Roden 626 Woseley W4A Viper 1:32

The British copy of the Hispano Suiza, known as the Wolseley Adder, differed from the original only in its compression ratio 4.7:1, as against the 4.8:1 of the original. These engines began to be installed in the S.E.5a, but the result left much to be desired the Adder appeared to be too capricious and did not achieve the required number of turns, etc.

The Wolseley engineers decided to perfect the design of the engine, and in due course appeared the Wolseley Viper quite similar to the Hispano Suiza, but a substantially modified engine on the whole. The compression ratio reached 5.3:1 compared with the Wolseley Adder's 4.7:1, the crankshaft defects were eliminated, its construction was strengthened, and most importantly, the engine functioned without any interruptions during flight. Mass production began immediately because many more of the new S.E.5a were needed on the Western Front. With the arrival of this engine in the S.E.5a one distinctive feature of some earlier machines disappeared, namely the 4-blade screw, because the Viper produced sufficient rotation with a two-blade propeller. At the end of 1917 the first S.E.5a with the Viper engine reached the Front, where it immediately proved its superiority over all other types of fighter. After that the early build S.E.5a's with the Hispano Suiza engine were sent for repair and refitting with the Viper engine. These engines were made in great numbers during 1917-1918.