Sat Jun 26 2010

Popup tipup modifications

Well, the past few days have been really busy with EAA work, so not much progress on the plane. Here, I'm looking at the right side canopy frame weldment pivot. I have the two pivots squeezed towards eachother with a QuickGrip clamp, but there's still about 1/8 inch gap between my block and the pivot. Ahh...wait a second...there's supposed to be a gap here since the popup arms will be 1/8 thick on either side of the pivot. Cool...I actually did this right.

Here I've drilled a starter hole for the popup arm pivot point. When the arm was positioned in the position I had originally planned, this hole ended up being very close to the right cleco shown here, so I elected to push the arm forward by about 3/16 inch and center the pivot between the rivets on either side.

In order to drill the hole through the inboard rib in perfect alignment with the outboard rib, I drilled a hole exactly perpendicular through one of my spacer blocks, then clamped the spacer block in position and used it as a drill guide for drilling the inboard hole. Worked great.

While trying to position the popup arms, I realized that the canopy frame weldment was leaning back too far. Based on an examination of the plans, the bottom edge of this frame is supposed to be parallel to the longeron. There aren't any dimensions that indicate this, but it sure looks parallel on the plans. I took a measurement at the front end of the weldment and made some 5/16 spacers to rest the back edge of the weldment on. Afterward, I taped these to the canopy rails so they wouldn't slide off.

The joint plates were covering up the interface of the popup arm and pivot, so I notched them out to see how they line up. Here you can see that I've got to shorten my arms by about 3/16 inch.

There's also the problem that the canopy frame weldment pivot on the right side isn't quite vertical.

I corrected this by twisting the weldment with a crecent wrench. If you do the same thing, be sure to use the wrench at the front end of this weldment rather than in the middle (as shown) to avoid the slight kink I got in this member.

After studying the plans quite a bit more, I decided it was going to be necessary to rivet the forward ends of the pivots to the canopy frame channels. With everything clamped in place, I used the 12" #30 bit to drill through the prepunched holes into the channels. Be sure these are pulled all the way up to the top flange of the channels before drilling these holes.

Since I'm making a significant modification to the forward fuselage structure, I'm not sure how useful these pages will be to someone building to the plans, but one thing I'd say is look at how the weldment is going to fit before drilling the UHMW blocks to the structure and definitely before drilling the pivot point. A lot of people have problems with this fitting correctly, and I wouldn't be surprised if it has something to do with the fact that the instructions don't have you rivet the pibot arms to the channels until later.

Here's one of the pivot arms riveted to its respective channel.

Last thing for the day was to fabricate the pivot blocks for the cross shaft which will actuate the popup mechanism.