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Building a P82 with YS60's

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Old 03-07-2008, 12:13 PM
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still4given
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Default Building a P82 with YS60's

Hi Guys,

I am just about complete with my P-82 from Nitroplanes. I have a pair of YS60's that have been looking for a home so I decided to use them for this. I didn't have two headers so I ordered one from Macs and then last night I began cutting the new one down to optimize the length. I'm spinning an APC 10x10 on it. When I reached the same length that I am running on the old one I noticed that I am getting a bit higher RPM on this engine than the one with the old pipe. The engine with the old pipe is turning about 14,100 peak and this one is turning 14,700. Header pipes are the same length and I was swapping the same tuned pipe between the two to eliminate any variance there. Both engines are transitioning well and seem to run the same but one is down a little in RPM. Normally I wouldn't worry about this but I'm thinking that a twin is not going to like this much.

I'm open to ideas about what might be causing this differential and how to fix it. I plan to use this plane for warbird pylon racing in three weeks so I would like to get some time in on it before then.

Blessings, Terry
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Old 03-07-2008, 01:17 PM
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Default RE: Building a P82 with YS60's

Are you testing these on a bench or in the airframe? The reason I ask is a slight kink or pinch in the fuel line could cause this issue. You could also try swapping the check valves to see if one is a little more restrictive than the the other and therefore you are not getting equal pressure in the fuel tanks. All of this also takes for granted that one engine is not more worn than the other.
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Old 03-07-2008, 02:03 PM
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Default RE: Building a P82 with YS60's

Testing on the bench right now. Same check valve, tank etc. Only thing different is the engine and header. I have no idea about wear. The one with the lower RPM I have had since 1989 but I don't think I put more than 2 gallons through it. The other I won on ebay and it looks well used but has great compression and feels equally as smooth as my original. Maybe I need to install new bearings. That engine sat in a box for almost 20 years.

Blessings, Terry
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Old 03-10-2008, 05:45 AM
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Default RE: Building a P82 with YS60's

May I ask for your header length? I am running the same engine but using a 11x10 APC prop for a little less rpm. Thanks.
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Old 03-10-2008, 09:40 AM
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Default RE: Building a P82 with YS60's

I'll measure it when I get home.
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Old 03-10-2008, 03:27 PM
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Default RE: Building a P82 with YS60's

What pipes are you using ? Pipes are often different. Even two from the same manufacturer can be different.

The "pipe system" length is more important than simply a measurment of the header length. If you have the high point of the pipe (or reflector baffles) at different distances, that will cause a different tuning point.

Easy fix for your observastion is to lengthen the pipe system for the "high" rpm engine an extra 1/4" and try it again. If they match closer, then clip the "low" engine a bit more to see if it will come up to match the 14,700 rpm side.

Bob
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Old 03-10-2008, 04:54 PM
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Default RE: Building a P82 with YS60's

Try a new glow plug in the slow one. Just because it runs doesn’t mean a thing. I've found bad bearings can have a surprising effect too.
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Old 03-10-2008, 08:42 PM
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Default RE: Building a P82 with YS60's

Hi Bob,

I'm not sure exactly which pipe I have. I know they are Mac's but I bought them 20 years ago and I haven't seen them anywhere lately. I first set up the header with the other pipe in the picture, but when I tried my muffled pipes I got the same RPM and they sound much better than the un-muffled pipe so I am going with them. The last time I ran the two engines they were within 300 RPM of each other so I may just pulling out the pipe on the faster engine to drop the rpm a touch. Who knows, they may get closer to each other once they unload in the air. I hope 300 RPM isn't going to make it too difficult to fly.

I did use new plugs in both engines.

Here's some pics
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Old 03-10-2008, 08:46 PM
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Default RE: Building a P82 with YS60's

Just another idea. Could a diaphram that is expanded(aged) or more or less flexible affect the rpm? I have a three YS 61s and have always been curious how a diaphram failure is exhibited. Does it just suddenly fail or can there a progressive deterioration in performance then a failure? Maybe someone could chime in that has experience with these.
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Old 03-12-2008, 12:56 AM
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Default RE: Building a P82 with YS60's

As long as each engine is "happy", you won't notice a difference of 700RPM in the air. The biggest mistake people make with twins is to "match" the two engines RPM's. Ultimately when doing so, they're making one engine less reliable.....and when that engine dies they'll have a much bigger RPM difference. If you adjust each engine so it's running well, ignoring the other, you'll be fine. It's also very possible that the two engines will be running closer together once they're in the air and unloaded. Ground RPM is about as important to a flying airplane as the air above it or runway behind it.
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Old 03-14-2008, 12:54 PM
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Default RE: Building a P82 with YS60's

The weather hasn't been cooperating so I have not been able to fly it yet but I did get a chance to run the engines together. They seem to get on step together pretty well. I have been running McCoy #59 plugs in most of my 2 stroke engines but they don't seem to like these YS 60's. I'm running 30% Heli fuel and running them pretty rich but it seems I can only get a couple of tanks of fuel through them before the plug starts failing. Do you think maybe an OS#8 might be a better match for these? Maybe a McCoy #9?

Thanks, Terry
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Old 03-14-2008, 01:15 PM
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Default RE: Building a P82 with YS60's

ORIGINAL: still4given

The weather hasn't been cooperating so I have not been able to fly it yet but I did get a chance to run the engines together. They seem to get on step together pretty well. I have been running McCoy #59 plugs in most of my 2 stroke engines but they don't seem to like these YS 60's. I'm running 30% Heli fuel and running them pretty rich but it seems I can only get a couple of tanks of fuel through them before the plug starts failing. Do you think maybe an OS#8 might be a better match for these? Maybe a McCoy #9?

Thanks, Terry
I'm running OS F plugs in my Rossi 61 and YS 61s. The F plug seems to help idle operation and last longer than OS 8's. I may have gotten the idea from bob27s. I would PM Bob, bob27s, and ask. He obviously is as knowledgeable as anyone on the forum.
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Old 03-15-2008, 04:16 PM
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Default RE: Building a P82 with YS60's

Maybe Bob will chime in here again. He is the one who gave me the idea to use McCoy 59 plugs in my Jett SJ50. They have been working very well for me. I'm just wondering if they are too hot for the YS 60 on 30%. Maybe I jsut need to lower the nitro.

Blessingsk, Terry
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