Whittle V8

[Peter Twissell]

Another simple rotary table fixture was used to machine the steel rockers. Note the roll pin which allows each rocker to be returned to the fixture in its original position for subsequent machining operations.
The heel radius was formed by moving the fixture on the rotary table to bring the centre of that radius to the centre of the rotary table.

 

[Peter Twissell]

Tappet adjusters were made from 10BA cheese head screws with sockets for the pushrods cut with a 1/16" ballnose.
A bronze bush was pressed into each rocker and reamed to finished size.

 

[Peter Twissell]

The materials kit from Hemingway included valve springs, so I didn't need to wind them as I have dne for previous engines.
Valve caps are from aluminium and the tiny C clips from silver steel and hardened.

 

[Peter Twissell]

Rocker pillars and exhasut stubs are from steel.
With the parts so far made, it's starting to look like an engine!

 

[Peter Twissell]

A simple tube bender was made per Erics drawing and the induction tubes bent, trimmed to length and soldered to brass flanges and T pieces.

 

[Peter Twissell]

I have made the twin carburettors to the drawing for initial running.
I intend to fit this engine to a model DH51, for which I have designed a manifold for a single carburettor which will lie horizontal over the timing gear housing.

 

[Peter Twissell]

The engine is stripped down for final assembly with appropriate loctites and sealant (Blue Hylomar).
There are a lot of tiny parts!

 

[Peter Twissell]

One of the features of this engine is the modified glow plugs. The small size of the combustion chambers does not allow for both valves and a plug. The heads have 3/16 x 40 holes drilled and tapped so that the drilling intersects the combustion chamber. This is visible in the second image in post #18.

Enya No.3 plugs are have their 1/4" threads turned down and are rethreaded 3/16 x 40. The bodies of the plugs are reduced to 0.270" diameter and the tops of the plugs are removed, leaving the small thread of the electrode exposed.
The drawing shows replacement plug tops, but I have elected to connect the plug wires directly to the electrode thread.
The small thread is probably metric, but a 9BA nut seems to fit nicely.
With no hexagon left on the plugs, it is necessary to make a collet tool to tighten them into the heads.

I have designed a dummy 'magneto' which sits on the back of the timing gear case and serves as a connector for my glow driver to connect to all 8 plugs.

I have the plugs wired so that the four plugs of the left bank are in series with the four plugs of the right bank.
My driver will be required to supply 12A at 3V - half the current which would be necessary if all the plugs were connected in parallel.
I am using a DC/DC converter to drive the plugs, with both voltage and current limiting. The driver can run on any DC source up to 32V and of course the higher its voltage, the lower the current demand. A 3S LiPo will only need to deliver a little over 3A.

I have not run the engine yet, I still need to make a test stand for it.

 

[petertha]

Looks fantastic. I'm very intrigued by your version of the modified glow plugs & torqueing in tool if you have some pics handy. I fiddled around with some dead plugs I had laying around to see if/how I could similarly reduce them, more out of morbid curiosity than any particular need. Jewelry work for sure.

 

[Peter Twissell]

This is my collet tool, made from an M8 cap head screw. The hex is bored out to fit the plug, chamfered on the back and split 4 ways with a junior hacksaw. A collar with an internal chamfer is pulled up onto the screw with an M8 nut, closing the collet onto the plug.
Also shown is a plug with the top removed and thread and OD reduced.

 

[kuhncw]

That is very nice work, Peter. Thanks for posting the parts and fixturing.

Chuck

 

[peterl95124]

wow, nice work all around, very inspiring !!!, but, if you're clever enough to miniaturize your glow plugs I'm pretty sure you're also clever enough to make miniature spark plugs ? !!!

 

[Peter Twissell]

There is a practical limit to the minimum size of spark plugs.
To create a spark hot enough for ignition under compression requires a certain minimum voltage, which in turn requires a minimum thickness of insulator in the plug.
About 1/4" is the minimum practical diameter for a spark plug.
All I did was to remove some material from some purchased glow plugs.

 

[peterl95124]

There is a practical limit to the minimum size of spark plugs.
To create a spark hot enough for ignition under compression requires a certain minimum voltage, which in turn requires a minimum thickness of insulator in the plug.
About 1/4" is the minimum practical diameter for a spark plug.
All I did was to remove some material from some purchased glow plugs.

Ooops, My Bad, for framing my post as a question, my V12 runs on #8-40 threaded spark plugs, there has never been an issue with them, even though I used corian insulators while I've switched to macor since then, rather I was afraid of scaling issues with the distributors so made larger non-scale ones that are hidden behind the display firewall along with moped coils (Barry Hares did make working true scale full blown *magnetos*, I think he's the exception that proves the rule !).

anyway, still admire your ingenious solution, that micro-collet is a neat trick !

 

[petertha]

my V12 runs on #8-40 threaded spark plugs...

Peter, I've watched your YouTube video & occasional build posts <drool>, but are your plugs & distributer & general ignition system detailed anywhere I may have missed? I would love to know more details of how you went about this challenge if its something you'd like to share. Its literally the Holy Grail of ignition miniaturization IMHO.

https://www.homemodelenginemachinist.com/threads/lawrence-merlin-v12.34432/

 

[Peter Twissell]

I have heard of a few examples of very small spark plugs, but they are indeed the exception rather than the norm and I can only congratulate you on making them work.

Since it is my intention to fly my engine in an RC model, I prefer to keep things simple and light.

 

[Basil]

Nice work Peter. What compression ratio will you be using? Methanol/Nitromethane being the fuel? Thank you for documenting the build.

 

[ozzie46]

I have heard of a few examples of very small spark plugs, but they are indeed the exception rather than the norm and I can only congratulate you on making them work.

Since it is my intention to fly my engine in an RC model, I prefer to keep things simple and light.

Tell that to Steve Hucks of Lil Demon fame. I’m running his 8 40 plugs in my Lil Demon with no issues. He manufactures and sells them. I think he even has a 6 32 size too.

I have heard of a few examples of very small spark plugs, but they are indeed the exception rather than the norm and I can only congratulate you on making them work.

Since it is my intention to fly my engine in an RC model, I prefer to keep things simple and light.

take a look at this site run by Steve Hucks of Lil Demon fame. I’m running his 8 40s in my lil demon with no issues

https://miniaturesparkplugs.com/
Ron

 

[Peter Twissell]

Nice work Peter. What compression ratio will you be using? Methanol/Nitromethane being the fuel? Thank you for documenting the build.

Thanks Basil, I haven't calculated the compression ratio, just built to drawings.
About 6:1 is normal for glow ignition.
I'll be using 12% nitromethane in methanol with synthetic 2 stroke oil.

 

[petertha]

take a look at this site run by Steve Hucks of Lil Demon fame. I’m running his 8 40s in my lil demon with no issues
https://miniaturesparkplugs.com/

Jeez, I've been asleep with my glow plug tunnel vision, LOL, how did I miss this?

Sorry for the post tangent @Peter Twissell