Ollie, thank you for matching the part number and the compression ration to Jupiter IX. Still, when I look in the IX manual, the finning is the ‘old type’. The only way this particular cylinder would make sense is as a test cylinder on what ultimately became the Pegasus development program. Certainly the histories show that Bristol Engines ran many trials on single cylinder test rigs.

Based on a Pegasus type cylinder, compression ration of 5.3:1, bifurcated inlet and nothing else making sense I now think this is a test cylinder or part of a Bristol Draco engine, an experiment in direct fuel injection.

Balance and the effort to balance

p&p#29: managing “creatives”. The British way (=class system) segregated “hands” totally: Fedden was not the only innovator to be denied Board status: WEW Petter, Barnes Wallis, AE Hagg (by Sir Geo. DH), J.Lloyd (by JD Siddeley), Whittle and O.Short (Nationalised, as “too difficult”)…many auto designers. S.Camm and G.Edwards were made to wait. Board issues were on a higher plane.

Today in such as media/advertising, the suits and the creatives only thrive if they find a way to bring ideas down to earth…unlike, say this Wallis quote: ‘“practical shop element of personnel (was) bitterly opposed to (my) geodetics” S.Ritchie,Industry & Air Power, P83, who adds: ‘(He) was persuaded to accept design changes in the interests of cheapening manufacture’. Quite. See Napier for the consequences of untrammelled creatives.

alertken, when the balance is found wonders can happen. I figure an ultimate creative was Churchill, often rejected in usual times, but supreme in unusual times. How much he internalised the tension between creativity and discipline or had the wisdom to surround himself with strong personalities to balance his own energy may never be clearly delineated. Alanbrooke, CIGS of British High Command certainly fought him ferociously, in goodwill, to align the war effort to what was possible.

Fedden himself was Bristol ‘Old Family’ certainly if he curbed his relentless energy he could have “fitted in” more easily, but he made it hard. He is one man who refused Churchill’s request to coordinate aircraft production during the war, citing his work at Bristols as being more pressing. So he certainly made it easier for his enemies to push him aside.

Nevil Shute in “Slide Rule” reflects that it was the British aristocracy, prior to estate taxes, that combined the surplus capital and eccentricity to fund highly risky ventures in aviation, and to do this on a grand scale. Bristols certainly took great risks in entering into aviation. Perhaps the closest analogy today is the money being spent by Virgin on spaceflight. If only Fedden could have bit his lip and if only the Bristols board could have been more patient. What has happened, has happened. Still, after all this time, stripped of high emotion, Fedden was an incredible inventor and the Jupiter a remarkable engine.

Forged

It looks forged to me. Difficult to tell without a close-up look but there doesn’t seem to be any casting ‘draft’ on the circumferential cooling fins above the cylinder. Is it in your possession?

Although many air-cooled radials had cast cylinder-heads the Bristol radial was a far superior product! 😉

Here are some close ups of the head, I would say forged, and with comments on further post, a late Jupiter cylinder. I have looked through all AP’s for Jupiter III, IV, VI, VII, VIII, IX, XI and Pegasus. It has the Jupiter features of the retaining bolts on either side of the pushrods but the fine finning of the Pegasus. The Pegasus had the same bore and stroke as the Jupiter, but with finer finning and other improvements it was decided to rename it the Pegasus. The Pegasus ultimately became a 1,000 HP engine, not a bad development cycle for a 1920’s design, testament to improving metallurgy, better production techniques, supercharging and higher octane fuel.

In ‘By Jupiter’ by Bill Gunston, pg 56
“By 1931 Fedden had supervised many thousands of hours of running of…new cylinders of Jupiter size…these had roughly 50% greater cooling fin area, obtained by deeper and more closely spaced fins…the crankshaft was redesigned with larger diameter crankpin and stiffer webs…the connecting rods were of different form..a new full skirt piston was designed and a very obvious change was was the redesigned valve rocker gear and pushrods were totally enclosed..When all the improvements were incorporated in the Jupiter sized 1753 cubic inch engine the result was such an advance it was given a new name in 1932 : the Pegasus”

Does anybody have any illustrated parts manuals for Jupiter engines or technical information on metallurgy or production ?
Can anybody match the parts numbers ?
How far is the school from Bristol ? I wonder if this cylinder was a lab rat used in the Pegasus development program.

Jupiter cylinder, we are on our way !

Here is a Jupiter cylinder that was found during a building demolition in 1983 and thankfully saved from the scrap bin. At this stage I cannot tell if it is a forged or cast head, but it is an early cylinder. I will have to go through the APs to try and identify the exact engine model. It has a great amount of detail, the valve gear, tappet arrangements, inlet and retaining arrangement. There is a wealth of detail for metallurgical analysis and reverse engineering. If it is possible to reverse engineer nine cylinders with all this detail then maybe 30% of a Jupiter is reborn !

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Here is the story of how it was found. If anyone knows the location perhaps its history and context can be more fully understood :

I was working as a excavator driver and was given the job of helping demolish the old Earls Colne grammar school , it was a school I had attended a few years earlier ( not a grammar school at that time as they were being phased out )
I looked down from the cab of my JCB and saw laying in the brick rubble this aircraft cylinder , at that time I was very much into motorcycles / engines etc so had a general interest in anything like that , it obviously did not interest any of the other workers as no one had picked it up so I jumped out and put it in the footwell of the JCB ,this would have been c 1983 .
I do remember an old wooden hut used by the Air Cadets after school hours ( I think it was sky blue and I’m sure even had the RAF bulls eye / target painter on the apex of the shed ( sorry I don’t know the correct term ) and I believe the cylinder must have come from there when the shed and school buildings were knocked down or dismantled .

To sum up Earls Colne Grammar was in Essex UK , I went to school there in c 1974 until 1976 before moving onto Halstead Essex Ramsey school leaving in 1980 ,and returned to Earls Colne to demolish it in 1983/ 1984 ( could be a year or two out on that ) I don’t know when the Air Cadets finished but the school was unused for several years before being demolished.