Author Topic: 12,6cc engine..  (Read 1182 times)

Offline Niels Abildgaard

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Re: 12,6cc engine..
« Reply #15 on: June 26, 2019, 11:20:59 AM »
Thank You for the answer and how do You fix it in the cylinder head?
I worked at the last factory in world making glowHEAD engines that run another process.
The dieseloil was ignited in a seperate prechamber by a piece of glowing stainless steel.
When that broke of and went through exhaust port it made havoc.

Offline Allen Smithee

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Re: 12,6cc engine..
« Reply #16 on: June 26, 2019, 12:06:23 PM »
Silencer is based on Robbies calculations, it has 2 expansion chambers and one side resonance chamber in the middle. It works ok, but I feel I could still have something quieter.

An apporach used by Irvine with their Q-series motor/silencers was to reduce direct sound radiation from the exterior of the silencer. Pete Halman did experiments and found that he could use the exhaust gas itself as a damping medium by arranging a thin (1.5mm I think) blanket of exhaust gas around the primary expansion chambers. The schematic layout looks like the picture below (drawn twice because when I drew the green gas flow arrows they hid the detail!).

The concept has an inner can inside the outer can, with a thin gap between the two. The inner can is open at the inlet end, and has a ring of bleed holes near that end. The incoming gas expands into the inner chamber and then bleeds into the outer chamber before escaping to the rear. The thin gas layer cools and de-energises more quickly, and the reduced pressure improves its performance as a sound-deadening blanket. It wrks well with a 2-stroke because it doesn't create too much obstruction to the mass-flow of gas, allowing the engine to breathe normally.

This principle was used on the Irvine 40Q engine which delivered reliable and quiet performance at 9-10,000rpm without the complixities of a 4-stroke. We also adapted it for use on the Irvine 40SP engine for Sport 40 pylon racing. This version had a phelan-type folded wave tuned exhaust* inside theis "Q-silencer" system. These motors raced at 16-17,000rpm and even at these rpm the Q-system was noticeably quieter.

I probably still have them in my engine cuboards (I never throw anything away), so if you want some examples of these things to look at just let me know and I'll dig them out.

AS

* as used in the "Phelan Magic Muffler", "Irvine Super Silencer" and the Rossi 40 R26 silencer
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Offline Lauri

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Re: 12,6cc engine..
« Reply #17 on: June 26, 2019, 12:40:01 PM »
Niels, the shaft (2mm) of umbrella is pressed in aluminium (#2024 T3) with 0.1mm interference fit, 3.5mm deep. They will never come out.

Allen,
Im aware of the Irvine Q40, and I have been planning to get one of them mufflers in my hands. So all info about their construction & dimensions would be highly appreciated.

Lauri

Offline dieselpilot

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Re: 12,6cc engine..
« Reply #18 on: June 26, 2019, 02:49:28 PM »
That muffler design is also called laminar flow in Blair's books.

Offline Allen Smithee

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Re: 12,6cc engine..
« Reply #19 on: June 26, 2019, 03:06:10 PM »
So all info about their construction & dimensions would be highly appreciated.

If I can make time when I'm back home at the weekend I'll find them and take some measurements/photos.

I'm guessing that for an F2a engine you're not interested in the "internal phelan pipe" version? I'm way out of date on C/L stunt - are you still using 4-2-4 running or do more people use actual throttles these days? Back when I was a teenager I built a Dumas P-51 stunter with a throttled Merco 35 using a home-made balanced 3-line belcrank system (I think I copied it from an Al Rabe design). but presumably these days a servo-throttle could be easily used?

AS
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Offline Lauri

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Re: 12,6cc engine..
« Reply #20 on: June 26, 2019, 03:14:27 PM »
That would be great, Allen. Thanks a lot.
I use very mild 4-2-4 break, its allmost like a constant speed run.
But I have an idea of what kind of back pressure I should have, and the sound spectrum that comes out of the engine. I know the max. outside dimensions, and once I have an idea of the structure, Ill let Rob take a closer look at the internal dimensions. L

Offline Lauri

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Re: 12,6cc engine..
« Reply #21 on: June 29, 2019, 12:10:52 AM »
Hi.

Here is some pictures of my piston rings.
First 2 show the ring after about 60 hours of use.
I think I'll make the next ones slightly conical, maybe a degree per side or so? I mean wider at top, that may help them seal even better.
3rd and 4th picture show the heat treatment jig. It's made of same material as the rings and the depth of cavity in jig is exactly same as height of ring.
The jig is closed with a screw, and sealed with paste mixed from methanol and borax. I also put a piece of oiled paper inside. It burns away the remaining oxygen and seems to prevent the ring from oxydizing too much. At least they end up nice & blue.
As heat treatment (or stress relieving treatment, I have ended up with 2 hours in 1000F/538C, then I turn off the oven and let it cool slowly.
Next 3 pictures show the fixture for finishing the rings to correct diameter. After stress relieving they are about 0,05mm oversize in diameter.
The ring is compressed to the fixture with a steel ring, tightened with a screw and then turned to final size.
I try to make the diameter to bore-0,002mm, according to trial & error it seems to work.
At last, the ring thickness is adjusted first with stone, then with 40-3 micron lapping films.

L

Offline Lauri

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Re: 12,6cc engine..
« Reply #22 on: June 29, 2019, 09:53:51 AM »
This is how the cylinder ports are made. It's a far too complex way, but I only make 1 or 2 cylinders per year so it has not yet affected my mental health too much.
To be sure that all ports are in right size and place, I must be able to remove the workpiece from mill for measuring several times during the process.
I use a microscope to set the workholder straight. After that the cylinder is allways aligned in it very accurately, with a very precisely made head bolt.
After that, I can set whatever port angles I need and start machining the ports.
So far I have managed to to get everything right within 0,01mm or so, but it's very time consuming and stressing.

Lauri

Offline Lauri

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Re: 12,6cc engine..
« Reply #23 on: June 29, 2019, 10:11:25 AM »
My milling machine is an Aciera F1+, it's about same size than the classic F1 but much more rigid. Many parts are interchangeable between the old and new version.
Before getting the mill I did everything with my 102 lathe, it's also very accurate but even more time consuming for this kind of work. L

Offline Allen Smithee

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Re: 12,6cc engine..
« Reply #24 on: June 30, 2019, 06:01:16 PM »
Lauri,

I found my one remaining Q40 silencer. Unfortunately while I can get the screws and pressure nipple out I cannot persuade the halves to separate. I suspect they are firmly gunged up with a combination of castor residue and aluminium oxide.

I may see if soaking in thinners for a week will help, but if you wish I'll put it in the post to you and you can have a go. Looking at your workmanship I'm pretty sure you could do a better job of it than I could!

AS
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Offline Lauri

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Re: 12,6cc engine..
« Reply #25 on: July 01, 2019, 06:52:28 PM »
Thank you, Allen.

Of course, I'm happy to pay something for the muffler, then I can play with it with a good conscience. L

Offline lohring

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Re: 12,6cc engine..
« Reply #26 on: July 02, 2019, 03:38:04 PM »
That's a very impressive engine, both with its design and especially with your machining.  You might enjoy Jim Allen's efforts in engine building for a very different application.  See http://www.modelenginemaker.com/index.php/topic,3890.0.html  Consistent rpm under various high load condition requires a very different design than a high rpm, high power engine.  There's a lot less design information for your application.  I applaud your experimentation and sharing.

Lohring Miller

Offline strictlybusiness1

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Re: 12,6cc engine..
« Reply #27 on: July 02, 2019, 04:30:32 PM »
Lauri,

Welcome to this very unique site which displays the talents that still exist by capable machinist using only manual machines. I will continue to follow, with great interest,  your progress & development of this particular type of engine. I should note that I also know Rob Metkemeijer, Henry Nelson, Lohring Miller & other very capable engine builders. I'm also very familiar with the Aciera Milling machine.

Jim Allen
« Last Edit: July 02, 2019, 04:43:24 PM by strictlybusiness1 »

Offline Lauri

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Re: 12,6cc engine..
« Reply #28 on: July 02, 2019, 10:48:09 PM »
Thank you, Lohring and Jim.

Yes I've read through Jim's stuff a few times and it's really awesome. I wish I had the time and machinery.
Of course the operation modes of a stunt engine and racing engine are differend but the fundamentals that make them predictable, stable and reliable are not.
I have worked with this allmost 10 years and I'm slowly getting familiar with the interactions that take place in the running engine. Some of our findings are very interesting, I would allmost say revolutionary. More about them later.
By the way Jim, does the Aero Precision make also the PA's for Randy or do they still come from Nelson?

Lauri

Offline strictlybusiness1

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Re: 12,6cc engine..
« Reply #29 on: July 03, 2019, 12:07:45 AM »
Henry still makes a few combat engines when he is not playing bridge. All the Nelson .45 long stroke pylon engines & their parts are made at Aero Precision Machine. The chroming & honing of the aluminum cylinders is also done on site & these things have been developed to the highest level.

JA