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Joe Baugher's Hayabusa files (part 2)

continued from part 1

Part two: Ki-43-II

In pursuit of better performance, five Ki-43-I airframes were modified in February of 1942 to be powered by the 1150-hp Type 1 engine (which was the Nakajima Ha-115, a development of the earlier Ha-25). This engine had a two-speed supercharger and drove a three-bladed constant-speed metal propeller. The supercharger air intake was moved from underneath the cowling to its upper lip, with the carburetor intake remaining underneath the cowling. The wingspan was decreased by two feet and the wing area by 6.46 square feet to improve speed at low and medium altitudes. The windshield and cockpit canopy were raised slightly and a new reflector gunsight was fitted. The wing attachment points were strengthened to carry 551-pound bombs. In response to complaints from the field that the Hayabusa was too vulnerable to superficial combat damage, some rudimentary armor protection was provided for the pilot and self-sealing tanks were installed in the wings.

The improved Hayabusa model entered production as the Army Type 1 Fighter Model 2A (Ki-43-IIa). As the Model 2A entered production, the earlier Model 1 was progressively phased out, until the 716th and last Model 1 left the line in February 1943.

The carburetor air intake was deepened early in the production life of the Ki-43-IIa. The major production version of the Hayabusa was the Ki-43-IIb, which differed from the IIa only in minor equipment changes. The oil cooler, which had been mounted in a ring inside the cowling ahead of the engine and around the propeller shaft, was replaced by a honeycomb unit mounted inside a still deeper carburetor intake. Late production IIbs had their underwing bomb attachment points moved outboard of the main undercarriage legs to prevent bombs from hitting the propeller during dive bombing attacks at steep angles. Later production IIb aircraft had the oil cooler moved backward from the carburetor air intake and relocated underneath the central fuselage.

The modifications progressively introduced during the Ki-43-IIb production run were standardized on the Ki-43-KAI. This aircraft was also fitted with individual exhaust stacks that replaced the exhaust collector ring of earlier versions, and provided some amount of residual thrust augmentation. This variant also saw the underwing attachment points moved outboard of the landing gear. Three prototypes were built between June and August of 1942, and the Ki-43-KAI entered service in the summer of 1943. Some sources refer to this variant as the Ki-43-IIc, although this may be a "retrospective" designation introduced after the fact by Western sources for clarity.

The Ki-43-II-KAI was capable of out-maneuvering every Allied fighter it encountered, but the P-38, P-47, and P-51 could all out-dive and out-zoom the Japanese fighter.

Two additional production facilities, the Tachikawa Dai-Ichi Rikugun Kokusho (First Army Air Arsenal) and the Tachikawa Hikoki K.K. (Tachikawa Aeroplane Company, Ltd), were given contracts to manufacture the Ki-43 under license. The Tachikawa Dai-Ichi Rikugun Kokusho began production of the Hayabusa from Nakajima-supplied components in October of 1942. Unfortunately, the Army Air Arsenal did not have the experience needed for the manufacture of modern fighter aircraft, and was ordered to cease production in November 1943 after the delivery of only 49 Ki-43-IIa fighters. The Tachikawa Hikoki K.K. contractor was more successful, and built 2629 Ki-43-II and Ki-43-III Hayabusas beginning in May of 1943, and ceasing only with the end of the Pacific War in August 1945.

A total of 2500 Ki-43-IIs were built by the Nakajima parent plant at Ota.

In September 1943, the Allies were able to rebuild a complete fighter out of several wrecked Model 2A Hayabusas found at Lae, New Guinea. This aircraft was flown in mock combat against several different Allied fighters. Allied pilots commented favorably on the Hayabusa's sensitive controls and extreme maneuverability. It had no vicious flight characteristics, and its turning and stall characteristics were better than those of any Allied fighter. It handled well in the air, and had phenomenal low-speed handling capabilities which were aided by its set of combat flaps. It had excellent low-speed acceleration and could leap from 150 mph to 250 mph with extreme rapidity. Nevertheless, the Allied pilots felt that the Ki-43 was outclassed by the P-47 Thunderbolt, the P-38 Lightning, the Supermarine Spitfire, and even by later models of the P-40 Warhawk. The Hayabusa was appreciably slower than most Allied fighters and could usually be evaded by diving. The Hayabusa lacked effective firepower and its lack of effective armor protection made it vulnerable to superficial combat damage and often disintegrated in the air when hit. Nevertheless, Allied fighter pilots were always well-advised to avoid combat with the Hayabusa at low speeds since its rapid acceleration and excellent low-speed maneuverability made it a deadly opponent in such situations.

Specification of Ki-43-IIb:

One Army Type 1 (Nakajima Ha-115) fourteen cylinder air-cooled radial rated at 1150 hp for takeoff and 980 hp at 18,375 feet driving a three-bladed propeller.
Performance: Maximum speed 329 mph at 13,125 feet, climb to 16,405 feet in 5 minutes 49 seconds. Service ceiling 36,750 feet. Normal range 1095 miles. Maximum range 1990 miles.
Weights: 4211 pounds empty, 5710 pounds loaded, 6450 pounds maximum.
Dimensions: wingspan 35 feet 6 3/4 inches, length 29 feet 3 5/16 inches, height 10 feet 8 3/4 inches, wing area 230.34 square feet.
Armament: Two 12.7-mm Type 1 machine guns in the engine cowling. Two 66-pound or 551-pound bombs could be carried underwing. Two 44-imp-gall drop tanks could be carried.

Part three: Ki-43-III

Despite the obsolescence of the basic design, developmental work on the Hayabusa continued until the end of the Pacific War.

The Ki-43-IIIa was the last Hayabusa variant. Ten prototypes were built starting in May of 1944. It was similar in airframe and armament to the Ki-43 KAI, but was powered by a Najajima Ha-115-II Sakae air-cooled radial rated at 1230 hp at 9185 feet. This engine employed individual exhaust stacks to provide a certain amount of exhaust thrust augmentation. Production began in December of 1944, most of the aircraft being built by Tachikawa Hikoki K.K..

The Ki-43-IIIa was assigned to units defending Tokyo and other major Japanese cities and was also used in numerous suicide attacks during the final phases of the Pacific War.

Tachikawa also built two prototypes of the Ki-43-IIIb, which was a specialized interceptor version powered by a 1250 hp Mitsubishi (Ha-33) 42 (Ha-112) fourteen-cylinder air cooled radial. The pair of 12-7-mm machine guns (which had remained the standard Hayabusa armament since the Ki-43-Ic) were replaced by two 20-mm Ho-5 cannon, which made the Ki-43-IIIb the first Hayabusa variant to carry large-caliber armament. Further changes were made to the fuselage and wing structure as well as further modifications to the exhaust system. Overall wing span was similar to that of the Model IIIa, at 35 feet 6 3/4 inches. This version was under test when the war in the Pacific ended and brought further work to a standstill.

After the war, a few Hayabusas left in the East Indies by the withdrawing Japanese forces were salvaged by the Indonesian People's Security Force and used in 1946 in fighting against the Dutch. A few Hayabusas were confiscated by the French upon their return to Indo-China and were flown by pilots of the French Groupes de Chasse I/7 and II/7 against insurgents. These were replaced by Spitfire IXs shipped from France.

The only known surviving Ki-43 is a Model 2 (-IIa) that was on display at Clark AFB in the Philippines. With the departure of the Americans from Clark, I am not sure that this plane is still there.

Specification of Ki-43-IIIa:

One Army Type 1 (Nakajima Ha-115-II) fourteen cylinder air-cooled radial rated at 1300 hp for takeoff and 1230 hp at 9185 feet driving a three-bladed propeller.
Performance: Maximum speed 358 mph at 21,920 feet. Climb to 16,405 feet in 5 minutes 19 seconds. Service ceiling 37,400 feet. Normal range 1320 miles. Maximum range 1990 miles.
Weights: 4233 pounds empty, 5644 pounds loaded, 6746 pounds maximum.
Dimensions: wingspan 35 feet 6 3/4 inches, length 29 feet 3 5/16 inches, height 10 feet 8 3/4 inches, wing area 230.34 square feet.
Armament: Two 12.7-mm Type 1 machine guns in the engine cowling. Two 66-pound or 551-pound bombs could be carried underwing. Two 44-imp-gall drop tanks could be carried.

Sources:

Famous Fighters of the Second World War, Second Series, William Green, Doubleday 1967.

The Nakajima Ki.43 Hayabusa, Martin C. Windrow and R. F. Francillon, Aircraft in Profile, Doubleday, 1969.

Warplanes of the Second World War, Fighters, Volume 3, William Green, Doubleday, 1964.

Japanese Aircraft of the Pacific War, Rene J. Francillon, Naval Institute Press, 1979.

To which the webmaster adds the following:

The Ki-43 was developed before the Navy's Zero, but proved too sluggish in combat trials. The enclosed cockpit could not have been seen as a drawback, as Joe suggests, because the front-line army fighter (Nakajima Ki-27 "Nate") had just such a cockpit. All three fighters--Ki-27, Ki-43, and A6M--had bubble-type canopies and excellent rear version as compared to western fighters of the time. Because of its maneuverability problems, however, the Ki-43 was shelved and its engine was used for the Zero instead.

When Japan decided to prepare for war in Southeast Asia, the army needed a fighter that could fly 400 miles, fight, and go home, a capability utterly beyond the fixed-gear Ki-27 "Nate." The army's leading fighter pilot and group commander, Kato Tateo, was brought in to save the Hayabusa. It was evidently his idea to add butterfly combat flaps, which actually enabled the Hayabusa to turn inside a Zero. The Hayabusas that Kato commanded in the 64th Sentai, and I think also those in the 59th Sentai, were actually pre-production models. It was the late start, and especially the fact that it never saw service over China, that caused the Hayabusa to be unknown to western air forces. The British in Malaya identified it as a Zero, and so did the AVG Flying Tigers in Burma. However, British intelligence officers in Rangoon correctly determined that it was a Model "01" from Nakajima, though failing to realize how different it was from the fixed- gear model did most of the fighting in Southeast Asia. (Type One Army Fighter was the Hayabusa's shorthand identification, based on its its year of introduction, just as the A6M was the Type Zero Carrier Fighter.)

The great weakness of the early Hayabusa was how its wings were joined to the fuselage. (The plane was built with its engine compartment, cockpit area, and wings as a unit, with the tail attached to that.) At least one plane shed its wings in combat over Malaya, and another pilot was killed on 25 Dec 1941 when he collided with a Tomahawk flown by Parker Dupouy. (Don Lopez of NASM is another American pilot who collided with a Hayabusa and lived to tell about it.)

There is some confusion as to whether the early-model Hayabusas had two 7.7mm guns, or one 7.7 and one 12.7mm. In any event, when the 64th Sentai was reequipped with Ki-43-II models in April 1942, both nose guns were large-caliber. However, the rate of fire was so slow that many or most pilots had one gun taken out and replaced with a faster-firing 7.7mm. These were the models that fought the AVG on 28 April 1942 near Lashio, Burma.

A fascinating sidelight of the Hayabusas of 1941-42 was that they still relied on hand signals and other visual cues. They had radios as original equipment, but these never worked air-to-air, even after the pilots tried suspending them in a sort of hammock to protect them from vibration.

At least 7 Hayabusas still exist, including 4 incomplete models at the Australian War Memorial in Canberra and 1 in somewhat better shape in Scone NSW Australia. There is an apparently fine model at the Museum Pusat Tni-Au in Indonesia, and a beauty at Oskkosh WI that actually belongs to NASM.

In addition to the books Joe Baugher cited, see the following:

Nakajima Ki.43 Hayabusa I-III, by Richard Bueschel (Arco, 1970; Schiffer, 1995).

Flying Tigers: Claire Chennault and the American Volunteer Group, by Daniel Ford (Smithsonian Institution Press 1991). A lot of stuff here from the Japanese, not otherwise available in English, even if I do say so myself.

Broken Wings of the Samurai: The Destruction of the Japanese Airforce, by Robert Mikesh (Naval Institute Press 1993). The Oshkosh Hayabusa is pictured here.

Two good first-person accounts in Japanese are Tusbasa no Kessen and Hayabusa Sentotai cho Kato, both by the sergeant-pilot Hinoki Yohei (Kojinsha 1984 and 1987). And two movies, interesting even to those of us who don't know the language: Aa Hayabusa Sentotai cho Kato, a 1943 propaganda film about the 64th Sentai; and Aa Hayabusa, a documentary made in the 1980s and featuring Sergeant Hinoki himself, both produced by Toho and available on videotape.