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09 Jun 2022 21:41 #3534

Hi David,
I've gone back and studied my Advanced Pilot Seminar notes and remembered that the red box/red fin is where the mixture produces the highest internal combustion pressures, CHTs and EGTs are at peak or near peak.
One of the instructors, John Deakin (who wrote a very interesting series titled "Pelican's Perch" on Avweb) told me this, "If you're at 65% power of so, 50 deg F ROP (rich of peak) probably won't get you in trouble and will give you close to maximum power for that manifold pressure and RPM. But the fact is that 50 deg F ROP will produce the absolute hottest possible temperatures for all parts of the engine."
I have attached a chart that shows the relationship between EGT, CHT, Internal Combustion Pressures (ICP), HP and Brake Specific Fuel Consumption to better illustrate this.
Best,
Steve

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18 May 2022 20:46 #3521

I received a response from GAMI so was very thankful for that.
Although there was no specific failure mode associated with the "Red Box", it is associated with reduced engine life and as such there are no catastrophic failures associated with it. This probably explains some of the controversy.

I appreciate the lead.

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11 May 2022 13:41 #3506

Thanks Steve, looks like a good place to start.
Dave

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10 May 2022 15:21 #3501

Hi Dave,
The red fin or red box came out of a class developed by General Aviation Modifications, Inc, also known in the industry as GAMI.
GAMI is based in Ada, OK and is headed by George Braly. Everything Savvy Aviation passes on came from GAMI.
GAMI hosts what it calls the Advanced Pilot seminars. Years ago I sat in class for 2 days when the class was presented in Ada. Two of the presenters are no longer able to work so the Advanced Pilot seminar is now an online course. You can access is at www.advancedpilot.com .
I would start your search there.
Best,
Steve

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06 May 2022 01:12 #3492

Having taken some college courses in internal combustion engines (I'm an engineer), going through my textbooks (2 volume set of "The Internal Combustion Engine in Theory and Practice), and using some of my career in ignitions, I think I have some familiarity with engines. When operating a typical small airplane piston engine, the EGT and CHT as a function of load and mixture looks like this below. These are taken from resources.savvyaviation.com//wp-content/..._red-box-red-fin.pdf but are typical of what a lot of resources present. Seems like everyone references these diagrams. My basic question is what is the stressor or failure mode that is driving the “red box” or “red fin”? Some articles indicate high cylinder pressures, but the would create more torque and doesn’t coincide with the peak power mixture (providing the pressure/angle curve doesn’t get altered somehow). Detonation might be a possibility but increasing the octane rating doesn’t seem to alleviate this problem. My best guess is strictly thermal, especially since the CHT peaks right at the center of the Red Box. I've toyed with created a lumped parameter model of the piston and cylinder but haven't gotten around to it yet. The articles that I've researched don't seem to be specific with respect to this failure or stressor, so I'm hoping someone could shed some light on this. (or at least get me a contact at Lycoming I can have a conversation with)

Thanks for the help!
Dave P

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