Red Box (Lycoming)

RyanB

RyanB

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Talk to me about the “red box”.

I know there’s a lot of BS that gets slung around on the web, but still, I’d like to know more.

O-360-A4M which I usually run at ~65%. I don’t have any CHT instruments, just a single probe EGT on #4. If I lean til rough and enrich just a hair til smooth at 65% am I outside of the red box? I assume it’s unlikely that you could burn valves at 65%, but I still usually run it a bit past the ‘peak’ RPM just to be safe, but I realize I’m in the 50-100ROP range when doing so.

So, 65% power, lean til rough, enrich just til smooth, am I outside the red box? When do I need to worry about being at a certain F ROP to avoid burning valves and such?
 
RyanB said:
Talk to me about the “red box”.

I know there’s a lot of BS that gets slung around on the web, but still, I’d like to know more.

O-360-A4M which I usually run at ~65%. I don’t have any CHT instruments, just a single probe EGT on #4. If I lean til rough and enrich just a hair til smooth at 65% am I outside of the red box? I assume it’s unlikely that you could burn valves at 65%, but I still usually run it a bit past the ‘peak’ RPM just to be safe, but I realize I’m in the 50-100ROP range when doing so.

So, 65% power, lean til rough, enrich just til smooth, am I outside the red box? When do I need to worry about being at a certain F ROP to avoid burning valves and such?
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I’m resisting the urge to go down into the gutter with this:nono:. I haven’t heard of the red box before but I’m getting a good idea what it’s about. What exactly is it supposed to mean?
 
Based on your description you will be out of the red box for sure if you start at 65% ROP and then lean, dropping the power about 5% as you do so. You can verify this by comparing TAS drop with the POH. A 5% power drop (65 x .95 = 61.75%) will be about a 2.5% speed drop. Verify the actual drop against your POH for more precision. Depending on where your engine smooths out, you may be even leaner having dropped more than 5% power.
 
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luvflyin said:
I’m resisting the urge to go down into the gutter with this:nono:. I haven’t heard of the red box before but I’m getting a good idea what it’s about. What exactly is it supposed to mean?
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The red box is engine settings that supposedly result in high cylinder pressures and should be avoided. Of course mixture settings outside of the red box are considered fair game. My thing is, I have no way of knowing what my CHT’s or EGT’s are, so I really can’t know if I’m operating in the red box or not. The single probe EGT doesn’t tell me anything in reality.
 
RyanB said:
I suppose I’m having trouble interpreting the graph.
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From the link below looks like they're going to have seminars again. Also put an old link that talks about the seminars. Maybe attend one or sign up for their online class if they still offer it. There are a number of other videos out there but not by APS. However, I've been told these guys are the ones to learn from.
https://www.advancedpilot.com/
https://generalaviationnews.com/2017/02/13/attending-the-church-of-lean-of-peak/
 
I think it's more critical on big continentals since our exhaust valves are made of spun glass and will burn if you fly them in moonlight or say the incantation "chinesium" in their presence.

This might be a better primer, from Busch: https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

I think at 65% any setting you use is fine, but sounds like you're describing 50d ROP which could be in the red box, but I think every O360 in the world is flown that way so party on.
 
William Pete Hodges said:
Based on your description you will be out of the red box for sure if you start at 65% ROP

What is 65% ROP?
65% power and on the rich side of peak? But where exactly? 10 or 50 or 75 degrees ROP.
The single probe EGT tells you LOP or ROP on that cylinder, so at least you can fly that cylinder at peak (best economy) or 100 dF ROP (best power). The EGT for one or more of the remaining cylinders might well be either LOP, peak or ROP. All fair game as apparently no red box under 65% power.
How is % power determined? MP and RPM combo? Instrumentation correct? Like to learn more about this stuff.
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Having fallen down this rabbit hole for the O320, O360, O470, and O200... in my non-expert opinion, on a normally aspirated, low compression engine running 100LL... don't worry about it at 65%.
 
According to the Advance Pilot seminar course material I have, it looks to me that at 65% power you could possibly be in the "red box" till you're about 100 degrees LOP/ROP (EGT).

That being said, since you don't have balanced fuel injection, or an engine monitor with fuel flow and individual CHT and EGT sensors for each cylinder, its gonna be difficult to measure this exactly.

My recommendation would be to not worry about "the red box", and follow the procedures in the POH or engine manufacturer's operating manual. If you have that small analog EGT gauge typically installed on pre-digital era light aircraft, I'd just about be willing to bet you're around 100 degrees ROP when the engine smooths out.
 
You won't do crap to that Lyco with the red knob at that power setting. Don't worry about it. Fidgeters are gonna fidget.
 
Your O-360 is an 91 octane engine. If you are using 100LL , I doubt that you have a red box at 75%!
 
I flew 1.4 tonight. 100F ROP at 65% seems to be good. Got a bit under 9gph.
 
Given what you have, fly it by the POH/AFM and don't worry about it. Without an engine monitor you're never really going to know for sure. My Skyhawk has an O-360-A4M and all I had was the same EGT on one cylinder. I had an engine monitor installed when the engine was overhauled and it was eye opening...
 
schmookeeg said:
…I think at 65% any setting you use is fine..
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My understanding has always been that short of an injected motor with sensors on each cylinder/exhaust there is no real way to find find a red box. Maybe I’m wrong, but I’ve always flown behind Lycos.
 
idahoflier said:
Given what you have, fly it by the POH/AFM and don't worry about it. Without an engine monitor you're never really going to know for sure. My Skyhawk has an O-360-A4M and all I had was the same EGT on one cylinder. I had an engine monitor installed when the engine was overhauled and it was eye opening...
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What did you discover?
 
RyanB said:
What did you discover?
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My CHT's on two cylinders ran a lot hotter than what I would have thought. I just looked at the engine logbook and the same cylinders that I see running the hottest, 1 & 4, ended up getting replaced. On a warm day if I leaned in cruise-climb I would see both cylinders approach 400°. One day when I was operating out of a high DA strip I leaned for takeoff and didn't watch the CHT for a minute and #4 was at 428° and likely would have kept climbing. So now I usually run rich until cruise altitude. I also had a Mapleleaf fairing installed and that helped quite a bit.

Both cylinders had ~ 1300 and 1420 hrs respectively before being replaced and it appears low compression (0 and 5 respectively) wasn't discovered until a 100 hour or annual. I have no way of knowing how the aircraft was operated prior to when I took ownership, but my take away is it's possible you may end up in the "red box" or "red fin" at times on an O-360-A4M following the POH/AFM but you will likely get at least 1000+ hours on your cylinders. Of course this is all anecdotal...
 
When I had an A4M I would basically fly by GPH. I leaned to about 8.5. Temps were always good. I tended to fly between 6k and 8k for reference.
 
I asked a very knowledgeable Lycoming representative at Oshkosh last year what they recommend at 65% on an O-360.

“Peak EGT.” He said.

Essentially, run what you want at 65%. I’ve been leaning to rough and then just slightly rich of that and getting 6.5 - 7 gph when not in a hurry.
 
Salty said:
I thought at 65% and below you are always out of the box.
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Yep, and similarly Continental says that as long as you at or below their max continuous setting you can do anything you want with the mixture from full rich to so lean that the engine is misfiring without doing any damage.
 
It's more like an inverted red triangle, with the bottom point around 65% power. As power % increases, the "danger" zone gets wider. At 75% you want to be either 25-50 lop or 50-100 rop. Obviously this is the very simplified version.

You probably can't run lop with the carbureted engine in the archer, and without an engine monitor you won't know what's going on. The egt is installed on the theoretical leanest cylinder, so if it's 25 lop, the others are probably at peak and right in the middle of the red zone.

At 65% you're safe to run at peak egt/rpm, and you're probably better off there as going much richer will probably drop your cht's enough that lead deposits start to become an issue. Not to mention wasted $7 fuel.

Eta: Mike busch and eaa have several very good webinars on leaning/ the "red box" concept available on YouTube. They're long and a bit dry, but the information is worth it imo. 1.25x playback recommended.
 
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In addition to the detonation margin (which the red box is all about), it's also best to keep richer at high power settings for cooling. Usually, these are accompanied by higher angles of attack/lower airspeeds for a climb so you want all the cooling you can get.
 
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