Tue Jul 20 2010

Popup tipup modifications and misc work

Yesterday evening, I ran over to my friend Greg's house to borrow some extended reach 3/32 clecos. I needed them to hold these lever arm assemblies together so that the rivet holes could be drilled up from #40 to #30. So today I did just that. I also countersunk all the rivet holes.

I was procrastinating on working on the next part of the popup tipup modifications, so I decided to reinstall the pitch servo. The job went much better this time and only took two tries to get the safety wire right. It's not the prettiest safety wire job, but it'll do.

Afterwards, I ran out to TSC to buy some paint. I had been told that the Valspar Ford Grey was a very close match for the powder coating color Van's uses. The bellcranks were starting to show some rust, so I wanted to get them primed and painted before they got too bad. Unfortunately I only got them primed. The primer seems to dry very slowly even on a hot day like today. Maybe I'll put the parts in the oven to get the primer fully dry.

Later in the evening, I decided to work on fitting the canopy frame. First thing to do was install the top, forward fuselage skin. It's not fully installed in this photo...I'll cleco it down along the sides when it's necessary.

I could see that these welds would cause the canopy skin not to lie flat, so I took the weldment down the basement for some filing.

The weld is now filed tangent to the surface of the aft frame tube, but you can see there is still a slight step down to the plate which connects the aft frame tube and the forward channels. Looks like I'll need a spacer on top of this plate.

Sure enough, it looks like I need a spacer all along this thing. It'll need to be about 0.032 thick at the forward end and about 0.016 thick at the aft end. The other plate is similar.

Since I had the frame down the basement, I decided to get rid of any other bulges I found. Here is some weld that bulged through from the other side.

Nice and smooth now. :-)

Likewise with this weld where the tube meets the side member.


Yeah, I'm being picky, but this had been bugging me for a while. Pretty much any welder will tell you that if you're welding a gusset in place, don't extend the ends of the gusset down to a point. Those pointy bits will just melt away. You can see that the welders just stopped the weld short to avoid that problem, but it left a hook to snag on stuff. I resolved to trim this off.

Much better.

Before going back up to the garage, I went ahead and deburred all the remaining edges of this weldment. Because of the awkward shape, this took quite a while.

Back in the garage, I positioned the weldment and clecoed on the canopy skin.

The sides are under a lot of tension. This photo is taken from low alongside the fuselage looking up at the edge of the skin which is supposed to come down on top of the canopy rails. You can see that even fully clecoed-up, the skin isn't pulled tight to the weldment.

The rivet holes don't show up in this photo, but the curvature of the tube is too much for the skin to follow. This results in a gap between the skin and the tube for the outer three holes. This is a common and well documented problem with the tipup canopies.

Although the top, forward fuselage skin and the canopy skin were butted together near the centerline, a gap was apparent along the sides.

Ahh, I see...my wood spacer blocks (held on with blue tape) are too thick. I'll have to place some thinner spacers in and recheck the fit.