"Bristol Aero Engines Ltd." started building engines in 1920 but it all started when in 1910 the "British Colonial Aeroplane Co." began to construct aircraft.

-Later it became “Bristol Aeroplane Co. Ltd.”.

“Logo Bristol”

-Throughout its history it was absorbing companies. The first important one was "Armstrong-Siddeley" towards 1958 and the company was renamed "Bristol-Siddeley Ltd (Armstrong-Siddeley belonged to Hawker Siddeley Group at that time).

“Jupiter”

-At the same time, Bristol, entirely or partly, collaborated with, and built under license from other companies such as Gnome, Snecma (M-45), KHD, Fiat, Alfa-Romeo, Hindustan, GE, Turbomeca, SFA and many more.

-The products from the acquired brands made that Bristol's range of engines was one of the most important. Eventually, Bristol was incorporated into Rolls-Royce.

“Anuncio en Francia”

-It is convenient to deal here with the fact that in the Great War, Roy Fedden (later Sir) was technical director and chief engineer of Brazil-Straker, manufacturer of the Straker-Squire automobile engine and in times of war they also constructed the "Falcon", a 275 hp aircraft engine under license from Rolls-Royce for the Bristol fighter and the "Hawk" 100 hp engine for submarine-chaser dirigibles).

-In that period Fedden designed his own engines and when he left, the company became known as Cosmos Engineering Co. (see Cosmos).

“Bristol-Cosmos”

-The first Bristol designs were precisely those from Cosmos.

-They were the “Mercury” that gave 315/347 hp, el “Jupiter” delivering 450 hp and the “Lucifer” with 100 hp.

-The first one that flew was the "Lucifer" and already in 1919 it was tested by Fedden on the Avro 504K.

“Bristol Mercury, drawing”

-With natural development, the Mercury XIV reached 700 hp at 2,600 rpm and the XV model reached 840 hp at 2,750 rpm.

-The XX model delivered 850 hp at 2,650 rpm.

-When in 1920 the Cosmos rights were acquired by Bristol, they installed the Lucifer on the Bristol Monoplane (that during the war was fitted with the 110 hp "LeRhone"), winning in 1922 the Air Derby.

“Lucifer”

-The "Lucifer" was an air-cooled, 3-cylinder, inverted Y engine . It had four valves per cylinder, actuating in pairs.

-The "Lucifer" had several developments, the 118 hp, the 130 hp and in the case of "Lucifer" IV, it was 140 hp.

-The "Mercury" that actually was the first project, was a 9-cylinder radial engine.

-The "Jupiter" was Fedden's second design that even had more power initially. It was in the range of 450 hp.

“Bristol Jupiter, rear view”

-The evolution of the "Mercury" and "Lucifer" was also applied to the "Jupiter", which furthermore proved to be an engine of success.

-This "Jupiter" evolution lasted until WWII, with conventional accessories such as reduction gear, 1- and 2-speed superchargers and turbo chargers,

“Supercharged Jupiter”

-Below, we can see the turbocharged "Jupiter".  We see that the exhaust ducts come together and continue towards the turbo on the top.

“Jupiter turbocharged”

-The Jupiters that were fitted on the Blenheims were already in the range of 800/900 hp while the "Mercury XXXI" reached 950 hp when installed, curiously, in a Hamilcar glider.

“Jupiter VIII F”

-In this early period there was also the "Cherub", which was the lightest of all early Bristol engines with two horizontally opposed cylinders. The Cherub I gave 25 hp at 2,500 rpm, the Cherub II gave 34 hp at 4,000 rpm and the third delivered 32 hp at 2,900 rpm.

-The Cherub model evolution we see in the two figures below. The first one has straight and simple lines.

“Cherub, first versions”

“Three Cherub I views”

-As it was fitted on many light aircraft, the "Cherub" also had a resounding success.

“Another Cherub variant”

“Cherub III, with gear”

-The "Titan", a 5-cylinder radial engine that gave 200 hp, had few applications compared to its fellow engines, but there is no doubt that it helped with their experiences.

-The engine size was small as we can see by the propeller hub.

“Titan”

-The "Neptune" was a rather unknown radial engine that had seven cylinders. It was from 1929 and delivered 300 hp.

“Neptune”

-In 1934, the Bristol Phoenix appears, a supercharged radial Diesel engine with a power output of 635 hp.

-Diesel engines require some supercharge to maintain power at high altitudes, because the power decreases rapidly as during ascending air density decreases. So the low level needs to be restored and the cylinder has to be filled to the maximum so that when compressed, fuel ignition temperatures are reached.

“Bristol Phoenix”

“Bristol Phoenix, rear view”

-In the Phoenix side view we see the front cover of the gearbox, and at the rear stand out the two monobloc diesel fuel injection pumps.

-The next engine was the "Orion" (this engine should not be confused with a later turboprop with the same name). In fact, the "Orion" was a turbocharged "Jupiter".

-The turbocharger is at the rear of the engine at a lower level.

“Bristol Orion”

-The "Pegasus" began its power career at 650 hp and in the beginning it was fitted on Vickers Valenta airplanes (successor of Victoria). The Pegasus 38 with a one speed supercharger already had the power increased to 1,000 hp.

"Bristol Pegasus"

-The "Pegasus" was a 9-cylinder radial and large in size.

-And we use this chapter to show a clearer photograph of the Bristol Pegasus that gave 930 hp at 2,250 rpm.

"Bristol Pegasus"

-The "Draco" was another Pegasus Diesel derivative that was half supercharged. It had nine cylinders and also nearly the identical size.

“Draco”

-And, in the realm of extraordinary engines, we reach the "Hydra", one of the brand's last conventional-valve engines with 16 relatively small cylinders in two radial rows, eight cylinders in each. They faced each other in a way that front and rear cylinders could use the same camshafts on the cylinder heads.

“Bristol Hydra”

-Geared it gave 870 hp at 3,620 crankshaft rpm. This engine did not go into production, for Bristol already concentrated its efforts on engines with sliding sleeves.

-The "Hydra" was called colloquially "Double Octagon".

-Bristol's sliding-sleeve piston engines are the ones with more charisma and which we remember most, against all the engines related in this chapter so far.

-Therefore we have two main groups: conventional-valve engines and sliding-valve engines.

“Double Octogon or Hydra”

-There is mentioned the existence of an engine called Janus with centrifugal compressors and fitted back-to-back.

-These two groups can be listed as follows due to the unique mechanism of the latter:

-First group with conventional valves:
Mercury
Jupiter
Cherub
Lucifer
Titan
Neptune
Orion
Phoenix
Pegasus
Draco
Hydra

-Second group with sliding sleeves:
Perseus
Aquila
Taurus
Hercules
Centaurus

-The origin of the slide valves in Bristol dates back to 1926 when a new line of engines was planned.

-There are several systems of sliding sleeves, and most of them were rejected for their technical and mechanical complexity.

-In fact only two systems survived: Knight and Burt-McCollum, and Bristol decided for the latter.

“Burt-McCollum sleeve”

-The first test was done with a two-cylinder V-engine, after some years of continuous testing, in 1930, they were ready to build an engine of this kind.

-The sliding sleeves were made of austenitic steel, so they could support their new job.

-The conventional valves had prospered because they were filled with sodium, which, when liquefying through the heat, aided cooling and prolong its life, as they were subjected to hard work and heat.

"Cylinder with sliding sleeves"

-With nitrided liner surfaces, the first experimental Bristol motor run at 2000 rpm for 10 hours, in March 1931.

-The most important step taken to advance this engine was the introduction, a year earlier, of a cylinder head with an integral deflector for the mixture turbulence around the spark plug. This process was followed in the following engines, including the Centaurus.

"Sir Roy Fedden"

-The person behind the development of these engines was the omnipresent Roy Fedden.

-Bristol's decision was forced by a number of comparative tests with conventional valves of similar sizes.

-Sleeve-valve engines admitted a higher compression ratio with an equal octane number in the fuel.

-They also improved the engine's atmospheric capacity in its final intake and exhaust stages.

"Bristol Perseus"

-The first sliding-sleeve engine at normal scale was the 9-cylinder, 25-liter engine called "Perseus I" (later the VIII model reached 825 hp and the X gave 950 hp).

-Comparing the Perseus sliding-sleeve cylinder and the Mercury poppet-valve cylinder, we list the following features.

-Perseus :
Diameter/Stroke, 5.75” x 6.5”
Displacement, 168.8 cu.in.
Fin surface area, 2970 in2.
Weight, 42.1 lbs.
m.e.p, 138 lb/sq.in.
rpm. max., 3200.

Mercury:
Diameter/Stroke, 5.75” x 6.5”
Displacement, 168.8 cu.in.
Fin surface area: 2364 in2.
Weight, 46 lbs.
m.e.p, 130 lb/ sq.in.
rpm max., 3000.

-The “Perseus” was followed by the “Aquila”, the “Taurus” and the “Hercules”.

"Bristol Aquila"

-From the "Hercules", which was the one who had more luck, they derived the "Centaurus" as logical development and in search of more power.

"Bristol Aquila, rear view"

"Bristol Taurus"

"Bristol Taurus"

-The Taurus we see above, with 14 cylinders in two rows, gear, and here in the picture, with three-bladed propeller hub without blades.

"Nice gear train on the Taurus"

"Bristol Hercules"

-During WWII they planned to build twin-engined airplanes that were larger than the DH Mosquito and Beaufighter. One of these projects was the Avro Manchester with the "Centaurus" engine that was intended for that aircraft.

-However, because of the difficulty of obtaining great powers, initially four-engine bombers were designed, where, "Hercules" engines were widely used.

-The "Hercules" was built in countless versions in the range of 1,200 / 2,000 hp.

"Bristol Hercules"

-It went into regular operation in 1937 and in 1945 it had increased its capacity by 30% at the expense of only a 10% weight gain.

-The Mark II versions or series were fitted in the Beaufighter; the III, VI, VII and VIII in the Halifax, Lancaster II and Stirlings I, III and IV and also in the York II and in other variants such as Albermale I and II, Wellington, Sunderland, etc. They had 14 cylinders.

-Among the civilian aircraft they were mounted on HP (Handley Page) Hermes, Halifax Transport, Bristol Freighter, Bristol Wayfarer, Viking, ...

-In Spain they were fitted on CASA Azors, and in France it is known that the Noratlas Nords were fitted with them, but in France these engines were produced by Snecma under license.

-The Hercules 100, 120, 130 (series 100) were similar in power at takeoff: 1,675 hp, varying performances of maximum power and maximum continuous. The 630 already gave 1,800 hp.

“Hercules Power Egg”

-The Hercules engines have been in production for many years and until recently they were in operation.

-On the Casa Azor and on the Noratlas (Nord 2501), the conventional, maximum performance fairing, known as "Power Egg", has not changed in essence. It remains essentially the same on the Sunderlands, etc.

-Sleeve-valve engines have little frontal area, as the cylinders do not have heads with valves, which makes the fairing ring to have less diameter and be significantly smaller.

-In many cases the cooling air is forced with front fans that are fitted on the propeller hub.

"Bristol Centaurus"

-The "Centaurus" accumulated 2,500/2,800 hp with 18 cylinders in two rows with a two-speed supercharger.

"Bristol Centaurus"

-By 1945 the "Centaurus" was only 3'3 inches more in diameter than the "Hercules", it was one of the most powerful engines in the world at that time and at the end of the war there was a comparison table with the following engines:

W. Cyclone R3350	18 cyls.	55.1	lts.
Napier Sabre	24 cyls.	36.6	lts.
PW D-Wasp R-2800	18 cyls.	45.9	lts.
DB 603	12 cyls.	44.5	lts.
Hercules	14 cyls.	38.7	lts.
RR Griffon	12 cyls.	36.7	lts.
Centaurus	18 cyls.	55.6	lts.

"Centaurus, accessory side"

-From the Centaurus 660 series, the 661 and its military version (the -165) are presented below. These pictures are taken from the factory's presentation catalog.

"Centaurus 661"

-Each of the 18 cylinders is placed within an integral deflector giving the engine a completely different look than usual. It has 3,270 cubic inches of displacement. The military version had water/methanol injection for takeoff.

“661 cylinder”

-The Centaurus had its most outstanding applications in the Tempest II fighter, the Shetland seaplane, in the Warwick V and the "Double Centaurus" version with 5,000 hp for the Bristol 167 "Brabazon" with contra-rotating propellers.

"Double-Centaurus"

-To complement the picture of the two Centaurus engines for the Brabazon aircraft, below, we show the whole in a diagram, with its gearbox and transmissions for the two contra-rotating propellers.

"Double Centaurus diagram"

-The "Saturn" (BE-22) that gave 3750 lbs. of thrust, went on the Folland Gnat.

-The "Zephyr" was a commercial two-shaft turbojet derived from the Olympus 2000, and delivered a thrust of 16,000 lbs.

-Other information indicates that it was the proposed name for the Orion when it was passed to Wright (USA).

-Reviewing sleeve-valve engines, we go back in time to show some piston engine ads such as this Perseus one from 1939.

"Bristol Perseus ad"

-And the Bristol Taurus and Hercules ad from 1942, during WWII.

"Bristol ad during WWII"

-Towards the end of WWII, Roy Fedden initiated the study and construction of another "Orion" that had 18 cylinders and a displacement of 4142 cubic inches, rated for 4000 hp, but ....

-Bristol started its entry into the turbine era with turboprop "Theseus", although confidences within the company mention early experiments with gas turbines in 1924.

"Theseus diagram"

-However, the Theseus is from 1945.

-It was the first officially approved turbine in turboprop version in the world.

"Theseus, cutaway"

-It made the first flight occupying the outboard engines of an Avro Lincoln.

-The Type I's power was 1950 SHP (hp at shaft) plus 500 lbs. of thrust provided by the exhaust.

"Theseus"

-A double turbine drove a 9-stage axial compressor and one centrifugal compressor. A third turbine drove a 4-blade propeller (initially).

"Theseus with 5-blade propeller"

-The twin-Theseus, or "Double-Theseus" was fitted on the "Brabazon II".

-The Bristol "Proteus" was produced after the experiences with the "Theseus", under direction of Chief Engineer F. W. Owner.

"Proteus diagram"

-The "Proteus" is characterized by its reverse flow compressor. It delivers over 4,000 SHP and has, until recently, its main application in the Bristol Britannia and the Canadair CL-44.

“Two views of a Proteus”

-From the Proteus they made a turbojet version called "Phoebus".

-The "Double-Proteus" was installed on the Princess, a huge Saunders-Roe flying boat.

"Double - Proteus"

-The opposite is true for the B-25 that was a byproduct of the "Olympus". For example, the Olympus from which it was derived delivered 4990 Kgs. of thrust, and the BE-25 gave 4300 SHP at an altitude of 5300 meters.

"Bristol BE-25"

Go to Bristol part 2