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  #21  
Old 08-12-2022, 12:04 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
Some thoughts:
- CHTs. Yep - get more power out of a cylinder and CHTs go up. Take the timing too far advanced and the CHTs goes up. PMags are close to base timing (whatever you set them at) on take off and full power - so results will be very close to a mag set at that same timing.

Carl
That is not really correct. As the plane climbs, the MAP naturally decreases as the altitude grows, even when WOT. By about 7K, you are below 25" and the advance starts increasing. HOWEVER, most pilots are still ROP at this point and 25* or a bit less is a much better setting when ROP at 25". The higher the climb the greater the advance (the table gives greater and greater advance as the MAP drops), even though it is not helping performance. It is just raising temps. Level off in cruise and go LOP, THEN the advance provides benefits. If you climb LOP, this does not apply.

When I used an advance map similar to what Pmag uses (didn't fully understand the issue at the time), I would start to see CHTs rise to undesirable levels once I got to 7 or 8K and would get worse and worse the higher I climbed until I leveled off and went LOP. I now use 21-25* (same as a mag) when ROP and all CHT issues went away (reductions of 40 degrees) with no performance drop. Simply put, advance levels beyond 25* are only beneficial when Peak or leaner and detrimental when at best power or richer.

If you reduce the base timing then the CHT problems when ROP go away, but you are also now less advanced in cruise and have given up part of the benefit of increased timing advance in the dominant flight configuration.

This is one of the key flaws with preset advance maps. They have no method of determining how rich or lean the mixture is and mixture has the greatest impact on optimal advance, as mixture predominately dictates the flame front travel speed. The best way to overcome this is wtth an EI product that lets you tell the system whether you are LOP or ROP and alter the tables accordingly. This is how auto systems work. They control both fuel and ignition, so can tailor the advance to the current mixture level.

Larry
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Last edited by lr172 : 08-12-2022 at 12:25 PM.
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  #22  
Old 08-12-2022, 12:15 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by MacCool View Post
Of course, one key component in doing one’s homework on a Van’s RV maintenance topic is a post on VAF asking for opinions from the many knowledgeable folks here. I wouldn’t view that as building my airplane on consensus, but rather using that consensus as a starting point in doing my homework.
Many of the posters on this forum are very, very forthcoming with data and educated advice. Those posts exist today, and are available for the reading for anyone to take the few moments to do a simple search. The OP asked, by name, for a "consensus".

I can tell you for a fact that the opinions I have posted in this thread are a result of a lot of avgas burned a lot of discrete data collected, and have been posted many times before. A search will uncover my and other posts directly related to this subject. To start yet another thread as the begining of "homework" is a bit "disrespectful" to those of us who have taken the time to collect, reduce and present flight test data countless times over the years.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #23  
Old 08-29-2022, 04:58 PM
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akschu akschu is offline
 
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I break down EI systems into two camps.

1. Direct Mag replacement. The unit goes into the mag hole and uses the gears for timing.

2. Replace mag system. The unit goes in the cockpit with coils mounted on the engine or firewall with a crank position trigger.

System 1 has electronics bolted to a hot vibrating thing and depends on bearings/gears/etc. The best one is probably a pmag because it has a generator to eliminate the need for backup power and it's very popular.

System 2 has electronics insulated from the hot vibrating thing and only mechanically depend on a crank position trigger which is a magnet passing a sensor. The best one is probably the SDS CDI 2 because it has the ability to hookup a small backup battery that is completely separate from the rest of your electrical system and the unit maintains it.

So, what makes you feel more comfortable? A backup generator bolted to a hot engine or a backup battery in the cockpit? Making the argument that one doesn't depend on electrons is not true, they both do.

Also, Would you rather not know what your timing is or purchase an external box, or would you like the programming and timing right on the panel? Would you rather inspect the unit on the back of the engine and periodically pull it to look at bearings/etc or would you rather inspect the crank sensor and wires at the prop?

Once I considered these things I knew which system I wanted.

schu
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  #24  
Old 08-30-2022, 05:15 AM
nohoflyer nohoflyer is offline
 
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Quote:
Originally Posted by MacCool View Post
Of course, one key component in doing one’s homework on a Van’s RV maintenance topic is a post on VAF asking for opinions from the many knowledgeable folks here. I wouldn’t view that as building my airplane on consensus, but rather using that consensus as a starting point in doing my homework.
What he said.

For those of you who say “do your homework”, that is what this site is for me. A jumping off point. Personally I’m not a mechanic and have no experience with engines at all. And everything I know is all jets (don’t even know what LoP means yet!) In fact, though I’m far from making this decision, it has mulled over me. So I come here and usually use the search function. When I don’t find what I’m looking for I ask the question. A simple response like “look at power plants and there was a good discussion on this about 8 months ago” would suffice.

If you don’t want to answer than just don’t. Nobody is making you reply to any post. The reason this place works is that usually someone will and it will either be with an answer based on their experience or some advice on where to look. Also, realize that most post are hidden after six months and if you use the pull down you can see older ones (something I just learned).

This site doesn’t work when the reply is “do your research”.

JMHO.
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Last edited by nohoflyer : 08-30-2022 at 05:40 AM.
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  #25  
Old 08-30-2022, 06:12 AM
Dad's RV-10 Dad's RV-10 is offline
 
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Quote:
Originally Posted by nohoflyer View Post
... Also, realize that most post are hidden after six months and if you use the pull down you can see older ones (something I just learned)...
FYI, if you click "User CP" you'll see "Edit Options" listed on the left under "Settings and Options."

You can change the "Default Threads Age Cut Off" to "Show all threads."

Also, you can choose to receive email notification of new Private Messages (and thread subscriptions). I mention this because I think many users are unaware. They post things like "I don't check the forum often" or they simply never open a message that's sitting in their Inbox.


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  #26  
Old 08-30-2022, 08:17 AM
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Tankerpilot75 Tankerpilot75 is offline
 
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I’ve appreciated the responses received to my initial request for PMag PIREP information. However I have been somewhat offended by the responder who claimed the post was “disrespectful” of their previous posting efforts. Frankly, if everyone who had a question searched every previous posting on this forum there would be fewer and fewer postings and information exchanged.

I’m not an engineer, nor a serious wrench jockey. I am someone who wants his RV to perform the best it can within my realm of affordability and capabilities to maintain and operate. I’ve gleamed a lot of information from this thread - as is the purpose of the forum and made a decision to go with dual PMags on the rebuild. If CHTs become a problem then at least I have a better idea of the probable cause and possible solution.

My request is simple. Be respectful of an OP’s question. Maybe they’re not the expert you are but being willing to politely share your knowledge and possibly educate them is what’s important. Moderator, please close this thread!
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  #27  
Old 08-30-2022, 08:30 AM
Bavafa Bavafa is online now
 
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Quote:
Originally Posted by Tankerpilot75 View Post
I’ve appreciated the responses received to my initial request for PMag PIREP information. However I have been somewhat offended by the responder who claimed the post was “disrespectful” of their previous posting efforts. Frankly, if everyone who had a question searched every previous posting on this forum there would be fewer and fewer postings and information exchanged.

I’m not an engineer, nor a serious wrench jockey. I am someone who wants his RV to perform the best it can within my realm of affordability and capabilities to maintain and operate. I’ve gleamed a lot of information from this thread - as is the purpose of the forum and made a decision to go with dual PMags on the rebuild. If CHTs become a problem then at least I have a better idea of the probable cause and possible solution.

My request is simple. Be respectful of an OP’s question. Maybe they’re not the expert you are but being willing to politely share your knowledge and possibly educate them is what’s important. Moderator, please close this thread!
Before it gets close, I just want to say well said here, I completely concur.
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  #28  
Old 08-30-2022, 08:44 AM
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Aviator Aviator is offline
 
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So this a thread with a lot of detail and information.
Why should it be closed.
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  #29  
Old 08-30-2022, 08:47 AM
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RicoB RicoB is offline
 
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He could of at least sent the link for the thread that he was talking about.
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  #30  
Old 08-30-2022, 09:11 AM
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MacCool MacCool is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Many of the posters on this forum are very, very forthcoming with data and educated advice. Those posts exist today, and are available for the reading for anyone to take the few moments to do a simple search. The OP asked, by name, for a "consensus".
Many of the posters on this forum are very, very new at airplane building/maintenance and new to this forum. The search that some think is so “simple” for them is impaired for the newbie by the “you don’t know what you don’t know” concept, not to mention cumbersome limitations imposed by vBulletin’s arcane search engine. It would seem reasonable to hope that if an “expert” would take the time to read the post and type the response “do a search”, maybe he could help out a less knowledgeable poster and take a little extra time and provide a link. Otherwise…maybe just skip over the post altogether….always an option.
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Last edited by MacCool : 08-30-2022 at 09:19 AM.
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