The Blackburn Cirrus Major started as a development of the original ADC Cirrus series of aircraft engines which progressed through a number of variants, each with slightly different displacement and power outputs. First run in 1936, the Cirrus series was later bought by Cirrus Aero-Engines (later known as the Cirrus-Hermes Engine Company) which produced the Cirrus Hermes I, II, III and IV, again each differing slightly in displacement and power.
In 1934 Cirrus was bought again by the Blackburn Aircraft company and later that year the Cirrus Minor was produced. In 1935 the Cirrus Major entered production. Approximately 700 were built.

Applications:
Auster Aiglet
Auster Autocar
Blackburn B-2
Chrislea Skyjeep
de Havilland DH.60 Moth
Fairey Primer
Foster Wikner Wicko
General Aircraft Cygnet
General Aircraft Owlet
HAL HT-2
Hendy 302
Miles Aerovan
Miles Aries
Miles Gemini
Miles Hawk Major
Miles Hawk Trainer
Miles Mercury
Miles Messenger
Portsmouth Aerocar Major
Simmonds Spartan
Stampe SV.4

Cirrus Major I
Type: Inline air-cooled inverted 4-cylinder
Bore: 4.72 in (120 mm)
Stroke: 5.51 in (140 mm)
Displacement: 385.64 cu in (6.31 L)
Length: 50 in (1270 mm)
Width: 17.5 in (444 mm)
Height: 30 in (762 mm)
Dry weight: 310 lb (141 kg)
Valvetrain: 1 inlet and 1 exhaust valve per cylinder
Fuel system: 1 Claudel-Hobson carburettor
Fuel type: 73 octane petrol
Cooling system: Air-cooled
Power output: 135 hp (101 kW) at 2,350 rpm
Compression ratio: 5.1:1
Power-to-weight ratio: 0.43 hp/lb (0.71 kW/kg)

Cirrus Major II
148 hp variant.

Cirrus Major III
Higher compression engine
Power output: 150 hp (116kW)

The Blackburn Cirrus Minor is a British four-cylinder, inverted, in-line air-cooled aero-engine that was designed and built by the Cirrus Engine Section of Blackburn Aircraft Limited in 1937.

The Cirrus Minor started as a development of the original Cirrus series of engines which progressed through a number of variants Cirrus I, II, & III. Each with slightly different displacement and power. Later Cirrus was bought by Hermes Engine Company and they produced the Cirrus Hermes I, II, III and IV. Again each differing slightly in displacement and power.

In 1934 Cirrus was bought again by the Blackburn Aircraft company and later that year the Cirrus Minor was produced and in 1935 the Blackburn Cirrus Major was produced.

By 1949 the 100 hp Minor II was permitted to run 800 hrs before overhaul. An increase of 200 hours.

The Minor was known for excellent reliability, and had a major “win” when it was selected to power the RAF’s Taylorcraft Auster observation aircraft. The RAF’s version had several modifications, known as the Series I. Although externally identical, the Series II engine was redesigned to operate on 77 octane fuel, as opposed to the original’s 70, increasing power to 100 hp (75 kW).

Applications:
Arpin A-1 Mk.2
Auster J-1 Autocrat
Auster J-4
British Aircraft Swallow
Deekay Knight
General Aircraft Cagnet
Hillson Helvellyn
Marendaz Trainer
Miles M.68
Miles Gemini
SAI KZ III
Taylorcraft Auster I
Taylorcraft Plus C2
Taylorcraft Plus D
VEF I-12

Cirrus Minor I
Type: Inline air-cooled inverted 4-cylinder
Bore: 3.94 in (100 mm)
Stroke: 5.00 in (127 mm)
Displacement: 243 cu in (4 L)
Length: 39.9 in (1,013 mm)
Width: 17.9 in (455 mm)
Height: 25.6 in (650 mm)
Dry weight: 200 lb (91 kg)
Valvetrain: 1 inlet and 1 exhaust valve per cylinder
Fuel system: 1 Claudel carburettor
Fuel type: 70 octane
Cooling system: Air-cooled
Power output: 90 hp (67 kW) at 2,600 rpm
Compression ratio: 5.8:1
Power-to-weight ratio: 0.45 hp/lb (0.73 kW/kg)

Cirrus Minor II
Power output: 100 hp

The Blackburn Cirrus Midget was a British four-cylinder, inverted, in-line air-cooled aero engine designed and built in 1937 by the Cirrus Engine Section of Blackburn Aircraft Limited. Little is known of its development and use, its sole aircraft application is reported as the Chilton D.W.1 although it is possible that this did not transpire.

Cirrus Midget
Type: Inline air-cooled inverted 4-cylinder piston engine
Bore: 85 mm (3.35 in)
Stroke: 100 mm (3.94 in)
Displacement: 6.33 L (386.3 cu in)
Length: 33.6 in (853 mm)
Width: 14.18 in (360 mm)
Height: 21.65 in (550 mm)
Dry weight: 155 lb (70 kg)
Valvetrain: Overhead poppet valve, one inlet and one exhaust valve per cylinder
Fuel system: Single downdraught carburettor
Fuel type: 87 octane petrol
Cooling system: Air-cooled
Reduction gear: Direct drive, left hand tractor
Power output: 55 hp (41 kW) at 2,600 rpm (maximum power)
Specific power: 0.35 hp/cu in (6.5 kW/L)
Compression ratio: 6:1
Power-to-weight ratio: 0.35 hp/lb (0.58 kW/kg)