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  #31  
Old 09-11-2018, 05:49 PM
tgmillso tgmillso is offline
 
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I've contacted Avstar directly to get their recommended values. Will fill you in once I have the details.

Tom.
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  #32  
Old 09-11-2018, 06:03 PM
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Quote:
Originally Posted by DanH View Post
Listening to folks insist on fat mixtures for cooling may be Earth's closest equivalent to Vogon poetry.
Iím with you on that one Dan - especially for those of us living at high density altitudes! Donít Panic......
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  #33  
Old 09-11-2018, 11:16 PM
tgmillso tgmillso is offline
 
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After speaking to Avstar they directed me to the test report that came with the engine. Sure enough, my engine is on the low side of the calibration limits. The highest fuel flow test was performed with an airflow of 1004 pph. The 180hp rated power test was at 1116.59 pph airflow. Therefore the rated power test was 1.112 times the AF-1000 test. Multiplying the fuel flow in the AF-1000 test by 1.112 gives 93.75 pph, which equates to 15.6gph, which is still slightly above what I was observing during the takeoff run via my FT-60 fuel flow meter.
Going back to the chart and applying the same 1.112 ratio to the lower and upper fuel flow limits, this gives a lower limit of 92.6pph or 15.4gph, and an upper limit of 102.63pph or 17.6gph at 180hp rated power for the IO-360M1B. Thus at an FT-60 reading of 15.1gph, it appears I am below the lower limit. Keeping in mind that I am at a 500ft elevation and have calculated that my full throttle maximum power is 176hp, applying a ratio of 176/180=0.978, this would make the lower limit of the fuel flow 15.06gph, pretty much smack on what I was reading from the FT-60. I have not calibrated the FT-60, so who knows, even that may be incorrect. All we do know for sure is that during the AF-1000 test, the engine was 1pph richer than the lean limit. I'm still going to work with Avstar to see how possible it is to adjust things so they are closer to the midrange, however in the interim I have continued work on my baffles to try and ensure every scrap of air is being put to use.

Tom.

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  #34  
Old 09-12-2018, 12:10 PM
F1R F1R is offline
 
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Quote:
Originally Posted by DanH View Post
Listening to folks insist on fat mixtures for cooling may be Earth's closest equivalent to Vogon poetry.
As Dan said a few years ago "There are better ways to cool an engine than mixtures that are richer than 3 feet into a cows back end."

What Dan was trying to draw attention to with some good humour is that if a Lycoming in an RV is cowled and baffled and ducted properly CHT's will NOT reach 400F in in a FULL power climb in air that is over 100F.

See the full story here:http://www.vansairforce.com/communit...ferrerid=13191

Or else go to the traditional engine section and read the sticky "Engine Cooling"
seen here: http://www.vansairforce.com/communit...ferrerid=13191


Michael Robinson has done a lot of good work with the pay off as quoted below:

"OK, its now six months later and I had a chance to really check this mod out today. I left Phoenix at noon with the temp passing through 105. On my normal stair step climb to the west staying clear of the class B sections, the CHT often runs right past 400 on a few cylinders within minutes, but not today. I maintained WOT and best power EGT for the entire 15 minutes it took to get out from under the PHX airspace and I never saw anything hotter than 385. Once to 8500 feet and LOP, the temps settled to 325 -350.

I know that 1 data point does not make a trend, but my first "hot" flight of the season sure went well.

Soon, I will try a climb at VY all the way to altitude and see how it behaves.
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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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Last edited by F1R : 09-12-2018 at 12:14 PM.
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  #35  
Old 09-12-2018, 05:00 PM
tgmillso tgmillso is offline
 
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Hi All,

I received the following response from Avstar last night:
"I reviewed your data with my engineer and we both agreed that enrichment of your top end fuel flow for lower CHT's would be beneficial for your engine life."

In a nutshell, I'm removing my servo and sending it back to them for a little enrichening. I'm not looking at this thing draining the middle east of liquified dinosaurs everytime I push the throttle to the firewall, but I think something closer to their midrange of the recommended flow values would be more ideal, especially given that I'm seeing up to 440degF CHT's on cool springtime days even with shallow climbs. I've tweaked the baffle seals a little, but I can't see how I can improve them any further.
Tom.
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  #36  
Old 09-12-2018, 06:49 PM
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Quote:
Originally Posted by tgmillso View Post
I received the following response from Avstar last night:
"I reviewed your data with my engineer and we both agreed that enrichment of your top end fuel flow for lower CHT's would be beneficial for your engine life."
Did you discuss full throttle, full rich EGT in relation to peak EGT?
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  #37  
Old 09-13-2018, 12:09 AM
tgmillso tgmillso is offline
 
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No Dan, we haven't discussed EGT. The EGT at takeoff was around the 1350degF mark, 1250degF in cruise and the highest recorded was 1450 during the engine runup process. I didn't pull the mixture back at all during the flight. Given that the fuel flow was 11.1GPH at 24 square, which is about what I was going to lean it to anyway, and given my higher than expected CHT both in the shallow climb (420-440degF) and cruise (approx 365-385degF) I thought I should leave the mixture full rich. I'm open to whatever information you have to help resolve the issue.
Tom.
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  #38  
Old 09-13-2018, 08:08 AM
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Originally Posted by tgmillso View Post
No Dan, we haven't discussed EGT. The EGT at takeoff was around the 1350degF mark, 1250degF in cruise and the highest recorded was 1450 during the engine runup process.
Tom, do yourself a favor and forget about fuel flow. You're trying to determine mixture at full throttle. Without a mixture check, both you and the Avstar guy are guessing.

More later, but just from the above, your servo is probably set correctly.
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  #39  
Old 09-13-2018, 06:22 PM
tgmillso tgmillso is offline
 
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Thanks Dan. Avstar are pretty keen to get this servo back, however I won't take it off until I hear back from you. Thinking about the whole detonation and pre-ignition deal, which is my ultimate concern, if my understanding is correct, with a mixture richer than stoichiometric, the excess fuel is simply providing evaporative cooling, so there should be no reason why this task can't be provided by cooling air over the outside of the cylinder. It leads me to also thinking that so long as I am running the recommended octane values and staying below the 500degF published CHT limit, that the detonation or pre-ignition should be a non issue. I did build a row of nutplates into the lower firewall flange so I could create a Dave Anders inspired outlet ramp if I ever needed it. Sounds like I may need to execute this concept. 12 year screwing wind turbines into the ground, and a lifetime of operation basically only electric or diesel equipment means that my spark ignition knowledge isn't where it needs to be.
Tom
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  #40  
Old 09-14-2018, 09:30 AM
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Quote:
Originally Posted by tgmillso View Post
Thinking about the whole detonation and pre-ignition deal, which is my ultimate concern, if my understanding is correct, with a mixture richer than stoichiometric, the excess fuel is simply providing evaporative cooling, so there should be no reason why this task can't be provided by cooling air over the outside of the cylinder.
Evaporation makes only a very small contribution to cooling. An excessively rich mixture delays peak cylinder pressure and lowers combustion temperature. The overall result is a power reduction.

The other big factor is mass flow, as noted way back in the pre-WWII NACA papers. The previous paragraph can be considered a "per cycle" reality, while mass flow translates directly to RPM, i.e the number of those heat generating cycles in a given time. One of the easiest ways to drop CHT is to simply pull the prop back a little.

And yes, heat transfer to the air is the best of all.

Quote:
It leads me to also thinking that so long as I am running the recommended octane values and staying below the 500degF published CHT limit, that the detonation or pre-ignition should be a non issue.
Add OAT, ignition timing, compression ratio, RPM, and manifold pressure to the list. High intake air temp, advanced timing, and high CR are pro-detonation. Reduced RPM combined with high MP is pro-detonation.

Given enough octane, a stock engine, stock timing, and basic adherence to the power chart, yes, you're safe. It's why the manufacturer did a detonation survey.

Gather basic EGT data. Climb to 3500 or so, and allow CHT to settle to a cruise value, which I assume to be well under 400. Now lean to a stable peak EGT on the cylinder of your choice. Record the value. Push mixture to full rich, again allow EGT to settle, and record the value. Report back.
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