Cirrus aero engines


The Cirrus and Hermes or Cirrus-Hermes are a series of British aero engines manufactured, under various changes of ownership, from the 1920s until the 1950s. The engines were all air-cooled, four-cylinder inline types, with earlier ones upright and later designs inverted.
The first Cirrus design was created for the planned de Havilland Moth light aeroplane and, when it appeared in 1925, created the market for private flying. It and its successors were widely used for private and light aircraft from that moment on.

Design and development

ADC

The Cirrus engine originated in Geoffrey de Havilland's 1924 quest for a powerplant suited to a light two-seat sports biplane which would become the de Havilland Moth. No suitable engine existed at the time combining an appropriate level of power with light weight, low cost and high reliability. The Aircraft Disposal Company, also known as Airdisco and ADC, were producing the low-cost Airdisco V8 which had been developed by Frank Halford from their large stocks of war surplus Renault V8 aero engines. The Renault had been renowned for its reliability. De Havilland realised that half of this engine would make an air-cooled four-cylinder inline engine of just the right size and at low cost. He persuaded Halford to undertake its design and development.
The cylinders, pistons, con-rods and gearing were taken from the Renault, with the valve gear based on the Airdisco, and a new five-bearing crankshaft and cast crankcase were designed. Developing in normal flight it became the first Cirrus engine, and the first air-cooled four-cylinder inline aero engine, to go into quantity production.
The Cirrus was launched onto the market in the de Havilland Cirrus Moth, first in a long line of Moths, in 1925. The engine proved to be ideal for private light aircraft and it created a new era of private flying in the UK, in both the Cirrus Moth and other similar aircraft. It was simple enough to be understood and looked after by the private owner, while its reliability made private flying safe for the first time. Moreover it achieved these at an affordable cost.
The uprated Cirrus II, with slightly greater displacement, delivered from 1926. Halford ended his association with ADC at the end of the year, but development continued. The Cirrus III was introduced in 1928 with even greater displacement and power of.

Cirrus Aero Engines

As ADC began to rum out of the Renault engines in 1928, Cirrus Aero Engines Limited was formed at Croydon to manufacture the Cirrus models from scratch.
Although Halford was no longer associated with it, the Cirrus company continued to develop new models, with the uprated Hermes appearing in 1929. It had been developed by ADC to provide more power than even the Cirrus III. Overall slightly shorter but with much the same overall weight, it delivered.

American Cirrus Engines (ACE)

American Cirrus Engines, Inc. was a subsidiary of Allied Motor Industries, Inc. set up at Belleville, N.J. in November 1928, initially to manufacture the Cirrus III under license. Having developed the American Cirrus III engine at New Jersey, the company moved to Marysville, Michigan, where it set up production. The engine was rated at at 2100 revolutions per minute. The company became known as the A.C.E. Corporation.
A new range of inverted engines was branded Hi-Drive and appeared under names such as the Hi-Drive Cirrus III and Hi-Drive Ensign. The Hi-Drive was supplied in direct and geared drive options, and was designed to accept a de Palma supercharger for increased performance.
In 1935 A.C.E. was taken over by Menasco, who developed the inverted engine as the Pirate, sold from 1936, and a six-cylinder derivative as the Buccaneer.

Cirrus-Hermes

The independent Cirrus-Hermes Engineering Company was formed in 1931. The Hermes models I, II, III and IV were produced ranging in power from 105 hp to 140 hp depending on type.
While the Hermes II and III were uprights like their predecessors, the Hermes II B introduced a major change with the cylinders being inverted for the first time. The resulting high propeller line allowed the top of the engine to be lowered, which significantly improved the pilot's view in a single-engined type. All subsequent models would be inverted.
By this time C. S. Napier, son of Montague Napier, had joined as Technical Director and engine designer. He began work on two new engines but before they could be finished the company came under new management.

Cirrus Hermes

In 1934 the company was taken over by the Blackburn Aeroplane & Motor Company and moved to Brough in Yorkshire. Napier remained Technical Director and, while he completed the development and initial sales of the Cirrus Minor and Cirrus Major, Blackburn kept Cirrus Hermes as a separate company. Although completely new designs, they were of broadly similar layout to the previous inverted engines,with the Minor in the 70-80 hp class and the Major giving 125 hp in normal use. Coming to the market almost together in 1935, they rationalised and replaced the previous ranges.

Blackburn

Once the new Cirrus engines were established, in 1937 the company became the Cirrus Engine Division of Blackburn, which itself had been incorporated into Blackburn Aircraft Limited.
The Blackburn Cirrus Midget was a smaller version developed in 1938 but it failed to enter production.
During and after WWII Blackburn produced uprated versions of the Cirrus Minor and Major. In 1948 it introduced the Blackburn Cirrus Bombardier with fuel injection and a higher compression ratio, giving increased output.
When Blackburn Aircraft merged with General Aircraft Limited in 1949, becoming Blackburn & General Aircraft Limited, it continued to market the Minor, Major and Bombardier range until the late 1950s.

Variants

;Cirrus I
;Cirrus II
;Cirrus III
;American Cirrus III
;American Cirrus Hi-drive
;Hermes
;Hermes II
;Hermes IIB
;Hermes III
;Hermes IV and IV A
;Cirrus Minor
;Cirrus Minor 100 hp
;Cirrus Minor II
;Cirrus Major
;Cirrus Major 150 hp
;Cirrus Major II
;Cirrus Major III
;Blackburn Cirrus Midget
;Blackburn Cirrus Bombardier

Applications

List from Lumsden except where noted. The list includes trial installations where a different engine was principally adopted.

Cirrus

Cirrus I

Cirrus III

Hermes I