THE PETROL MOTOR 539 
form is believed to be an exceptionally reliable power unit. 
:¢ firm has also turned out the Napier Cub of 1,000 h.p., 
th twenty cylinders divided into five blocks of four 
linders each. This engine, though more or less experi- 
:ntal, has been actually installed in a good many aircraft. 
Under class two the Bristol Aeroplane Co. and Sir W. G. 
A rmstrong Whitworth Aircraft Co. produce the only large 
2 v-cooled aviation engines. The former firm has produced 
- ¢ Bristol Jupiter 420-h.p. 9-cylinder radial air-cooled 
-. @ ‘gine, and, it is understood, will shortly produce a modified 
5 ipiter of 700 h.p., to be called the Mercury. The Jupiter 
x considered by some to be the most reliable aeroplane 
_ gine on the market to-day. The Armstrong Whitworth 
= 'm has also produced a Jaguar engine of 400 h.p., which, 
¥ is interesting to note, was used by Sir Alan Cobham in his 
> ghts to Australia and to the Cape. This engine is also 
:gely employed in His Majesty’s Service. 
Under the third class of light aeroplane engine several 
ms are well known, such as Bristol Aeroplane Co., 
ackburn Aeroplane & Motor Co., A. V. Roe & Co. 
Wd Sir W. G. Armstrong Whitworth Aircraft Co. The 
st-named firm has for some years produced the Cherub 
cylinder 48-h.p. engine, which, it may be noted, won the 
ympne Light Aeroplane competitions last year. 
& As to the re-constructors of war engines, Aircraft 
isposal Co. of Croydon is the only firm seriously engaged 
the adaptation of this kind of engine—namely, the 
imbus and the Cyrrus types. The former is a 300-h.p. 
odified Siddeley Puma; it is believed to be a very reliable 
nit. The Mark 1 Cyrrus engine is a modification of 
‘¢ old 8o-h.p. Renault war-type air-cooled engine, and 
1s been used in the De Havilland Moth aircraft with 
ccess, 
x Under the fifth class the designers of and the experi- 
enters with heavy oil engines are actively occupied in 
§