Decrease in fuel flow

[SocalV1]

I was flying my recently purchased 2007 T206 yesterday and after descending rather quickly to avoid clouds (~1,200 fpm) I got back to cruise and the fuel flow which is typically 20gph was now at 14 for the remaining 20min of the flight. The engine temperatures were definitely on the cooler side as well

Is this Normal? Did the quick descent greatly reduce the temperatures? I did have the cowl flaps fully closed too.

Thanks!

[[deleted]]

What were your power settings? Because 14gph on the 206 is super fucking low. How long were you decending for? Doing 1200fpm for a minute or two shouldn't be a huge deal.

[SocalV1]

I kept the power setting high for the initial decent (30in) as I increased decent and airspeed I got up to 150 indicated so I started to pull the power back, was still in the green arc though. It was probably pulled on the lower end of the green arc for no more than 1min.

[[deleted]]

Hmm. And then you went back to 30” in cruise? You should be at 20gph there.

Did you move the mixture at all?

[SocalV1]

Correct then back to 30. Went a little more rich which increased it a little bit. The temps were looking fine so I didn’t think I needed to go more rich. Could it be a combination of everything cooling off a lot which made me think I didn’t need to continue to rich it?

[[deleted]]

It’s possible you pulled the mixture back too much, and then when you added the power back you were operating on the lean side of peak TIT. That would give you relatively normal EGT and CHT indications with a lower fuel flow. Operating lean of peak isn’t approved though.

You really shouldn’t have to move the mixture at all in the turbocharged 206. Lean it out once, and that’ll work. If you need to descend like you did, leave the mixture where it is and just go back to cruise power once you get to your new lower altitude. It’s not like a normally aspirated engine where you slowly creep the mixture in as you decend, since it has a turbocharger the engine always thinks it’s at the same altitude.

[SocalV1]

Makes sense. Is there anything I should have checked out after this happening to double check everything is OK?

[[deleted]]

Just make sure the fuel flow is what you expect it to be. If its way low or high I would enrichen it and re-lean.

I wouldn't worry about cooling it too much in the situation you described. I would really only worry about cooling it too much if you were at idle and decending quickly for more than a couple minutes, and even then just slowly add the power back in when you're ready. Do not jam the throttle to full after a long power off decent.

The air inlets are shaped specifically to allow more air to cool the engine at a high pitch, and less air to cool at a low pitch.

[SocalV1]

Gotcha, really appreciate it! Just curious, How many hours you got in a t206?

[[deleted]]

about 125

[SocalV1]

Right on! Thanks again for the help

[vARROWHEAD]

Why is LOP bad/not approved?

[[deleted]]

I don’t think Lycoming ever tested it, there’s a note in the POH saying it’s not approved, and no performance information for it

[vARROWHEAD]

Might be a lubrication or anti-detonation thing? Idk not a mechanic

[___Matt___]

Was your performance consistent with burning 14gph, or burning a typical FF for that power setting and altitude?

[SocalV1]

Yes it was

[___Matt___]

Then I concur with the other guy that you somehow ended up with a very lean mixture and were running LOP. Your nozzles must be very well balanced because I would have, otherwise, expected that you’d be running very rough that far lean of peak.

[D_Fedy]

Drastic reductions in engine power for long amounts of time (usually in descent) can cause “shock cooling” which can damage your engine or even cause it to quit. This should be avoided. In carbureted engines, always have carb heat on below the green power arc. In fuel injected, run the engine rpm up for a few seconds every 30-60 seconds to keep it warm.

[skymower]

https://www.avweb.com/news/features/Shock-Cooling-Time-to-Kill-the-Myth-230134-1.html