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  #71  
Old 08-11-2011, 08:36 AM
RV8R999 RV8R999 is offline
 
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I'm interested it what he thinks is going on between 8-9K to develop the severe knee in the curve? Everything is linear up to this point and all of a sudden a big discontinuity...
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  #72  
Old 08-11-2011, 08:45 AM
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Originally Posted by Moura View Post
Michael, 395 and 380 EGT aren't too high for LOP ops?
...I think you mean 395 and 380 CHT...

As far as I'm concerned, that's too high for continuous ops, period. However, there is no chance of detonation at this altitude, so any side of peak EGT makes the CHT cooler. I just picked LOP because it has the same effect on CHT (on this airplane) as ROP, but is much cheaper. The high CHT shown (or more to the point, the wide spread between cylinders) is another issue I'm trying to resolve. I have yet to determine if I have a baffle problem, incorrect fuel scheduling, the wrong nozzles or something else. As pointed out in the thread where this picture originates, it may be a combination of multiple problems.

For the purpose of this thread however, the engine seems perfectly happy running LOP at altitude.
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  #73  
Old 08-11-2011, 08:47 AM
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Originally Posted by RV8R999 View Post
I'm interested it what he thinks is going on between 8-9K to develop the severe knee in the curve? Everything is linear up to this point and all of a sudden a big discontinuity...
...And why does it go perfectly flat at 9.5? No data?
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  #74  
Old 08-11-2011, 09:32 AM
David-aviator David-aviator is offline
 
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Originally Posted by Toobuilder View Post
...And why does it go perfectly flat at 9.5? No data?
The answer is power and speed. Here's what he has to say about it.

The same chart can be used for illustrating the climb, if you climb as I suggested a couple of columns ago. Leaning to that target EGT as you climb produces pretty much what you see on the second chart, just rich of the red box. Once you get to your altitude (the example is at 4,500 feet), do the "big mixture pull," and set LOP. The green lines show a good area to be in when running LOP, up to about 9,000 feet altitude. At and above that point, you probably want to switch over to ROP to keep the power up as much as possible.

For efficiency LOP is very good. Fuel mileage is up, consumption is down, and so are EGT's and CHT's.

His chart is an illustration of going LOP in climb which I think is a bit over the edge. Why sacrifice power in climb to be LOP and then go ROP for power and speed in cruise? This all just talking stuff. It makes more sense to me to get to altitude ASAP and cruise at whatever you want - speed or efficiency.

There certainly is no problem LOP at altitude unless you need a warmer EGT for cabin heat.

The temps will run very cool which is a life extended for these engines, no doubt about it.
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  #75  
Old 08-11-2011, 10:06 AM
nucleus nucleus is offline
 
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Talking LOP at altitude

Deakin has his little green lines move to ROP at altitude for speed and power reasons - I run LOP at altitude all the time... There is no "red box" at altitude - no risk of detonation.

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  #76  
Old 08-11-2011, 10:23 AM
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Quote:
Originally Posted by David-aviator View Post
Michael,

...I have not compared every statement and written word by Deakins and Busch, but they generally are in agreement...
Thank you for taking the time to write that response David. I am certainly an advocate of LOP ops when appropriate, and do not fear it at all. The only possible danger of running lean that I can see is detonation, and this is where most of the confusion and arm waving is found. Take detonation out of the picture, and the advantage of running LOP is clear - cooler, cleaner, cheaper flying. However, the detonation issue clouds things up and injects fear into the debate. Some will say with near certainty that "our" engines have a very wide detonation margin, while others take a more cautious approach. Lycoming itself publishes "limitations" based on the ability to monitor the engine: If you have a MP instrument, then the limits apply, if you don't, then don't worry about it. And let's not also forget that Lycoming also endorses operating continuously at PEAK EGT!

Anyway, the fact that this discussion has turned to detonation is the right one IMHO. 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.
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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.

Michael Robinson
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1984 L39C
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  #77  
Old 08-11-2011, 03:39 PM
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Quote:
Originally Posted by Toobuilder View Post
The only possible danger of running lean that I can see is detonation, and this is where most of the confusion and arm waving is found. Take detonation out of the picture, and the advantage of running LOP is clear - cooler, cleaner, cheaper flying. However, the detonation issue clouds things up and injects fear into the debate. Some will say with near certainty that "our" engines have a very wide detonation margin, while others take a more cautious approach ....

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 dont see how detonation can be occuring without associated high CHTs. Since we can monitor CHT on all cylinders with modern equipment, why the fear and mystery?


erich
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  #78  
Old 08-11-2011, 03:48 PM
RV8R999 RV8R999 is offline
 
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"For efficiency LOP is very good. Fuel mileage is up, consumption is down, and so are EGT's and CHT's."

How do you define efficiency?
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  #79  
Old 08-11-2011, 04:28 PM
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RV10inOz RV10inOz is offline
 
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Dan

Yep! Like I said we did a very through check of everything. OAT would have been pretty warm coming into our summer time, but I do not recall now. CHT's on a couple of cylinders went racing past 400. In the time it took to get to 500' and look at the EMS and say WTF??? and then pull back the MP to 20-23" and come back round and land.

And while I think of it, our standard IO540, including the grey paint from Lycoming is 260HP. On a per cylinder basis its slightly less than the IO360 180HP, so you guys with anything more per cylinder than me, who think it can't happen, think again. Think about the differences in our engines....not many are there? When all is running well, and you are getting correct fuel flow on takeoff at FULL EVERYTHING, I agree its pretty hard to get, but it only takes one small thing. EMS devices pay for themselves. Ours owes us nothing now.

By the way, fuel flow needs to be in a standard atmosphere your HP divided by 10 in GPH when full bore. In my case 26GPH +/- 5%.
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  #80  
Old 08-11-2011, 04:45 PM
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Quote:
I dont see how detonation can be occuring without associated high CHTs. Since we can monitor CHT on all cylinders with modern equipment, why the fear and mystery?
This is my point.......not everyone does and can. The next point is you have to know what the instrument is telling you. What any changes or trends mean, and why some good value education is important. Most of us do not know enough, we all know too many OWT's and not enough fact. Too many years of stories bantered around flying schools and aeroclubs....Chinese Whispers if you like.

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. A CHT steady all round at 420F does not mean you have detonation, but when they should all be 330 and one or more are racing through 400 and beyond like the EGT numbers do when you start up....
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