Sun May 25 2008

F-715 and F-623 rib work

The first thing I did today was to use the fluting pliers to put the curve in the F-715 seat ribs. I wasn't sure where I could flute, so I clecoed the aft end of the F-715 ribs to the F-705 bulkhead and stuck a sharpie though each rivet hole and wiggled the forward end of the rib back and forth to draw a line on the rib flange. This should give a rough idea of where not to flute.

It worked out well. As you can see, after fluting the rib, I clecoed it back in position and used a fine tipped sharpie to draw circles through the rivet holes. Adding the curve to the rib hadn't changed the position much where the rivets would go through the skin into the rib flange, so the fluting locations turned out just fine.

This is how I got the curve correct...I just held the rib up to the curved row of rivet holes to check where I needed to flute a little more or less. Worked great!

Then it was on to working on the F-623 corner ribs. I set the flanges at 90 degrees.

Then I decided to match drill the F-776 bottom skin to the F-716 seatribs, the F-725, F-726, and F-727 baggage ribs as well as the F-704 and F-705 bulkheads.

After flipping the assembly over and putting it on sawhorses, I started work on the F-623 corner ribs. The forward end needed trimmed some to allow me to get the corner of the rib to align with the corner of the skin.

I realized that if I trimmed the rib back far enough to clear the bend radius of the F-705D channel, the edge distance would be questionable. So I left the F-623 a little extra long and filed a bend relief so that I could bend the end of the flange over to clear the bend radius.

Fits much better. :-)

Hrm...this is a problem. The angle of the F-623 doesn't match the F-776 bottom skin very well. Here I've got the forward leg of F-623 aligned with edge of the skin...

...but back here, the aft leg of F-623 is pulled about 1/16 inch inboard. I did some searching on the net to see if anyone else had this problem. Brad Oliver apparently ran into the same issue and he made the forward leg match and let the aft leg be biased inboard. That makes sense because the side skin actually rivets to the forward leg, and the aft leg will just be buried under the baggage compartment floor. I chose to do the same thing.

Around this time I noticed that the web of the F-623 was interfering with the bend radius of the F-705A bottom channel so I filed another bend radius and bent the tab up slightly just like I had done on the side.

To get ready to trim the aft end of the F-623s, I checked the edge distance at the forward most row of rivets on the F-7?? tailcone bottom skin. It measured about 11/32 inch.

I rounded this up to an even 3/8 inch and transferred the measurement to the matching row of holes on the F-776 center section bottom skin. The F-623s need to stop at this line.

Some quick work with the bandsaw and sander and they were trimmed up.

Before drilling these ribs to the bottom skin, I had to use fluting pliers to straighten them out. I held the forward leg of the F-623 rib up to the side skin to mark where the rivets would go. Then I just fluted in between the marks.

Well, I drilled the F-623s to the bottom skin, and noticed something afterward. The bottom flange of F-705A was holding the F-623 rib off the bottom skin. Dunno why I'd have expected anything different since there's no joggle there. I went upstairs for a while to see what others have done.

Well after some internet research, the consensus seems to be that the plans and instructions are very vague here. Both Brad and Dan just trimmed the ends off. While I'm sure that would be fine, it didn't sit quite right with me. I mean...why would Van's go to the trouble of putting a joggle on the outboard flange if they were just planning on having you hack it off? I decided I'd keep the outboard flange and trim everything else off. Here, I've drawn a mark roughly where I need to trim.

This came out pretty well. I'll be able to drill and rivet the outboard flange to the F-705D side channels, but the web of F-623 now lies flat on the F-776 bottom skin. Mo' betta!

Here's what the forward ends of the F-623s ended up looking like.

Then it was time to fabricate the F-623A-FWD tie plates. I used some scrap .032 thick sheet. They came out fine except that this tie plate is covering one of the inboard holes. You can see it just barely peeking out from under the tie plate next to the cleco.

So I filed a little relief in the tie plate to make room for the dimple and the shop head.

Since I knew the aft ends of the F-623s were shifted inboard I pretty much disregarded the plans when fabricating the F-623A-AFT tie plates. Instead what I did was start by drawing a line on the skin along the inboard edge of the rib.

Then I clamped a piece of scrap .032 sheet on the line and drew a cut line on the underside using the skin edge as a guide. By the way, this piece of material is scrap from cutting out the notch in the F-711 bulkheads.

Once I had the basic triangular shape, I clamped my 24" scale to the bottom skin. I positioned it so that I could use it to draw a line on the tie plate that would result in 5/16 inch edge distance. I also marked on the tie plate where the end of the F-623 rib was and how much I had to relieve the tie plate to allow for the bend radii of the rib.

Here are the cut lines.

...and here's how it came out.

I duplicated the process for the left side, but the edge distance isn't so good on the left side since the aft leg of that F-623 is shifted inboard even more than the one on the right side. I'll decide tomorrow if it's good enough or if I need to redo it.