Alvis Leonides


The Alvis Leonides is a British air-cooled nine-cylinder radial aero engine first developed by Alvis Car and Engineering Company in 1936.

Design and development

Development of the nine-cylinder engine was led by Capt. George Thomas Smith-Clarke. The prototype engine, called 9ARS and which weighed 693 lb and developed 450 hp, was run in December 1936. In 1938 Airspeed Ltd lent their test pilot, George Errington, and their much rebuilt Bristol Bulldog, to carry out test flights. Development was continued at a reduced pace during the Second World War and following testing in an Airspeed Oxford and an Airspeed Consul. Alvis was ready to market the engine in 1947 as the Series 500 for aeroplanes and Series 520 for helicopters.. The first production use was the Percival Prince, which flew in July 1948 and the Westland Sikorsky S-51 and Westland WS-51 Dragonfly helicopters. From 1959 the stroke was increased to 4.8 inches for the Series 530 rated at 640 hp. It was Britain's last high-power production piston aero-engine when manufacture ceased in 1966.

Variants

Notes: LE designations from Air Ministry system ; 500 series designations from Alvis company designation system; Mark numbers for civil variants.
;Alvis 9ARS: pre-war precursor to the Leonides – / 0.5:1
;LE.1M: – /3,000 rpm/+6.6 lb boost/ 0.5:1
;LE.2M: – 0.625:1 reduction gearing, remote accessories
;LE.3M: – 0.5:1 reduction gearing, remote accessories
;LE.4M: – 0.625:1 reduction gearing
;LE.12HMH: Horizontal direct-drive for helicopters
;LE.21HMV: Vertical direct-drive for helicopters
;LE.23HM: Vertical direct-drive for helicopters
;LE.24HMV: Vertical opposite rotation reduction-geared drive for helicopters
;LE.25HMV:
;Leonides 501:/3,000 rpm/+6.6 lb boost/ 0.5:1
;Leonides 502:
;Leonides 503:
;Leonides 504:
;Leonides 514:
;Leonides 521:
;Leonides 522:
;Leonides 523: Helicopter vertical drive
;Leonides 524: Helicopter vertical drive
;Leonides 525:
;Leonides 530: Long stroke
;Leonides 531: Long stroke, supercharger ratio 6.5:1
;Leonides 532: Long stroke, supercharger ratio 7.91:1
;Leonides Mark 22:
;Leonides Mark 24:
;Leonides Mark 50:
;Leonides Mark 70:
;Leonides Mark 125:
;Leonides Mark 125 01/2:
;Leonides Mark 126:
;Leonides Mark 127 01/2:
;Leonides Mark 128:
;Leonides Mark 130:
;Leonides Mark 138: Long stroke
;Leonides Mark 173:

Applications

Preserved Alvis Leonides engines are on public display at the following museums: