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Gas Struts Installed – 2 hrs

June 1, 2012 Leave a comment

Friday June 1, 2012

The drawing says “CRITICAL DIMENSION” on the spacing between the C-725 and C-728 strut mounts. To get the spacing right I made a tool made of scrap aluminum angle with holes drilled precisely 9-11/16 apart. This post is a little light on photos but in this one you can see my tool in use. I used the ball stud on the C-725 to attach the tool and I just used a 5/16 drill on the aft end at the C-728. You can’t see it but I also taped a small piece of angle to the far side of the C-728 that sat on the side rail to locate the position of the C-728 vertically. Then I drilled.

To mount the C-728s I followed a suggestion I found on the web to rivet a couple of nutplates to a small piece of aluminum sheet to replace the washers and nuts on the inside of the side rail which are very hard to install. I forgot to take a picture but you can imagine these are very simple.

With the gas struts installed I tested the action. It works as advertised although the frame is very light at this point without the canopy so the struts overpower the frame. By the way, don’t try to install the gas struts with the canopy frame down.

I was aware that the gas struts would likely make the canopy frame shift due to the force they exert with the canopy closed. Indeed they did. You can see in the photo the outline of the forward top skin forward edge I drew on the side skirt before the struts were installed. The line is now about 1/8 inch forward of where it was before.

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Gas Strut Mounts – 1.5 hrs

May 31, 2012 Leave a comment

Thursday May 31, 2012

The gas strut mounts are another one of those items shown on the drawings but the written instructions don’t even mention them. I followed the drawing and what I could learn from others on the web. I placed the C-725 block 3/8 inch forward of the C-613 splice plate but that made it overlap one of the rivet holes for the C-702 skin so I moved the block forward about 1/8 inch to clear the rivet head. With the block held firmly in place I drilled through the WD-716 canopy frame and C-702 skin using the C-725 as a guide.

Next I dimpled the holes in the C-702 skin. Under that, the WD-716 needs to be machine countersunk but the drawing warns that these countersinks will go through the material. So I made a couple of little sacrificial plates to back up the WD-716 and help keep the counter sink centered on the hole. You can see one of those in this picture.

The countersinks turned out fine with this method.

Then I removed the C-725 blocks and tapped the holes. The upper and lower holes are 8-32 and the center hole is .312-18 thread.

Then I put it back together to check out the fit. It looks good from the outside. These screws will end up being glassed over after the canopy is bonded.

On the inside it looks good too. You can see the rivet hole I dodged just aft of the C-725 block.

Drilled WD-725 Side Rails to WD-716 Canopy Frame – 3 hrs

Sunday May 6, 2012

This morning I made the C-729 spacers for the gas strut mounts. There was just barely enough raw material in the kit to make these. One hole was drilled in each spacer to the drawing dimensions and the other hole was match drilled to the C-728 mount. That’s why I marked them L and R, so they stay as matched sets.

The C-728 mounts needed to be countersunk for a #8 screw so I did that also.

The primer was well dry so I riveted the C-613 splice plates to the WD-725 side rails.

I have decided to use Sika Flex to bond the plexiglass canopy to the frame. Sika Flex needs a gap between the faying surfaces of ideally 1/8 inch or more to allow for the differential thermal expansion of the materials, however the stock design of the canopy assembly does not provide a gap between the plexi and the frame. So the question is how to set up the canopy to provide an adequate gap? The first step is to shim up the plexiglass canopy to achieve a 1/8 inch gap across the top of the bow frame and on the front deck. That is the easy part because it requires not structural modifications. However, it does not provide any additional gap along the side rails. I was worried about that because I surely don’t want the bond breaking on an extra hot day or at high altitudes where it is cold. I found a few builders that modified the side rail installation by adding 1/8 inch shims that offset the WD-725 rails inboard, thus allowing a suitable gap between the rail and the plexiglass for the Sika. Other builders make no mods there and bond the side rails to the plexiglass with a very thin bond line. I was skeptical about go this way until I talked to a builder who flew his RV-7 to 27,000 feet with his canopy built this way. So in my usual conservation style I decided to add .062 to the side rail gap just to add some margin there. It’s not a full 1/8 inch but it is an easier and lighter modification and helps me sleep at night. I ordered some .062 thick by 1.5 inch wide Alclad strips from Vans for this mod. You can see one of the strips clamped to the WD-725 in the picture below. This gives the extra .062 gap along the side.

Then I clamped the side skirts on to align the WD-725 with the skirt flush to the side skin of the fuselage.

I had to bend the little tabs on the canopy frame  where the WD-725 mates to allow for the offset and I had to put a .062 shim between the C-613 splice plate and the canopy frame. I actually used double sided tape to hold the shim to the C-613 during the assembly. When everything was aligned as well as I could get it I drilled through the C-613, the shim, and the canopy frame to lock these parts together.

I also drilled through the aft end of the WD-725 side rails to lock those to the F-631A bow frame parts. I am now committed to this alignment and bonding approach.

Canopy Lift Strut Parts – 2 hrs

Saturday May 5, 2012

This morning I went out to the Planes of Fame airshow at Chino airport. Each year Dave Klages hosts an RV fly-in at the airshow and about 30 RVs showed up. It was a great opportunity to browse around and see how some of the RVs were constructed and outfitted. I think every model RV was represented except the 12 and the 1 (of course).

After arriving back home I went back to my “pieces-O-RV” and resumed work on the canopy frame. I decided to go ahead and pre-drill the C-613 splice plates to the WD-725 side frames. This gives me two less pieces to clamp while aligning the canopy frame. I drilled them using the C-613 holes as a guide. I still need to open these holes up to #30.

I cleaned all the parts and applied spot primer to the surfaces that I will rivet together.

Then I started working on the parts that will be used to mount the gas struts that lift the canopy. The first were the C-728 mounts. I marked the outline of the parts and the hole centers on the raw stock. Then I pilot drilled all the holes with a #40 bit.

Then I enlarged the holes to the final size, which is #19 for the two end holes and 5/16 for the large hole.

Then I cut the pieces out, sanded the edges to final size and deburred everything on the scotchbrite wheel.

Next I cut the raw stock for the C-725 mounts ( 2 pieces).

I marked the location for the holes and drilled pilots with a #40 bit.

Then I enlarged the end holes to #21 which is the pilot hole for a 10-32 tap. I need a F drill for the center holes so that will have to wait until tomorrow when I can pick one up at the hardware store.