[1] Like the wings the fuselage was wooden, with four longerons defining its flat-sided form; it, too, had stressed birch ply skin.
A 30 kW (40 hp) Train 4T four-cylinder, air-cooled, inverted straight engine drove a two-blade propeller.
Its empennage was conventional, with a horizontal tail mounted on top of the fuselage and strongly straight-tapered like the wing.
The elevators were inset and separate, with a gap between them to allow the movement of a deep, balanced rudder mounted on a small fin.
[1] The Régnier 12 was registered as OO-REG on 8 August 1936;[2] the date of its first flight is not known, though tests with an unknown type of 20 kW (27 hp) engine had started before May 1937.