# Nakajima Kikka

The Nakajima Kikka (橘花, "tachibana orange blossom"), initially designated Kōkoku Nigō Heiki (皇国二号兵器, "Imperial Weapon No. 2"), is Japan's first turbojet-powered aircraft. It was developed late in World War II, and the single completed prototype flew only once, in August 1945, before the end of the conflict.

## Design and development

After the Japanese military attaché in Germany witnessed trials of the Messerschmitt Me 262 in 1942, the Imperial Japanese Navy issued a request to Nakajima to develop a similar aircraft to be used as a fast attack aircraft. Requirements included being built largely with unskilled labor, and that the wings should fold. This would enable the aircraft to be hidden in tunnels and aircraft shelters around Japan as the navy began to prepare for the defense of the home islands. Nakajima designers Kenichi Matsumura and Kazuo Ohno laid out an aircraft that bore just a superficial resemblance to the Me 262.
The Kikka was initially to use the Tsu-11, a motorjet engine that was essentially a piston engine with a ducted fan with an afterburner, similar to those used in Russia and Italy at the time. Subsequently the Ne-10 (TR-10) centrifugal-flow turbojet, and the Ne-12, which added a four-stage axial compressor to the front of the Ne-10 were evaluated, however tests revealed that these did not produce enough power, and the project stalled. It was then decided to use a new axial flow turbojet based on the German BMW 003.
Development of the engine was troubled, as it was based on little more than photographs and a single cut-away drawing of the BMW 003, however, the Ishikawajima Ne-20 was quickly built and by mid-1945, the Kikka project was progressing again. At this stage, due to the deteriorating war situation, it is possible that the Navy considered the Kikka for kamikaze missions, but this is questionable due to the cost and complexity. Other more economical projects designed for kamikaze attacks, such as the simpler Nakajima Ki-115 Tōka (which used obsolete engines), the pulsejet Kawanishi Baika, and the rocket Yokosuka Ohka, were either underway or already in mass production.
Compared to the Me 262, the Kikka airframe was noticeably smaller (with just 4/5ths of the span) and more conventional, with straight wings (lacking the slight sweepback of the Me 262). The triangular fuselage cross section characteristic of the German design was also absent. To accelerate development, the main landing gear was adapted from the A6M Zero and the nose wheel from a Yokosuka P1Y bomber tailwheel.

### Designation

The Kikka is sometimes identified as the J9N1, or occasionally J9Y1, which according to a National Air and Space Museum researcher is incorrect and no such designation appears in any records associated with the design. The official name assigned was Kikka (橘花) and like some other Navy aircraft at the very end of the war, it received only a name. Imperial Japanese Naval aircraft until then had normally designated with a similar system to that used on U.S. Navy aircraft of the time, in which the first letter denotes the role, a number denotes the design in the sequence (starting with 1), and a second letter denotes the company that developed it, followed by a number indicating subtype.

## Operational history

The first prototype commenced ground tests at the Nakajima factory on 30 June 1945. The following month, it was dismantled and delivered to Kisarazu Naval Airfield where it was re-assembled and prepared for flight testing. The first flight took place on 7 August 1945 (the day after Hiroshima was bombed by atomic bomb), with Lieutenant Commander Susumu Takaoka at the controls. The aircraft performed well during a 20-minute test flight, with the only concern being the length of the takeoff run. For the second test flight, four days later (four days prior to Japan's declaration of surrender), rocket-assisted take-off (RATO) units were fitted to the aircraft. The pilot had been uneasy about the angle at which the rocket tubes had been set, but, with no time to correct them, they decided to simply reduce the thrust of the rockets from 800 kg to only 400 kg. Four seconds into take off the RATO was actuated, immediately jolting the aircraft back onto its tail leaving the pilot with no effective tail control. After the nine-second burning time of the RATO ran out, the nose came down and the nose wheel contacted the runway, resulting in a sudden deceleration, however, both engines were still functioning normally. At this point, the pilot opted to abort the take off but fighting to brake the aircraft and perform a ground loop only put him in danger of running it into other installations. Eventually, the aircraft ran over a drainage ditch, which caught the tricycle landing gear, and the aircraft continued to skid forward and stopped short of the water's edge. Before it could be repaired, Japan had surrendered, and the War was over.
At this point, the second prototype was close to completion, and approximately twenty-three more airframes were under construction. Five of these were two-seat trainers.

### Postwar

After the War, airframes 3, 4, and 5 (and possibly other partial airframes) were brought to the U.S. for study. Today, two examples survive in the National Air and Space Museum: The first is a Kikka that was taken to the Patuxent River Naval Air Base, Maryland for analysis. This aircraft is very incomplete and is believed to have been patched together from a variety of semi-completed airframes. It is currently still in storage at the Paul E. Garber Preservation, Restoration and Storage Facility in Silver Hill, Maryland. The second Kikka is on display at the NASM Udvar-Hazy Center in the Mary Baker Engen Restoration Hangar. Correspondence in 2001 with Japanese propulsion specialist Kazuhiko Ishizawa theorized that Nakajima constructed the Museum’s Kikka airframe for load testing, not for flight tests. This may explain why the engine nacelles previously fitted on the Museum’s Kikka airframe are too small to enclose the Ne-20 engines. However, Ishizawa later stated that a limited survey at the Paul E. Garber facility concluded that this Kikka may not be a strength-tester due to the presence of wiring, hydraulics and controls. Furthermore, Susumu Watanabe, who was in charge of engine outfitting for the Kikka, recalled that the engine nacelles of the strength tester were the same as the standard aircraft, and that the strength tester was stressed until failure. Based on this information, the mock nacelles were potentially added for display purposes after transit to the United States.
Two Ne-20 jet engines had been taken to the US and sent for analysis to the Chrysler Corporation in 1946. This was only revealed in 2005 by W. I. Chapman, who was in charge of the project at the time. A working engine was assembled with the parts of the two Ne-20s, and tested for 11 hours and 46 minutes. A report was issued on 7 April 1947, titled "Japanese NE-20 turbo jet engine. Construction and performance". The document is now on display at the Tokyo National Science Museum.

## Variants

Nakajima Aircraft Company developed some variants of the aircraft:
Five of the planes under construction at the end of the War were to be completed as two-seat trainers. Other follow-on versions proposed included a reconnaissance aircraft and a fighter armed with two 30 mm Type 5 cannons with 50 rounds per gun. The fighter was expected to be powered by a more advanced development of the Ne-20, known as Ne-20 Kai 6.37 kN (650 kgf), which was planned to have approximately 30% more thrust than the Ne-20.

## Operators
### Japan

* Imperial Japanese Navy (planned)

## Specifications (Kikka)

Data from Kikka, Monogram Close-Up 19
General characteristics
* Crew: 1
* Length: 9.25 m (30 ft 4 in)
* Wingspan: 10 m (32 ft 10 in)
* Height: 3.05 m (10 ft 0 in)
* Wing area: 13.2 m$^2$ (142 sq ft)
* Airfoil: K125 at root, K309 at tip
* Empty weight: 2,300 kg (5,071 lb)
* Gross weight: 3,550 kg (7,826 lb)
* Max takeoff weight: 4,312 kg (9,506 lb)
* Powerplant: 2 × Ishikawajima Ne-20 axial-flow turbojet engines, 4.66 kN (1,047 lbf) thrust each
Performance
* Maximum speed: 696 km/h (432 mph, 376 kn) at 10,000 m (33,000 ft)
* Range: 948 km (589 mi, 512 nmi)
* Service ceiling: 12,000 m (39,000 ft)
* Time to altitude: 6,000 m (20,000 ft) in 12 minutes with bomb load
* Wing loading: 269 kg/m$^2$ (55 lb/sq ft)
* Thrust/weight: 0.27
Armament
* Bombs: 1 × 500 kg (1,102 lb), or 1 × 800 kg (1,764 lb) bomb