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  #21  
Old 04-14-2017, 07:10 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Tomcat RV4 View Post
Come on guys & girls ,it's about time aviation moved into this century, in 1995 I would not trust electronic ignition, but today ,no reason not to use it along with NORMAL spark plugs !
Perhaps it's time to follow the discussion a bit more closely, which is not about mags vs EI, or inductive vs CDI, or self-powering vs external power.

This is about selecting optimal advance values for the two very different mixture regimes, economy lean of peak and best power rich of peak. The available data says the P-mag's advance map is reasonable for LOP operation, but very poor for ROP operation. The result in the field has been hot cylinder heads in climb, or step climbing, or low rate, high speed climbs, or reworked fuel controls to pour on excess fuel.

Moving forward in technology would be an ignition which provides for two individual maps, one for each operating regime. Even with the addition of an EI Commander, P-mag users can't do it...which is not to say it can't be done. We're talking about a toggle switch and a software change, with maybe a chip swap or two in the bargain. Dual map ignition controllers are available to the car guys for peanuts. The two I'm flying cost me $140 each on sale. It's not cold fusion.

BTW, moving into this century would require an engine management system linking ignition advance to mixture state at the chip level, and varying it automatically...very limited advance while ROP, and much more advance with LOP mixture and low MP. Ross at SDS has already stated his intent to start system development now, in anticipation of widely available no-lead avgas, which will allow reliable exhaust sensor operation...you know, like cars.
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  #22  
Old 04-14-2017, 07:25 AM
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rv6ejguy rv6ejguy is offline
 
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As far as ignitions go, we're already offering fully optimized timing, albeit manually controlled at the moment. We typically program WOT ROP timing at around 24-25 degrees on 100LL and about 22 on 91 mogas. We may advance about 4 more degrees at MAPs down around 20 inches and a couple degrees around 25 inches. In any case, the CPI is user programmable in logical 1 degree increments for both rpm and MAP should you want to change the curves to suit different compression ratios, fuels or special flight conditions.

With the LOP switch, you can add whatever you want to the basic, automatic mapping. Users are typically adding about 4 to 7 degrees more timing with the LOP switch. One Lancair user adds 10 degrees (base rpm timing 24 degrees) as he flies high and LOP almost all the time.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm


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  #23  
Old 04-14-2017, 07:32 AM
KatanaPilot KatanaPilot is offline
 
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Originally Posted by DanH View Post
http://www.vansairforce.com/communit...d.php?t=148100

Get an online subscription to Kitplanes. You can read everything in current issues plus all the back issues.

Here on VAF, the quick version:

http://www.vansairforce.com/communit...6&postcount=15



Bill, are you listening to yourself? You and your partner created a device to modify the supplied p-mag advance values.

The result is still not anywhere as good as a dual map system, but that's not your fault.
It appears to me that the baseline advance is a bit high. My very simple understanding of the Pmag believes that can be easily fixed using either programming an offset or by "fooling" the system by physically retarding the Pmag by a couple of degrees from TDC prior to setup.

The slope of the advance curve seems a little steep and starts a little early. That would be a bit harder for the user to correct.

I've asked the Emag folks to respond to my concerns brought to light by you and Nigel.
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  #24  
Old 04-14-2017, 07:42 AM
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Quote:
Originally Posted by rv6ejguy View Post
With the LOP switch, you can add whatever you want to the basic, automatic mapping. Users are typically adding about 4 to 7 degrees more timing with the LOP switch. One Lancair user adds 10 degrees (base rpm timing 24 degrees) as he flies high and LOP almost all the time.
Ross, confirm my understanding please.

In the context of separate, switch controlled ROP and LOP advance values, the CPI is an offset system, i.e. the LOP switch adds an offset to the base map, that offset being a single value?

Simple example; assume a base map with no advance, just a fixed 25 degrees BTDC for all RPM and MP conditions. The LOP switch allows adding one value to all points on the base map, i.e. if the owner selected 5 degrees, flipping the switch would result in 30 BTDC at all RPM and MP points?

If so, then it is not possible to create two independent maps, one with limited or no advance (flat across all conditions), the other with advance ramping up significantly with reduced MP (a steep slope)?
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Last edited by DanH : 04-14-2017 at 07:47 AM.
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  #25  
Old 04-14-2017, 10:06 AM
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Quote:
Originally Posted by DanH View Post
Ross, confirm my understanding please.

In the context of separate, switch controlled ROP and LOP advance values, the CPI is an offset system, i.e. the LOP switch adds an offset to the base map, that offset being a single value?

Simple example; assume a base map with no advance, just a fixed 25 degrees BTDC for all RPM and MP conditions. The LOP switch allows adding one value to all points on the base map, i.e. if the owner selected 5 degrees, flipping the switch would result in 30 BTDC at all RPM and MP points?

If so, then it is not possible to create two independent maps, one with limited or no advance (flat across all conditions), the other with advance ramping up significantly with reduced MP (a steep slope)?
Default timing is generally set for ROP operation with the LOP switch off.

Your example is correct.

It's not possible or probably necessary to have two independent timing maps for a Lycoming unless you're running 2 different fuel octanes and want to increase detonation margins.

Normal map is programmable to let you have total timing wherever you want to make best power ROP. If we go LOP, and flame speed drops by 30%, when we throw the LOP switch, we initiate ignition say 5 degrees sooner to make up for the slower flame speed and still get peak cylinder pressure (PCP) at the optimal point for extracting best power and energy from the fuel.

The standard map if done correctly, has already optimized for rpm and MAP variables so LOP slower burn speed is the only significant one left to compensate for.

Most flight and dyno data show Lycomings are relatively insensitive to timing regarding power at WOT, ROP. 22 to 27 degrees.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi2.htm


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  #26  
Old 04-14-2017, 10:13 AM
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N941WR N941WR is offline
 
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Nigel's engine is an IO-360 parallel valve with 10:1 compression pistons and was used for all of his testing.

How much of an impact would this have on his results over a standard 8.5:1 compression engine?
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  #27  
Old 04-14-2017, 11:11 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
Ross, confirm my understanding please....
I know this is directed at Ross, but let me help out as a user of this system until he weighs in...

Yes, the LOP feature of CPI throws a set value (4 degrees, in my case) on top of whatever point in the curve you happen to be at. So no matter where you are from idle to WOT, if you flip the LOP switch you get 4 more degrees of advance.

While this is not a "dual map" scenario you envision, we need to keep in context the laws of diminishing returns for "absolute" optimization. Keep in mind that even the tightly controlled, squeaky clean world of automobile emission compliance a WOT acceleration run is "open loop" and very rich, to the point of intentionally dumping raw fuel into the exhaust just to keep the cats alive. Even in cars, there is a optimized "normal" condition, and a "close enough" outlier condition. It's hard to expect even tighter optimization in airplanes.

I think that for most people, LOP ops is most often a very specific flight condition, not used for general utility. And while I have not done specific testing of optimized LOP ops at anything other than my normal cruise altitude of 8500, I do often go LOP during cruise formation work, LOP climbs as a means of CHT temp control, and low power, low altitude cruising around stuff. In short, I am LOP anytime I am not asking for big power from the engine, and I'd bet that the added 4 degrees I find optimal at 8500 cruise LOP is going to be pretty dang close at my other LOP conditions too. Yes, I know I need to prove it.

So while a dual map (LOP/ROP) would be "neat", I'm questioning how much practical utility one would derive beyond what is available today. And considering just how radically the ignition advance curve ramps up with the distance from peak, can you really have just one map for LOP? It's a slippery slope.
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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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  #28  
Old 04-14-2017, 01:31 PM
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Quote:
Originally Posted by Toobuilder View Post

So while a dual map (LOP/ROP) would be "neat", I'm questioning how much practical utility one would derive beyond what is available today. And considering just how radically the ignition advance curve ramps up with the distance from peak, can you really have just one map for LOP? It's a slippery slope.
Aaahhh - and that's where we get into good oxygen sensors and precision injectors with flow monitoring, and a 3D surface for the mapping rather than a simple 2D curve. How far down the rabbit hole shall we chase?
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  #29  
Old 04-14-2017, 02:06 PM
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erich weaver erich weaver is offline
 
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Quote:
Originally Posted by airguy View Post
How far down the rabbit hole shall we chase?
Not very far. The big takeaway from Nigel's article seems to be that the potential gains from timing tweaks are pretty small and as you state, things get a little messy when throwing mixture into the mix

I retarded the timing on my Pmags across the board by moving the flywheel off of TDC by a few degrees during set up to fix a recurrent kickback issue on start up. Didn't realize it til later, but that change also signiicantly lowered my in-flight CHTs while not having any noticeable negative effect on speed. I'm calling it good.

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  #30  
Old 04-14-2017, 02:08 PM
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DanH DanH is offline
 
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Originally Posted by rv6ejguy View Post
It's not possible or probably necessary to have two independent timing maps for a Lycoming unless you're running 2 different fuel octanes and want to increase detonation margins.
Certainly possible. I'm flying a system with two independent maps right now, switchable in flight.

Certainly not necessary. After all, we've been flying fixed timing for a long, long time with satisfactory results. Variable timing is about optimizing.

Different octanes wouldn't require independent maps. An offset would work fine.

Quote:
Most flight and dyno data show Lycomings are relatively insensitive to timing regarding power at WOT, ROP. 22 to 27 degrees.
Exactly, which is why a P-mag ramping to 38 is fine for LOP, but a poor choice for ROP. All it does it increase CHT.
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