Cockpit Eyeball Vents

 
 
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I chose to go with RV type vents in my plane. Vans sells a combo kit with the NACA scoops, SCAT hose, and Eyeball vents for about $60. Using the supplied template, I transferred the cutout shape to the fuselage, keeping the vent as high and far forward as possible (according to this layout). I then drilled end holes in the corners with my uni-bit.
The holes allowed me to slip my nibbler in to remove the inside portion of the vent cutout.
The nibbler is a copy of a "Jilson Nibbler" by Harbor Freight. It is part number 00539, and runs about $6.00 It makes a pretty clean cut. There is very little edge disturbance if you are careful.
However, as you can see, trying to cut out complicated shapes is hard. The tool is not maneuverable enough to cut right along all the lines, and I needed to clean things up a bit with my dremel tool and file.
Vent cutout edges dressed and ready for NACA inlet.
The inlet is held to the sidewall with Permatex 599BR RTV Silicon adhesive. It is silver in color, and labeled as a gasket maker-adhesive. It seemed to really hold those vents in place!
Everything is glued in and drying. Prior to gluing I sanded the inlet (it's a molded plastic) to ensure the paint would stick properly.
The Wisperflow Ventilators (eyeball vents) from Vans Aircraft are pretty nice looking. They are molded plastic (ABS I think), attractive, and seem to function pretty well. However, the movable vane in the middle serves to cut off airflow when the vent is closed. It does not fit very tightly, and requires some help to get a good seal. Left as they are, even closed, a fair amount of air would blast out of them :-(
The vane is held in place with two allen screws, and is easily disassembled.
My first approach was to use a bead of clear silicon around the edge of the vane. The idea was to trim that silicon into a tight fitting gasket, thereby shutting off any remaining airflow. Unfortunately, there just wasn't room to form a good gasket and still easily open the vane.
The next attempt was more successful. This time, I applied the bead to the inside of the eyeball itself, and simply let the vane close against it. I protected the vane with petroleum jelly to keep the silicon from sticking.
The seal was then trimmed with a sharp exacto knife. It worked very well indeed, and doesn't look half bad!

 

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Updated: 22 May 05