Author Topic: Bristol Mercury revisited  (Read 1556 times)

Offline Vixen

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Bristol Mercury revisited
« on: August 30, 2019, 12:57:48 PM »
Some years ago I built two 1/4 scale models of the Bristol Mercury MK VIII radial engine. One of the engines was displayed in an 'exploded' format so as to show both the external and internal details. The other engine has been assembled and one day will become a runner.

The 'exploded' Mercury was mounted on two display stands. One showed the external or outer components, such as the crankcase, the supercharger housing, the reduction gearbox housing etc. While the second display stand showed the internal workings, such as the crankshaft, conrods and pistons. In fact, the mechanisms from each of the engine's subsection was displayed individually and each was able to rotate to demonstrate it's function. The nine cylinders were distributed between the two display stands with outline drawings of the missing cylinders, where appropriate.



Here are the two display stands as they were exhibited at the 2010 Model Engineer Exhibition at Sandown Park. The Bristol Mercury was awarded the Bradbury Winter Trophy and a Gold Medal. A full write up on the displays can be found at http://modelengineeringwebsite.com/Bristol_Mercury_VIII.html. Click on any image and it will enlarge, click on it again to zoom right in and see all the detail.

Although the two display stands were award winners, I was never fully satisfied with them. Two stands required a lot of table space and storage. I also felt they divided the viewers attention between the two. So I decided I would try and combine the two display stands into one and still be able to tell the story of how each component worked as part of the whole engine.

I made a start by combining the accessories gearbox and drives into the rear casing of the engine. I still wanted to show the accessories gearbox.in the 'exploded' format.







As you can see the accessories gearbox is a complex affair. The inertia starter motor is attached to the rear face. The interrupter gear, which prevents the machine guns from shooting off the propellor, sticks out of the top. The dual magnetos attach to either side and the pressure and scavenge oil pumps do likewise at a lower level. The long quill shaft takes the stater motor power into the heart of the engine and is also used to transmit engine power to drive all the accessories. it is possible to turn the quill shaft by hand which rotates all the internal gears and drive shafts.

The centrifugal supercharger drive were the next components to be combined.





The star shaped impeller and the spiral diffuser vanes can be seen at the rear of the supercharger core. On the other side is the 'speed up' gear train which spins the impeller at 7 times engine speed. The central gear is a 'spring gear' which cushions the high speed gears from any engine crankshaft  fluctuations.

There is a lot more work still to be completed. The biggest challenge being a new central  clear perspex panel to display all nine cylinders, pistons conrods, crankshaft within one half of the crankcase housing.

Hope you will like the new display

Mike
« Last Edit: September 06, 2019, 09:01:49 PM by Vixen »
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Offline steamer

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Re: Bristol Mercury revisited
« Reply #1 on: August 30, 2019, 01:49:12 PM »
 :o :AllHailTheKing:

Oh man that is beautiful work Mike!   Are you getting finished detail drawings of the original to start with, or are you taking pictures and diagrams and making the drawings yourself?

Dave

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Online b.lindsey

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Re: Bristol Mercury revisited
« Reply #2 on: August 30, 2019, 02:03:09 PM »
Totally awesome Mike!!  Wow!!

Bill

Offline Johnmcc69

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Re: Bristol Mercury revisited
« Reply #3 on: August 30, 2019, 02:55:12 PM »
What a beautiful display! I look forward to your progress with it.

  :ThumbsUp: :popcorn:

 John

Offline Old Bill

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Re: Bristol Mercury revisited
« Reply #4 on: August 30, 2019, 03:17:18 PM »
Hi Mike.

I must admit that I do like your display. This is such a complex engine that when assembled, one cannot appreciate the work involved and it is wonderful to be able to see how it works. The only down side is that you had to make two! I look forward to seeing it again in its new incarnation.

What do you do in your spare time?

Steve     :ThumbsUp:

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #5 on: August 30, 2019, 03:18:52 PM »
  Are you getting finished detail drawings of the original to start with, or are you taking pictures and diagrams and making the drawings yourself?

Dave

I have the Works handbook for this engine. I contains over 30 small size copies of the original builders blue prints. They are highly detailed and very accurate. I have digitised these into AutoCAD and have produced a full set of model part drawings form them. There must be several thousand piece parts in that engine. I have also had complete access to photograph stripped down Mercury Mk VIII engines at ARC at Duxford. So no excuses for lack of detail.

Mike
« Last Edit: August 30, 2019, 03:24:00 PM by Vixen »
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Offline Vixen

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Re: Bristol Mercury revisited
« Reply #6 on: August 30, 2019, 03:22:39 PM »

What do you do in your spare time?

Steve     

Steve, I don't have any spare time, I'm retired. :old:

I was busy building  these two Bristol Mercury engines when we worked together, and that was a long time ago.

Mike
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Online Jo

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Re: Bristol Mercury revisited
« Reply #7 on: August 30, 2019, 04:51:48 PM »
The sectioned Mercury always went down well with the public at shows, you will have to starting bringing it out again  8)


What do you do in your spare time?

Steve     

Steve, I don't have any spare time, I'm retired. :old:

I was busy building  these two Bristol Mercury engines when we worked together, and that was a long time ago.

I agree being retired does not mean you get any spare time  :disappointed: :toilet_claw:

Mike thought you were working on your ploughing engine back then :noidea:

Jo
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Offline Roger B

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Re: Bristol Mercury revisited
« Reply #8 on: August 30, 2019, 05:36:43 PM »
That is a splendid display  :praise2:  :praise2: I would like to see it for real one day  :)  :wine1:
Best regards

Roger

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #9 on: August 30, 2019, 05:56:28 PM »
The sectioned Mercury always went down well with the public at shows, you will have to starting bringing it out again  8)
Mike thought you were working on your ploughing engine back then :noidea:

Jo

I took/ take the Mercury to all the indoor shows I can get too. Unfortunately they are now very few in number, now that Guildford, Bristol and the MEX at Sandown have all stopped.

I started the Mercury engines and drawing more than 20 years ago, I cannot remember precisely when Steve left us.. The Fowler Plowing Engine was started back in the mid 1980's soon after I moved to Hampshire and set up my first ever machine shop.

Mike
« Last Edit: August 30, 2019, 08:55:19 PM by Vixen »
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Offline Ye-Ole Steam Dude

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Re: Bristol Mercury revisited
« Reply #10 on: August 30, 2019, 06:42:39 PM »
Hello Mike,

Incredible work and a wonderful display.

Have a great day,
Thomas

Offline Admiral_dk

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Re: Bristol Mercury revisited
« Reply #11 on: August 30, 2019, 09:11:23 PM »
Wow - jaw dropping .... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #12 on: September 02, 2019, 04:19:48 PM »
.... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:

Per; Every big project is really a series of small projects joined together.      As for easy... what's the challenge in that?.



There are some more photos of the Mercury supercharger assembly.

The supercharger's outer cover was a single casting on the full size engine, I machined mine from solid, as you can guess, there was not much left of the billet when I had finished, it did produce a bucket full of chips.

In these photos you can see the machined from solid rear cover, the machined from solid carburettor inlet manifold and the nine lost wax cast outlet manifolds which feed the fuel mixture to the nine cylinders, two pipes per cylinder. The copper pipework is part of the fuel priming system used during engine start up. The bearing in the center of the unpainted cover disc, supports the quill shaft for the Accessories Gearbox, featured in the first post of this topic.








The supercharger drive gearbox with the star shaped impeller and diffuser fits inside the rear cover to form the outer annular space (plenum chamber) which feeds the outlet ports.

The fuel mixture from the double barreled, updraft, carburetter enters the bottom of the supercharger at the rear. The fuel mixture spirals inside the rearcover into the centre hole, where it enters the eye of the fast rotating impeller. The fuel mixture if flung outwards at high velocity into the diverging diffuser ducts. The airflow velocity is slowed down in the diffuser ducts, which convert the velocity change into a pressure change. The pressurised fuel mixture collects in the outer annular plenum chamber and is distributed equally to the nine cylinders.







The supercharger assembly forms a very compact unit which bolts to the rear of the engines crankcase by the same nine bolts which hold the two halves of the crankcase together

I am proposing to keep the two halves of the supercharger separated on the display stand, so that the internal workings can be seem and explained.

Mike



« Last Edit: September 06, 2019, 07:30:56 PM by Vixen »
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Offline Vixen

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Re: Bristol Mercury revisited
« Reply #13 on: September 06, 2019, 07:28:51 PM »
Some more work combining the two 1/4 scale Bristol Mercury display stands into one.

The next section to receive attention was the Cam Gear, which is located at the front of the front Crankcase half. The circular cam barrel is driven from the crankshaft via an eight to one gear reduction; it rotates coaxialy around the crankshaft, but in the opposite direction. There are two cam rings, the forward one operates the inlet valve pushrods and the rear one the exhaust push rods. Each cam ring has four lobes which act against a total of eighteen roller cam followers.

As you can see, the Cam Gear is very compact and neatly integrated into the front half of the crankcase.

In the working engine, the bearings for the intermediate gears of the eight to one reduction.gear train, are part of the adjoining thrust plate. I had to make a small perspex bracket to support the bearings for this exploded display.

That twenty tooth wheel in the centre, is the splined coupling which connects the crankshaft to the reduction gearbox, located at the very front of the engine. I will get to explain the reduction gearbox a little later.
 







I decided to make a start on the new central perspex panel, which will eventually support the cylinders, pistons, conrods and crankshaft. The new clear perspex panel measures 19" by 16 " and is 8 mm thick. I knew it was going to be a fight to machine all of the cutouts on my small mill. It has a total travel of only 8" x 4". but this was just enough.  The panel needed to be carefully positioned for each cutout, as the confines of the machines cabinet only added to the fun and games. Eventually, I was able to machine about 80% of the features and completed the remainder with a saw and hand files.

The intention is to have the bottom four cylinders bolted to the crankcase while the upper five cylinders are displaced outwards to reveal the workings of the master and slave conrods.







The biggest drawback with machining and handworking perspex is the enormous amount of fluffy white swarf it produces. The only answer is to have the Vacuum extracting the fluff and dust continuously. A very noisy process.

Mike

« Last Edit: September 06, 2019, 08:05:53 PM by Vixen »
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Offline Admiral_dk

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Re: Bristol Mercury revisited
« Reply #14 on: September 06, 2019, 09:53:02 PM »
Quote
Quote from: Admiral_dk on August 30, 2019, 10:11:23 PM
.... Mike do you EVER do things the easy way ...?... or for that matter have any small projects ...  :thinking:

Per; Every big project is really a series of small projects joined together.      As for easy... what's the challenge in that?.

OK - I admit, that was the wrong question ..... probably because most of my constructions are meant to go into production, where simpler (usually) => the smaller amounts of errors and time consumed => less cost, etc.

I look forward to see the end result  :cheers:   :popcorn: