Bristol Orion

Nick Sumner

Live! From the Belly of the Beast!
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31 May 2006
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I hope the moderators won’t mind me posting this here – the ‘Engines’ forum seems to be only about jets.

There is some info about a Bristol aero engine named the Orion in 'Fedden - The Life of Sir Roy Fedden' by Bill Gunston published by the Rolls Royce Heritage Trust. Pages 244 - 248 has information, diagrams and comparative drawings of both the Orion and a 4 row 28 cylinder 5 3/4 in bore by 7 in stroke engine.

The Orion was basically a bigger Centaurus, ie 18 cylinders in two rows of nine, 6 1/4 in bore and 7 1/2 in stroke. It was expected to achieve 4000hp.

The unnamed 28 cylinder does not appear to be a 'corncob' design from the diagram, it looks similar to the BMW 803 layout - ie row 3 is directly behind row 1 and row 4 is directly behind row 2. However, although it has Centaurus bore and stroke, 28 cylinders means 4 rows of 7 rather than 4 rows of nine so there is more room for the air to circulate. It is also noticable that the cowling outline is well clear of the cylinder heads - again giving more circulation room - whereas Hercules, Centaurus and Orion were (or were to be) very closely cowled.

Here are links to the drawings of the Orion, 28 cylinder engine and a couple of other interesting tidbits from 'Fedden - The Life of Sir Roy Fedden' by Bill Gunston. A fascinating book, I recommend it.

I apologise for the large file sizes but there is a lot of detail and some tiny printing I thought might be useful.

Obviously this is copyright material so personal use only!
Thanks a lot for the post Nick, very interesting!

Amazing engines...we are really talking about 4500 hp? :eek:

About the topic, I think that it would be better posted at "engines" but Paul will see...don't worry.


Here is the text from the book relating to the Orion

"The team at Somerdale was enlarged, and work began on what Fedden had finally concluded must be started at the earliest possible date: a new engine much more powerful than the Centaurus. Under the revived name Orion, a study was made for an 18-cylinder radial with a bore of 6'/a in and capacity of 4,140 cubic inches. It incorporated several features planned for future models of the Hercules and Centaurus. One was an exhaust system with the pipes discharging straight to the rear from aft­facing ports. Another was a new design of head consisting of a close-finned copper base, with nickel-plated flame face, shrunk into a steel body. The Orion was drawn in detail by Butler in early 1941, and promised to be a superb engine rated at an initial power of about 4,000 hp. Several airframe constructors welcomed it, and Arthur Gouge (Short Brothers) and Rex Pierson (Vickers) began projects for large bombers and flying boats using four or even six. Such very big machines appeared certain to be needed - in peace, if not during the War - and the one thing Fedden wanted to avoid was having to couple together groups of smaller engines.

"With the Centaurus he had what appeared to be the most powerful aero engine in the world. With the Orion added at the top end of his family he considered the Bristol company would be able to offer an unbeatable range of engines, not only to win the War - which he said in 1941 would probably last until 1946 - but also to win the fierce commercial battles of the ensuing peace.

"Fedden was frankly and totally committed to the sleeve-valve piston engine, which he was certain would be needed up to at least 1955 and probably later. He had no doubt his company could - if it had the strategic judgement and motivation - be the world leader in piston aero engines during the whole of this period, providing the foundation for a world-beating series of British aircraft. It is characteristic of Fedden that, in early 1941, in the grimmest period of the War and long before the formation of any Brabazon Committee to study the problem, he was deeply engaged in considering the design of the aircraft for the post-war period. It was partly because of this that he appreciated the importance of the Orion."

I can't recommend the book too highly - its excellent. Fedden did two reports on the UK aircraft and aero engine industries, one, before the war as a comparison with the German aircraft industry and one at the end of the war in comparison with the US industry. They make for fascinating reading.
Perhaps the best location for this? Un-used high-powered Bristol

Centaurus 663: Development of the 661 designed for the Type 175 Britannia, used water-methanol injection to achieve 2,850hp
Centaurus 873: Commercial version of the 373 (used in the Beverley), water-methanol injection Direct-Petrol-Injection (D.P.I) for 3,160hp at take-off and capable of 3,220hp max at 3,000ft
Turbo-Centaurus: Stage II 373 development rated at 3,600hp (I assume turbo-compound), not pursued

Hercules 815: 2,310hp, reported in the late 1950s, I assume D.P.I development of the earlier 730 series
Fascinating and excellent stuff.......
Would it be possible to amend the topic's title to make clear that it refers to the Orion piston engine, and thus avoid confusion with the later Orion turboprop?

robunos said:
Fascinating and excellent stuff.......
Would it be possible to amend the topic's title to make clear that it refers to the Orion piston engine, and thus avoid confusion with the later Orion turboprop?


And 1940s Orion piston engine at that, there was one in 1926 as well, a turbocharged Jupiter variant; the name does not seem to have been lucky for Bristol!
JFC Fuller said:
... there was one in 1926 as well, a turbocharged Jupiter variant...

That's a new one for me...


Clearly the injected Centaurus never made it on to the Beverley or, indeed, anywhere else.
Johnbr said:
Did the Orion get to the prototype stage.

Unclear, it seems that prototype cylinders were built but I can not find any evidence to say how far construction of the whole engine got. It was apparently started in August 1942 and was cancelled some time in 1944, at the very least a single cylinder rig was run.
Yes it did .. I'll add to this post after a dig....
See also my posts on 'increasing the charge' here.
The 1920s saw a great deal of turbocharger work in the UK driven by Jimmy Ellor at RAE (who became in mid 20s RRs Supercharger guru after he helped sort out the Kestrel supercharger).
A Jupiter was modified (lashed up!) to take a turbo and was successful enough on the Seely Tourer aircraft for a 'proper installation to be designed under a Ministry contract. This was designed around the Jupiter VI and an RAE turbo design becoming the Orion. It ran in 1928, installed in a Gloster Gamecock it went to 20,000 ft in 12.75 minutes and delivered 495 bhp at that altitude. Cooling problems were severe however with the casing distorting enough for the impeller to rub. The Air Ministry lost interest at this stage and Roy Fedden although excited by possibilities of the system had too many other challenges to contemplate spending Bristol cash on this one so it was put on the back burner.
The picture shows 'spaghetti junction ' Jupiter on left; Orion on right.


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I'm not sure if this is a new source of info for the experts

Membership is only $12
Charleybarley... it is a link Orion radial piston engine.
This seems like the most appropriate thread for this, the Hercules VIII, this apparently being from the family with the two-stage Supercharger as described in "By Jupiter: The Life of Sir Roy Fedden" by Bill Gunston.



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