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Old Jul 13, 2011, 05:28 PM
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Originally Posted by JohnAV8R View Post
Earlwb, have you run your Parra yet. I wouldn't go pushing it over 20K unless you have a spare rod. I got the first ones with the steel liner. I'm happy to keep the revs down with large props. Mine came with an Enya muffler and an MVVS RC carb.
John

newer gold head Parra
http://www.clubtamaran.com/parramotorING.htm
Not yet, I plan on running it on a plane that uses a 7x6 to 8x4 prop. so I doubt I'll be exceeding any RPM limits. But Parra might have changed something along the way to improve the rods too.
I thought about the Enya Muffler, but the mini-pipe just looks so cool and fast.
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Old Jul 14, 2011, 04:38 AM
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Originally Posted by earlwb View Post
John left out the part about that they were discussing the old style large paddle props of the time period that people were using for combat at the time. Thus the those props would be below the RPM range that the engine was designed for.
Just acquired an original Bugl (in the wood box) earl and I think these are the most clever and beautifull diesels ever to be produced, that bell rear intake man that is so finely made and no cnc in those days remember ?
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Old Jul 14, 2011, 05:14 AM
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Originally Posted by Reginald View Post
Just acquired an original Bugl (in the wood box) earl and I think these are the most clever and beautifull diesels ever to be produced, that bell rear intake man that is so finely made and no cnc in those days remember ?
Hi Reg,
You'r leaving us drooling around.
Pictures, pictures, pictures........ in close up!
What ???? You didn't take it with You to the coast ???
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Old Jul 14, 2011, 06:32 AM
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Originally Posted by Reginald View Post
Just acquired an original Bugl (in the wood box) earl and I think these are the most clever and beautifull diesels ever to be produced, that bell rear intake man that is so finely made and no cnc in those days remember ?
Do post some pics. Nice find. Is it like one of the Valentine Reproductions?
ref http://www.ronald-valentine-engines....5_DR_Mk_I.html
You know, I never thought about using a fuel tank pressure tap straight off the exhaust port on the engine before.
I wonder how well that worked on generating a little fuel tank pressure.



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Old Jul 14, 2011, 07:53 AM
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I think the fitting is used to prime the exhaust not to pressurize the fuel tank .

Mike1484
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Old Jul 14, 2011, 08:04 AM
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I suspect this tap is for priming...or it's just wrong thinking....

My practical experience is that a pressure tap positioned anywhere on the 'high velocity' part of the exhaust (i.e. before the expansion chamber) will result in no pressure, or even negative pressure (syphone effect)

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Old Jul 14, 2011, 08:37 AM
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They didn't use mufflers or tuned pipes back then. Sometimes they had the occassional short stack or straight pipe, but it was to keep the plane less messy. Besides with the small exhaust outlet on that particular engine, even if you slipped on a clamp on muffler, it would block the fitting on the side edge.
They could have the inside protrusion on the fitting, angled so that some of the exhaust gasses would be diverted into it. Sort of like the water cooling line on a model boat, where they angle it forward to scoop up water better off the prop.
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Old Jul 14, 2011, 10:12 AM
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In any case, exhaust pressure with diesels is bad news...unlike glows, they don't like water in fuel.
Beautiful engine!
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Old Jul 14, 2011, 10:28 AM
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In any case, exhaust pressure with diesels is bad news...unlike glows, they don't like water in fuel.
Beautiful engine!

That is most unusual. Quite a few people suggested to use exhaust pressure with a muffler on the RC diesel engines. I tried it and it worked great. especially on the glow engine diesel conversions with larger bore carbs. I haven't had any problems with moisture in the fuel that way, nor does it cause a explosion either. Earlier I had concerns about the ether being ignited by the exhaust gasses or flame from the exhaust, but it hasn't been a problem.
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Old Jul 14, 2011, 10:58 AM
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Originally Posted by earlwb View Post
Do post some pics. Nice find. Is it like one of the Valentine Reproductions?
ref http://www.ronald-valentine-engines....5_DR_Mk_I.html
You know, I never thought about using a fuel tank pressure tap straight off the exhaust port on the engine before.
I wonder how well that worked on generating a little fuel tank pressure.



It is a 15 of 1972 looks like the Valentine repro, I will make some pics when back home on monday
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Old Jul 14, 2011, 11:15 AM
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Quote:
Originally Posted by earlwb View Post
That is most unusual. Quite a few people suggested to use exhaust pressure with a muffler on the RC diesel engines. I tried it and it worked great. especially on the glow engine diesel conversions with larger bore carbs. I haven't had any problems with moisture in the fuel that way, nor does it cause a explosion either. Earlier I had concerns about the ether being ignited by the exhaust gasses or flame from the exhaust, but it hasn't been a problem.
Was fuel tank positioning a factor for pressurizing or just down to the large bore carb not producing enough suction?
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Old Jul 14, 2011, 12:04 PM
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many years ago we didn't use mufflers. So we flew with the tank vent open to the atmosphere. But you usually had to leave the engine set a little more on the rich side as it leaned out more as the fuel tank got low. Fuel tank position was more critical too, you usually had the fuel tank sitting a little higher than normal too. The engines at the time had small intake venturi's or smaller bore carbs on them, in order to improve fuel draw. With the RC engines when you went to low throttle, the fuel draw was even more weak, so the fuel tank location was quite critical.

Later we were required to start using mufflers as part of the club rules. But no one used muffler pressure still. The fuel tanks also didn't come with muffler pressure taps on them either. We all ignored the pressure taps for sale at the LHS too. Then one day a fellow shows up at the flying field with muffler pressure and his engine ran great, much better than how ours were working. Then the model airplane magazine had a article on it that month too. Within a month most all of us were converts and had switched over to muffler pressure.

Now with people using muffler pressure, the engine companies started putting on larger and larger carbs (besides other changes) to increase the performance.

I tried one of my glow engine diesel conversions without muffler pressure and the engine didn't really want to idle well at all without it. But it idled good with some muffler pressure. So it helps if the carb is a larger bore on the engine conversion. But if the engine has a small bore carb, it may or may not make much if any of a difference then. of course the glow engine conversions are using glow carbs and maybe in some cases the fuel metering isn't as compatible with the diesel fuel as the diesel engine can run on a much leaner air/fuel ratio than it does with a glow engine.
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Old Jul 14, 2011, 03:22 PM
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I understand that it's a cumulative problem Earl..takes a while to show up...water collects in the bottom of the tank and suddenly the engine gets a big dollop of H2O...glow engines actually run better with moist fuel so long as it's evenly distributed ! Ever noticed your car engine runs more smoothly on a rainy day? And Carrier aircraft in WWII used water injection as a power boost, but only for limited emergency intervals as the power boost was so strong.

Irvine converted their glow 20 to diesel and supplied the same glow muffler, but without the pressure tap, to avoid users running across this problem.
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Old Jul 14, 2011, 03:39 PM
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Quote:
Originally Posted by Chas View Post
I understand that it's a cumulative problem Earl..takes a while to show up...water collects in the bottom of the tank and suddenly the engine gets a big dollop of H2O...glow engines actually run better with moist fuel so long as it's evenly distributed ! Ever noticed your car engine runs more smoothly on a rainy day? And Carrier aircraft in WWII used water injection as a power boost, but only for limited emergency intervals as the power boost was so strong.

Irvine converted their glow 20 to diesel and supplied the same glow muffler, but without the pressure tap, to avoid users running across this problem.

had an old rambler that loved rainy and very humid days, never knew why!
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Old Jul 14, 2011, 10:33 PM
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Perhaps this might interest someone. It is an MAN .19 diesel that I have built from a design published in Model Airplane News in 1956. It started life as a lump of aluminium 2 1/2 inches diameter. It runs well and starts easily although making it was a bit more involved than I expected.
Charlie
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