LH FUEL TANK PAGE 2

I intend to prime the outboard rib and the tank skin where it overhangs the baffle.  I will need to do much more masking than if  I had done it the way that you see here.  I learned for the RH side.

To the left is a shot of the tank with the inboard rib installed.  The tank vent fitting is installed and sealed.  The vent line is connected to the fitting. A “BNC” connector is installed just aft of the vent fitting.  This is the electrical connection for the fuel quantity system.  The photo below is a close-up of the fuel pick-up fitting in the attach bracket.

 

Inboard end rib installed Fuel pick-up fitting close-up view

Paul Boy Paul Boy

I am finally going to close up the tank.  Before I do, I decided to have someone inspect it.  Paul Boy (above) is the Chief Inspector for Jet Harbor, Inc.  He was in Gallatin to work on one of our customer airplanes.  He gladly accepted the opportunity to inspect and critique my work.  After I corrected the discrepancies that Paul found it was time to close the tank.  First I took a couple more pictures of the inside of the tank (directly below).  The left picture shows the flop tube with the tank inverted.  Notice that all of the protective coating has been removed.  the right photo is of the fuel cap area.

“Flop”  tube inverted view Fuel cap inverted view

Below are photos of the baffle in place.  I dimpled the holes in the baffle instead of countersinking them per the plans.  The metal is too thin for a countersink.

Baffle in place Another view

Lower flange rivets in dimpled holes Baffle and rib corner gap

The photo left above shows a close-up of the dimpled holes in the flange of the baffle.  The photo above right shows a problem area.  There is a gap in the corner, top and bottom, where each end rib meets the baffle.  A lot of sealer needs to be put in this area before the baffle is installed.  I also made sure that the sealer squeezed out as I installed clecos.  This area is a leak just begging to happen.

Here is a shot looking inside the tank looking through the access hole at the skin where it attaches to the baffle.  I wanted to make sure that sealer was squeezing out along this seam.  You can only see the seam in this bay but this is an indicator of how much sealer you put on the flange of the baffle.  Both top and bottom looked OK so hopefully I have sealed the flange correctly.  This would be a nasty area to fix a fuel leak.

View of baffle to skin seam thru access hole  

Outboard “Z” angle  

The “Z” angles that attach the tank to the spar are next.  As with everything else on the tank these are installed wet with sealer.  The two attached to the end ribs get solid rivets (above left).   The 5 inner ones are attached with blind rivets.  The kit had hardware store “pop” rivets.  I elected to use CR3213-4 aircraft blind rivets instead (above right).

The tank is now assembled.  I wonder if it is going to leak.  I am not sure how I am going to leak check it yet.  There is a suggestion in the plans.  There are some more methods on some internet sights.  After what I went through to complete the tank,

I think I will procrastinate on the leak check.  The euphoria surrounding a completed task like this could be collapsed if there is a fuel leak.  I will save this risk for another day.

Assembled left fuel tank  

For now I am going to locate the tank to the wing the way I think it should be done.  At the beginning of this narrative, I told about how Vans plans said to locate the “Z” angles.  I cringed when the said to “slot the 3/16” holes as necessary.”  If all went well when I cleco the tank to the spar through the 3/16” holes, the skin to spar holes will be lined up or very close.  So here we go.

Tank attached to the spar Hole in tank skin looking thru spar hole

The photo on the left above shows the tank cleco’d to the spar at the “Z” angles.  The photo to the right shows a tank skin hole looking through a spar nutplate hole.  They line up.  I love it when a plan comes together!!  Now to finish the spar and tank screw holes.

This photo shows a 1/8th cleco in every spar to tank skin screw hole.  The tank skin holes are slightly smaller than the spar skin holes.  I put all these clecos in to make sure that all of the tank skin holes were inside the spar skin holes.  If they weren’t the cleco would not go in.  All the clecos went in.  So far so good.  

The next thing that I did was to remove every other cleco and upsize the hole to 5/32” or a #21 drill (next 2 photos).

1/8th cleco in each screw hole  

Upsizing the holes to 5/32 Bottom flange ½ upsized

The above photos show the upsizing of the screw holes in progress.  After all the screw holes were upsized countersinking the holes was next.  I have read several accounts on the internet of people struggling with the countersinking procedure.  Most of the problems involve a countersink that chatters in the hole.  There is a good reason that the countersink chatters.  The spar flange is not thick enough for a #8 screw countersink.

Thickness of a #8 screw head Thickness of the spar

 The photo on the left above shows the thickness of a #8 screw head.  The photo on the right shows the thickness of the spar.  When the cutting edge of the countersink gets through the spar the pilot on the countersink is no longer doing anything.  The pilot of the countersink is what keeps it from chattering.  So what is the solution.   As long as the counter sink cutter is going to completely penetrate the spar, the pilot hole may as well be larger so that the spar hole does not get knife edged. 

The photo at right shows the spar holes being enlarged to 3/16”.  The tape is on the Unibit to keep from going too deep. 

After the holes were enlarged to 3/16” (#12) I set up a 3/16” countersink and countersunk the holes for a #8 screw. 

  Enlarging the spar holes with a "Unibit"

As you can see from the photos below, I got good, no chatter countersinks in the spar without knife edging the holes.

Countersinking for #8 dimple with 3/16 cutter Finished hole, no chatter, no knife edge

#8 screw in hole Scrap of aluminum dimpled for test

The above photos are self explanatory.  The chattering countersink problem is solved.  Nice holes ready for nutplates.

All screw holes countersunk, no chatter Rivet holes countersunk

A picture of all the countersunk holes is at left above.  The right photo was taken after rivet holes were counter sunk.

The installation of the nutplates on the spar will be covered in the Left Wing, Ribs and Spars section.  The next item for the tank assembly is to nutplate the “Z” angles.  The photo below left shows the #10 nutplate jig being used on the “Z” angles.  A little over a month later I installed all of the nutplates.  Photo at right below shows the nutplate installation.  What was the 1 month delay on the nutplates all about?  The outboard leading edge needed to be constructed and installed.  See the “Leading Edge” section of the left wing for details.  I had to remove and re-install the tank several times during the leading edge assembly and clecos were easier to use than bolts for temporarily attaching the tank to the spar.

Using the nutplate jig on the “Z” angles Nutplate installation

The photo at left makes it look like the tank is finished.  I have primed all of the external bare areas (except for the outer skin) and I am ready to install it for the final time, except, the access panel is not installed.  Naturally I did not want any fuel leaks from the access panel and to help insure that there wouldn’t be any, I decided to deviate from the plans slightly.  The photo at right below shows a screw, a washer and a “Stato-seal” which is a washer with an O-ring built in.

Nearly completed tank Screw,  washer and  “Stato-seal”

The photo below left shows a screw, washer and “Stato-seal” properly assembled and ready for installation.  This is common hardware on certificated airplanes and I thought that using these seals would be insurance against leaks.  The right photo below shows the access panel installed.

Screw ready for installation Access panel installed

There were two more details to finish prior to installing the tank for the final time.  The first one is a biggy.  I had to check the tank for leaks.  I used a Pitot-Static tester to do the leak test.  We own this tool and we normally use it to check instrument systems for leaks but I thought it may come in handy here. (Note: The Pitot/Static tester in the photo was due for calibration when I used it or I would not have performed the leak test with it.  The volume of the tank is such that I put the tool in jeopardy but I was careful and did not hurt it.  The leak-check procedure that Van 's recommends is fine and should be used.) I  plumbed the airspeed line to the tank and ran the airspeed indicator to 70 knots.  Too much pressure could damage the tank so I felt that 70 knots would be enough (See the photo below left).  I was in luck.  There were no leaks.  The only detail I had left was to seal around the edge of the access door and put some sealer over the screws for added fuel leak protection.

Leak checking with a Pitot-static tester Access door with added sealer

The left fuel tank is now complete and ready for its final installation.  The next thing to assemble is the left wing ribs and spars.