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While my STOL 750 was down for annual, I decided to frame the belly hatch to stiffen the edges and provide a good seal against the belly skin. I had noted previously that there were some exhaust stains that seemed to indicate exhaust was being pulled into the rear fuselage through the belly hatch! The original hatch doesn't seal very well since the material is so thin - typically, when the screws are tightened, you get a "wavy" edge with gaps between the screws. Also, the edges of my hatch were beginning to chip in places, again probably due to the flexibility of the hatch's edge.
I had some aluminum L approximately 1/16" thick, so I cut one flange down to just a couple of mm. with my bandsaw. I mitered the corners, but found it very difficult to get a perfect fit, plus, there's a screw hole exactly in the center of where the miter joint runs! So, I didn't worry about a perfect fit and made square corner pieces to hide the miters and also better distribute the pressure from the corner screws.
I powder coated the framing pieces and the corner squares. The Eastwood Gloss White powder coat is actually a fairly good match with my Matterhorn White paint on the belly. It doesn't match that great now until it accumulates some exhaust stains, but eventually I think it will blend well! I used West System's #650 "G/Flex" epoxy to bond the edge pieces to the hatch and the corner pieces to the edge pieces. It is especially suitable for bonding aluminum to plastics as in the catalyzed urethane paint on the belly hatch and the powder coat on the edge pieces. The aluminum was prepped by scuffing it with coarse aluminum oxide paper through a thin layer of wet epoxy prior to clamping.
The end result was rigid and straight belly hatch edges that properly compress and seal the weather stripping I have on the inside edges of the hatch.
As usual, a PROfessional job! Probably gained 5 mph in airspeed? Were you worried about CO in the cabin?
Now my problem is picking a gel coat color to match the red pain on my struts.
I was getting CO from somehwere in my 701. Turned out to be the hellhole cover(taped it up and the CO went away).
Pulled it off and riveted 1/2x1/2 AL angles inside just inside the edges of the hole. Then weather stripped with 3/16 foam. It's tight and looks lots better.
I've occasionally had CO in the winter when I'm not using much cockpit ventilation - it's been manageable by adjusting the vents. Since my doors are weatherstripped, etc, I've always suspected it might be coming in through the belly hatch - especially since there were exhaust stains running under the lip of the hatch!
With the hatch's improved fit and seal, it will be interesting to see if it recurs this winter.