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Old Feb 14, 2012, 06:12 PM
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Sundancer, nice pictures, great memories. You were very lucky to have had a sister that shared your interests.
How did the Eureka with the ETA 15 Mk I compare to the one with the Cox .15?
If the Dixielander and Eureka are the same size, assuming all similar weight, how would you compare or place the AM 3.5, ETA 2.5 and Cox .15 ?
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Old Feb 14, 2012, 07:49 PM
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Very nice pictures Sundancer. They look so evocative. Thanks for posting them here
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Old Feb 15, 2012, 01:54 AM
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Originally Posted by JohnAV8R View Post
Sundancer, nice pictures, great memories. You were very lucky to have had a sister that shared your interests.
How did the Eureka with the ETA 15 Mk I compare to the one with the Cox .15?
If the Dixielander and Eureka are the same size, assuming all similar weight, how would you compare or place the AM 3.5, ETA 2.5 and Cox .15 ?
The original, as per Norman Marcus's plan, Eureka was OK with the ETA15, but had the unfortunate habit of stalling off the top of the climb and never pulling out sometimes. My modified verion, with sheeted leading edge and some other changes, subsequently published in Aeromodeller, cured this problem and was a decent model with the ETA or AM35. Fitting a Cox 15 introduced a new set of problems in coping with the extra power and further mods proceeded until resulting in the last model, the Long Eureka IIIA (lengthened tail moment, different flat bottom wing section, stiffer structure) shown and this was a superb model. The Dixielander did not really suit the heavier ETA, with the AM35 it was a wonderfully consistent performer, capable of maybe 3.1/2 to 4 minutes from 10 second runs without lift. But directly substituting a Cox 15 running on high nitro turned it into an animal! We found out that to cope with the extra power and speed you needed to reduce the wing wash in from 3/8" to 1/4", reduce the wing tip washout from 3/8" to 3/16" and trim for a single wide turn in 10 seconds. Widening out the glide turn also improved the performance and you finished up with a model which would deliver close to 5 minutes from a 10 second run, but required care in launching it at exactly the right angle etc. - in other words it became a lot less forgiving of mistakes than the AM35 Dixielander.

How would I rank the three engines for use in open power models? The ETA was heaviest, smoothest running and a lovely handling engine, well suited to the Eureka in it's original form, less so to the Dixielander. The AM35 was light, powerful when swinging the right prop, vibrated a bit more than the ETA and didn't handle as easily but was a perfect match for the kit Dixielander built exactly as per plan producing an easy to trim and very consistent contest model. The Cox TD15 (and later Special 15) were light and incredibly powerful on small props and high nitro fuel, too much for the original Eureka layout and the Dixielander as trimmed for an AM35. In the right airframe (the lengthened Eureka or readjusted Dixielander) however, there was no contest - the Cox had it every time.
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Old Feb 15, 2012, 03:35 AM
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With the benefit now of around 30 years of hindsight, can I pose these three question to all Diesel lovers........
1) Was there any real advantage in having a Schnuerle ported Diesel ?
2) Was there any real advantage in having a Diesel with ABC metalurgy ?
3) Was there any real advantage employing both of the above technologies together in a model Diesel engine ?
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Old Feb 15, 2012, 10:26 AM
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With the benefit now of around 30 years of hindsight, can I pose these three question to all Diesel lovers........
1) Was there any real advantage in having a Schnuerle ported Diesel ?
2) Was there any real advantage in having a Diesel with ABC metalurgy ?
3) Was there any real advantage employing both of the above technologies together in a model Diesel engine ?
Not considering myself an 'expert' in any way, my comments are based on a blurry mix of experience and 'feel', accumulated over a fairly long period of time....

1) I think, generally, yes..! The 'hotter' ported diesels (Schnuerle or Schnuerl-ish) I've had the pleasure to try, have all showed very good running properties, i.e. in my lower revving world beeing easy handling, and not least, improved throttling... Torque-wise (ability to pull even larger props) though, I cannot say I've noticed any major improvement....
Experiments with 'hotter' portings on diesels, were/are probably mainly meant as 'rev-boosters' with small props, but IMHO these mods make the engines much nicer to handle even at more low-revving ('sports') applications.

2 & 3) Other than lower friction / higher revving on small props, I cannot see the ABC technology beeing any contribution to the diesel development....and do we have an oil issue here...?...(this is beyond my practical experience)

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Old Feb 15, 2012, 02:09 PM
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My Irvine. 20D (all three of Bob's attributes) runs a little more powerfully than my Oliver Tiger Major ... but not as far above it as I would have thought.
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Old Feb 15, 2012, 04:28 PM
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I don't know if any scientific proof or data exists on this, but one of the unofficial laws of 2 stroke technology (that I was taught anyway) is that a Diesel design does not work all that well when converted to glow ignition. This appears to be because the gas passages, which are entirely adequate in a Diesel, are undersized when transposed to a glow. Thus, we had the PAW glows which weren't very powerful or successful, and several other British designs over the last 50 years. From this, I deduce that a Diesel doesn't need to have as much fuel mix going through it, to produce the same (or better) performance than an equivalent glow. It would seem then, that Schnuerle porting in a Diesel is entirely superfluous..........?
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Old Feb 15, 2012, 05:36 PM
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items 2&3
The last MVVS 2.5 came with either diesel or glow.
The new Parra 2.5 diesel can also be had with the glow head.
The Parra "steel" has much less porting than the AAC version.
Both engines started out as diesels, but may put out more power on glow, especially if you let them reach high revs.
My guess would be they are similar on 8x4 to 8x6 props.
For comparison, my Cox Conquest would turn an 8x4, 15%, on the ground, an easy 18,500 rpm. My K&B .21 RE puts out more power and burns more fuel than an old OS .50 in a Fun Fly model, but the OS 50 is much more enjoyable.
John
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Old Feb 15, 2012, 05:54 PM
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Another Schnuerle related enquiry I have is this - how thick must the cylinder liner in a Schnuerly be, before the ports can be considered "directional" ie. influence the angle of gas flow ? If you can imagine two identical cylinders - one is half a millimeter thick, the other 5 mm thick and both with the same ports, cut through at the same angles, there is no way the thin liner ports could be called "directional", but just merely "holes" surely.
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Old Feb 15, 2012, 07:12 PM
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My Taipan Mk 5 "goldhead" schnuerle TBR converted to diesel.

Easy 18,500 RPM on a master 8x3 prop.
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Old Feb 15, 2012, 07:51 PM
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Another Schnuerle related enquiry I have is this - how thick must the cylinder liner in a Schnuerly be, before the ports can be considered "directional" ie. influence the angle of gas flow ? If you can imagine two identical cylinders - one is half a millimeter thick, the other 5 mm thick and both with the same ports, cut through at the same angles, there is no way the thin liner ports could be called "directional", but just merely "holes" surely.
Bob, even if the liner was only a few thou thick, if the bypasses in the case are angled to get the gas flowing in the right direction, and the liner ports match up, that should be all that is needed.
Charlie
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Old Feb 15, 2012, 07:54 PM
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I had a K&B 4011 glow I flew CL stunt with. It turned an APC 9,700 about the way I would set it to fly. I used some Eric Clutton Old English fuel. After leaving the glow plug lit for maybe 20 sec after starting, it ran nice with the needle (ST NVA) turned in 1 1/2 turns, 9, 700

First model Drone diesel, same fuel, a hair overcompressed, 6,900 on MAS 11 x 9, Put on Drone glow head, 10% nitro fuel, very smooth, turned the needle in a little, 6,900.

I understand a 2-cycle engine as basically an air pump. How fast it runs depends on how fast air can go through (with proper fuel mixture, of course). So I am not surprised that an engine runs similar power both diesel and glow. I did not try larger props. Perhaps the diesel would out perform the glow on a bigger prop.
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Old Feb 15, 2012, 08:22 PM
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Bob, even if the liner was only a few thou thick, if the bypasses in the case are angled to get the gas flowing in the right direction, and the liner ports match up, that should be all that is needed.
Charlie
Charlie, the assumption then is, that the bypass channels in the case are of primary importance - the liner ports secondary ?
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Old Feb 15, 2012, 09:02 PM
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Originally Posted by Twin-Stack View Post
With the benefit now of around 30 years of hindsight, can I pose these three question to all Diesel lovers........
1) Was there any real advantage in having a Schnuerle ported Diesel ?
2) Was there any real advantage in having a Diesel with ABC metalurgy ?
3) Was there any real advantage employing both of the above technologies together in a model Diesel engine ?

1) Maybe, it depends on the porting. But many model diesels appear to have something quite similar if not the same as Schnuerle porting in them already. So one may or may not see an improvement. But the modern model diesels seem to be Schnuerle ported.

2.) yes I think there is, granted a good tapered steel cylinder with a good lapped iron piston works a lot like a ABC setup, the piston in the ABC engine is more light weight and they can get it to turn even higher RPMs than a lapped iron piston engine.

3.) Yeah I can see it as being better. My Para engine runs really superb as a diesel and it has all these things in it. Of course they offer the engine with a steel sleeve, ABC and AAC. Now then AAC seems to offer a advantage in more limited situations than ABC does. I remember seeing some other engines like that but I forget their names at the moment.
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Old Feb 15, 2012, 09:04 PM
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Charlie, the assumption then is, that the bypass channels in the case are of primary importance - the liner ports secondary ?
I am considering a typical Schneurle ported engine here. I think that it is a combination of the two. If the liner was only a few thou thick, but the ports matched the bypasses then the bypass would be the only important thing to set the flow direction. However if the liner is say 1/16th thick, but the ports in the liner are not cut at the correct angle to match the bypass angle (perhaps just milled in radially), then you will probably get all sorts of turbulence at the port causing disruption to the required loop flow of the gas. Another thing ( off topic and unrelated to port angles) is the internal finish of the gas passages. In my opinion, although smoothness and flow direction is important, polishing is not. I think that the best surface is about like fine bead blasting. Mind you there is no guarantee that I am right.
Charlie
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