rectangular opening in bottom cowl

B

Brendan Carmody

New member
My 14-13-3 came to me with an STCd 180 Franklin installation. On the bottom cowl sheet metal, on the starboard side of the carburetor air inlet, there's a rectangular opening (the long side of which is parallel to the airplane centerline) opening into a formed aluminum fitting riveted inside the cowl, which fitting has a circular opening facing rearward inside the cowl. It appears this fitting MAY have had a piece of scat tubing attached to the circular opening, but there's nothing attached to it now. In fact, the fitting has been "squashed" to some extent to accomodate my larger engine, but the circular end is still circular (i.e. not squashed) Can anyone identify the function of this obvious outside air duct and opine whether I might drill out the rivets and remove the fitting entirely, and then close the rectangular hole in the bottom cowl sheet metal?
 
hey brendan!
i'm not intimately familiar with the F-180 installation in the cruiseair, but what you describe sounds like someone's rough approximation of an NACA scoop or some sort of flush inlet. without seeing some pictures, it's difficult to say for sure. if there's nothing in your installation that needs the inlet air, i'd remove it and build a flush patch over the hole. otherwise, it's reducing the effectiveness of the low pressure side of the engine cooling plenum. hope this helps!
blue skies,
vic & N522A
 
That's what I thought, too. But I didn't want to eliminate the scoop if it had some purpose -- like cooling the accessory section of the engine [admittedly unlikely since it's on the low pressure side of the engine compartment].

I looks like a factory installation left over from the original 150 hp Franklin, which had to be squashed to get the 180 Franklin in. But then I ask myself: why didn't the guy who installed the 180 just remove the scoop instead of squashing it? And, in squashing it, why did he take pains NOT to squash the round end (the scat tube end)?

So, does anyone out there have a 150 (or 165) hp factory Franklin installation with such an air inlet/scoop. If yes, what is it used for?

Thanks all.
 
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