Wednesday, May 29, 2013

#6 Repair and Prep For Pre-Rig

Drilling and riveting the upper wing was easy because both spars were new and had no holes so I just drilled using the gussets as my hole template. When I went to align the lower wing on the fixture, I found that the impact had tweeked the lower panel enough to where I felt I needed to move the internal strut location to reduce the chord spacing back to it's original. I decided to accomplish this by moving the LE gusset location outboard toward the tip by ¼ inch. I cut new LE gusset plates that were longer than the originals so that I could still use the three original rivet holes in the spar. This shot shows the rivet holes I must hit exactly if I want to avoid ordering new material to fabricate a new diagonal strut and also the pre-bent LE spar (big incentive here to find a way!).
Here's the new gusset in place (now hiding where I need to drill the rivet holes)
In order to drill and exactly hit these old rivet holes in both the lower wing spars and internal diagonal strut (which I am re-using since they were not bent) I had to find a way to do this using the newly made larger gussets. There is a tool they call a “hole finder” which I borrowed from one of the EAA members but I found it to be too, thick and stiff to get under the gusset without moving it out of position. I made my own out of much thinner material I cut out of some scrap sheet metal with a metal shears.  I put two pop rivets in the one end forming a long tweezers-like tool. On the hole finding end, I clamped the ends together and drilled a rivet hole through both and then installed a rivet into one of these holes only, the other hole ends up on top of the gusset and acts as my drill template.
This next shot shows the finder ready to insert into an existing hole.
Once this is done, I slip the gusset into position as shown here and mark the hole location for drilling.
A word about other tools...... I wore out a pop rivet gun and the only symptom apparent was I started having more and more rivet stems break off leaving a long stem sticking out of the piece but not long enough for the tool to grip and finish the pull. I then had to break off the tail and drill out the rivet and install another rivet. Here's the old tool....
These are only $20 tools so it's not a big deal until you spend your $20 and get home and actually use the new one when you realize they aren't all made the same. The one I wore out was cheaper looking but actually worked much better because of the handle design. The new one has a handle spread in the open position that is made for someone with hands the size of large dinner plates so in order to squeeze the handles it becomes a two handed operation for us “normal” people.
Shop around.
Repair and re-assembly of both upper and lower left wing panels is now done.
Right wing panel pre-rigging
The next photo shows me attempting to get the upper right wing in position over the lower right wing which is positioned in the floor frame.
It's a good idea to make at least one reference mark on one of the spars relative to the fixture on the floor just in case something gets bumped accidently. The plan directions are a bit sparse as to how to do this and I found that suspending the upper wing in rough position was the easiest thing to do. You can see the cords coming down from the garage rafters.
Next I just followed the Pre-Rig instruction sheet of the plans to set the wing stagger (top panel forward of the bottom panel) and dihedral (top panel outboard of the bottom panel). The stagger is set at 14 inches and the dihedral is set to 6 inches.
Once I got it on the mark in the upright position, I used Pony clamps to hold the brackets in position and also made a reference mark on the spars then installed the struts including the rudder. Next I folded the wing down to check for binding. My wings weren't perfectly parallel when folded down but there was no binding and the upper wing plumb lines were withing an 1/8 inch of the marks so I called it good enough and drilled through the brackets into the spars to rivet them in place. If you were building the wing you would not yet have the bottom brackets set but I'm doing a repair and they are all riveted in place already. I think this is the weakest part of the plans. It is difficult to get all this done and get it to come out right. Later on, during final assembly there is reference to a) extending or lengthening the spar plugs when you mount them in the spar ends and also b) bending the spars to get things to fit. I believe if there was a better way to do the Pre-Rig, you would end up with everything coming out right. The other source for error is the plan calling for a flat floor to set the lower wing panel spar rotation (this sets both the sweep and the dihedral for the spar end that is pre-bent. The plan specs this to 1/16 of an inch........over a 14 X 3 ft would need to be REALLY flat to get the end of those spar ends to within a 1/16 of an inch of the spec the plan calls for.
That completes the left wing except for using the rib stitching knot to wrap the upper wing ribs and to strip the old glue from the lower panel spars and internal struts. Removed all the external struts and stored the wing panels in prep for the right wing.
Right Wing Panel Pre-rigging
The lower right wing panel is the only one left with it's original covering intact. There were some significant tears on the bottom of this panel that you can't see here. Hmmmmmmm, to strip or repair? I already forked out the money for cloth to cover all four wings and this would be nitrate/butyrate dope vs the Polyfiber covering system I have pretty much decided to use which would be a difference in weight.
I decide to strip it. This photo shows the hardest portion (it containes the strapping tape, the adhesive on it is really tough).
Next I'll get the upper right wing panel and lay it in position over the lower panel in it's approximate fold down position and install the struts. Be very attentive when installing the struts to use the right bolt. There are two sizes within an eighth of an inch difference which is enough to compress 1” tubing permanently if you use the wrong one in the specified bracket. Since these remain in place on the finished glider, there is no need to worry about them later but I suggest that you color code them during assembly since you'll install them now, remove them when done and then re-install them during final assembly so there is ample opportunity to mix them up.  Note that the wing panels have the LE facing to the left here....same end of fixture requires the panels to face the opposite of the left hand wing panels.  That wraps up this entry.

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