RPM and manifold pressure questions

[Blackdog_kt]

Originally Posted by The Stalker

Great thanks, I've read your post!

Would some care to explain the purpose and difference of best and economy cruise settings. I think I know what they are but not entirely.

Ok, first of all the engine runs best at certain proportions of fuel-to-air mixture. The less fuel-more air mixture setting is obviously best for fuel economy without losing power, or at least not a lot of it. Remember, just as you can choke the engine with too much fuel, you can over-lean it too and have it lose power due to not enough fuel. The economy setting is the sweet spot where you get the highest amount of power for the least amount of fuel expense. The drawback to this is that since richer mixture has the effect of cooling the engine, lower fuel content means slightly higher temperatures.

With that in mind, this is used for cruise mostly. When using higher power settings, during climbs or combat for example, the cooling difference shows and you will either overheat or have to use radiators and cowl flaps to keep the temperatures within limits. This means that even if you don't overheat, the added drag from the open cowl flaps defeats the purpose and you end up being worse off in the net result of things.

This is when you use the richer mixture setting. In that sense, this setting is the sweet spot where you get the maximum amout of fuel in the mixture for cooling without chocking the engine and losing power. I'm not entirely sure it provides added power for the same manifold pressure and RPM, but it definitely enables you to run higher MP/RPM with less heat build-up. That obviously comes at the cost of fuel economy.

Hope it helps.

By the way, i'm no authority on these things so any corrections are welcome. What i know comes mostly from flying FSX on a friend's PC, going through some of the flight school/interactive lessons in that sim and flying some 3rd party payware add-on aircraft that are done with a higher degree of realism than the stock ones provided by M$. I'm not a real world pilot so i guess there's a world of info i'm missing here, but for simulator purposes and through whatever testing i have been able to undertake it seems to work as described.

[JG53Frankyboy]

but as always, keep in mind that the engine/propeller settings you can read that were used with REAL engines has almost nothing in common with the game !

the CEM is a gamefeature to "simulate" at least a little bit the engine managment the real pilots had to do (or not keep some one-lever-systems in mind ) , nothing more, nothing less !

[Blackdog_kt]

I didn't say anything different, i'm just saying how it works in the game

[The Stalker]

But I figured the cruise settings were about RPMs, not fuel mixture?

[Splitter]

Originally Posted by The Stalker

But I figured the cruise settings were about RPMs, not fuel mixture?

In real life (and most good flight sims), it's a balancing act that includes mixture.

The pilot is always seeking to fly efficiently while conserving fuel and engine performance.

As altitude increases, mixture needs to be leaned out to provide the proper fuel/air mixture for combustion in the engine. Lean it out too much and the engine operates inefficiently and may be damaged. Make it too rich and not only do you burn excess fuel but you can foul the engine.

There are optimum cruise altitudes for aircraft where RPM's, manifold pressure, and mixture all come into the best balance. These altitudes will give the best fuel efficiency, speed, and engine wear. Pilots are often making trade offs....speed for fuel efficiency, etc..

Those are some reasons why pilots are never bored and some of us really enjoy civilian flight sims too .

Splitter