Cowl-Flap negative setting

[PMSoares 7]

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! 

[downscc 1,327]

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.

[TheFinn88 13]

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

[SO666 4]

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.

[onduty 5]

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

[metzgergva 28]

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

[PMSoares 7]

Good explanation guys! Thanks!