Mon Apr 19 2021

Rain gutter experiments

As you may recall, one of the reasons I'm deviating from Van's design in the area of the canopy skin and upper, forward fuselage skin is to prevent water from getting into the plane, particularly above the electronics. So, in contrast to the flanges of Van's sub panel bulkhead parts (which have several gaps), on our -7A, there will be a continuous strip of aluminum laying under the the (minimal) gap between the aft edge of the upper, forward fuselage skin, and the forward edge of the canopy skin. Here's how it will look in cross section.

...and here's a mockup of the various layers. I'll do some simple experiments to see how water behaves in the vicinity of this joint.

Clamped up at an angle to represent the area of the upper fuselage as it curves downward towards the sides.

Using a disposable dropper to drip water directly on the gap. First observation is that water doesn't really go down in the gap very well. That's good, but I'll still expect some rain to find it's way in there.

Any water that did find its way in just ran down the gap to the bottom as expected. However, this isn't quite what I want. If water just runs to the end of the channel, it's going to dump itself out on the longeron, and, in the interest of minimizing the potential for corrosion, I'd like any water in the "rain channel" to exit before getting to the longeron. Assuming I make a break in the continuous strip an inch or two before the longeron, how can I control where and how the water will drip out? First test was to bend a tab on the end.

If the goal is to have the water drip out aft of the sub panel, but forward of the canopy frame, this didn't work. The drips just ran out the end. I need them to travel to the aft edge of this rain gutter strip.