One of our stated aims at PMDG is to provide technically accurate and realistic simulation products for simmers to use, enjoy and learn.
With each product release, we generally have to spend a bit of time helping to kill off something we call "Simmerisms."
What is a Simmerism? It is an incorrect understanding of how something is supposed to work. For example, when we released our 737NG in 2003, we were immediately taken under heavy criticism because users found it very difficult to slow the airplane while descending. All of their previous simming experience told them that in order to slow down while descending, you simply pulled the throttle to idle... Which of course- is NOT how it works in the real world...
We spent quite a bit of time teaching users the correct technique and how to use the data tables to verify the accuracy of the model- and sure enough 13 years later most simmers understand how it works...
The DC-6 is going to be the same. There are some incredible misconceptions about how these old radial engines behave that come from inaccurate and/or exaggerated sim experiences in the past- lack of knowledge- and lack of experience.
So with that- I'm going to throw a few simmerisms into this thread in hopes of helping you to help us to keep people from sounding dumb in public.
Simmerism: "I closed the cowl flaps and the engines didn't overheat."
Good! They shouldn't.
On some engines the result of closing your cowl flaps MIGHT be an eventual overheat- but generally speaking, that is not going to be the case with a DC-6 unless you have certain, specific, underlying engine health issues at play as well.
In the radial engine world- heat is the enemy. Heat damages your engine by softening the various metals used and allowing the normal operating pressures and forces to damage things such as cylinders and rods at a faster rate than damage accrues at lower temperatures.
If you take two radial engines and rig them in such a way that one engine always runs 50C warmer than the other- I would bet the house on experiencing higher maintenance costs, greater rates of cylinder replacement and an earlier outright failure of the engine that is run at a warmer temperature.
Which brings us back to those cowl flaps... Use your cowl flaps in accordance with the guidelines described in the manual in order to keep your engine temperatures in the optimal range. If you close them, and sit there running the engines, you will notice that the cylinder head temps climb, and since heat is the enemy- you are in effect doing long term damage to your engine...
But the thing isn't going to explode gloriously aflame like an Independence Day firework display.
The reason we work so hard to keep the engines cool on the ground (By opening the cowl flaps) is so that we can get more work out of an engine if it is needed in the air. For example, in the DC-3 that we operate, our CHTs with the cowl flaps open normally run around 100C with the cowl flaps open. When we initially level off at cruise power, our CHTs tend to be around 160C... and then they cool back to 140C and stay there until landing.
If I close the cowl flaps and run those engines on the ground, the CHTs will increase 30C on the left side and 45C on the right. The right engine is older and creates more friction internally... Thus it creates more heat. (Yes- we tested this as part of the airplane's initial rigging when we replaced the engines!) If I then take off, I would expect we will see temperatures around 220C on both engines when we level off at cruise power- and then they will cool back to 145C or so.
Now imagine we have an engine failure and have to climb out on one engine... If we take off with a cool engine- we are going to be able to run it at METO power quite a bit longer than an engine that was 30C warmer at takeoff... Which is another thing to consider carefully...
So- why allow that amount of heat to accumulate? Heat is Damage... Heat is the Enemy. Heat is Bad...
We open the cowl flaps and keep the engines as cool as possible... You should do the same. If you leave them closed- you aren't going to see a fireball. At least... not right THEN... It will happen some night when fully loaded, taking off into IMC and rising terrain... cuz that is how Murphy's Law works.
Okay... Simmerism "closing the cowl flaps should kill my engine..." Yeah... not true...