Red Box chart for TIT

[Jetpilot86]

Red Boxes for EGT are a dime a dozen.  Anyone seen, or know where to find one based on the TIT we use?

Thanks!

[alextstone]

I keep my TIT at 1550 or below.  

[802flyer]

The box itself is actually arbitrary. If you look at the way Savvy and others define it, it often starts with “we’ll highlight the range of EGTs that result in CHTs over 400F on this representative chart, and we’ll call the range of EGTs in-between the red zone.”

Example here: https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

It is a useful concept to understand that there’s a danger zone around peak, more so on the rich side, and it’s wider as you get further above 65% power. But there’s no specific magic numbers that are actually derived from EGTs or TITs other than the temperature correlation with too-hot CHTs from above.

TIT limits for particular engines certainly exist, and keeping some margin from them makes sense. But that’s more of an engine-specific limitation.

If you work through the logic backwards (ie we started with the premise that CHTs are a proxy for high internal cylinder pressure, and derived EGT limits from that…. therefore maybe I’ll just skip the arbitrary EGT limits and make sure my CHTs stay cool enough) then you’ll actually wind up with Mike Busch’s bottom line. He doesn’t advocate for finding peak on every flight and setting a certain margin below it; rather, he advocates for a Big Mixture Pull to be safely lean, and then adjusting fuel flow to achieve your desired speed/economy, assuming CHTs remain reasonable and your TIT isn’t too high for the turbo’s health. Not everyone agrees with this and I believe some of the APS gurus still advocate for achieving a known margin from peak.


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[Rick Junkin]

I use the same delta parameters from peak for TIT as are recommended for EGT. Both are proxies for where peak ICP occurs and TIT correlates directly with EGT. Here's a chart I put together for my Bravo. Its an amalgamation of data from a number of different sources, Savvy and COPA among them, and serves as reference for the edges of the "sort of bad" (orange fin) and bad (red fin) places to be. The granularity of the numbers in the chart may be misleading in that they are general references for adjusting the temperatures and not definite prescribed points to adjust to. I primarily use the 70% line at 30"/2200RPM and TIT ~45d LOP, which well exceeds the orange fin 25d LOP  minimum from the chart. To get the red fin boundary numbers, subtract 50 from the ROP numbers and subtract 40 from the LOP numbers.

In reality this is way overthought, in my true engineering fashion. In practice I set 30/2200, adjust FF to 13.2, and check that my TIT is <1600. I built the chart to have references should I choose to do some experimenting with different power settings and fuel flows.

EDIT: I should mention my CHTs are in the 330s - 350s in cruise. As @802flyer points out above, maintaining the CHTs lower than 380/400 (Continental/Lycoming) is the real objective, referencing CHT as a closer proxy to ICP. My TIT runs about 1585-1600, well below the recommended 1650 redline and nowhere near the POH 1750 redline.

Cheers,
Junkman