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  #81  
Old 08-11-2011, 05:03 PM
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Quote:
Originally Posted by Toobuilder View Post
Detonation is really the only important factor in the entire LOP subject, and the one that seems to have the most mystery surrounding it.I suspect that resolution would lift the fog surrounding LOP ops once and for all.
Yep.

Refer back to post #41 and the standard Lycoming power chart.

Quote:
Originally Posted by David-aviator View Post
I don't know if Lycoming meant that line to be a detonation line or not....
Oh ye of little faith

Lycoming offers some discussion of the limit line in Lycoming Flyer Key Reprints (page 44, lower left), but like some of you I prefer straight data. The following charts are from a Lycoming test cell, detonation runs made with 100LL for baseline comparison to the same IO-360 on an ethanol fuel. It takes more than three charts to illustrate the entire limit line as found on the power charts, but you can get a taste.

Look close at the operating temperature conditions. All the runs are made in accordance with FAR 33.47 and its companion AC 33.47-1 dealing with how detonation tests shall be conducted. At least one CHT must be at max and the others close to it, oil temp is near max, and intake air temperature is ~100F......pro-detonation conditions.

First up, 26.8 MAP and 2700 RPM. From the top down you have CHT, EGT, power, BSFC and detonation. The detonation graph is expressed as a percentage of firing events. In this test they pulled mixture from rich through peak to 40-60 degrees LOP. Detonation percentage is zero:



Let's make things more difficult, full throttle, 28.5 MAP and 2700 RPM. Again mixture is pulled from bog rich to LOP. There's a slight nibble of detonation right at peak EGT (less than 5% of firing events) and well lean of best power:



Ok, let's see that detonation limit. This run is again 28.5 MAP, but the RPM is hauled back to 2400 RPM....ouch. It detonates 10%, maybe 12% at ~25 ROP, a little lean of best power. You could even argue power fell off because it started to detonate. Whatever, it's the limit:



28.5 and 2400, the upper end of the limit line on the power chart. There's your red box for a low compression NA Lycoming on 100LL:



Keep it cool and pay attention to what you do with the prop control, and it becomes difficult to hurt it with the mixture control. You don't need twenty pages of Deakin or a trip to charm school. You really don't need to understand much more than the basics, the very first graph in the first post of this thread.....information published by both GAMI and Lycoming.



Of course if you run more ignition advance, less octane, high compression pistons, a turbo, or anything else which steps away from the base version, you get to find your own detonation limits.
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Last edited by DanH : 11-24-2014 at 12:40 PM.
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  #82  
Old 08-11-2011, 05:26 PM
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erich weaver erich weaver is offline
 
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Originally Posted by RV10inOz View Post
Now maybe I am being picky, and you may not have meant it this way, but Detonation will occur without high CHT's, .....but not for very long. the rapidly rising CHT is a symptom of detonation, its how you spot it happening.
Absolutely. Thanks for fine tuning my previous statement.

erich
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  #83  
Old 08-11-2011, 05:54 PM
asav8tor asav8tor is offline
 
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Quote:
Originally Posted by DanH View Post
Yep.




Ok, let's see that detonation limit. This run is again 28.5 MAP, but the RPM is hauled back to 2400 RPM....ouch. It detonates 10%, maybe 12% at ~25 ROP, a little lean of best power. You could even argue power fell off because it started to detonate. Whatever, it's the limit:



28.5 and 2400, the upper end of the limit line on the power chart. There's your red box for a low compression NA Lycoming on 100LL:


looks like you could use a rule of thumb..........

RPM/100 + 4 as an absolute limit,

2000 rpm, max MAP 24

2300 rpm, max MAP 27

etc,
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  #84  
Old 08-11-2011, 06:56 PM
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Dan,

Great work!

Quote:
You don't need twenty pages of Deakin or a trip to charm school.
As for the trip to charm school, well thats a bit unfair. You and I might understand test data, and in this case you have explained a lot of stuff with a page or two, but we are only talking about one small matter of running an aero engine. APS do not spend two days talking about this one thing.

What charm school does is educate people on the wholistic understanding of engine operation and fault finding. not sure what you do but I guess you work for lycoming or somewhere where good data and knowledge exists, or are just one of the few real enthusiasts. Either way many aircraft owners are not degree qualified engineers specialising in areas that make this stuff easy to pick up and understand. Most Lawyers and accountants would struggle with the concept of torque on a bolt and nut and how that relates to tension in the bolt. Let alone any of this.

So Charm school as you call it is about the only available resource anywhere in the world, and for those of us on the other side of the planet the online version is about as good as it gets. trust me in a so called 1st world country, I only know of one engine shop in Australia that understands this stuff and has a similar dyno stand, albeit without all the sensors plugged into an engine as GAMI do.

Anyway, do you have the same test charts for an engine at say 350F. This would be more representive of how we all operate, and while detonation margin is a semi-fluid thing, it would show a smaller red zone no doubt.

Again....I appreciate your input, you have more patience or time to find all this stuff than I do.
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  #85  
Old 08-11-2011, 07:26 PM
David-aviator David-aviator is offline
 
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Good research work, Dan.

Now we know why that line is there and it is a detonation line.
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  #86  
Old 08-11-2011, 07:29 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
...At least one CHT must be at max and the others close to it...
So do we mean 500 degrees for CHT as the "max"? If so, then I would suspect a huge detonation margin at even the "too hot" 400 that most of us use as a limit, let alone the more typical mid 300's.

I would expect the thing to detonate at idle with a CHT at the limit!
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  #87  
Old 08-11-2011, 09:55 PM
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Quote:
Originally Posted by Toobuilder View Post
So do we mean 500 degrees for CHT as the "max"?
Look at the very top of all three charts Mike. AC33.47-1 requires one cylinder be within +-10 degrees F of maximum when leaned to highest CHT, and all others must be with 50F of the hottest one.

Quote:
Originally Posted by RV10inOz View Post
Anyway, do you have the same test charts for an engine at say 350F. This would be more representive of how we all operate, and while detonation margin is a semi-fluid thing, it would show a smaller red zone no doubt.
No doubt.

Having been schooled, can you tell us why the suggested mixture setting on the red box graphic suddenly shifts to ROP above 9000 MSL?
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Last edited by DanH : 08-11-2011 at 09:59 PM.
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  #88  
Old 08-11-2011, 11:45 PM
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erich weaver erich weaver is offline
 
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Quote:
Originally Posted by DanH View Post
Having been schooled, can you tell us why the suggested mixture setting on the red box graphic suddenly shifts to ROP above 9000 MSL?
It's been awhile, but I went through the Deakin articles (although not the school) pretty carefully in the past, and I don't recall this shift to ROP being recommended or discussed. Does someone have the reference for this?

Regards

Erich
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  #89  
Old 08-12-2011, 12:34 AM
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You guys are smarter than this, or is this a bait?

Once you get to a height where say 60% is achieved, you can put the mixture/RPM wherever you like it to achieve the speed or MPG as you choose.

I get a bit of RAM AIR effect compared to say a C182 might, so the difference of 7500-9000' is a bit variable but even my RV does not generate enough MP at 8500+ to be an issue. So I would suggest from 9000' onwards you can do what you like. No risk. 50ROP gets a nice TAS up high for no more fuel flow than down lower at 20-40LOP and a lower TAS.

Go try it for yourself. Early FL's will show you. Or attend the course and ask the question of the APS team. Of which I am not one of!

Seen this before anyone? Take note of the second line....of text that is

________________________________________
Red Box = No Fly Zone
• At and below about 60% power, there is no red box. Put the mixture wherever you want it.
• At about 65% power or so, 100ºF ROP to Peak.
• At about 70%, 125ºF ROP to 25ºF LOP.
• At about 75%, 180ºF ROP to 40ºF LOP.
• At about 80%, 200ºF ROP to 60ºF LOP.
________________________________________


________________________________________
Outside the Box
• At 65% power, use richer than 100 ROP, or leaner than peak EGT.
• At 70%, use richer than 125ºF ROP, or leaner than 25ºF LOP.
• At 75%, use richer than 180ºF ROP, or leaner than 40ºF LOP.
• At 80%, use richer than 200ºF ROP, or leaner than 60ºF LOP.
________________________________________


PS: RE the 60% >>> With cool most of the engines we use, between 60 and 65% its probably OK, it should be remembered these are not hard and fast numbers, bit of give and take is allowed here.

Last edited by RV10inOz : 08-12-2011 at 06:44 AM. Reason: typo and adding the PS bit
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  #90  
Old 08-12-2011, 01:19 AM
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John Clark John Clark is offline
 
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Quote:
Originally Posted by erich weaver View Post
It's been awhile, but I went through the Deakin articles (although not the school) pretty carefully in the past, and I don't recall this shift to ROP being recommended or discussed. Does someone have the reference for this?

Regards

Erich
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