Originally Posted by Otto
Why not do a cowl flap? That's what NACA designed for reciprocating aircraft engines such as B-17, B-29, etc.. In other words, put a hinge on the leading edge of the rectangular piece you cut out, and control its upward deflection with a cable or just let Mother Nature set the angle as a consequence of pressure differential below and above the flap. Do internal exit ducting with Coroplast or similar to make a smooth exit path. You want the exiting air to be as parallel to the slipstream as possible, i.e., point it to go smoothly back over the hood. The only downside is that such heated air may be drawn into the cabin via the vent inlets of the high pressure area just in front of the windshield, but that won't amount to much if you are not racing.
When parked, the cowl flap sits in flush position with the same contour it now has, and keeps the rain out.
That's what I plan for my Porsche 944 Turbo, which has a well engineered intercooler inlet, but they sorta forgot about the outlet. Stock, the cooling air is supposed to find its way somehow down and out the bottom of the engine bay past various obstructions to flow. Ungood, especially since heat rises. I figure that in addition to sucking the spent intercooler cooling air out, it will also draw off radiator and underhood air, with otherwise heat soaks the engine. BTW, this reduces nose lift on the car, as undercar flow and pressure is reduced, and the flap also acts as a lift spoiler for the hood. So, she rides a bit lower, less drag from that and less lift on the nose for better high speed handling. Win, win, win.
For a hinge(s), I'm considering those nylon ones used on RC model aircraft from a hobby shop. Gonna fix it in position on the underside of the sheet metal BEFORE I make the cut. That way, I know the flap alignment will be perfect.
What do you think?
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