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My TBM700 neighbour that...

Red line with an engine trend monitor is tricky. They get you fast even if you are within the transient limits. Try 2 seconds, 2 degrees over redline. No big deal but it isn't nice seeing exceedances even when you know they are not relevant and don't require any actual follow up.

EGTK Oxford

the 'red line' (a needle)

It's not a red line in the sense of a limit marker.

It can be set to peak EGT so you have a reference when you want to lean 50F ROP, for example. So it's purely there for convenience.

LSZK, Switzerland

Thanks tomjnx

Never had this explained (instructed) succinctly - or I've never quite 'got it'.

Lean till the EGT needles 'peaks' (goes no higher) - set the 'red needle' as a guide (tell tale) and one comes back 50°F rich of that 'peak'.

However, I'm instructed on the Arrow to lean till the consumption shows 10 US gal/hr.

Is there a conflict here?

Regret no current medical
Sandtoft EGCF, North England, United Kingdom

Lean till the EGT needles 'peaks' (goes no higher) - set the 'red needle' as a guide (tell tale) and one comes back 50°F rich of that 'peak'.

That's how I was taught to do it.

However, I'm instructed on the Arrow to lean till the consumption shows 10 US gal/hr.

That's about right for 65% (2400RPM and 22MP) and relatively low altitudes. At ~8000ft it shoud be closer to 9USG/h, at ~12000ft around 8USG/h (normally aspirated IO360C).

LSZK, Switzerland

I don't think any non-turbo engine has an EGT limit. CHT limit, yes, but not EGT.

one comes back 50°F rich of that 'peak'.

That's not so good, because 50F ROP is the max CHT point. It doesn't matter at low power settings, but at say 75% you are just heating up the engine for little gain.

The simple way to lean a non-instrumented engine is to lean until the power output (as evidenced by the IAS, or prop rpm if fixed pitch) suddenly drops, and then restore (enrich) the mixture to just before it dropped. That should give you roughly peak EGT which is the best-economy point.

If one enriches the mixture too far, one will reach the highest-CHT point, which is a bit "pointless".

The best-power point is about 130F ROP and that is necessary for reaching the operating ceiling. You are burning about 10% more fuel there, relative to peak-EGT.

Administrator
Shoreham EGKA, United Kingdom

That's about right for 65% (2400RPM and 22MP) and relatively low altitudes. At ~8000ft it shoud be closer to 9USG/h, at ~12000ft around 8USG/h (normally aspirated IO360C).

I'm mainly at relative low altitudes non turbo Arrow IV and full 'guide lines' from the group are:-

2400RPM 24MP and fuel at 10 USG/h - i.e. 24 square as they say, not 24/22

If I ever get up to 8000' ish on a long trip I'll remember to bring the fuel back to 9 USG/h.

Still 24/24 or happen 24/22 ????

Regret no current medical
Sandtoft EGCF, North England, United Kingdom

The method described is right but when you get more familiar with a particular engine and aircraft you can lean straight to a fuel flow number that gives the right temps. That also avoids too much time spent at peak temps if you want to run higher power settings.

EGTK Oxford

2400RPM 24MP and fuel at 10 USG/h

From Operator’s Manual, Lycoming, O-360, HO-360, IO-360, AIO-360, HIO-360 & TIO-360 Series, 8th edition:

2400/24 gives you 140BHP @ sea level, so 70%, and 145BHP @ 3000ft, so 73%.

Best Economy (aka peak EGT) setting for 140BHP is about 9.5USG/h, Best Power (aka 100F ROP) is about 11USG/h.

So you come out slightly ROP, at about max CHT.

50F ROP is already past max CHT, but not by much. Cooling during cruise is no problem IMO, so it hardly matters where exactly on the mixture chart you are. I tend to use peak EGT.

Climb is another can of worms, the standard AFM climb gets me too close to redline for my taste, so I climb at a faster IAS.

Still 24/24 or happen 24/22 ????

Without a turbo or compressor, you'll have a hard time getting 24/24 at 8000' - with WOT (wide-open throttle), you'll get maybe 21MP...

LSZK, Switzerland

2400/24 gives you 140BHP @ sea level, so 70%, and 145BHP @ 3000ft, so 73%.

I too thought that 24/2400 is going to be ~70% of max rated power, for any NA engine.

It is perhaps a bit too high for cruise. I think many pilots would say 65% is better long term (23/2400 or so).

Administrator
Shoreham EGKA, United Kingdom

It is perhaps a bit too high for cruise. I think many pilots would say 65% is better long term (23/2400 or so).

The beauty of the rule above in a club setting, with relatively inexperienced pilots on type, is that it's easy to remember and comes out about right. I can hardly believe that 65% vs. 70% is making a lot of a difference, plus you'll have to pull the engine at TBO anyway.

LSZK, Switzerland
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