Step 7.3, Fitting the wing tips

When life happens it's not always convenient.  I've been away from this blog due to some unforeseen unpleasantness in my continued employment, or sudden lack thereof.

Fortunately for me, my layoff didn't take. I've been hired by another company whose forward thinking and innovation have proven very successful in a similar market.  I couldn't be happier. Yea!

So I've been working on fitting the wing tips.  The tips are a fiberglass affair that must be trimmed to fit.  But the first thing to do is to fix the aileron in the neutral position as seen in the previous post.  Only this time, the jig must be removed so that the wing tip can be fitted.  After a few unsuccessful Rube Goldberg-esque attempts, I finally just made wooden clamp shown below.  It's just a piece of oak with a hole drilled through for the aileron push tube.  Screws in the top provide the clamping force and screws in the front fix the clamp the the inboard rib.

The clamp is tightened while the neutral position jig is still on the outboard wing rib and aileron is held in place nicely.

The next thing I noticed is that the wing tip had a bulge along its outside edge.  Using a laser line generator (leveling device) I could determine the location and amount to trim over the compound curvature.

I traced the laser line across the length of the wing tip with a sharpie and then used a DA to sand the edge straight.  The next step is to fit the tip on the wing and trim the moulded recess to fit the wing.

It's a bit messy while triming, but once its done... Well once it's done, you find out it doesn't fit.  My tips were off along three different planes.  First, the back edge of the tip is supposed to align with the trailing edge of the aileron.  My tips were longer than the aileron.  They were also lower than the neutrally positioned aileron by about an inch.  And finally, the trailing edge of the tip was not in parallel to the trailing edge of the aileron.

I don't know what else could have been wrong with these tips.  I'm not at all certain that they were made for an RV-7.  Oh Well.  Using the laser again I was able to force the trailing edge of the tip to get in line with the aileron.  I positioned the laser line on the trailing edge of the aileron and then taped a block of wood to the tip to catch the line.  Adjusting the tip until it was parallel to the aileron and then match drilling the inside tip edge to the wing fixes the tip in position.

But the tip edge is still not an inch off of the aileron.  This is where the cut-off saw makes another appearance.  The whole trailing edge and half of the outside edge are split to allow the tip to be moved up.

Once the tips are trimmed and split, they must be epoxied back together.  Only this time, unlike when they were originally manufactured, the trailing edge curvature matches that of the wing and aileron.

While I had the epoxy out, I laid up a couple of strips along the inside seam to offset the fiberglass that was sanded off while straightening out the outside edges.

With the epoxy cured the tip stiffening rib is riveted in place.  It's only clecoed in the photo above.  The final step is to rivet on the 38 nutplates the will finish the attachment of the wing tip.  One tip down and one to go.  

Although the tip is fitted, there is still a fair amount of finish work to be done before it will be ready for paint.  The re-glued seams for example, will require significant attention.

And now the good news:  My fuselage kit has been ordered and is scheduled to ship in the first week of April.

Step 7.2, Hanging the ailerons

I thought I would move on to the wing tips now the that bottom skins are firmly attached.

Well, that is what I thought, but it seems that I'm not quite ready for wing tips because the exact position of the tips is determined in part by the "in trail" or neutral position of the ailerons.  That is, that the end of the wing tip nearest the aileron trailing edge must match when the ailerons are in the neutral position.  To make that adjustment, the ailerons have to go on the wing first.

In the photo below, the wing is on the right and upside down on the work table.  The aileron is on the left.  The aileron actuator push tube is visible at the bottom of the photo. 

The ailerons hinge on AN3 bolts through the aileron bracket (white) and through the aileron to wing attach brackets which contain the ball-swivel type bearing that does the actual hinging.  The bearing is not visible in the photos because it is inside the attach bracket in the center of the photo.

Getting the ailerons attached to the wing is a bit of a fiddly process because of the many small washers and spacers.  Fortunately, there are tools to help.  The wrench looking things on the left are washer holders that are very useful.  The washers snap into the end and permit the washer to be held firmly while it it slid into position.  The do dads on the right can be used temporarily in place of a AN3 bolt.  These are nice when a lot of test fitting is required because the ends are not threaded.

With the aileron hanging on its hinges it is now necessary to make the adjustment for neutral position.  The position is set by first securing the bellcrank to its center position using a Van's supplied jig,  W-730.  This jig keeps the bellcrank in a known position so the the aileron actuator push tube can be adjusted for length.  The ball-end bearings on the push tube ends can screw in or out to make the final adjustment.  The end of the push tube is visible in the first photo.

So changing the length of the aileron push tube moves the aileron up and down, but how do we know that it is in the trailing or neutral position?

Fortunately, Van's has provided tooling holes in the wing ribs that are aligned to the cord line of the wing.  A jig is constructed that extends this line rearward when bolted through the tooling holes.  At that point is is a simple matter to adjust the actuator arm until the aileron is in the neutral position.

I've drawn a center line on the inside edge of the jig that bisects the attachment holes in the alignment jig.

And the aileron is adjusted until the center of the trailing edge is brought to the line.