Step 6.5, Landing light install

The main activity for this posting is the landing and taxi light installation.  I have not yet decided what kind of landing and taxi lights to go with so I will just be fitting the attach brackets and lenses.  I will undoubtedly go with an LED technology because of the lower power, but I have yet to be see a landing light kit that I can get really excited about.

While I wait for the ideal LED solution to make itself apparent, I will go ahead and put in the light mounting bracket and make the cut outs in the leading edges of both wings.  I have purchased a lens and mount only kit from Duckworks Aviation.  The kit comes with all of the hardware and instructions necessary for putting a big hole in your recently completed wing and, thankfully, a much smaller hole in your wallet.

To start, use the supplied template to mark the cutout location.  Then using your choice of implements, brutalize your unsuspecting wing.  I started with the cutoff wheel and then finished the rounded corners with the saber saw.  I don't blame you if you are feeling a bit queasy at this point.  You're just experiencing sympathetic nervousness at the whole the idea of it.  Fear not, and read on.  It all works out in the end.  So here's a close up of the leading edge after the first saber saw attack.  

Some might call the previous photo gratuitous aluminum gore, but it is included here because I feel that it is important to be true to my artistic vision for this blog.  Not to mention my desire to increase the readership in the all important 18-35 age demographic. 

Once the rough cut was made, I smoothed the edges with a file and a 1" Scotch-Brite wheel in the die grinder.

Then  match drill the backing plates for the lens.  These reinforcing plates will get nutplates later on  for screws attaching the lens.

After cutting out the leading edge section, the lens itself must be cut to size which is about 3/4" larger than the hole.  The lens comes already bent to the shape of the leading edge which makes trimming the plastic somewhat more adventurous.  I used the band saw for this and had no real difficulty, but I did worry a bit.  But not too much.

I put masking tape on the lens while I was armed with sand paper.  The edges of the plastic are sanded smooth on the belt sander and then finished with a fine cut file, some sandpaper, and a trip past a buffing wheel with plastic compound.  Although I don't have a calibrated baby's bottom handy for comparison, I would say the edges of the plastic would be in the same ballpark.

Once the edges are smooth the mounting holes are match drilled through the wing skin and lens insuring a perfect fit.  Then the skin is dimpled and the holes in the lens are counter sunk.  There is a foam sealing tape included in the kit to apply to the inside edge of the cut out that will seal against the forward edge of the lens.  I put the lens in a plastic bag before installing it.  This will offer a modicum of protection against me during the balance of this aircraft's construction.

And there it is!  The right one anyway.  The left one looks just like it.  The wing is upside down on the bench so you're looking at the bottom side.  And that's all he wrote.

Step 6.4, Fitting the fuel tanks

With the fuel tanks complete, it's time to actually mount them on the wings.  First though, I primed the outside of the rear baffle and the outboard end of the tank since they will be concealed when the tank is mounted.

I didn't realize it then, but the Pro Seal fillet along the edge of the rib was about to become a problem.  I set the tank up on the wing and used some straps to provide some down force on the tank.  I began to see that it wasn't going to line up along the inboard edge where is connects to the W-423 splice plate.

Fortunately my X-ray vision really helps out in situations like these and  I was (eventually) able to figure out that it was the Pro Seal preventing a good fit.  So the tank came back off of the wing for some Pro Seal surgery.

After I removed the fillet, I smoothed down the area with an Scotch-Brite pad on the angle grinder. Then re-prime and I'm back in business.

Now the the tank fits well against the outboard leading edge skin but the gap on the top skin is not as tight as the gap on the bottom skin.  I tried to pull the tank skin down tighter with the straps, but it just wasn't having any of that...  So I decided to forgo my Oshkosh Grand Champion builder's trophy on this plane and just let it be.  There really isn't any discussion in the build manual on what the gap should be.  I just assumed that the amount was zero.  Luckily, the gap is a uniform 1/32" along the length of the tank and is not really likely to draw too much much derision from my fellow builders.  I just can't understand why the gap had to be on the top of the wing and not the bottom.

Once the periphery of the tank is screwed down, the AN3 bolts that attach to the back of the tank via the Z brackets are applied.  This is where I thought the real difficulty would occur.  The bolts have to mate with the nutplates on the Z brackets through holes drilled through the main spar web. The slightest misalignment could prevent the bolt from threading into the Z bracket.  Here are the AN3 bolts and torque wrench ready for action.

The view inside the wing.  Getting ready to tighten these three down.  There are a total of 21 bolts for each tank.  To my surprise and great delight, all of the bolts in both wings slid right in.  It seems oddly unlikely and somehow inappropriate;  Like I was using someone else's luck.  I'm used to things being far more difficult than I expect and this just seemed wrong.

The last Z bracket is accessed from the forward side of the spar.  Note that I am working around that stupid balloon.  I've been so impressed that my tanks are actually holding air that I haven't wanted to disconnect the balloon (nearly a week at the time of this photo).

And that is it for the tank attach.  Up next,  landing and taxing light install.

6.3 Fuel tank leak test

After a very long, tedious, and messy job of finishing the fuel tanks, one may wish to know whether or not they will leak.  I know I did, but I'm just kind of curious in that way.  There's a fuel tank test kit from Van's which I dutifully purchased.  The contents were a Schrader valve, a cap for the fuel line and a page of xeroxed instructions for testing the tank.  Not too bad for six bucks, I guess.  For those not familiar, August Schrader is the guy who invented the valve we all use to keep the air in our tires.

The Schrader valve is placed into the fuel drain fitting and the AN cap over the fuel line, and a balloon over the vent line.  The balloon was not included in the kit.  The instructions were simple: just tape over the fuel cap (I guess the fuel filler caps are not air tight).  Then put the balloon on. Then fill the tank with air.

I attached a short section of aluminum tube to the vent fitting to make a right angle turn providing more room for the balloon.  Also, using a surprising amount of electrical tape, I made the end of the tube larger to better fit the balloon.  Then using safety wire around the neck of the balloon it is fastened to the vent pipe.  

It is at this point that the tanks are ready to fill with air.  The purpose of the balloons is to protect the tanks from over pressurizing and to provide a visual indicator of success!  If the tanks are overfilled, the balloons will just burst before the tanks are damaged.  Which is exactly what happened to my first few balloons.  The air filling the balloons is definitely a lagging indicator because of the small diameter vent line.  Eventually I learned to stop filling the tank when the balloon was only 2/3 full and it will coast on up to full as the pressure in the tank and the balloon equalize.

Once the balloons are full, each rivet and seam is tested with soapy water.  Initially, I had some leakage around the access plate on both tanks.  Tightening the screws did the trick.  All that is left to do is  wait...

Waited long enough?  

Well, I waited 3 days with no discernible loss of pressure.  That is really all I would expect the balloons to last anyway.  If I had been a little smarter, I think I would have inflated a few 'control' balloons as a test of their ability to just hold air.  I'm hoping that if air can't find its way out in 72 hours, then aviation fuel won't either.  Fingers crossed.  

Incidentally, I took the tape off of my fuel filler caps to test their leakage.  They are not leaking, so it seems that the tape was unnecessary.  That must be the deluxe part of my "Deluxe locking fuel cap."

Time to move on.

Step 6.2 Fuel tank assembly

To begin the assembly of the fuel tanks the first thing to do is get the ribs in place.  The area under each rib is thoroughly cleaned with a Scotch Brite pad and then with MEK.  The edges of the ribs get the same treatment.  The is where the Rick Galati fay sealing method begins.  Fay sealing just means that the two surfaces to be joined are both 'buttered' up before assembly such that the sealant is trapped in place by the fasteners (rivets).  What makes the Galati method different than that described in the build manual is that he does not immediately rivet the wet sealant.  Instead, using the Galati method, one clecos the parts together and allows the sealant to cure for some time before riveting.  The cure time is what makes this  method more attractive as the final result is less messy.  Trying to rivet the nose ribs is tough enough without having to do the rivet wrestle with wet sealant oozing everywhere.

Here Carol is putting the final touches on the stiffeners by covering the rivet tails with a blob of Pro Seal.

Each riveted hole in the tank is sealed in three ways.  The rivet head to the wing skin outside surface is sealed before the rivet is driven by placing a blob of sealant in the dimple.  The mating surfaces between the inside skin and the rib or stiffener is sealed when the pieces are brought together. And finally, the edges of each piece (again, rib or stiffener) are sealed by applying a fillet of sealer around the perimeter of the piece.

The ribs are first attached with cleco through the nose so the the rib can be placed without rubbing off the sealant by trying to slide the rib in place. 

In the two photos that follow the process begins.  The top and bottom of each rib has sealant as does the inside of the skin where they meet.

When the inside ribs have been fastened through the leading edge, the skin can be closed around the ribs using the wing fixture to hold the skin closed.

The rear most clecos are put in first in order to pull in the skin tight around the rib.  This takes a bit a force as the skin's lifelong preference has been to do otherwise.

Once the rear most cleco is in place, all of the other holes along the rib will be aligned. The rest of each rib continues without much drama. Occasionally a hole may not line up enough to get the cleco in. A dental pick our other sharp tool will usually to the trick. At this point the dimpled holes really want to just snap into place.

In the photos below, the rib under this line of rivets has already been glued with Pro Seal using the Galati method. The the dimple is then lightly counter sunk to clean the dimple of semi-dried Pro Seal. This allows the rivet to be set at the correct height with the addition of Pro Seal under the head.

Next a dab of Pro Seal is applied to the dimple.

Then the rivet is set in place.  The excess Pro Seal is pushed out at both the top and bottom, insuring a good seal.  Then the rivet is driven normally.

After riveting the skin to the internal ribs there were a still few details I had to complete before putting on the end ribs.  

In the photo above the "anti-hangup"  bracket is installed across the access plate in the tank that has a flop tube fuel pickup.  The idea here is that the flexible nature of the flop tube could somehow allow it to get hung up on the access plate, so this bracket is attached across its diameter.  I curved the center of the bracket to give some additional rigidity to the structure.

Here is another anti hangup detail.  The diagonal brace keeps the flop tube out of trouble on the other side of its bay.  In the right wing, the standard fuel pickup tube is fabricated and attached to the access plate.

This is the bulkhead end of the flop tube just before installation.  Note that the safety wire prevents the flop tube from unscrewing itself from the right angle bulkhead fitting.  If this were to happen, it might be the pilot and passenger that were screwed.

Don't panic, the tail end of the safety wire was neatly trimmed and curled over before the flop tube was installed.

Fuel tank vent line.

This is inside showing the vent line connection to the inboard rib and the doubler plate at the leading edge.   In this photo the tank is upside down.  When this photo was taken, the inside edge fillet had not yet been completed.  Note the difference in the fillet between the inboard rib at right and the other rib at left.

Capacitive fuel level sending plate is installed.

Finally the fuel tank attach flange is riveted in place.

By this point the dogs have had enough and, no doubt, so has my gentle reader.  The little dog takes the big bed.

And Carol was heading out as well.  But not before we had attached the rear baffle.

The next day we riveted the skin to the rear baffle.  All that remained for the left tank was to Pro Seal in the shop heads on the rivets we just drove and pray that it doesn't leak.

That's it for the left tank.  And as for the right tank, you may recall the immortal words of Herman's Hermit's 'Henry the eighth':

"Second verse, same as the first"

So, I'll be kind and spare you the Pro Sealed messy details.