Author Topic: The other Bristol Mercury engines  (Read 85 times)

Offline AVTUR

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The other Bristol Mercury engines
« on: September 07, 2019, 09:32:43 AM »
Edit Jo: I have extracted this very interesting discussion from Vixen's Bristol Mercury build so it is not lost and to let his thread focus on his excellent modelling:
 

Sir Roy Feddon, Bristol's chief engineer, had an entirely different view, he loved complexity and elaboration in his engines. He could not leave a design alone, he always wanted to change and 'improve' it. He nearly bankrupted the Bristol Aircraft Company, before they eventually sacked him. I have always been fascinated by the man and his over complex engines. That's why I build so many of them.

Mike

Feddon designed another Mercury. It was a 14 cylinder radial with seven conrods and bigends on each crankpin (unlike a master rod).  The two banks of cylinders were arranged helically around the crankcase. It flew in 1918 in a Bristol Scout and could have been a successful engine if the Ministry of Munitions had not ordered the ABC Dragonfly (probably one of the two worst engines of all time).

AVTUR
« Last Edit: September 09, 2019, 07:29:16 AM by Jo »
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Offline Vixen

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Re: Re: Bristol Mercury revisited
« Reply #1 on: September 07, 2019, 11:31:03 AM »
Hello AVTUR,

Me? I'm strictly AVGAS.

Thanks for reminding us of the earlier 14 cylinder Mercury.

I just happens that I have some full size blueprints for the Brazil-Straker 14 cylinder Mercury dated June 1918. Feddon was the design genius and Butler was his brilliant design draftsman who converted Feddon's dreams into reality. That partnership lasted for over 25 years. You may be able to see the parts callout; all start with FB.

The BS Mercury was unusual in as much as the conrods were lined up one behind the other on the two crankpins. The 14 cylinders were arranged in a double helix rather than in two rows. Apparently the BS Mercury performed well and 200 were ordered for the Royal Navy Air Service. The order was subsequently cancelled, later that year, after the Armistice.

I also have blueprints for the ABC Dragonfly. It looked to be a reasonable engine on paper. In fact it was ordered straight off the drawing board before the first engine was built. By all accounts, it was a dreadful engine, very unreliable with the ability to cook itself almost every flight.

Mike

PS I have no intention of building one.



Brazil-Straker Mercury
« Last Edit: September 07, 2019, 12:24:26 PM by Vixen »
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Offline AVTUR

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Re: Re: Bristol Mercury revisited
« Reply #2 on: September 07, 2019, 12:01:04 PM »
Vixen

We, RRHT at Bristol, know it as the Cosmos Mercury. It looks far more complicated than the Jupiter. I am not sure where I got the idea it had 14 cylinders. The only pictures I have seen of it is in the Scout. Can I request a clearer, more in-focus, picture please?

The Dragonfly ran at a critical speed of its crankshaft.

AVTUR
There is no such thing as a stupid question.

Offline Vixen

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Re: Re: Bristol Mercury revisited
« Reply #3 on: September 07, 2019, 12:40:39 PM »
Hello AVTUR,

You are quite correct it was 14 cylinders and I have gone back and corrected my typo.

The aviation interests of Brazil Straker were purchased by Cosmas Engineering in 1919.  With the ending of the war, Cosmos had no production orders, and their engine repair work was quickly dwindling. The company was soon insolvent. The Cosmos company was then purchased by Bristol's in 1920.

Feddon and Butler joined Cosmos from Brazil Straker and went on to the Bristol Aircraft Company. Together they designed and built many notable radial engines, the Jupiter, Mercury and Pegasus poppet valve engines. Then later, the sleeve valve Hercules and Centaurus engines. And many others besides.

I am also a RRHT (Bristol Branch) member but live too far away to get there regularly.

Mike

PS. I will try and find a better camera to get a better photo of the blue print.
« Last Edit: September 07, 2019, 06:49:22 PM by Vixen »
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Offline Art K

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Re: Re: Bristol Mercury revisited
« Reply #4 on: September 08, 2019, 03:19:10 AM »
Mike,
Sorry I just caught up with this one. Impressive engine and stand to display it, wow. I was trying to find out more about the Brazil-Straker Mercury, you wouldn't believe all the garbage you find when you are looking for one particular thing. I finally found a fuzzy photo on wiki, I'm not picturing the engine layout, does anyone have other photos. I mean it's not even mentioned in Hirschel Smiths book which is sort of the bible of piston aircraft engines, intriguing.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline AVTUR

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Re: Re: Bristol Mercury revisited
« Reply #5 on: September 08, 2019, 09:04:46 AM »
Art

Brazil-Straker Mercury was Feddon's first aeroengine. Before that he and B-S had modified other companies engines particularly the Curtis OX-5. They also made Rolls-Royce engines which precluded Feddon from designing straight or V engines.

The Mercury had a stroke and bore of 5.183" & 4.375" and produced 300hp. In 1918 it flew in a Bristol Scout and impressed the authorities with its performance.

I have no idea how many were made, it may only have been one. I would be very surprised if any still exist. The RRHT has a few photographs of the Scout fitted with the engine.

I think it is very much in the realm of myths and legends.

Mike will probably know more.

AVTUR
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Offline Vixen

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Re: Re: Bristol Mercury revisited
« Reply #6 on: September 08, 2019, 09:42:33 AM »
Hello Art, AVTUR,

There seems to be more interest in the Brazil Straker / Cosmos, 14 cylinder Mercury than in the later 9 cylinder Bristol Mercury

Further reference to the B-S / Cosmos  Mercury can be found in Alec Lumsden's "British Piston Aero-Engines and also in Bill Gunston's "Feddon", RRHT  Historical Series No 26. I will attempt to create a new topic including better quality images of my B-S Mercury blueprints but the will have to be in a few weeks, due to other personal commitments.

As far as I can determine there was only the one example built, which flew successfully in the Bristol Scout. All the photos I have found are small, grainy and fuzzy, printing techniques were not too clever 100 years ago. The original plate photos as well as the engine are lost forever.

Mike
« Last Edit: September 08, 2019, 11:37:30 AM by Vixen »
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Offline Vixen

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Re: Re: Bristol Mercury revisited
« Reply #7 on: September 08, 2019, 11:25:03 AM »
Hello Art, AVTUR,

Did you know there was yet another Feddon designed engine to bear the Mercury name before the definitive Bristol Mercury entered mass production?

The Mercury Mk1 was designed and built in 1926 to compete in the Schneider Trophy seaplane contest held in Venice. This engine was a racing 'special', based on the Jupiter VI but with a shorter stroke, to permit higher revs, and special F alloy cylinder heads. This ground level supercharged racing engine, developed 960Hp on the bench. The Schneider Trophy seaplane was the Short-Bristow Crusader. Unfortunately it crashed before the context, due to a rigging error with the aileron controls. We will never know if it would have beaten the Rolls Royce or Italian contestants.

Mike
« Last Edit: September 08, 2019, 01:00:15 PM by Vixen »
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Offline AVTUR

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Re: Re: Bristol Mercury revisited
« Reply #8 on: September 08, 2019, 05:53:56 PM »
Mike

This is where I get confused. I have assumed that the Schneider Trophy engine was the prototype, or pre-prototype, of the Mercury.

I work in the RRHT archives at Bristol one or two mornings a week. Until recently I knew a lot about gas turbines and almost nothing about the piston engines. (I knew that the Jupiter was Bristol's first engine and the Hercules and Centaurus were the last. I know quite a bit about sleeve valves and I read the book on Feddon many years ago). Our archivist, a couple of months ago, persuaded me to index the engine flight test bed photographs. These cover the whole of the period from the Cosmos Mercury to the RB199 and may be later. I have suddenly become knowledgeable about radial engines, well a little bit more knowledgeable.

I have not seen any photographs of the Short Crusader. The first photograph we have of a Bristol Mercury in an aircraft is dated 1928. The aeroplane is the Bristol Bullpup. The Short Stroke Mercury, a one off, was flown in this aircraft in 1931. We still have that engine in our museum. I attach a photograph of what might be the Short Stroke Mercury. (I am told it is easy to identify, it has fewer cylinder fins than the Mercury. Unfortunately I do not have easy access to one).

I am sure we have documents pertaining to the Schneider Trophy engine but I have not looked for them.

AVTUR
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Offline Vixen

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Re: Re: Bristol Mercury revisited
« Reply #9 on: September 08, 2019, 06:27:14 PM »
Hello AVTUR

That looks like the Schneider Trophy Mercury Mk 1. The straight, no reduction, propeller drive is the give away. The Mk1 Mercury was really a racing 'special' based on what was available at the time, the Jupiter V1 bottom end with a shorter stroke and cylinders together with all the goodies from the future design development shop added. The later marks of the Mercury were a completely different engine with a new crankcase and bottom end and a much improved engine accessories gearbox added to clean up the rear. Each successive mark had an ever increasing number of cooling fins to increase the cooling area as power levels increased with each new mark. Feddon was forever making changes to his engines to constantly increase both power and reliability.

You should find photos of the Short-Bristow Crusader if you can find a copy of the Feddon book in the archives. If you can locate a copy of Lumsden's book, it will help you trace the development history of the various Bristol engines.

The Mercury remained as the smaller diameter, short stroke engine, intended for fighters and fighter bombers. The almost identical Pegasus retained the long stroke dimensions of the Jupiter and was used to power the heavier bombers, transports and seaplanes.

It's a while since I visited the archives at Bristol. I would love to have the opportunity to come and visit you and dig around in the archives to do some research on my  1/3 scale Bristol Jupiter Mk V111. Perhaps we could arrange to meet up. I could bring the Mercury and Jupiter engines with me for the other Trust members to see. Also, I could bring the Brazil Straker Mercury blueprints for you to copy, That's assuming Bristols still have a print room in this modern digital age.

Mike

« Last Edit: September 09, 2019, 07:50:53 AM by Vixen »
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