Author Topic: Bristol Mercury revisited  (Read 1558 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:

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #15 on: September 06, 2019, 11:33:18 PM »
Hello Per,

You make a very good point about production v simplicity = minimum errors, least time and lowest cost etc.

I believe Henry Ford's design philosophy was "simplify and add lightness". The Ford Motor Company didn't do too badly.

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.

For a successful business, "time is money", however, when you are retired "time is for pleasure"

Mike
« Last Edit: September 06, 2019, 11:42:29 PM by Vixen »
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Online Jo

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Re: Bristol Mercury revisited
« Reply #16 on: September 07, 2019, 06:21:03 AM »
For a successful business, "time is money", however, when you are retired "time is for pleasure"

I prefer to think that in retirement that "both Time and Money are finite" the trick is to make sure one doesn't run out before the other and to make the most of both of them  ;)

Jo
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Offline Vixen

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Re: Bristol Mercury revisited
« Reply #17 on: September 08, 2019, 05:47:10 PM »
So back to the plot. It's time to put away the history books and look at progress with the new Bristol Mercury VIII display stand.

The new central display panel will mount all nine cylinders and the crankshaft assembly. Here you can see the crankshaft assembly. The difference in robustness of the master rod compared to the eight slave rods is quite noticeable. The single throw crankshaft is made of two pieces, which are bolted together at the rear by the large maneoton pinch bolt. The mass of the pistons and conrods is counterbalanced by adding weights to the  crankshaft. The weight on the rear half is slightly larger than the front to counteract the added weight of the maneoton bolt. At the front, is the splined coupling which drives the 2:1 reduction gearbox.







I have decided to bolt the lower four cylinders in place on the rear crankcase half and position the other five cylinders outboard, so that the interior details remain visible.







It was Bristol's practice to position the master rod in one of the lower cylinders, number 6. The lower cylinders are always more oily than the others, due to gravity. The master rod does it's own share of the work plus a small contribution of work from each the other eight cylinders and so benefits from the additional lubrication.







This is the new central panel with all nine cylinders attached. The pistons for the five upper cylinders are guided by clear perspex shoes running in radial slots. The whole assembly will rotate to demonstrate the fluid motion of the nine pistons but at the moment it is very stiff. I am trying to avoid the use of any oil, because it dries out over time and is bound to leak, just like any other radial engine.







I am pleased with how this new symmetrical display has turned out. There is still work to be done with the cam gear and reduction gearbox sections but they should not take too much effort. Then everything needs to be taken apart, cleaned dusted and polished before the final assembly.

Mike

« Last Edit: September 09, 2019, 11:46:29 PM by Vixen »
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Offline Vixen

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Re: Bristol Mercury revisited
« Reply #18 on: September 09, 2019, 08:19:33 AM »
A new topic titled "The other Bristol Mercury engines" has been specially created  for discussions relating to the Mercury emgine's background and history.

Mike
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Online sco

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Re: Bristol Mercury revisited
« Reply #19 on: September 09, 2019, 12:20:01 PM »
Terrific pictures of the new display layout Mike - would love to see it in the flesh too!

Simon.
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Offline Vixen

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Re: Bristol Mercury revisited
« Reply #20 on: September 09, 2019, 12:37:17 PM »
Hello Simon,

We need to arrange a visit to you up in Brackley.

Mike
« Last Edit: September 09, 2019, 09:02:58 PM by Vixen »
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Offline Craig DeShong

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Re: Bristol Mercury revisited
« Reply #21 on: September 09, 2019, 11:21:36 PM »
Mike

I open ALL your new posts and read and look through them but I usually close them without making a comment.  I do this, not because I have no comment to make, but because they always leave me speechless. 

I have no words to describe the caliber of work I see in your posts, but I do enjoy reviewing them.  Thanks for bringing them here for me (and us) to enjoy.
Craig

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #22 on: September 10, 2019, 08:19:46 AM »
Hello Craig,

Thanks.  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Model engineering is very important to me. It gives me immense pleasure and satisfaction and somewhere to go when life gets tough. I feel lucky to be able to share what I do, with you guys and gals on the MEM forum. It's the membership of the MEM forum who make it such a very special place to hang out.

Mike
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Offline Johnmcc69

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Re: Bristol Mercury revisited
« Reply #23 on: September 10, 2019, 02:52:34 PM »
 :ThumbsUp:
 Outstanding work Mike! Really going to be a spectacular display!

 John

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #24 on: September 11, 2019, 02:41:22 PM »
Thanks John,

The final part of the Bristol Mercury jigsaw is the propellor speed reduction gearbox, which is mounted at the very front of the engine. The 2:1 reduction is achieved in a compact bevel, epicyclic gear set. The large bevel gear at the front, is rigidly bolted to the bell shaped outer cover and does not rotate. The large bevel gear at the rear is rotated by the engine's crankshaft via the splined coupling. The three smaller bevel pinions rotate the splined propeller shaft at half the speed of the crankshaft. The 2:1 speed reduction allowed a much larger diameter and therefore more efficient propeller to be used. The large diameter thrust bearing at the very front, transmits the whole of the propellers thrust into the bell shaped cover. The engines crankshaft does not see any of the propeller's thrust force.

The normal cruising speed for the Mercury Mk VIII was 2400 RPM, while the maximum speed (at takeoff boost) was 2650 RPM. The actual propellor speed being half of that.






For the 'exploded' display, I did not want to hide the reduction gears within the bell shaped cover, in there, it would have been completely out of sight. I decided to manufacture a completely new perspex front upright, so that the reduction gearbox could be displayed immediately below the bell shaped outer cover.




This is how the front of the new display turned out. A few weeks work has completely transformed the 'exploded' display.
That's my other big radial engine, the 1/3 scale Bristol Jupiter in the background




There are still one or two bits to sort out, but the majority of the changes to the 'exploded' Bristol Mercury Mk VIII display have now been completed. My wife and I are about to depart for a late summer holiday to belatedly celebrate our 50th wedding anniversary. I will quickly finish the Mercury display when we return, then it's back to work on the Jupiter engine.

Mike




« Last Edit: September 11, 2019, 02:45:42 PM by Vixen »
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Offline AVTUR

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Re: Bristol Mercury revisited
« Reply #25 on: September 11, 2019, 03:40:41 PM »
Mike

Have a good holiday. I think you need it after such a tour de force.

AVTUR
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Offline cnr6400

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Re: Bristol Mercury revisited
« Reply #26 on: September 11, 2019, 06:57:36 PM »
Outstanding work Mike, well done!  :ThumbsUp: :ThumbsUp: :ThumbsUp:

Offline Admiral_dk

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Re: Bristol Mercury revisited
« Reply #27 on: September 11, 2019, 10:07:38 PM »
Enjoy the holiday with the missus Mike  :cheers:

I really think you dramatically improved the display of you fantastic build here - before it was almost two not related engines, and now it really appears as a single unit - just slightly "exploded" to allow an inside peak  :whoohoo:

Per

Offline Steamer5

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Re: Bristol Mercury revisited
« Reply #28 on: September 12, 2019, 05:46:39 AM »
Hi Mike

Thatĺs just jaw dropping......

Cheers Kerrin
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Offline steamer

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Re: Bristol Mercury revisited
« Reply #29 on: September 12, 2019, 02:08:54 PM »
Thanks John,

The final part of the Bristol Mercury jigsaw is the propellor speed reduction gearbox, which is mounted at the very front of the engine. The 2:1 reduction is achieved in a compact bevel, epicyclic gear set. The large bevel gear at the front, is rigidly bolted to the bell shaped outer cover and does not rotate. The large bevel gear at the rear is rotated by the engine's crankshaft via the splined coupling. The three smaller bevel pinions rotate the splined propeller shaft at half the speed of the crankshaft. The 2:1 speed reduction allowed a much larger diameter and therefore more efficient propeller to be used. The large diameter thrust bearing at the very front, transmits the whole of the propellers thrust into the bell shaped cover. The engines crankshaft does not see any of the propeller's thrust force.

The normal cruising speed for the Mercury Mk VIII was 2400 RPM, while the maximum speed (at takeoff boost) was 2650 RPM. The actual propellor speed being half of that.






For the 'exploded' display, I did not want to hide the reduction gears within the bell shaped cover, in there, it would have been completely out of sight. I decided to manufacture a completely new perspex front upright, so that the reduction gearbox could be displayed immediately below the bell shaped outer cover.




This is how the front of the new display turned out. A few weeks work has completely transformed the 'exploded' display.
That's my other big radial engine, the 1/3 scale Bristol Jupiter in the background




There are still one or two bits to sort out, but the majority of the changes to the 'exploded' Bristol Mercury Mk VIII display have now been completed. My wife and I are about to depart for a late summer holiday to belatedly celebrate our 50th wedding anniversary. I will quickly finish the Mercury display when we return, then it's back to work on the Jupiter engine.

Mike

Epicyclic tooth form!.....wow!    That's unusual for power transmission...at least to me over the last 35 years....  Why that form do you know?

Dave
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Damned ijjit!

Offline Vixen

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Re: Bristol Mercury revisited
« Reply #30 on: September 12, 2019, 04:44:40 PM »
Thanks everyone for calling in and for your generous comments.

Dave,

The bevels are standard straight cut bevel gears, nothing special. They are arranged to form a very compact epicyclic gear reduction set. If you study the layout closely, you will be able to see the input bevel is the sun, the three pinion bevels are the planets and the fixed bevel in the front is the annulus. You may need a bit of imagination, as the epicyclic function  is folded in upon itself; but it's there and it works.

This form of bevel gear reduction was used on all the Bristol radial engines from the Jupiter through to the mighty Centaurus. It was light, very compact and very reliable. The 2:1 reduction was the most common, but other reduction ratios were available to match different aircraft performance requirements, by changing the tooth count.

Cheers

Mike
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Offline steamer

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Re: Bristol Mercury revisited
« Reply #31 on: September 12, 2019, 07:45:12 PM »
Ahh    not tooth form but gear arrangement.    I think I understand now

Dave
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Damned ijjit!

Offline Roger B

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Re: Bristol Mercury revisited
« Reply #32 on: September 20, 2019, 11:36:37 AM »
Mike, excellent work as ever  :praise2:  :praise2: This type of folded epycyclic (like a differential gear set) was used in the Automotive Products automatic transmission. Some details are given here:

http://www.austinmemories.com/styled-105/index.html
Best regards

Roger