Dear DC-6 fliers,

 

What's the function of the cowl-flaps negative ( -2 and -4) settings? Looking the model from outside I noted that in the -4 setting they are fully closed, as opposed to the 0 setting where it seems that they are in "trail" position. I thought that by keeping them at -4 I would get more airspeed, since the cowl-flap drag would be lower, at the expense of some engine higher temperature, but I have noted that by setting the cowl-flaps to -2 or -4 I get both higher temperatures (as expected) AND lower speeds. Is that correct? I could not find any reason to set them at negative values, neither in PMDG manual nor in the real plane's manual. 

 

Thanks for the help! 

Yes this is correct behavior.  I suspect that the negative settings are to allow reduced airflow with less penalty than opening into the slip stream.  The emergency procedures for engine feathering or shutdown include a closed cowl flap (I assume to be -4).  It is interesting to note that the cruise performance tables by Douglas set cowl to -1; however, our aircraft only has either 0 or -2.... I asked about that and didn't get a direct answer.

A negative cowl-flap setting disturbs the airflow over the engine-cowling, and any disturbance in airflow will cost you some knots in airspeed.

Hi.

I have spoken with an ex military navy mech who worked on connies and DC-4 aircraft , his explanation is 0 setting the cowl flaps are flush with enginine cowl , but you still have an air gap for airflow through the engine cowl for cooling.

A -2 or -4 setting was used at high altitudes in extream cold conditions which closes the cowlflaps fully , to keep engine cylinder temps at optimum working temps for engine operations , but the down side is a slight turbulance around the cowls because they are effectivly below the engine cowl on the trailing edge.

regards alan cottrill.

Good explanation SO666! It's good to know that guys are still with us with all that historical knowledge. Thanks for that. I wondered quite a bit what the meaning of those negative values is in cowl flap setting.

 

Cheers,

 

Tamas

Just to confirm Alan’s explanation. It’s also my understanding when we designed the functionality in the sim.

Good explanation guys! Thanks!