Nakajima Kitsuka II


Set up in warehouses belonging to a tobacco factory, the Ne 20 group comprised 10 officers and 200 men. Here, two bench testing stations were created and Ne 20 development and testing continued. The process revealed numerous flaws. At one stage the pressure of the axial-flow compressor was found to be too low. Nagano came to the conclusion that the camber of the stators was not correct and so he took them out, bent them on an anvil and then reinstalled them. These were tested in the second Ne 20 to be built. Yet another difficulty arose with the thrust bearings on the compressor which was burning out very quickly. Nagano solved the problem by revising the bearings and bearing rings. One problem that reappeared was blade cracking. The blades were made from manganese-chromium-vanadium steel and not the more suitable nickel alloy. These blades were then welded to the disk and, as such, the blades did not have the strength to withstand the operating stresses of the motor. After one to two hours of operation, cracks would appeare on the blade roots at the point where they connected to the disk. The solution was to thicken the blades but this lowered the efficiency of the engine. However, the Ne 20 was able to run for four or five hours before cracks appeared and while the engine could have run longer, there was no guarantee when blade failure would occur. With these improved results, work began to produce a small number of engines.

25 April 1945 would see the first Kitsuka fuselage completed. This was then subjected to stress and load testing which began on 20 May, but with the stipulation that the fuselage was not to be damaged during tests. Nakajima was scheduled to produce 24 Kitsuka aircraft by June 1945 and with the availability of six Ne 20 engines. On the surface, the Kitsuka project looked to be moving along. The reality was a far different story.

On 13 June, Vice Admiral Wada held a meeting to discuss the Kitsuka. Wada addressed a number of issues that were becoming problematic. Nakajima’s G8N1 Renzen program had to be stopped in order to free up production capacity for the Kitsuka as both a special attack aircraft and an interceptor. More troubling was that unless the stock of aluminium was conserved the supply would be exhausted by September 1945. At best, even with conservation, by the close of 1945 there would be no more aluminium available. As a result, only steel and wood would be left and to use such materials would, again, have caused a revision to the Kitsuka design. The final blow was that high grade aviation fuels would only be available for the Homare series of radial engines. All other engines, including the Ne 20, would have to make do with poorer quality fuel. This, coupled with defeat after defeat for the Japanese military, cast a very serious cloud over the Kitsuka project and some no longer saw value in continuing with the aircraft. Others however, had a strong desire to see the Kitsuka taken to completion because it would put Japan into the jet age.

On 25 June 1945, the first Kitsuka was completed but without its engines. Although externally the Kitsuka bore a resemblance to the Me 262, that was as far as it went. The wings of the Kitsuka had a total of 13° sweepback, the centreline of the wings being at 9°. Wing tip slots eliminated the tip stall discovered during wind tunnel testing and split flaps and droop ailerons were fitted to compensate for the heavy wing loading. Nakajima K series airfoils were used – a K 125 airfoil at the wing root and a K 309 airfoil at the wing tip. The wings were of double spar construction with nine main support ribs, all covered with steel and duralumin skinning. Mitsubishi A6M Reisen flap hinges were used on the trailing edge flaps and the wing tips were fabricated from wood and steel sheeting. The outer wing folded upwards. The Kitsuka had a slight gull wing form thanks to 5° dihedral of the centre span and 2° dihedral of the outer wing. All control surfaces were fabric covered. The fuselage had a slight triangular shape, being composed of three sections (nose, centre section and aft). The centre section had the centre wing span built into it and much of this and the other two sections were constructed from sheet steel due to the unavailability of duralumin in quantity. Twenty-four bulkheads were contained within the complete fuselage with two bulkheads coming together where each section met, which were then bolted together to complete the fuselage. Two fuel tanks were fitted, one in front of and the other behind the cockpit. The tail of the Kitsuka was fairly conventional and the aft fuselage line was kept high so that the stabiliser would not be effected by the jet efflux. For the tricycle landing gear, the main gear (to include the brake system) from a Mitsubishi A6M Reisen was modified to suit the Kitsuka and the 600mm x 172mm-sized wheels retracted into the wing. The 400mm x 140mm-sized nose wheel was taken from the tail wheel of a Kūgishō P1Y Ginga and it retracted into the rear of the nose.

After being assembled the Kitsuka was then broken down, loaded into trucks, and moved to Nakajima’s Koizumi plant where two Ne 20 engines awaited it. By 27 June, the Kitsuka had been put back together and the engines installed, and two days later weight and balance checks had been completed. The Kitsuka was then declared ready for flight testing. On 30 June 30 1945, both Ne 20 engines on the Kitsuka were started and run for a short time. Flight testing could not be conducted at the airfield at Koizumi because the runway was too short and had many approach restrictions. Misawa Air Base (Misawa Hikōjō), in Aomori Prefecture 684km (425 miles) north of Tōkyō, was also considered since it had open approaches and was rarely visited by Allied long range fighters. However, because of the great distance it was ruled out. Finally, it was settled that the airfield at Kisarazu Air Base (Kisarazu Hikōjō) would be the location for the first flight because it was far closer to Yokosuka than Misawa. Once more the Kitsuka was disassembled, loaded into trucks, and moved to the Kisarazu airfield, adjacent to Tōkyō Bay.

On arrival, the Kitsuka was reassembled and made ready for its first flight. Unfortunately, on 14 July, during engine testing, a loose nut was ingested which completely shattered the blades in one of the compressors. The damage to the engine was so extensive that repairs were simply not possible and replacement the only option. This delayed the flight for many days. As the Kitsuka was being repaired, the personnel for the 724 Kōkūtai, which had been designated a special attack unit and which would fly the Kitsuka in service, had been assembled at Yokosuka after its formation on 1 July 1945. On 15 July, the new unit moved to Misawa Air Base where it began training using Aichi D3A1 and D3A2 carrier bombers (known as Val to the Allies), which had been relegated to the training role.

On 27 July, Lieutenant Wada conducted some successful taxi tests with the Kitsuka. High speed taxi tests, however, were prepared by appointed Kitsuka test pilot Lieutenant Commander Susumu Takaoka. Two days after the initial taxi tests, Takaoka ran the Kitsuka up to 129km/h (80mph) and then applied the brakes to test their effectiveness. He found that their stopping power was not adequate, though he felt the problem was not so severe that flight testing had to be stopped. Ground testing was finally completed on 6 August, the same date that Hiroshima was devastated by the ‘Little Boy’ atomic bomb dropped from the B-29 ‘Enola Gay’. News of this strike soon reached the Kitsuka crews, technicians and engineers.

7 August 1945 would see excellent flying conditions and the Kitsuka was made ready for flight. Weather reports stated a 24km/h (15mph) southwest wind and a crosswind blowing from the right across the 1,692m (5,550ft) length of Runway 20 that pointed towards Tōkyō Bay. The Kitsuka was only given a partial fuel load to keep the weight to 3,150kg (6,945 lb); this allowed for approximately 16 minutes of flight time. No RATO bottles were fitted so that the take-off characteristics of the aircraft could be assessed. Takaoka climbed into the cockpit and made ready to take-off. On his signal the Ne 20 turbojets were started and he was soon taxiing out to the start of the runway. Once there, he extended the flaps to 20° and kept the brakes set. So as not to cause a compressor stall, Takaoka slowly eased the engine throttles forward and when both had reached 11,000rpm, he released the brakes and the Kitsuka began to roll. Twenty-five seconds later and after a run of 725m (2,378ft), the Kitsuka was airborne and went into the history books as the first Japanese jet to fly.

At 610m (2,000ft), Takaoka levelled off. He was instructed to not retract the landing gear nor exceed 314km/h (195mph). As a test pilot he was used to hearing the roar of a conventional aircraft engine and used such noise as a means to detect problems. However, Takaoka was not prepared for the whine of the turbojets that told him almost nothing outside of what his instruments reported. He circled Kisarazu airfield, keeping it in sight in case of a failure and because the airspeed kept rising, Takaoka had to constantly throttle back to keep from exceeding the gear down speed limit. A brief test of the control sensitivity showed that the rudder was stiff, the ailerons were heavy but were working and the elevators were overly responsive. When his flight time was up, Takaoka was wary of how he would land. He did not want to drop the turbojets to below 6,000rpm since that risked a flameout from which he would likely not recover in time. Therefore, he chose a long, shallow drop, lowered his flaps 40° and brought the turbojets down to 7,000rpm. On touchdown, he only needed moderate braking to bring the Kitsuka to a stop using only a little under 610m (2,000ft) of runway. Takaoka brought the Kitsuka back to the ramp amid throngs of cheering men. The total flight time was 11 minutes. In his immediate report on the flight, Takaoka stated he had experienced no problems with the engines and had no recommendations for improving the aircraft. During his debriefing, technicians had removed the cowlings to the Ne 20 turbojets and examined each engine. They found no faults and so gave the Kitsuka clearance for another flight, scheduled for 10 August 1945.

For the second flight, more fuel was to be stored and RATO bottles used; this would allow for a longer flight and test the RATO units as boosters. Takaoka would again pilot the Kitsuka. Prior to the flight Takaoka examined the RATO bottles which were fitted to the underside of the fuselage and found fault with the angle at which they were set. However, to adjust them would have taken too much time and so instead of 800kg (1,763 lb) of thrust, the bottles were reduced to 400kg (881 lb) each.

On the day of the second flight, Allied air power was highly active and any flight attempt was bound to be spotted putting the Kitsuka at risk. Consequently, it was decided to wait until the following day on 10 August. However, it would be remembered for the drafting of the Imperial Rescript on the Termination of the War by the Japanese cabinet at the behest of Emperor Hirohito, though the populace had no knowledge of this.

11 August 1945 shared a similar weather pattern to the day the Kitsuka had first flown. The difference was that several IJN and IJA officials of high rank had arrived to witness the second flight. Once more Takaoka climbed into the cockpit, signalled for engine start and taxied out to the runway. As before he extended the flaps 20°, and after receiving the signal to takeoff, he slowly opened the throttles until the engines had reached 11,000rpm before releasing the brakes and the Kitsuka rolled forwards. At four seconds into the take-off roll, Takaoka activated the RATO units. Immediately, the acceleration caused the nose of the Kitsuka to pop up, the tail slamming onto the runway. Takaoka fought to get the nose down by jamming the stick forwards but he received no response from the aircraft’s elevators. The two RATO units burned for a total of nine seconds and during eight of those seconds Takaoka was helpless and unable to correct the nose up condition. One second prior to the units burning out, the elevators finally took effect and the nose came down so hard Takaoka was sure the front tyre had blown when it contacted the runway. Takaoka felt a sense of deceleration as the Kitsuka reached the halfway point on the runway – his speed at that point was 166km/h/103mph. A second later, with the feeling of deceleration still present, Takaoka decided to abort the take-off and he cut the power to the engines. Unfortunately, the brake issue Takaoka had discovered during highspeed taxi tests now came back to haunt him.

Despite maximum application of the brakes, the Kitsuka showed no signs of slowing and Takaoka was rapidly running out of runway. As he neared one of the taxiways, Takaoka held the left brake in an attempt to make the Kitsuka bring its left wing down into the ground to bleed off speed (known as a ground loop). The Kitsuka’s nose turned slightly but this then put the aircraft on a crash course with a group of hangars and buildings. Takaoka reversed the braking, holding the right brake. The Kitsuka came back around onto the runway and despite Takaoka working the brakes, it was to no avail. The aircraft ran out of tarmac and crossed the 100m (328ft) of grass overrun before the landing gear caught in a drainage ditch and collapsed. The Kitsuka slid along its belly until finally coming to a halt by the edge of the water of Tōkyō Bay. The damage to the Kitsuka was extensive. In addition to the mangled landing gear, the two Ne 20 engines were badly damaged, having been jarred from their mounts but still remaining attached to the wings. Initial assessments suggested that the damage was so severe the Kitsuka could not be repaired. On the positive side, the aircraft did not catch fire and causes of the accident were swiftly looked into. IJN Captain Itō, who was present for the flight, was thankful that the Kitsuka did not become airborne with the nose high attitude during the RATO burn. Had that happened and once the RATO bottles cut out, the Kitsuka would have most likely crashed into the ground. A motion picture camera captured the flight and the film developed to see if it could shed any light on the crash.

On 15 August, the film of the ill-fated flight was studied but proved inconclusive as to whether or not the Kitsuka was airborne once the RATO bottles were exhauasted, as was suspected. This would have explained the heavy impact of the front landing gear on the runway and the sense of deceleration experienced by Takaoka. In any case, the Kitsuka would never fly again for at 12.00pm the Imperial Rescript on the Termination of the War was broadcast on the radio bringing World War 2 to a conclusion.

The end of the war would see none of the Kitsuka production plans realised. Nakajima, by the close of December 1945, was to have produced 200 Kitsukas. In reality, Nakajima completed only one with a further 22 under construction. The Kyūshū Hikōki K.K. was, also by the end of the year, to have turned out 135 Kitsuka aircraft but was only able to begin construction of two aircraft, started in July 1945, which remained unfinished by the close of hostilities. A third producer, the Sasebo Naval Arsenal (Sasebo Kaigun Kōshō), was scheduled to have begun production of the Kitsuka in September 1945 with 115 completed by the close of December. The fourth production line was to be at the Kasumigaura Naval Air Arsenal with the commencement of Kitsuka construction scheduled for October 1945; 80 aircraft were to have been completed by the end of December.

A number of variants of the Kitsuka were planned, none of which would see completion come the capitulation. One of these was a two-seat trainer. Given the nature of the Kitsuka, it was appreciated that a trainer would be required to help the conversion of pilots used to conventional piston engined aircraft to the peculiarities of a turbojet powered aircraft. Five of the Kitsuka airframes under production by Nakajima were modified by including a second cockpit for the instructor. Outside of the inclusion of the additional cockpit, it is unknown exactly what other changes were made in the Kitsuka to accommodate it. If there were a parallel to the German Me 262B-1a two-seat trainer, the rear fuel tank would have been removed to make room for the instructor’s cockpit. The German solution to the loss of fuel was to utilise the two front bomb racks for drop tanks. Whether Nakajima considered the use of drop tanks (as the Kitsuka could use them) or simply accepted the reduced endurance for the sake of expediency is not known. The two-seat trainer would be the only variant of the Kitsuka to reach the production phase.

It was planned that some of the two-seaters were to be modified for reconnaissance roles. The instructor’s cockpit was to be removed and replaced with a crew position for an observer. He was to have a Type 96 Model 3 radio set at his disposal for use in relaying target information to other aircraft. It is unknown if any cameras were to be fitted but it would not be unreasonable to conclude that the observer would at least have had a hand-held camera.

An interceptor version of the Kitsuka was discussed, as previously mentioned, and a number of general arrangements for it were considered. One of these was the inclusion of a single Type 5 30mm cannon with 50 rounds of ammunition installed in the nose. A second design was to feature enlarged and extended wings incorporating flaps and double-edged leading slots. A more definitive interceptor was to replace the Ne 20 engines with either Ne 130 or Ne 330 turbojets. A second cannon was to be added in the nose. Interestingly, it appears that if the IJA had used the Kitsuka, the Type 5 cannons would be replaced with two Ho-155 30mm cannons. This may have been a stopgap or fallback if the IJA’s own Ki-201 Karyū failed to materialise. With the heavier weight the structure of the Kitsuka, including the landing gear, would have been strengthened. A fighter-bomber model was envisioned for the definitive interceptor by including a fitting for a single 500kg (1,102 lb) or 800kg (1,763 lb) bomb.

As originally planned, a model of the Kitsuka was proposed for shimpū missions. Similar to the Kitsuka as constructed, this version was to carry either a 500kg (1,102 lb) bomb, a 250kg (551 lb) bomb or two Type 99 20mm cannons. With the latter, it could be assumed the cannons would be used for self-defence and for firing at the target before ramming the aircraft into the victim using any remaining fuel and ammunition as the secondary explosive element. A variant of this Kitsuka was to utilise a 200m (656ft) launch rail that Kūgishō had been designing and which they expected to have ready for testing by September 1945. Using a rocket booster, the Kitsuka would leave the launch rail at 220km/h (137mph) at an acceleration of between three to four ‘g’.

In regards to the 724 Kōkūtai, with the end of the war they would never see their Kitsuka aircraft. It was planned that by November 1945 the unit would have been based near Yokosuka at a site along the Miura Peninsula, west of Tōkyō Bay. It was expected that by then the unit would have received sixteen Kitsukas. In addition, the unit was to use one of the handfuls of Kawanishi E15K1 Shiun (meaning ‘Violet Cloud’; codenamed Norm by the Allies) reconnaissance floatplanes, which were removed from active service following their disastrous combat debut in 1944. The Shiun, operating from a nearby harbour, would locate the shipping targets, mark them and then loiter in the area to broadcast radio signals. The Kitsukas would then be rapidly launched and, by means of the radio signals received through the Kuruku system, attack the ships at low level with bombs and ramming tactics. Had the reconnaissance version of the Kitsuka gone into production, the 724 Kōkūtai was to receive it as a replacement for the far more vulnerable Shiun.

Finally, with the close of the war, none of the projected turbojet successors to the Ne 20 would enter production. One prototype of the Ishikawajima Ne 130 had been completed by June 1945 but testing was unfinished by the time the war ended. Nakajima started development of the Ne 230 in May 1945 and had three under construction by August 1945. However, none of the engines were completed or tested. Mitsubishi was unable to construct a Ne 330 and so it remained on the design board.

A note about the use of the name Kitsuka as opposed to the more commonly used Kikka. Kitsuka is the proper translation of the kanji characters. However, it is pronounced ‘kikka’. Kikka was used in post-war reports as phonetically it approximated to Kitsuka and thus has become the accepted name of the aircraft. Neither name is incorrect. Also, some sources use the J9Y1 (or sometimes J9N1) designation for the Kitsuka. While logical for the interceptor version of the Kitsuka, there is no evidence in wartime Japanese sources to support the designation. One may also find the designation J8N1 used but this is not supported.