Step 7.4, Wing tip lens

At night and at some distance, it can sometimes be difficult to readily determine if an aircraft is coming at you or going away.  For this reason, it is required to have position lights on your aircraft if you want to fly at night.  Position lights are red on the left side of the plane and green on the right.  In addition to the position lights, most aircraft also have strobe lights on the wing tips and/or tail to enhance visibility.

On the RV, the position and strobe lights are mounted within a recess on the wing tips.  The recess is covered with a clear plastic lens that comes with the kit.

The first thing you notice with the lens is that it is a single piece of vacuum formed Plexiglas that must be cut in half for the two wing tips.

And so the lens is pictured above after the first cut to separate the halves. The next challenge is deciding where to start the fitting process.  It is obvious that the vacuum formed edge has to go, so I decide to start at the leading edge and take off just enough to remove the lip and give a good finished edge.  This will be the forward reference point.  The next cut is to set the rear most point of the lens in the recess.  Now that both the front and back fit within the recess, the rest of the recess edges can be traced through using a sharpie to mark the lens.  A few more cuts are necessary here because I want to sneak up on the actual dimension carefully rather than risk going too far.

After this it is a matter of carefully sanding down the edges until the fit is good.  The belt sander makes this process a snap, but many trial fittings were required.

When the lens fits snugly with a small, but even gap all the way around it's ready for the edge finishing.  I used #320 and #800 sandpaper on the edges and finished with plastic compound on the buffer.

The next step is to set some nut plates in the wing tip to retain the lens.  With the lens in place I drilled a hole through the lens and wing tip for the screw.  Then with the nutplate located, the ears can be drilled through.

So here is the nutplate ready for rivets.  Because the recess edge was so close to the rivets, I had to use a back-set which is much smaller than the mushroom set I would normally use for a counter sunk rivet. 

And that's about it for one lens.  One more to go.

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. 

Step 7.1, Bottom skins

Not really looking forward to this after the life threatening tedium of riveting the top skins.  I really shouldn't say things like that as it gives the impression that there is something else to do that would be more fun.  Sometimes it's hard to remember that you are having the time of you life when you are drilling out a rivet gone bad for the second time.  The truth is that all of it is better than not building an airplane, but some of the processes are more fun than others.

The real trick to doing the bottom skins is getting past the first part.  I guess that could be true with  just about any task.  Just beyond the procrastination lies the productivity.  I eventually got into it and discovered right off, that the area under the wing walk is a real bitch because of the closely spaced ribs.

To work the bottom skins by oneself, ideally, one would be equipped with the long arms of a basketball player and be crazy skinny too, like a vegetarian.  A second elbow joint in the center of your forearm wouldn't go unappreciated.  If you don't happen to have these attributes, it is best to  find a helper, preferably a woman, to help you.  You'll need very small hands to get between the ribs at the small end of the wing.

We elected to hang the skins while the wing remained on the stand, rather than placing the wing on a table as the manual suggests.  I just felt the my reach would be better if I didn't have to lean across the leading edge of the wing first.

Duct tape is employed along the way to hold the skin back.  Notice the little tray of rivets perched on the bottom of the stand.  Guess how far those little boogers go when you knock the tray off.  The answer is I don't know for sure because I haven't found them all yet.

So here I am finishing up the first bottom skin.  The next skin overlays the inboard skin as we work outward towards the tip.  But, since this is the left wing, the Pito tube must be installed first.

It's just a matter of getting the Pito mast through the hole we put in the skin earlier.  It's a tight fit and takes a little wiggling to get through.

With the mast in place we can continue on with the riveting of the skin.

The picture above was taken later showing the same area below the mast while I was trying to connect the Pito and AOA plumbing.  The inspection mirror becomes your best friend during the bottom skinning process as very little of the work is directly visible.

And so we continue to pound those rivets...

And eventually we move on to the right wing.

At the start of this post I mentioned the need for skinny arms.  The next picture illustrates the extent to which my arm can extend through the lower middle lightening hole.  About half way, which is kind of a problem because my favorite bucking bar only just reaches the furthest rivets in the lower part of the bay and very little pressure or control could be applied.  It was the wild west down there.

Well, along the way there were a few dents, and a few rivets had to be replaced but, perseverance pays and we eventually got through it.

One tool that is absolutely indispensable and, strangely, was not included in my tool kit was a sharp pointy thing.

The sharp pointy thing is used to bring the parts to be fastened into alignment prior to inserting the rivet.  Shown above, it's the unsung hero of aluminum aircraft construction.  Place the pick in to the hole above the one that won't accept the rivet.  This is usually enough to convince the hole in question to allow the rivet without further comment.  Occasionally the obstinate hole itself must be probed before it will allow the rivet in.  Don't feel sorry for the hole, it had it coming.

And finally, the last few rivets in the last bottom skin go in.  Whew!

Step 7.0 Ailerons

It turns out that the ailerons are a lot like the flaps in construction and size.  For those not familiar, the ailerons are located just outboard of the flaps and occupy about half of the trailing edge of the wing.  The purpose of the aileron is to provide a banking action to the aircraft which is helpful when it comes time to turn.  Although it is possible to turn an aircraft with the aileron or rudder alone, it really takes the combined action of the rudder and the ailerons to maintain coordinated flight through a turn.

The big difference in the construction of the ailerons vs. the flaps is that the ailerons use stiffeners internally rather than the rib construction that the flaps used.  Each aileron uses 16 stiffeners which is quite a lot considering that each one is individually cut from the Van's supplied angle stock.  Each stiffener has two tapered sides and two straight ends to cut.  That all means a lot of time in front of the band saw.  As always, the first step is to get the blue plastic off.

Match drilling the stiffeners to the skin.

Then deburred and dimpled, the stiffeners are ready for primer.

Then the rest of the aileron frame is assembled and match drilled.

Here's a tool I made to dimple the leading edge.  The standard dimple die is too large in diameter to fit inside the curved leading edge.  I drilled and counter sunk a 1/2" piece of bar stock to make a female die that can fit inside the leading edge.  A larger diameter bar would have been better, but 1/2" is what I had on hand.  

With the female die inside the leading edge, a nail fits through the back of the die then through the leading edge where it meets the the male half of a pull rivet based dimpler.

And the dimpled leading edge.

 

Here's the first 16 stiffeners in the paint booth. Lots of steps were performed, but not pictured, to get to this point. They are mostly omitted here so as not to induce a reader coma this early in the posting. You can thank me later.

After the primed stiffeners are riveted to the skin it's time to bend the skin down.  When the skin reaches the correct angle, the top and bottom just fit over the spar.  The last time we saw this homemade bending brake was for bending the elevator skins.  I'm sure glad I didn't throw it away.

So here is the counter balance weight that will be riveted to the inside of the leading edge.  This thing is heavy!   It is basically just a big pipe similar to galvanized water pipe.  The purpose of a counter balance is to dampen the tendency of a control surface to flutter.  Aerodynamic flutter can, in an extreme case, rip the control surface right off the airplane in a matter of seconds.  Midair disintegration of an aircraft is very rare, but when it does happen flutter is often suspected.

Let's take a break from building to watch Carol using the iPad to fix the Dish satellite reception.  Isn't technology great!  Notice the coat though.  She's arctic ready.

Now take a look at the actual temperature in the shop taken at the time of the photo above:

Out of the paint booth and the parts are ready for riveting.

And here is the right aileron finished.  Well almost finished.  I still had the hinge brackets to bolt on after this photo was taken.