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Old Aug 23, 2012, 05:25 AM
Heathkit DX-100 son of Bullet
Gary Cee's Avatar
United States, MI, Marysville
Joined Apr 2010
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The size of the restriction can play a huge part in the function here . The system is similar to a resistance/capacitance in series between the source and load . At some point a "resonance" effect could nullify the pressure pulse . A larger tube on the pulse line in some cases may actually make the situation worse as it would present a larger volume to absorb or dampen the pulse .
In other words your larger fitting may have been exactly what you needed .
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Old Aug 23, 2012, 06:58 AM
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Yes you are correct in that the small fittings with the small inside hole would act as a resistor to the crankcase pulses. Thus it would tend to moderate the strength of the pulses quite a bit, especially at higher RPMs. It may even block the pulses completely at WOT. I did notice that with the OEM stock fittings, that if the tubing came off it had no effect on the engine when it was running. But with the larger fittings, the engine would sag in RPM or power and lean out more if the tubing was pulled off.

When I was thinking about this, I remembered the old Kustom Kraftsmanship Cox Tee Dee .049 engine pressure backplate. They had made the crankcase pressure fitting with a tiny hole and a reverse rocket nozzle shape to it, so that the pressure pulses would go out but meet resistance coming back in and thus served as a one way valve on the engine. Thus it would pressurize the fuel tank really well too. My old MVVS 35cc gas engine and my SV 17cc engine both have large fittings on them for feeding the crankcase pulses to the Walbro carburetor. Anyway that was where it got me to thinking about it, when I was setting up the Walbro carb modification on the one 9cc engine. I had the question at the time as to why they used larger fittings and tubing to hook up the pulse pressure line to the carb pump.









Cox KK Pressure backplate they have a tapered nozzle on the inside and a tiny hole on the outside, it serves as a resistor preventing the pressure from bleeding off when the engine is running.
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Old Aug 23, 2012, 09:36 AM
Heathkit DX-100 son of Bullet
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United States, MI, Marysville
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Quote:
Originally Posted by earlwb View Post
Yes you are correct in that the small fittings with the small inside hole would act as a resistor to the crankcase pulses.
The other component in the equation is the tubing volume . The tube itself is like a capacitor with a resistance in parallel . The reisitance is a function of the length to diameter ratio and the capacity is basically the volume . As you go to a smaller diameter the resistance of couse increases . As the diameter increases the capacity grows . When the capacity becomes large enough the pulse is seen less and less at the load (diaphram) end . This is probably why the larger hole helped while a larger tube amy actually become counterproductive .
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Old Aug 23, 2012, 11:01 AM
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Interesting thought. I'll have to try the smaller tubing on the pump line and see what happens. I used the larger tubing because the other brand engines using a external pump pulse setup were using the same stuff. So I figured they had optimized it already. Especially MVVS, I figured they were on the ball with engine designs.
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Old Aug 23, 2012, 11:46 AM
Heathkit DX-100 son of Bullet
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United States, MI, Marysville
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Yes, there should be an optimum size . The smallest diameter that will still allow sufficient volume in the time allowed . The larger fitting is the way to go in any case . The small diameter will give a cleaner pulse . Think compression ratio.
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Old Aug 23, 2012, 04:51 PM
A trail of smoke is GOOD!
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USA, TX, Springtown
Joined May 2008
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OK, I just received one of these today. I don't know if I should start it or ship it back. Is anyone flying this engine stock? I don't intend to spend a lot of money making this ready to fly.

Second, them manual says this is 0.8hp. Is this anywhere near right? I was expecting to have it replace a 50 size engine. Is this what you guys are finding?

What prop is this think spinning/rpms?

I have read about 20 pages already and it is mostly about modifications.

I just want to break it in, mount it, and fly it. If this is not going to work, please let me know so I can return it.

Thanks,
Wayne
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Old Aug 23, 2012, 05:20 PM
Demonstrations on Saturdays!
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United States, CA, Woodland
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Stock mine did not. Got just over a gallon through it when just because of what I was seeing posted I opened the back and the rod was on its way out.

You could post pics of what you got to see if they made any mods but I would wager to say there's no way they've had time to.

2 cents worth for 'ya!

The post I put up with pictures appears to have been deleted possibly due to the line I jokingly put in there saying "anybody want to buy a junk engine". Posting a sale in a forum I'm sure is a no-no. Geez.
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Old Aug 23, 2012, 09:32 PM
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Quote:
Originally Posted by waynemia View Post
OK, I just received one of these today. I don't know if I should start it or ship it back. Is anyone flying this engine stock? I don't intend to spend a lot of money making this ready to fly.
Second, them manual says this is 0.8hp. Is this anywhere near right? I was expecting to have it replace a 50 size engine. Is this what you guys are finding?
What prop is this think spinning/rpms?
I have read about 20 pages already and it is mostly about modifications.
I just want to break it in, mount it, and fly it. If this is not going to work, please let me know so I can return it.
Thanks,
Wayne
It is a tough call. Apparently quite a few people bought them,and aren't complainign about problems, and I only see a few of us with issues. So it is hard to say if you should keep it or not. I'll just have to let the overall thread speak for itself. But usually if a person isn't having any issues, they seldom speak up about it or write about it for that matter too. Some of the online stores sold out of the engines several times over so far. Unfortunately we don't know what the sales figures are though.

The engine turns a 11x7 prop as good as the old baffle piston .60, .61 engines do. It feels like a .40 or .45 Schneurle engine as to power when flying one on my plane. A .50 glow is still more powerful than a .56 (9cc) gasoline engine.

The engine I am flying turns a 11x7 Master Airscrew prop at about 10,500 RPMs which is about 0.738 HP using my spreadsheet calculator here at home. Which is about 70mph for calculated airspeed. It might do better if I fiddle with the ignition timing too.

Use extra oil, a really good oil too. I am now running a 15:1 oil ratio instead of the 20:1 oil ratio they suggest. I am presently using Amsoil 2 stroke oil (the 100:1 stuff). Going with a 10:1 oil ratio might be wise until it gets run in good too. Don't let it go lean as gasoline runs at a much more lean air/fuel ratio and the engine can run out of oil fast in lean running situation.

In case people didn't read it earlier on. Go 6 turns out on the low speed needle and 1 and 1/2 turns out on the high speed, maybe a 1/2 turn more to start with. Idle speed is with the throttle 1/2 open, yeah it's weird the way the carburetor works.
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Old Aug 24, 2012, 12:38 PM
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Canada, MB, Winnipeg
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Quote:
Originally Posted by waynemia View Post
OK, I just received one of these today. I don't know if I should start it or ship it back. Is anyone flying this engine stock? I don't intend to spend a lot of money making this ready to fly............
Thanks,
Wayne
I think Earl is right when he talks about what others are saying. It is typical when it comes to people that for every 1 person that complains there are 10 that are doing ok, are happy, and don't complain. I believe that Earl has done more experimenting than anyone else with this engine, so he has good advise. The 2 biggest problems are the quality control (hit-n-miss), and the con-rod being weak sometimes and it's fit. So use extra air cooled 2 stroke engine oil and apply the mod that Earl found for the pump (larger nipples and hose). As for warranty, it seems that Micheal Chow is more than willing to help out. Oh, if you are going to use 10% ethanol fuel change the pump valving to the teflon (White) ones. Been using these ones for 30 years whenever I can on my 2 strokes, they last a lot longer with gasahol fuel.

Good Luck
Ray
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Old Aug 24, 2012, 01:03 PM
A trail of smoke is GOOD!
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USA, TX, Springtown
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Thanks guys. I am sending it back. I would rather eat the $20 for shipping both ways than have to deal with any potential issues.
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Old Aug 24, 2012, 07:23 PM
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Originally Posted by waynemia View Post
Thanks guys. I am sending it back. I would rather eat the $20 for shipping both ways than have to deal with any potential issues.
Good on ya Wayne if everybody did this than they might think twice before putting out stuff before its ready . Cheers the pope
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Old Aug 25, 2012, 02:36 PM
Heathkit DX-100 son of Bullet
Gary Cee's Avatar
United States, MI, Marysville
Joined Apr 2010
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Amen to the Pope ...and Earl . All a part of the journey . Not all that bad anyhow !
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Old Aug 25, 2012, 05:59 PM
Demonstrations on Saturdays!
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Joined Jan 2012
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Good for you Wayne. If you work for your money you want to send the popes message.
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Old Aug 26, 2012, 02:46 PM
SBP
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United States, PA, Waynesboro
Joined Aug 2011
97 Posts
Electric for now

I've purchased a used electric powered ESM Beaver w/59 in wing span that I would like to convert to gas. I had hoped the problems with the 9cc engine would have been solved by now. I really wanted to try this engine but I believe I'll wait a little longer before I spend a couple hundred dollars to be disappointed. Many thanks to all for the posts on this engine.
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Old Aug 26, 2012, 06:48 PM
Heathkit DX-100 son of Bullet
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United States, MI, Marysville
Joined Apr 2010
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Some folks actually enjoy the journey .
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