PDA

View Full Version : Cowl Flaps



RacerOne
03-16-2007, 05:31 PM
I was messing around with the cowl flaps on the Corsair today and a thought occured to me. Why do theY open into the slipstream, acting as a speed brake? It would seem to make more sense for them to have been hinged on the aft side and then "suck in" to the fuse. Maybe I'm not understanding the whole concept here but just a thought!

FritzGryphon
03-16-2007, 05:44 PM
Some do open inwards. I think La-5 and FW-190 do that.

I understand that most of the drag is caused by the additional air flowing over the engine. The drag on the flap itself would be minor in comparison.

Also, it's rare that the flaps would be open fully, if ever. Normally they're closed, or just open a little.

Kettenhunde
03-16-2007, 05:56 PM
Because the cowl flaps are exit's for the cooling system flow and not intakes.

The FW-190 "gills" open outward and again function as exit's for the cooling system flow.

All the best,

Crumpp

Spectre1968
03-16-2007, 06:01 PM
Originally posted by RacerOne:
I was messing around with the cowl flaps on the Corsair today and a thought occured to me. Why do theY open into the slipstream, acting as a speed brake? It would seem to make more sense for them to have been hinged on the aft side and then "suck in" to the fuse. Maybe I'm not understanding the whole concept here but just a thought!

The cowl flaps are not there to let cold air in but to let hot air out and increase airflow through the engine.The increased airflow through the engine cowling offsets the drag of the cowl flaps somewhat

RacerOne
03-16-2007, 07:21 PM
I think FritzGryphon understands what I'm talking about and his explanation pretty much makes sense but the pics I've found of the FW-190 show the flaps opening out, and I'll be darned if I can even find the flaps on the La-5! I understand that the cowl flaps are airflow exits and that opening them up increases the airflow through the engine cowl and engine, exiting out the flaps therefore letting the now hot air escape. Maybe a picture would help (don't laugh, my paint skills aren't good)

http://img466.imageshack.us/img466/773/cowlflapscz5.jpg

As you can see, cold air still enters the cowl front, flows over the engine and exits out the cowl flaps. The only difference is, in the first case the flaps are sticking up into the airstream creating additional drag, while in the second they are neatly tucked inside out of the way. Like FritzGryphon said, maybe since they are not open very much, very often the penalty is considered negligable in relation to the the drag created by the engine itself, but in the case of the F4-U, we are talking about many additional square feet of aluminum sticking out into the airflow at full or even partial extension. Just a thought.

tomtheyak
03-16-2007, 09:18 PM
its probably a safety redundancy; whilst I wholeheartedly agree with your idea, what happens if say the cowl flap actuating mechanism fails? In the prototypes as long as they are not jammed solid the airflow through the engine will at least force the flaps open and allow engine cooling; worst case scenario: you lose a few knots of airspeed but you're generally serviceable.

in your example it looks suspiciously like the cowl actuators are opening against the flow of air; result if the actuators fail? the airflow forces the doors closed resulting in rising engine temps. What then? well at best case you're forced to fly at reduced power settings in order to keep the engine temp down; at worst you're engine continues to overheat till seizure or god-forbid a fire!

This is just a theory, please feel free to pick holes, but is plausible wouldnt you agree?