunition available.
The blister-type turrets, built by General Electric, were operated by a gunner who sat in the aft fuselage. He could not control the firing arc of the guns, particularly if both turrets were firing simultaneously. To resolve that problem, an interrupter device would automatically cease firing whenever any part of the airframe came in conflict with the firing arc. The lower turret protected the airplane from below, but the upper turret required a more complex interrupter sequence because of the twin vertical stabilizers, wing tips and propellers. To increase offensive firepower, the pilot could command the gunner to rotate and lock the lower turret in the forward position. According to Beech Aircraft records, the XA-38 was only vulnerable to attack from the rear, but to cope with that possibility the top turret guns could be aimed to fire between the two stabilizers. That capability, coupled with the airplane’s high speed, was thought sufficient to limit any enemy fighter to only one firing pass.
Having a wingspan of 67.08 feet, a length of 51.7 feet and standing 8 feet tall from the ground to the cannon barrel, the Destroyer was not a small airplane. Contrary to “hearsay history” and myth, neither was it based on the Model 18 Twin Beech, but was a totally clean-sheet design that approached medium bombers such as the Martin B-26 Marauder and Douglas A-26 Invader in size and weight. Weighing in empty at 23,300 pounds with a design gross weight of 29,000 pounds, the XA-38 could carry external stores including drop tanks, bombs, depth charges and even torpedoes, as well as a variety of fuel loads that increased maximum allowable weight to an impressive 36,332 pounds.
The landing gear and flaps were powered hydraulically by pumps driven from the accessory section of each engine. If the pumps failed, the gear and flaps could be lowered using a hand pump in the cockpit. A conventional landing gear configuration was selected because it was well suited to operation on crude, rough airfields such as those commonly found on Pacific islands. The main gear featured conventional oleo-pneumatic shock struts and hydraulic brakes, while the slotted-type flaps could be lowered to 45 degrees. A 24-VDC electrical system was powered by dual, engine-driven generators, and an auxiliary unit located in the radio compartment could be controlled by the pilot and was used to start engines and remained active during takeoff and landing.
The fuel system was a marvel of engineering and innovation to suit the mission. Because the Destroyer was designed specifically for a ground attack role, it would always be forced to operate in close proximity to the enemy. All tanks, including engine oil tanks, 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 of 1944. These were followed by Army flights later that year. It quickly became apparent that when it came to speed, the Beechcraft design team had created a winner. With 4,600 horsepower on tap, the Destroyer was not only aerodynamically clean but on one flight attained a maximum speed of 376.5 mph at a takeoff weight of 32,000 pounds, albeit using war emergency power.
A well-known anecdote to the XA-38’s story stems from a flight aimed at calibrating the airplane’s airspeed indication system. Plans called for flying a commercial, twin-engine Model 18 as a “chase” aircraft to document the tests and to photograph the latest Beechcraft. As airspeeds increased, however, the Model 18 proved woefully inadequate and soon fell behind the XA-38. To solve that problem, the engineers obtained a factory-fresh North American P-51B Mustang fighter and resumed the tests. Much to everyone’s surprise, even the speedy P-51B could not keep pace with the big Beechcraft as speeds approached 375 mph!
Army pilot captain Jack W. Williams was among the service pilots who conducted a series of flights in the XA-38. From Oct. 13 to Oct. 24, 1944, he flew the first XA-38 at the Beech Aircraft factory. The 75-mm cannon and two machine guns were installed for these flights, which also checked operation of fire extinguishing systems. At a takeoff weight of 32,001 pounds and flaps deflected to 15 degrees, Williams calculated that the airplane should lift off at 105 mph but found that the airplane could be “flown off” at speeds as low as 91 mph. Normal takeoff procedure called for leading power application with the left throttle until an indicated airspeed of 55-75 mph was attained and the two rudders became effective, at which point both throttles could be advanced together.
Williams rated the gunship’s overall controllability as “good for all normal conditions of flight.” Although he noted that the elevator and rudder forces were “heavy at high speeds,” he added that both flight controls were highly effective. “It is very maneuverable for an airplane of its size and handles well in making sideslips, skids, loops, half rolls on top of loops and slow rolls.” Completing aerobatic maneuvers with that kind of ease was no mean feat for an airplane that was a large as a North American B-25 Mitchell bomber and weighed 16 tons! The attack aircraft’s stalling characteristics were relatively straightforward, with generous buffeting of the empennage before the stall break occurred.
Williams wrote in his report that the Destroyer’s landing characteristics were similar to those of the military C-45 Beechcraft, with good visibility thanks to plenty of window area in the cockpit. Typical approach airspeed was 125 mph, with flaps fully deflected to 45 degrees. The XA-38 also proved easy to maneuver on the ground, regardless of whether it was operating on smooth, paved taxiways and ramp areas or on rough airstrips.
The final phase of the gunship’s evaluations by the Army focused on armament, particularly the 75-mm cannon. It was fired for the first time July 1, 1944, at the Great Bend Army Air Base gunnery range in Great Bend, Kansas, but the majority of firing tests were conducted by the second airplane built. It first flew September 22, 1945, again with Vern Carstens at the controls. After completing a series of flight tests at Great Bend, it was flown to Eglin Field, Florida. During its time at Eglin the XA-38 was flown by a number of Army pilots who wrung out its weapon systems, particularly the cannon, for another 38 hours.
Flight testing clearly demonstrated that Beech Aircraft engineers had not only succeeded in meeting the military’s specifications for a ground attack airplane, they had created an aircraft that had no peer. To add another feather to their cap, the engineers won praise from the Army when the second airplane accumulated a reputation for high reliability and availability during the tests.
Despite its advanced design, performance and potential as the world’s most powerful ground attack aircraft, a combination of factors relegated the Destroyer to obscurity. First, Germany had been defeated and Japan was about to capitulate in the wake of its nuclear devastation. Second, the Wright radial engines that were essential to the XA-38 program were needed for the Boeing B-29 Superfortress. Third, the ground attack role had changed during the war and although the need for such a versatile aircraft continued, that task could be accomplished with single-engine airplanes such as the incomparable Douglas Skyraider.
One XA-38 was eventually assigned to Davis-Monthan Air Force Base in 1948 and was scheduled to be displayed at the Air Force Museum in Dayton, Ohio, but it never arrived. The fate of both airplanes has yet to be accurately determined. Apparently, at some point after the war both of the Beechcrafts fell victim to the cutting torch. One fact, however, is known: Beech Aircraft Corporation records state that all lofting and engineering information for the company’s XA-38 program was destroyed
June 2, 1955.
The Destroyer holds a special place in the history of Walter and Olive Ann Beech’s company. It can be said that the XA-38 represented the pinnacle of Beechcraft engineering during the war, but it also contributed greatly toward the company’s legendary reputation as an innovator and manufacturer of purpose-built aircraft. Its powerful cannon was never fired in anger, but Beechcraft’s ultimate gunship will not be forgotten.