Mixture full rich at start of descend?

[Dooga]

Hi all, am reading the manual right now, in anticipation before getting back to my rig tomorrow.

Came upon the descend checklist where it says mixture full rich, and wanted to ask whether this really is unanimous sop for this kind of engine?
My thinking is that you've just pulled the throttle, thus massively lowering combustion temperatures - if you now add full rich mixture, you're effectively flooding the cylinders with cold gasoline from the wing tanks on top of that. I have read recommendations to avoid this with flat fours/sixes, and am wondering why you'd treat a wasp differently?

[Scott - A2A]

Dooga,

When you talk about discussions of shock cooling and such, you will have different camps arguing different things. I personally just play the safe route and use common sense. In this case, maybe avoid putting in full mixture and reducing the throttle simultaneously. Reduce the throttle, wait a few min, then add full mixture.

Scott.

[AKar]

To my knowledge, there are no technical reasons to go full rich at the start of descend. However, the issue is that you can't "set & forget" the engine if you leave the mixture leaned. Actually, you can flame-out an engine during descend due to too lean mixture and it can even go unnoticed until power is requested - and unlike in our flat ones in GA fleet, most radials don't take too well any extended periods of 'negative torque' due to lubrication issues. A lack of an EGT gauge can make the issue worse.

I'd guess it comes down how comfortable one is on adjusting the mixture as required while riding the plane down.

Regarding the effect of cool fuel, it should be noted that the R-1340-AN1 has the supercharger impeller downstream from the carburetor. Whenever the engine turns for whatever reason, it will add heat into the mixture due to inefficiencies in mechanical compression.

-Esa

[Dooga]

Damn this engine is supercharged and I completely missed that? Gotta get on wiki asap

Thanks for the replies, I understand that it's a workload/safety issue more than an engine-management one; no simple answer I guess, as so often where these engines are concerned...