The sole prototype Kawasaki Ki-48-II "Lily" with the Ne0 ramjet engine hanging under its fuselage. The pod beneath the fuselage was hollow, with the fuel and nozzle housed within the bomb bay.
As the Second World War intensified, the front lines demanded higher-performance propeller aircraft, leading to increased interest in jet engines. Almost simultaneously with the Navy commencing development of its turbojet engine, designated ‘TR’, the Army and the University of Tokyo Aeronautical Research Institute also established specialised departments and began research.
Engineer Hayashi Teisuke was appointed from the Army's Second Aeronautical Research Institute to lead the jet engine development effort on a one-year contract basis. In mid-November 1942, a team led by Hayashi, comprising nine subordinates from Kawasaki, commenced development. Alongside the main engine concepts proposed by the Tokyo Aviation Research Institute – the Ne* 101 motorjet and the Ne 201 turboprop – it was decided to develop motorjets and turbojets for auxiliary engines. As the characteristics of the engine types were unknown, it was decided to produce both compressor types: axial-flow and centrifugal:
1. ‘Ne1’ two-stage axial-flow motor jet
2. ‘Ne2’ single-stage centrifugal motor jet
3. ‘Ne3’ three-stage axial-flow turbojet
4. ‘Ne4’ single-stage centrifugal turbojet, and
5. ‘Ne0’ ramjet for fundamental research.
The Ne1 and Ne2 were auxiliary engine variants of the Caproni Campini-type engine-jet. They were intended for installation either aft of the fuselage in single-engine propeller fighters or behind the engine nacelle in twin-engine propeller aircraft.
The Ne3 and Ne4 were both primarily targeted for installation in single-engine or twin-engine propeller-driven fighters.
Work proceeded at considerable speed, with drawings largely completed within approximately six months.
The Kawasaki Ne0 ramjet engine.
The Ki-61 "Hien" was proposed as the primary candidate for a test aircraft**, with the Ki-45 Kai "Toryu" twin-engine fighter as the second choice. However, at a time when even a single front-line aircraft was desperately needed, neither could be obtained. Consequently, the slow-speed Ki-48 Type II twin-engine bomber "Lily" had to be used.
To minimise airframe modifications, a design utilising bomb racks to suspend the engine beneath the fuselage was developed with the cooperation of aircraft designers Imachi Isamu and Kitano Jun.
Illustration from Encyclopedia Vol. #IV
Ne0 was finished in November 1943, and on the morning of 23 December 1943, test pilot Kataoka Saizaburo*** took off from Kawasaki with engineers Hayashi and Nozu aboard. However, ignition of the combustor failed, necessitating a landing. After servicing the ignition plug, they took off again in the afternoon.
This time, the combustor ignited easily. The aircraft accelerated, delivering considerable shock to the passenger seats and momentarily causing the nose to pitch up. It then maintained high-speed cruise at an altitude of 800 to 1000 metres for approximately ten minutes before landing.
Subsequent multiple flights reportedly yielded preliminary results. Though abandoned after flight testing concluded, the entire airframe was transferred to the Army's Second Aeronautical Research Institute in July 1944.
Following Ne0 testing, research focus shifted to two of the four Ne1 to Ne4 variants—Ne3 and Ne4—with ground-running tests conducted on prototypes. However, due to the worsening war situation and the acquisition of engine data from Germany, all development of these Kawasaki jet engines was suspended during the prototype consolidation in July 1944. Consequently, no aerial tests were conducted before the war's end.
Specifications
Ne0
• Type: Ramjet
• Overall length: 2,100mm
• Maximum cross-sectional diameter: 600mm
• Thrust: 60kg (altitude 2,800m)
• Air flow rate: 8.1kg/s (altitude 2,800m)
• Compression ratio: 1.12 (altitude 5,800m, 550km/h)
Ne1
• Type: Motorjet
• Compressor: Two-stage axial flow, contra-flow type
• Length from rear edge of impeller to jet nozzle: 1,050mm
• Outer casing diameter: 600mm
• Thrust: 185.5kg × 2 (altitude 2,800m)
• Airflow: 10.4kg/s (altitude 2,800m)
Ne2
• Type: Motorjet
• Compressor: Single-stage centrifugal
• Thrust: 150kg (planned)
Ne3
• Type: Turbojet
• Overall length: 2,321mm
• Casing outer diameter: 760mm
• Total weight: 309 kg + (casing weight)
• Compressor: 3-stage axial-flow
• Turbine: 1-stage axial-flow
• Thrust: 348 kg (altitude 2,800 m)
• Air flow rate: 14.9 kg/s (altitude 2,800 m)
• Compression ratio: 1.71 (5,800 m, 550 km/h)
• Rotational speed: 8,300 rpm (altitude 2,800 m)
Ne4
• Type: Turbojet
• Overall length: 1,700 mm
• Casing outer diameter: 750 mm
• Total weight: 270 kg + (casing weight)
• Compressor: Single-stage centrifugal
• Turbine: Single-stage axial
• Thrust: 276 kg (altitude 2,800 m)
• Airflow: 10.35 kg/s (altitude 2,800 m)
• Compression Ratio: 1.98 (5,800 m, 550 km/h)
• Rotational Speed: 1,100 rpm (altitude 2,800 m)
*"ネ" (NE) was a common designation used by both the IJAAF and the IJNAF. At the time, both jet and rocket engines were collectively referred to as "燃焼ロケット" ("NEnsho roketo" combustion rockets).
**One can only imagine what a "Hien" would look like with a jet engine on its tail.
***A test pilot for the Imperial Japanese Army Air Force, he was responsible for the maiden flights of prototypes such as the Ki-61-II "Hien" and the Ki-78, manufactured by Kawasaki Aircraft. During the Ki-78 (Ken-3) test flight in January 1944, he recorded a top speed of 699.9 km/h, which remained Japan's speed record until the end of the war.
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