Author Topic: Bristol Mercury revisited  (Read 11849 times)

Offline MJM460

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Re: Bristol Mercury revisited
« Reply #240 on: March 22, 2020, 11:20:35 PM »
Hi Mike, like others, I am continually amazed at the work you are doing on those engines.  Also your design ability to make it all come together and your tenacity to keep at the project for so long.

I don’t often comment, but when you see the number of reads increase after each post, you can be sure that I am one of them.

MJM460

The more I learn, the more I find that I still have to learn!

Online Vixen

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Re: Bristol Mercury revisited
« Reply #241 on: March 23, 2020, 10:39:55 AM »
To all of you who called in, and to the many MEM members who are silently following. I know just how difficult it is to find the right words to reply. All I can think of to say to you all is

'Thank you all for your company on my long journey'

Stay safe

Mike
It is the journey that matters, not the destination

Online sco

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Re: Bristol Mercury revisited
« Reply #242 on: March 23, 2020, 12:03:33 PM »
To all of you who called in, and to the many MEM members who are silently following. I know just how difficult it is to find the right words to reply. All I can think of to say to you all is

'Thank you all for your company on my long journey'

Stay safe

Mike

 :ThumbsUp:
Ars longa, vita brevis.

Online Vixen

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Re: Bristol Mercury revisited
« Reply #243 on: March 25, 2020, 03:36:28 PM »
I thought I would put something on the forum to give everyone something to look at during our enforced 'home' time.

The second Mercury is very close to completion. Here is one of the pair of magnetos mounted on the Accessories Drive Gearbox at the rear of the engine. You can see the nine plug leads running from this, the starboard magneto, to the right hand spark plug in each of the cylinders. Each cylinder is equipped with two spark plugs fired from separate magnetos for safety and reliability reasons. There will be more photos in the next, possibly the last, installment of this build.

The best definition of a 'reliable engine' I ever heard, is one you always have to switch off at the end of a long flight. Engines which switch themselves off and stop mid flight aint worth having.

.atford


Somewhere along the way, I have lost the build photos of the magnetos. However, I did build six of them, two for each of the two engines. These four were configured only as distributors using external spark coils. The remaining two were intended to be used as spares or as the basis of self contained working magnetos, If I ever got that far.

From my box of spare parts I have been able to put together some recent photos of completed parts for the 1/4 scale Watford S.P. 9/6 Magnetos.

The first two photos shows a the main components. The little box under the distributor cap houses the ignition points, (actually Hall magnetic sensors on the model). Also shown is the input drive shaft for the separate ignition coil version. Note the offset horizontal key in the drive flange. This ensures the magnetos can only be installed with the correct ignition timing. The little pinion gear at the far end is part of the reduction gearing used to turn the distributor's rotor arm at the correct speed.






Here you can see the fully machined main housing and the gear case.




Here are the magneto coil cover and ignition point box



These parts are all machined from Delrin. They are the distributor cap, the rotor arm, the drive gear and the upper bearing housing.




Along the way, at one of the London shows,  I met up with Jan Mulder from Holland. Jan had succeeded in making a fully self contained 1/4 scale magneto for his DH Gipsy engine. He was very keen to help me do the same for the Mercury engine and provided a complete (but damaged during manufacture) magneto coil, an endless selection of fine magneto wire together with lots of help advice and information.

The photos show one of Jans magneto coils posing in one of the Mercury magnetos. The coill is minute, it contains many thousands of turns of the finest insulated copper wire, all insulated layer by layer and vacuum encapsulated in epoxy. The coil's iron laminates would eventually sit on the two pole pieces either side of the rotating magneto magnets.






Look at the attention to detail in Jans magneto coil. The little ceramic bead insulates the high voltage output where it feeds through the delrin gear and onto the rotor arm.




Here are some of the wire reels provided by Jan. From left to right, the wire diameters are 0.035mm (13 thou), 0.028mm (11 thou) and 0.026mm (10 thou)




I have yet to make a start on my working magnetos. First I would need to make a tiny coil wider and practice and practice. However I think I may have left it too late as this wire is thinner than an angles hair and very difficult (almost impossible) for these old eyes to see. :old:

Stay safe everyone.

Mike

« Last Edit: March 25, 2020, 03:49:57 PM by Vixen »
It is the journey that matters, not the destination

Offline Admiral_dk

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Re: Bristol Mercury revisited
« Reply #244 on: March 25, 2020, 10:58:56 PM »
Another set of magnificent parts Mike   :praise2:

My first thought as I learned in my late childhood (when Dad flew Gliders) that you always do a "Power Run" with the wheel brakes fully on - before take off - where you start the run on both systems and listen for abnormal noises from the engine etc.
If all's good, you switch to only magneto I (without touching the Throttle) and listen again for a minute - if that's good - switch to magneto II and repeat + there should be not drop out or lower RPM's at anytime during this test ...!!!! .... so I couldn't thinking if your wonderful setup allows you to do the same ? (without the taking off happening  ;) ).

The next one was after seeing the copper wires - I have never seen an Ignition Coil that has tree different wire sizes / coils - so what is the idea here  :headscratch:

ps - in case you wonder why a glide pilot would know this - sometimes they used a "Tow Plane" to get in the air .... though the really mind blowing experience was to be pulled into the air with their big American V8 sitting with gearbox and all on the back off a big old lorry. It had one exit from the differential blocked and the wire drum bolted on instead off the wheel in the other. The wire went out through an highpower cutter that was spring loaded - and a wire went from that to the Emergency handle in the operators booth (with protection for the opperator) behind the wheelhouse - and the "power wire" continued out through a few rollers. One of those sets controlled the wire in the Horizontal plane and the other set in the Vertical plane.
The funny thing from a boys point of view when being allowed to watch things next to the operator was the original speedometer from the "Donor Car" was still attached the gearbox and the max speed that the wire was pulled in, was an indicated speed off 180Km/h ~ 112 Mph.
I haven't got a real clue about how much it translated into in real speed - but I can tell you how shocking it was first time I was in the Glider being pulled up that way. I had seen it many times and also helped with holding the wingtip up to horizontal and run along during start - but being onboard was a very different experience :
The wire is first very slowly pulled tight and the moment it is tight - the "wingman" lowers his raised arm and start to run the moment the operator hits the Throttle - until he (or she) feels that the Glider holds a steady wing position by itself and let go and the Glider gets airborne (this is only a distance of about 10 meters ~ 30 feet. The Glider now rotates to almost Vertical and the operator floors the Throttle.
Onboard this shocking as you suddenly has your back Horizontal and a few seconds later you are at about 3500 Feet up in the air. Not even Fighter Jets gets to that altitude so fast !!!!  (but they continue much higher and faster).

Online Vixen

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Re: Bristol Mercury revisited
« Reply #245 on: March 26, 2020, 11:25:03 AM »
Hello Per,
Your father taught you well. The preflight test you refer to is known as the 'Mag Drop Test'.

Two totally independent ignition systems have been mandatory for manned flight ever since the early days of flight and need to be tested before every take off. When you have large cylinders, 5.75" (146.0mm) in the case of the Mercury engine, the combustion flame front takes twice as long to ignite the charge when there is only one spark plug operating. This represents a drop in efficiency and the engine revs will drop. The pilots notes for running the Bristol Mercury say to slowly bring the engine to take-off boost (power) which is 2,500 RPM. With either magneto switched off the drop in RPM should not exceed 120 RPM.

The model cylinder is only 36mm diameter so I do not expect to see a Mag Drop like the full size engine, However it will confirm that both sides are working correctly. There are two ignition switches, one for each independent system.

The three wire sizes were a selection of different wires from which, hopefully, I could eventually wind the secondary coil for the magnetos

I love the story of you and your father at the glider field. Yes, those cable launches were pretty scary. A cable break at full power could send the glider into a nasty hammer head stall. You needed plenty of altitude to recover. I used to drive the Ferguson tractor all day at our local gliding club. My job was to return the tow wires from the winch to the launch point. In return, I would get to fly a glider back to the hanger in the evening.

Stay safe

Mike
It is the journey that matters, not the destination

Online Vixen

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Re: Bristol Mercury revisited
« Reply #246 on: May 06, 2020, 12:02:10 PM »
The second Bristol Mercury is now very near to completion. Just one or two small parts to make and fit.

The Mercury oil pumps are located at the back of the engine in the accessories gearbox. There are two spur gear oil pumps combined in one unit. The smaller displacement pressure pump feeds pressurised oil to the engines lubrication system, the used oil drains down to the sump and is removed by the larger capacity scavenge pump. The used oil is pumped back to the oil tank via an oil cooler.

Here you can see the oil pump assembly. The high pressure pump is within the bronze housing on the left and the scavenge pump is within the aluminium casing on the right




The scavenge pump housing will be a challenge to make and will require several different set ups and machines. I started with a length of 30mm diameter HE30 bar, long enough for the scavenge pump housing and a short sacrificial chucking length.  The six sides of the scavenge pump base flange were machined in the mill, indexing the stock in my 4th axis unit.




The work was transferred to the lathe to turn the cylindrical parts of the pump housing. I used a parting tool with a 1mm radiused tip to do the profiling work. These parting tools will successfully cut sideways as well as plunge, provided the depth of cut is small.




The embryo pump housing was transferred back to the mill to machine the two pump lobe cavities.  The pump cavities are formed below the larger diameter counterbore in sacrificial chucking length.






The pump housing was inverted in the chuck and the external features were profiled with a combination of end mill and ball mill cutters.






Next, The pump housing was transferred to a tilt table to machine the angled face for the inlet pipe connections. The inlet ports were then drilled and tapped.








The final operation was to part off the sacrificial chucking piece and cleanup the rough edges of the scavenge pump housing.










All that remains to do is to make up the 7 inlet/outlet pipe connections and blanking caps and give the scavenge housing a coat of paint.


Stay safe, keep your distance. :Director:

Mike
It is the journey that matters, not the destination

Offline scc

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Re: Bristol Mercury revisited
« Reply #247 on: May 06, 2020, 03:50:04 PM »
 :popcorn: :popcorn: :LickLips: :praise2:    Terry

Offline awake

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Re: Bristol Mercury revisited
« Reply #248 on: May 06, 2020, 05:32:17 PM »
Incredible, impressive work!
Andy