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  #1  
Old 07-30-2011, 09:40 AM
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Toobuilder Toobuilder is offline
 
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Question Temperature Split Between L/R Side

I have a situation with temperatures that I don't understand and was wondering if any of you have run across the same thing. I have found that the CHT and EGT can be managed very easily at relatively low altitude by running LOP. If the CHT starts to get away from me, I simply lean it a little more and can get it right down to where I want it. Since I have dual electronic ignition, I can lean to 100+ cooler than peak or more with the engine still running smoothly. The problem I am having is the higher in altitude I go, the more the engine splits in EGT and CHT. 1 and 3 respond together, as do 2 and 4, but the temp split between the two sides of the engine gets quite wide with altitude. What this means is that if I'm trying to bring my hottest cylinder under control by leaning, my coldest cylinder is already way too cold and gets worse with every turn of the mixture knob.

Notice the major spread in CHT and EGT between the left and right side of the engine in this picture at high altitude. Trying to lean further to bring #3 under control would cause the already too cold #4 to plummet further.



Now, here at low altitude, also WOT and LOP, things are much more under control. The temperature split between EGT is very narrow, and CHT are nice and cool. This is what I want it to look like at altitude!



This is a 200 HP (angle valve) IO-360, Bendix FI with a standard Vans cowl, and baffles are new and sealing against the cowl. Also, the "tape over the cowl split" trick did not seem to make any difference.

So does anyone have any theories why I get this split with altitude, and more importantly, how do I fix it?

Thanks.
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  #2  
Old 07-30-2011, 09:51 PM
DENMACRES DENMACRES is offline
 
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Smile split

the fuel flow is very low at that alt. the fuel divider tries to equalize to each cyl. thinking eng. is at very low power. (idle) this screws up your balanced injectors. Dennis IO-360, -6
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  #3  
Old 07-31-2011, 12:59 PM
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Default So...

...Is this normal? I've never had an engine instrumented to this level before - is this another case of too much information?
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  #4  
Old 07-31-2011, 01:23 PM
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I seem to recall Don Rivera saying that at anything less than 7 GPH, flow division was at the divider, not the injector orifice.
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  #5  
Old 07-31-2011, 04:16 PM
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Quote:
Originally Posted by DanH View Post
I seem to recall Don Rivera saying that at anything less than 7 GPH, flow division was at the divider, not the injector orifice.
Not sure I follow you there Dan... Do you mean to say that at such low fuel flows, the nozzle ceases to perform a metering function, and the flow divider becomes more influential?

Perhaps I need to give Don a shout...
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  #6  
Old 07-31-2011, 04:19 PM
ao.frog ao.frog is offline
 
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Default Check..

... this tread: http://www.vansairforce.com/communit...&highlight=CHT

Maybe that could solve your problem too?
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  #7  
Old 07-31-2011, 04:28 PM
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Quote:
Originally Posted by Toobuilder View Post
...Is this normal? I've never had an engine instrumented to this level before - is this another case of too much information?
Interesting discussion Michael - I often wish that I would take the time to research the accuracy, repeatability, hysteresis, etc of our transducers. We might very well find out that we are chasing instrumentation in some cases.

For this specific question? I agree with the idea of calling Don at Airflow.

Paul
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  #8  
Old 07-31-2011, 07:36 PM
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Quote:
Originally Posted by Ironflight View Post
... We might very well find out that we are chasing instrumentation in some cases...
For all the wonders of the digital age, sometimes it makes one long for the good old days where we just leaned to a touch rich of rough and forgot about the engine for the rest of the flight.
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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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  #9  
Old 07-31-2011, 07:37 PM
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Quote:
Originally Posted by ao.frog View Post
... this tread: http://www.vansairforce.com/communit...&highlight=CHT

Maybe that could solve your problem too?
Thanks for that, but I tried that trick too. No difference..
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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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  #10  
Old 07-31-2011, 08:36 PM
David-aviator David-aviator is offline
 
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My take on the situation - if the transition from peak to LOP is occurring at or near the same fuel flow with each cylinder, the fuel delivery system is balanced. Individual CHT and EGT values are interesting but of no real consequence.

In Mike Busch's forum on going beyond TBO (his Cessna twin is doing well at 200% TBO) the #1 item is controlling rust and #2 is CHT. CHT should never be allowed to go over 400 and as a norm kept below 360. CHT is controlled with fuel flow and/or air flow.

If your injection system is balanced, the variance in CHT is an unbalanced air cooling issue. The challenge we have is that the conditions of flight are so variable it is nye impossible to balance CHT's all the time. My #4 runs about 20 hotter due to air stolen for oil cooling. Yours is running cooler, that doesn't make much sense assuming the cooler is located at #4. That's just the beginning of the mysteries surrounding CHT. As long as they run cool, I don't sweat it.

Your cylinders are running so cool, 299-338, they will last forever. That is good.
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