Mixture leaning

[severniae 78]

Hi All,

I have been putting some time into the DC-6 now and its going great, really enjoying this beautiful birdy.

I did a couple of long flights recently and honestly hadn't been to careful with my power settings when leaning out the mixture. One thing that surprised me was just how quickly the engines will detiorate when using high power with lean mixture. At one point I was literally watching my engines die!

It got me onto an interesting thought, in my PPL experience I've always been mindful of causing detonation through excessive leaning but was always under the belief that it is a 'over time' damage causer, not something that will wreck your engines in one flight.

What is it about the R2800 that causes it to shatter itself if high power and lean mixture is used? Is it something about the design of the pistons or combustion chamber?

[downscc 1,327]

7 hours ago, severniae said:

What is it about the R2800 that causes it to shatter itself if high power and lean mixture is used?

What it is first and foremost is an engine that has been pushed to near it's limits.  Take note that the race circuit is dominated by large inline water cooled engines.  Any detonation in the big Pratts can spell quick trouble, the aircraft had something not modeled due to complexity:  An ignition analyzer scope right in the cockpit used to ensure proper settings.  As you recall from PPL training, the fuel is also used to cool the cylinders so aviation aircraft typically run richer than required for pure stoichiometric combustion.  The first casualty is probably going to be burned valves, which is why you see a sudden loss of power.

[randomTOTEN 13]

8 hours ago, severniae said:

What is it about the R2800 that causes it to shatter itself if high power and lean mixture is used?

It has very similar metallurgy to your PPL piston engine, yet makes in the neighborhood of 10x the horsepower even at rated power, never mind TOGA!

As you can imagine, it's higher performance means it's that less tolerant of abuse.

Robert Toten

[severniae 78]

Ok, thanks all for the great answers. I didn't realise that the size and power of the engine made such a difference, but if I apply a little thought it makes sense.