Before and during the Second World War, the United States Army Air Force (USAAF) tested dozens of different models of aircraft with many unconventional configurations in layout and armament. Many of these interesting designs didn’t make it past the prototype stage for a variety of reasons. One such aircraft is today's topic: the Beech Model 28. Designated by the USAAF as the XA-38, also known as the 'Grizzly' and as the 'Destroyer'.
The second prototype with all guns and turrets mounted
Development on the plane was started in March 1942. The XA-38 was initially intended to be an interceptor, built to engage hostile long-range bombers. But the Curtiss-Wright XP-71 was chosen to fill that role instead. So, with a good design in hand, the Beech company decided that the XA-38 would become a ground attack aircraft. They submitted it to the USAAF as the Model 28 on September 23rd, and the only two prototypes were ordered on September 2nd, 1942. Its first flight was on May 7th, 1944.
Beech had designed a two-seater, narrow fuselage, mid-wing, taildragger, twin-tailed, monoplane. The entire skin of the aircraft was flush-riveted to reduce drag.
The XA-38 had a crew of two, the pilot and a gunner who were seated in tandem, and was powered by two of the mighty Wright R-3350 Cyclone engines, the same type that drove the B-29 Superfortress. Each engine put out 2,300 horsepower, for a total of 4,600 HP. These were a significant source of delays in the program, as the B-29 had priority over the new attack aircraft. But all the work in streamlining and the power of the chosen engines allowed the XA-38 to outrun a P-51B chase plane in tests. It was also by all accounts a maneuverable aircraft for its size and was very controllable. It was had a takeoff speed of only 97 MPH and could operate off a 2,500-foot runway. The two engines did not counterrotate, and each drove a 14' 2'' three-bladed propeller. It carried a total of 825 gallons of fuel internally, 640 gallons in the wings and 185 gallons in the fuselage behind the pilot.
The entire fuselage was built from four sections to allow easy repair and replacement of damaged sections, and the nose was designed to open like the hood of a car to load and service the main cannon. It could also be removed entirely, including the cannon, to allow the mounting of different weapons.
The first prototype (S/N 43-14406) with mockup gun turrets
Not only was it fast, it was well armed with a total of six .50 caliber machine guns, the single 75mm cannon, and was also able to carry more than 2,000 pounds of weaponry on four hardpoints under the wings. For defensive armament, the XA-38 carried the Browning .50 caliber guns in two remotely controlled turrets, one dorsal with two guns, and one ventral with two guns. The forward guns were what gave the XA-38s nose its distinctive pointed shape. There were two fixed .50 caliber machine guns, and the long 75 mm cannon originally meant to take down enemy bombers. The 75 mm had twenty rounds available, while the .50s had 3,000 rounds apiece. The nose could be swung open to maintain the guns, or could even be replaced entirely for different loads of weaponry. To add to the forward firepower, the ventral turret could be locked forward and fired by the pilot, giving a total of 4x .50 caliber machine guns, and a single 75 mm cannon.
A T9E1 75mm cannon in the USAF Museum
The cannon is really the most unusual part of the aircraft, and one of the hardest parts to get information on. There were other aircraft armed with 75 mm cannons, most notably the B-25G and the B-25H which used the hand-loaded M5. After nearly giving up, a Forgotten Weapons video on a series of books pointed me to the information I was looking for.
The autoloading M10 cannon in the XA-38 was made of three major components, the cannon itself [designated T9E2], the autoloader [designated T13], and the gun mount [designated T15E1]. The T9 (and the hand-loaded T13 which would become the M5) had their origin in May 1942 as a 75mm cannon that was lighter but matched the M4 75mm cannon in ballistic performance. The improved T9E1 (and T13E1) were the result balancing the recoiling parts of the gun around the centerline of the weapon.
But there was an issue with using a 75mm cannon from a moving aircraft. On the ground, an M48 75mm HE shell had a stability factor* of 1.373 when fired from an M5 cannon (1 rifling twist every 25.58 calibers). But from an aircraft at 228 MPH, that factor dropped to 1.0. At higher speeds, the shell became even more unstable because of the increase in linear speed without increasing the twist in the barrel. This reduced accuracy, and the effectiveness of the weapon with it. A serious concern with how few shells an aircraft could carry at a time. So two M4 prototypes were made with a 1 twist in 22 calibers, which when fired on the ground gave a stability factor of 1.857, and remained higher while at speed in an aircraft. The result of these tests, including two more guns and experimentations with types of rifling, were the T9E2 and the M5A1.
In August 1944, work was started at Aberdeen Proving Ground for a T9E3 cannon for the XA-38. This weapon was supposed to be lighter and possessed a modified recoil system, using a hydropneumatic system instead of hydrosprings. But work was halted before issues of rapid ejection were resolved.
A photo showing the nose armament of the XA-38, photo from The Machine Gun Vol. III
While I have not found specifics for the T9E2 cannon, I do have solid data on the T9E1 which was nearly the same in many respects. Overall, the cannon weighed 406 pounds, 763 with its mount. Its maximum rate of fire was 30 rounds per minute, but the average was between 3 to 4 shots per minute. The barrel was 84 inches long and weighed 178 pounds, and the overall length of the cannon was 116.375 inches. Rifling was a right-hand twist with a full revolution every 22 calibers along the length (for the T9E2).
The autoloading M10 cannon in the XA-38 was made of three major components, the cannon itself [designated T9E2], the autoloader [designated T13], and the gun mount [designated T15E1]. The T9 (and the hand-loaded T13 which would become the M5) had their origin in May 1942 as a 75mm cannon that was lighter but matched the M4 75mm cannon in ballistic performance. The improved T9E1 (and T13E1) were the result balancing the recoiling parts of the gun around the centerline of the weapon.
But there was an issue with using a 75mm cannon from a moving aircraft. On the ground, an M48 75mm HE shell had a stability factor* of 1.373 when fired from an M5 cannon (1 rifling twist every 25.58 calibers). But from an aircraft at 228 MPH, that factor dropped to 1.0. At higher speeds, the shell became even more unstable because of the increase in linear speed without increasing the twist in the barrel. This reduced accuracy, and the effectiveness of the weapon with it. A serious concern with how few shells an aircraft could carry at a time. So two M4 prototypes were made with a 1 twist in 22 calibers, which when fired on the ground gave a stability factor of 1.857, and remained higher while at speed in an aircraft. The result of these tests, including two more guns and experimentations with types of rifling, were the T9E2 and the M5A1.
In August 1944, work was started at Aberdeen Proving Ground for a T9E3 cannon for the XA-38. This weapon was supposed to be lighter and possessed a modified recoil system, using a hydropneumatic system instead of hydrosprings. But work was halted before issues of rapid ejection were resolved.
While I have not found specifics for the T9E2 cannon, I do have solid data on the T9E1 which was nearly the same in many respects. Overall, the cannon weighed 406 pounds, 763 with its mount. Its maximum rate of fire was 30 rounds per minute, but the average was between 3 to 4 shots per minute. The barrel was 84 inches long and weighed 178 pounds, and the overall length of the cannon was 116.375 inches. Rifling was a right-hand twist with a full revolution every 22 calibers along the length (for the T9E2).
Under the wings it could carry either 2,000 or 2,650 pounds (sources vary) of stores on the four hardpoints. These could include 600 more gallons of fuel in drop tanks, torpedoes, bombs, depth charges, or smoke generators.
The second prototype (S/N 43-11407). The 75mm cannon, .50 caliber guns, and hardpoints are visible.
Prototype One (Serial number 43-14406) was first flown by Beech test pilot Vern Carstens in May 1944 with dummy guns and turrets as the real ones weren't ready yet. In July it was flown to Tulsa, Oklahoma where the 75 mm cannon was fitted and ground fired, and later that month it was successfully fired in flight over Great Bend, Kansas. Further tests demonstrated the plane's excellent performance. On July 7th, 1945, it flew to Dayton, Ohio for further tests.
Prototype Two (S/N 43-11407) took flight on September 22nd, 1945. This prototype was fully armed and was sent to Elgin Field, Florida for flight testing. But by this time the war was over, and there was very little interest in the new aircraft. The B-29 had taken priority in production, meaning that there would not have been engines to build A-38s until mid-1945 anyway.
One prototype was scrapped, while the other was allegedly sent to Davis-Monthan AFB, Arizona. Unfortunately, its whereabouts are unknown, and it has probably been lost to history.
Specifications: XA-38
Two Wright GR-3350-43, 2,300 HP
Dimensions:
Wingspan: 67' .96''
Length: 51' 8.4''
Height: 15' 6''
Wing Area: 625.9^2 feet
Weight:
Empty: 22,481 lb
Gross: 31,250 lb
Maximum: 36,330 lb
825 gallons of fuel
Performance:
Top Speed: 370 mph @ 17,000 Feet
Cruising Speed: 350 mph @16,000 feet
Landing Speed: 97 mph
Service Ceiling: 29,000 Feet
Rate of Climb: 2,170 Feet/Minute
Maximum Range: 1,625 Miles
The position and original intent of the cannon in the nose bears an interesting similarity to the BK-5 50mm cannon that the Germans, on Hitler's orders, crammed into the Me 262 and the Me 410. It was less than ideal, with a very limited ammunition capacity (22 rounds), and a rate of fire of 45 rounds per minute. Less than 300 were built before the war ended, though a 50mm shell would certainly have been more than enough to cripple, if not outright destroy even the heaviest of heavy bombers.
The BK-5 on display at the USAF Museum beside a Me 262
What is Left?
The only things that seem to remain of the Grizzly are the two T9/M10 cannons located in the Museum of the United States Air Force in Dayton, Ohio, and the United States Air Force Armament Museum located in Elgin AFB, Florida.
Notes:
Information on the Grizzly is hard to come by. While most of the available sources agree, there are a few discrepancies between precise specs.
American Combat Planes lists the XA-38 with R-3350-53 engines in the stats block, but in the text tells that it had R-3350-43 engines.
It gives a ferry range of 1960 miles, and a range of 1070 miles with a 2,000-pound load.
It gives the landing speed as 103 MPH, maximum takeoff weight as 32,000 lb, gross weight as 29,900 lb, and empty weight as 22,480 lb. Figures for speeds and ceiling are similar.
*Stability Factor is a number ideally between 1.3 and 2.0, is calculated based on the properties of the projectile, and is used to determine the ideal rifling twist. At the time, the Greenhill method would probably have been used. A more detailed look is something that will have to wait though.
Sources:
American Combat Planes. Wagner, Ray
http://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/197613/t9e1-75mm-cannon/
https://www.militaryfactory.com/aircraft/detail.asp?aircraft_id=706
https://web.archive.org/web/20120205001945/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=3178
https://oldmachinepress.com/2013/05/12/beech-aircraft-company-xa-38-grizzly/
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-bi.html
The Machine Gun Volume III - Col. George Chinn, USMC (Ret.)
Photos:
https://web.archive.org/web/20120205001945/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=3178
The Machine Gun Volume III - Col. George Chinn, USMC (Ret.)
The Machine Gun Volume III - Col. George Chinn, USMC (Ret.)
Photos:
https://web.archive.org/web/20120205001945/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=3178
The Machine Gun Volume III - Col. George Chinn, USMC (Ret.)
Own work
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