Out of the redbox?

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astaib
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Out of the redbox?

Post by astaib »

Hello,

I re-read the book from Mike Busch 'ENGINES" and especially the chapter about leaning.

Despite the method he described about the peak EGT determination, he also wrote that he is not paying attention to it, because he prefers to look at CHT directly and only make sure that the CHT will not go above 380 for Lycoming (and he recommends to take 360 degrees for DA 40 and Cirrus).

I have to say that because I'm not a fan of determining the peak EGT with my VM1000, I apply this method and only target 360 for CHT (I assume that this is ROP cruise).

Lately I read about several post about EGT that has to stay below 1300 degres, but when I run with EGT at 360 as a target, I'm above 1300 degres with EGT.

I'm now afraid of being in the "red box" with this methods, I'm a bit lost!

What are your recommendations or experiences on this?

Arnaud.
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Rich
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Re: Out of the redbox?

Post by Rich »

Is use 1300 in climb, which takes continuous leaning as altitude increases. I only worry about CHTs. Articles by Mr. Busch contradict what you are saying. For Lycomings he recommend running somewhat higher CHTs than Continentals. So I don't worry about cruising at 380-ish. There is also a minimum sustained CHT of 350 degF in order to prevent lead-based exhaust contents from building up in the exhaust valve stems.

I just manage EGT to manage CHTs as best I can. In colder weather and low power settings I can have a hard time keeping the temperatures as high as I'd like. This is especially true on instrument approaches on the glideslope, where percent power is very low.
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Re: Out of the redbox?

Post by astaib »

Rich wrote: Mon Jan 10, 2022 3:24 pm Is use 1300 in climb, which takes continuous leaning as altitude increases. I only worry about CHTs. Articles by Mr. Busch contradict what you are saying. For Lycomings he recommend running somewhat higher CHTs than Continentals. So I don't worry about cruising at 380-ish. There is also a minimum sustained CHT of 350 degF in order to prevent lead-based exhaust contents from building up in the exhaust valve stems.

I just manage EGT to manage CHTs as best I can. In colder weather and low power settings I can have a hard time keeping the temperatures as high as I'd like. This is especially true on instrument approaches on the glideslope, where percent power is very low.
Thanks Rich, I lend my book to a friend so I can't verify. But I was not comparing Lyco VS Conti, just saying that he wrote that for modern aircraft like Cirrus or DA40 the CHT that he indicates has to be lowered by 20 degres. Which lead Lyco to 380-20= 360 and Conti to 400-20=380.

Can you explain: "I just manage EGT to manage CHTs as best I can". For cruise I mean. I understood for climbing and approach.

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Re: Out of the redbox?

Post by Rich »

astaib wrote: Mon Jan 10, 2022 3:32 pm Can you explain: "I just manage EGT to manage CHTs as best I can". For cruise I mean. I understood for climbing and approach.

Arnaud.
With the Surefly, especially, I'm finding CHT is very much affected by air temperature. And the variability of the spark advance also gets in the way. Examples (WOT and 2400 RPM both cases):

A couple of weeks ago, at 6000 ft, (MAP 23.5"") OAT -4 C, CHTs about 355-360, it took EGTs around 1460 to get it this warm.
Yesterday, at 8000ft. (MAP ~22") OAT +5 C, CHT's about 375, EGT about 1400.

The Surefly is a factor here, because at 23.5" the spark is hardly advanced at all compared to 22".

The other obvious case is when flying at reduced power settings when flying approaches. I'll be at reduced power settings from 15" to 9" MAP. CHTs then wind up at about 250 and there's no way to get them any warmer. I live with it because it's typically only 10 minutes or so.
Last edited by Rich on Mon Jan 10, 2022 3:56 pm, edited 1 time in total.
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Re: Out of the redbox?

Post by astaib »

475? Really?
Or it is 375?
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Re: Out of the redbox?

Post by Rich »

astaib wrote: Mon Jan 10, 2022 3:54 pm 475? Really?
Or it is 375?
375 was intended. I corrected it, thanks.
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Re: Out of the redbox?

Post by Rich »

It is my opinion the "red box" is irrelevant for our IO-360-M1A if it remains normally aspirated and you're using 100-octane fuel (pretty much all of us in the US). The reason for this outlandish statement? Because this particular engine variant is a low-compression engine certified for 91 octane. Market forces dictate we're stuck using 100LL, which gives us considerable margin above detonation conditions no matter what we do.

The various publications on the red box use analyses based on big-bore Continentals that require 100 octane. There are other Lycoming 360 variants that have higher compression and are certified as requiring 100 octane, but not this one.
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