When developing the Mitsubishi J8M1 (Me-163 copy) the Japanese were unfamiliar with the handling characteristics of aircraft lacking a conventional horizontal tail. To provide a means of expediting the training of pilots eventually to be assigned to the rocket-driven fighter, the Scientific Division of the Navy Air Technical Arsenal at Yokosuka had been assigned the task of creating a full-scale wooden glider version of the Shusui. While definitive design work and prototype construction proceeded at Nagoya, Hidemasa Kimura who had been responsible for the Tachikawa-built A-2600 that had created a new international closed-circuit distance record developed the glider which was known as the MXY8 Akikusa (Autumn Grass). This was flown for the first time at the Hyakurigahara airfield, the base of the 312th Naval Air Group which, it had been decided, would be the first recipient of the Shusui. This event took place on 8 December, its pilot being Lt Cdr Toyohiko Inuzuka who had taken the place of Lt Cdr One as the project test pilot after the latter had been taken ill. The Akikusa glider was towed into the air by a Kyushu K10W1 and its handling characteris¬tics received a highly favourable report from Jnuzuka. The second Akikusa was sent to the Army Aerotechnical Research Institute, the Rikugun Kokugijutsu Kenkyujo, at Tachikawa where it was tested by Col Aramaki with similarly successful results.
On 1 December, the completed structural test specimen was inspected and approved by both services, but a week later, on 7 December, the Tokai district, in which Nagoya was situated, was wracked by strong earth tremors and the airframe, which was undergoing loading tests, was overstressed and suffered distortion, On 18 December, the Ohe plant in which the “heavy gliders” were being built suffered a heavy attack from B-29 Superfortresses and it was decided to transfer the salvaged airframes, together with the structural test specimen, to a plant that had been created in a mountain cave at Taura, Yokosuka, although the Ohe plant continued, together with the Nanko plant, to build a number of pre-series Shusui interceptors. Despite these setbacks, the first “heavy glider” Shusui was test flown by Lt Cdr Inuzuka at Hyakürigahara airfield on 8 January 1945, after being towed into the air by a Nakajima B6N1 Tenzan attack bomber.
For the initial flight, the engineless Shusui weighed 2,286 lb (1037 kg) and the Cl was situated at 16.8 per cent of the aerodynamic mean chord, Inuzuka confirming that there was no difference between the handling characteristics of this “heavy glider” and the Akikusa apart from a minor change of trim at take-off. During subsequent flights, some devon vibration was experienced at gliding speeds in excess of 184 mph (296 km/h) but this was eradicated when the gap between the wing and elevon was reduced and the Frise balance near the devon tip shortened. Various problems were encountered in the oil pressure system, but these were quickly resolved and in March all Navy flight testing of the “heavy glider” was to be pronounced satisfactorily completed. The second “heavy glider” was tested by the Navy at the Kashiwa airfield, Chiba, and this was eventually to be tested also by the Army. These tests were not to commence until August, and at an early stage in the trials, the Shusui parted company with its towplane prematurely and crashed in a pine forest, its pilot suffering injuries.