by Frank Justice
Even if you are doing only one wing at a time work on both tanks
at the same time up through the point of drilling of the ribs
to the tank baffle. Also do both sets of things like spacers,
fuel pickup tubes, backup plates, etc. If the tank ribs have not
already been prepared, go back and perform the steps in the rib
preparation section.Alternate Constructions
Items not in the kit you will need and can get from Van's: Fuel
level sender for each tank; Pro-Seal (no more than 1 quart, and
if you are careful there will be enough left over for a friend
to do his tanks.) for sealing the tank.
There is also sloshing compound (no more than 1 quart); this is
put in the tank after it is finished and sloshed around to form
a solid film all over as added insurance against leaks. Some professional
builders and others do not use sloshing compound and they have
no trouble with leaks. You can always put it in later if you do
have a problem. Some sloshing compouds do not hold up well against
autogas and have been known to peel off in sheets and clog the
fuel intake. Randolph 912 is recomended. Also, you MUST clean
and roughen every surface inside the tank to ensure good adhesion.
Tank Access Plate
- Instead of making the curved-tube fuel pickup unit described in
the plans, a good alternate is a strainer screen attached to a
fitting that screws into a threaded plate attached at the lower
rear corner of the inboard rib. This was described recently in
the RV-ator. It allows you to remove the fuel pickup strainer
for cleaning without removing the access plate and possibly without
removing the tank. The strainer is available from Aircraft Spruce.
- Instead of making the large access plate for the tank the sender
unit could be attached directly to the rib if a suitable backup
plate were included to properly hold it. This would be less work
and reduce the chance of leaks, but would make it very difficult
to clean out the tank later. You would almost have to use the
fuel pickup described above, since it can be cleaned by unscrewing
it from the outside of the tank.
- You can install a low fuel level sensor, available from Aircraft
Spruce, which is just a float switch. Fit it after you have put
in the fuel pickup to avoid interference.
- You may also find it useful to install a fuel level indicator
tab at the filler hole so you can easily tell that there is a
certain amount of fuel in the tank.
Front Mounting Bracket
- Make sure you understand how the reinforcing ring, rib, and access
plate go together. The reinforcing ring is on the inside of the
tank on the side of the rib away from its flanges; the reinforcing
ring is held to the rib by the rivets that hold on the nutplates
that the access plate screws go into.
- Cut out the T-607 reinforcing ring and T-608 tank access plate
for each tank out of 0.063 (1/16") plate as shown in drawing 18.
Before cutting ake sure that the inner diameter of the reinforcing
ring is as large as the cutout in the rib; all the dimensions
for the ring and access plate may need to be increased from what
is shown in the drawing. Be sure to turn the circle cutter blade
to the proper orientation for outer edge versus inner edge cuts.
Don't worry about the guide bit hole in the access plate, you
will be cutting that part out for the fuel sender unless you are
doing the inverted fuel system pickup. To cut the reinforcing
ring, cut out the inner diameter first, then without moving anything
securely tape over the cut you just made and cut the outer diameter.
This will keep the ring from beating itself to death when the
outer cut finishes. Since the metal is so thick it is helpful
to use cutting oil to keep the cutter cool.
- Mark the hole pattern on one of the access plates, making sure
one of the holes will not come too close to the tooling hole in
the rib; the fuel sender hole center can be moved from the plans
location to where it takes out the circle pilot hole. Tape both
reinforcing rings and access plates together securely and pilot
drill all the holes #30. Enlarge the fuel intake elbow hole to
9/16" and the fuel sender hole to 1 1/2" diameter (or whatever
matches the sender you plan to use).
- Disassemble the stack and tape a ring to each access plate in
the same orientation as drilled. Take one set and determine which
side would be on the outside of the left tank. Put one light reference
mark with a center punch on each near the bottom hole. Do the
same for the other set except use two marks.
- Place a ring and access plate in the proper orientation on the
proper rib with the ring next to the rib; this way you can center
the plate accurately by eye on the rib cutout. Orient it as shown
in drawing 18 but rotated slightly as necessary to allow the rivets
that will hold the nutplates to be clear of the rib tooling hole.
Drill #30 through the plate-ring into the rib. Then enlarge the
holes to #19 or 11/64". (Drilling this way and using lots of clecos
and then #8 screws is necessary to keep the holes aligned; the
ring tends to move otherwise.)
- Disassemble and put the reinforcing ring only back on the rib
using short #8 screws and K1000-08 platenuts. Drill #40 through
the platenut mounting holes into the reinforcing ring and rib
or use a platenut hole jig.
- Disassemble. Enlarge all the screw holes to 3/16". Dimple the
#40 holes in the rib and countersink the #40 holes in the reinforcing
- Rivet the nutplates, ring, and rib together. Insert a screw into
each hole to insure that it will thread freely into the platenut.
- Make four spacers for proper fit of the bulkhead elbows out of
.032 or thicker material. Drill two pieces with a 7/16" hole and
two with a 9/16" hole, then cut away the rest of the material
leaving about a 1" square piece with the hole in the middle. (This
quantity for both sides.) Verify that what you have made is thick
enough that when the elbows are attached to a rib with a spacer
and mounting nut the elbows do not turn.
Make the bracket shown on drawing 18 that mounts at the tip of
each inboard rib. When drilling the 6 #30 rivet holes be sure
none of them will come too close to the tooling hole in the rib
that the bracket will mount on. Position the brackets on their
ribs and drill the corresponding holes in the ribs. Building the Skeleton
Assembly on Wing
- Mark the positions of the rib webs on the flange side of one of
the tank baffles T-602 as shown in drawing 18. Then mark the positions
of the rivet holes 5/16" away. Make sure the end holes will not
be too close to the ends of the flanges on the ribs. Try 15/16"
rivet spacing for the four internal ribs and 11/16" spacing for
the end ribs.
- Secure this baffle to the back of the other one. Drill the end
rib holes #41 and the internal rib holes #30.
- Separate the two baffles and deburr them.
- Mark a line on the end flange of all the ribs 5/16" from the web.
Clamp the ribs in their proper positions with the centerlines
showing in the baffle holes. Drill the ribs through the baffle.
Remove the ribs, debur.Put back on with the clecos on the rib
Rivet Spacing Templates
- Assemble the ribs to the baffle with the clecos put in from the
rib side. Secure the tip ends of the ribs with threaded rods or
your choice of materials as with the leading edge assembly. At
this point spacing need not be precise; you mainly just have to
secure the tiedown method at the outboard end because later the
leading edge skin will cover it up..
- Make eight spacer blocks, approximately 2 1/2" long, 15/16" wide
out of 1/2" or 3/4" wood. Place these blocks on the main spar
doubler to hold the tank in the proper position. Place the tank
skeleton on these blocks; modify the height of the blocks if necessary
so that the rib next to the leading edge skin lines up with the
flange piece on the leading edge.
- Put this assembly on the spar about 1/16" away from touching the
leading edge assembly at the closest point.. Secure the outboard
rib to the leading edge flange strip in the vertical position
with tape. Tape the baffle to the spar on the bottom side. Mark
the rib flange centerlines with a dark marker. Extend these lines
down onto the main spar flanges and top skin On the leading edge
skin mark the position of the leading edge of the main spar doubler
(this will be used later to locate the centerline of the skin
to baffle holes).
Drilling the Skin for Ribs
- Make a rib spacing template as was done with the leading edge
assembly. Use the edge of the leading edge skin as the reference
point. Mark the position of the centerlines of all the ribs on
it. Do not be concerned if the template marks for the top and
bottom side are not the same distance from the leading edge skin,
- Use the template to get the ribs straight and the noses secured
the proper distance apart. Secure the rib spacers using the bottom
side template, then use the top side template to twist the top
sides of the ribs into the proper spacing if necessary.
- Make an internal (the tank end ribs are different) rib rivet spacing
template for the top side of the tank skin on a strip of aluminum
at least 1" , preferably 2" wide. At the one end mark it "SKIN
EDGE" ; hold this end against the leading edge of the top skin
and mark the approximate position of the first, last, and a few
other rivet locations using the flats on an internal rib as a
guide. Line these marks up for best fit on the internal tank rib
fluting guide and mark the locations of all the rivets. Hold the
template up to the ribs to insure that the rivets all fall in
a flat spot and not too close to a flange gap. Mark this template
"TOP, INSIDE RIBS".
- Make a similar template for the top of the end ribs.
- Make similar templates for the bottom side, using the trailing
edge of the main spar flange as the reference point.
- Secure the tank skin onto the ribs with the straps as was done
for the leading edge assembly. Note how the edge of the tank skin
matches to the edge of the leading edge skin. If there is a gap
anywhere greater than 1/16 inch mark the tank skin for trimming,
remove it, trim it, and try again. Also check for gaps between
the tank and top skins. Clearly mark the top and bottom and the
tip end root edges of the skin.
- Mark the positions of the centerlines of the ribs back onto the
trailing edges of the tank skin. Use the rib spacing template
to mark the rib centerlines near the nose of the skin. Mark the
positions of the bottom side rivets using the rivet spacing templates.
Remove the tank skin from the wing.
- Use the templates to mark the top side rib rivet positions.
- Drill a few guide holes #41 in the skin for each rib; one at the
trailing edge, two at the leading edge, and two more in between
on top and bottom.
- Place the skin on the ribs in such a way that you can see most
or all of the rib centerlines through the guide holes. Secure
it in at least four places with the straps and spacer blocks as
was done with the leading edge. The skin should be right against
the leading edge skin.
- Drill the rivet holes #41, starting on the top side at the trailing
edge and working around to the bottom. Use the guide holes to
reposition the ribs if necessary; an ice pick or something similar
can be used for this.
Filler Cap and Drain
- Remove the clecos holding the top side of the skin, then loosen
the straps. Mark on the inside of the bottom the outlines of all
the ribs. Also mark the baffle location at the root end only.
Remove the skin from the ribs.
- On the inside of the bottom side of the skin mark two lines the
full width of the skin at 6 7/8" and 11 7/8" from its trailing
edge. Mark each position one through ten where a reinforcing rib
- Cut the reinforcing ribs from the 0.032" angle using the marks
on the skin as a cutting guide and mark each rib with its position
- Mark the skin-to-angle rivet positions on the inside of each angle,
1 1/4" or less apart. Tape each rib in position on the skin and
drill #41 (or #40) through it and the skin. Remove the angles;
cut off the ends of the upright sides (the ones without the holes)
at a 45 degree angle to allow more room for bucking rib rivets
later. Deburr the angles, the ribs, and the skin.
Finishing the Tank Structure
- Drill six holes #40 around the drain flange and ten holes #40
around the filler cap flange (do flanges for both tanks at the
same time). Countersink the holes in the drain flange from the
side with the raised rim for the valve (the drain flange goes
on the outside of the skin). If you will be dimpling the tank
skin countersink the filler cap flange from the side away from
the turned-up edge (the filler cap flange goes on the inside of
- Method Details: To accurately locate the hole circles and the
large center holes, use this procedure. Measure the diameter of
the flange, then set a compass to half that value and draw a circle
on a heavy piece of paper. Decide how far in from the outside
you want the center of the hole circle to be, decrease the setting
of the compass by that much, and draw another circle. Mark the
hole locations. For six holes the hole spacing is exactly the
same as the compass setting, so walk the compass around the circle.
For ten holes use a protractor and make the holes 36 degrees apart
using the center as the reference point. Place the flange on the
pattern and use it as a guide to trim the pattern to the exact
size of the flange. Place the pattern on the flange and center
punch through it to place the holes. Put the pattern on the skin
and center punch the center hole for making the drain and filler
Note: The plans call for using AN426AD4-7 rivets in the drain
flange and AN426AD3-4 in the filler cap flange. I have chosen
to use the 3-4 rivets in the drain flange because this is not
a structural joint and it would be difficult to work with the
- Place the drain flange on the outside bottom of the skin as close
as possible to the corner of the baffle and the root rib but not
so close that the shop heads on the flange rivets would hit either
the rib or the baffle. To do this place the flange on the inside
of the skin using the rib/baffle locations marks as a guide; drill
a small hole through the center of the flange; then place the
flange on the outside using the hole to locate it. Mark an arrow
on the flange to aid in aligning it properly later. Drill through
the drain flange mounting holes into the skin. Enlarge the drain
hole to 7/16".
- Place the filler cap flange on the inside top of the skin near
the tip edge as shown in drawing 18. This position is optimum
for an RV-6; some builders of RV-6A's place the filler hole 7
to 8" from the rear skin edge instead because the -6A sits at
a different angle. Note that the flange has a slight bow to it
so it will follow the curve of the skin; orient the flange so
this bow is in the proper direction. Drill through the two flange
holes into the skin which fall along a line between the tip and
the root. Cleco the top side of the skin to the ribs and cleco
the flange in place. Drill the rest of the mounting holes through
the flange. Mark the outline of the flange on the skin, then remove
it; remove the skin from the ribs.
- Locate the center of the flange on the skin using the paper template.
With that as a center point make a hole in the skin just large
enough to allow the top of the filler cap to pass through. Cleco
the flange onto the skin and enlarge the hole as necessary to
allow the filler cap to go in properly.
- Make two of the clamps that will hold the vent tube to the filler
cap flange as follows: Cut a strip of 0.032 aluminum about 3/4"
long and 1/2" wide. Drill a hole #40 1/4" from one end. Put one
with each filler cap flange.
- Drilling to the Baffle and the Spar
- If you plan to countersink the skin, cleco the angles and the
filler cap flange onto the skin.
- Cleco the skin back onto the ribs and baffle and put in position
on the spar. If there are gaps between the leading edge skin and
the tank skin, trim the tank skin until it fits like you want
- Strap the tank assembly down to the spar.
- Draw lines across the skin at 3/16" above (for rivets) and 1/4"
below (for screws) the leading edge of the spar doubler (the mark
you previously made on the leading edge skin). Mark another line
1/4" from the trailing edge of the tank skin for screws (on the
bottom side use the trailing edge that will exist after you trim
the skin). If the trailing edge of the tank skin extends farther
down the spar than the leading edge skin, mark a line even with
the leading edge skin. Mark another line for screws along the
skin edge next to the leading edge skin and 3/8" in from that
- Mark the rivet and screw positions. The spacing given in the plans
will work except for the following: the inboard-most screw hole
in the row along the trailing edge will have to be moved back
toward the tip by 3/4" or it will run into the end of one of the
spar flange strips; the screw hole in the same row at the outboard
end needs to be 1/2" instead of 3/8" from the edge so there will
be room to countersink the platenut screw holes easily; the next
screw in may be so close to a spreader angle that it will be difficult
to dimple the hole or squeeze one of the platenut rivets for it;
locate the six holes on each side along the skin edge so they
are between the big spar rivets so they can be reached with the
dimple tool later..
- Drill the screw holes #30, then drill the rivet holes #41 (or
Attaching Ribs to the Skin
- If you are countersinking the skin do all the rivet holes now
except the ones for the drain flange.
- Disassemble the structure and then put the end ribs back on the
skin. Check the amount of gap between the leading edge of the
skin and the nose of the outside ribs. If the gap is greater than
about 1/16", make plates out of thin scrap that fit the skin contour.
Put the sealing plates in place on the inside and drill them through
- Make four small, flat sealing plates out of thin scrap for each
tank to approximately fill the gap between the rib corners and
the baffle plate. Drill one hole #40 through each into the ribs.
Dimple the rib holes and the plates.
- Disassemble the tank and deburr all the holes.
- If you are dimpling the skin, dimple all its rivet holes except
the ones for the drain flange. Also do the holes in the ribs where
the skin goes as well as the stiffener angles. Countersink the
baffle rivet holes where the skin goes.
- Countersink the #40 holes in the baffle that connect it to the
- Trim the bottom side trailing edge of the skin if it extended
below the leading edge skin.
- Bevel the skin that is adjacent to the leading edge skin down
to the same thickness as he leading edge skin (.025).
- Drive a #6 rivet into the tooling holes in the outboard end rib
to close them (not the root rib).
- Initial Assembling and Sealing the Tank
- Since the Pro-Seal sets up fairly quickly, have everything ready
before you mix it. The cooler the temperature of the room, the
longer working time you have. At around normal room temperature
you will have about one hour before it begins to get stiff. If
you want it to set up faster for any reason you can use up to
twice as much catalyst without affecting the cured strength. Every
surface must be completely clean so that the Pro-Seal will stick
to it; Pro-Seal is not solvent-based so any contaminant at all
will make it come right off. If the Pro-Seal fails to stick the
tank will leak. If you do well enough with the Pro-Seal you will
not have to use sloshing compound. Pro-Seal will not come off
your hands; if you don't want black for a week use gloves.
- Roughen the mating surfaces of the rib flanges, reinforcing angles,
sealing plates and the inside of the skin with a stainless steel
brush (find in welding supplies) or a Scotchbrite pad. Clean the
surfaces well; methyl ethyl ketone is preferred. Acetone has been
known to leave a film that Pro-Seal will not stick to. Set out
the rivets you will need and clean them in solvent. Do not touch
any surface with your fingers after cleaning. You should actually
clean and roughen every surface inside the tank in case you have
to slosh it later.
- Set out palettes (squares of cardboard or wood) for mixing Pro-Seal
on and several strips of various thicknesses of skin scrap or
wooden popsicle sticks for applying and spreading it. You can
measure the proper amounts of the two compunds either by weight
or by volume. By weight the ratio is 10 parts of the resin (white)
to one part of catalyst (black); by volume it is about 7:1.
- You can make a simple balance scale to do this as follows: drill
three holes in a piece of wood about 1/4" x 1/2" x 12"; one hole
is 10" from the center hole and the other is 1" away in the opposite
direction. Hang this by its middle hole and make some light-weight
pans to hang from the other two holes. You now have an accurate
10:1 balance. You can also measure the material accurately enough
by volume by building one mound of catalyst and seven equal-sized
mounds of resin.
- Put rivets through the holes for the stiffener angles and tape
them in place. Spread a thin layer of Pro-Seal where the angles
go, especially around the rivets, and on the angles. Back rivet
the angles to the skin. Smooth down any excess Pro-Seal that came
out from under the stiffeners.
- Put Pro-Seal on the drain flange, the outside skin where it will
go, and the rivets. Assemble and rivet together.
- Put Pro-Seal on the filler cap flange, the rivets, and the inside
of the skin where it goes. Assemble the flange to the skin, clean
any excess Pro-Seal out of the countersink/dimples, and drive
only the two rivets on the outboard and inboard sides (note that
the skin isn't tight against the flange elsewhere). Attach the
outboard rib and the one next to it to the skin with just enough
clecos to get the skin into the proper curvature at the filler
cap flange. Drive the rest of the rivets except one toward the
leading edge. At that position attach the vent tube clamp strip
also. See the picture in the construction manual.
- Make up a wad of Pro-Seal a little less than the size of a golf
- Apply some to the flange of one of the center ribs as well as
the place on the skin where it will go. Put the rib in place with
one cleco on the top side and two on the bottom at the tip. Repeat
for the rest of the inside ribs. Put clecos in every other hole,
- Put the tank in a cradle if you have one or get a helper to hold
it. It must be supported securely for these rivets to come out
right. Clean any excess Pro-Seal out of the countersink/dimples
or the rivet heads will stand out after driving. Put clean rivets
into the open holes and wipe off the Pro-Seal that oozes out onto
the skin. These rivets may come out too high on the outside if
you are not careful; hit them lightly as you start to force out
any remaining Pro-Seal under the heads, then use a slight rocking
motion with the rivet gun to compensate for the fact that the
rivet set surface is slightly curved. Drive these rivets carefully.
If any go wrong complete the rest of the rivets before going back
to drill any out.
- Make up another batch of Pro-Seal about the same size. Completely
coat the end rib flanges, including filling the flutes and a heavy
bead around the tip. Put these into the skin and rivet on.
- Put a generous filet of Pro-Seal on the inside of the outside
rib-to-skin junction and a film over the rivets that seal the
tooling holes in the outboard end rib. Clean off all the excess
Pro-Seal on the inside of the skin at the outboard end where it
sits on the leading edge flange.
- Pro-Seal and rivet the T-605 attach angle (and sealing plate if
necessary) to the inboard rib. You ay have to notch the attach
angle to clear some of the skin to rib rivets. If necessary also
attach the nose sealing plate to the outboard rib. Pro-Seal and
rivet on the rib-to-baffle corner seal plates.
Fuel Level Sensor Installation
- Install the bushings in the holes in the inside ribs.
- Cut a piece of 1/4" tubing 46" long. Put a tubing sleeve on the
tube with its flange end toward the near end. Flare this end of
- Feed the other end of the tube through the root rib hole. Put
one of the smaller size tubing nuts on the tube with the threaded
end toward the flange. Feed the tube on in through the bushings.
- Put a gentle bend in the end by the filler cap flange and push
the tube in to where the root end is inside the tank.
- Put the long end of a bulkhead elbow through the root rib hole
from the outside with Pro-Seal and put one of the previously-made
square spacers and a nut on it to secure it to the rib.
- Secure the vent tube to the elbow.
- Bend the tube at the filler cap flange end so that its end is
close to the corner of the rib and skin (the highest point in
the tank). Secure the vent line with the metal strip on the filler
cap flange and Pro-Seal.
- Fuel Pickup Tube (not applicable to inverted fuel system; see
- Put a sleeve on the end of the piece of 3/6" soft aluminum tubing
with its flange toward the near end. Flange this end of the tube.
Put a tubing nut on the tube with its threaded end toward the
- Put the tank access plate on the end rib with two screws. Install
a large bulkhead elbow in the plate with the elbow inside and
pointing down. Bend the tubing so it will curve out from the elbow
to the lower rear corner of the tank. The tube can be bent around
an aerosol paint can if a tubing bender is not available. Cut
off the tube so it will end just before it touches the tank baffle.
- Pinch the end of the tube closed. Make about six cuts three-fourths
of the way through from the top side of the tube just above the
crimp with a thin saw blade.
- Make another tube just like it for the other side and put with
the other tank parts.
- Secure the pickup tube to the elbow and the elbow to the access
plate with Pro-Seal. Make sure the tube end is down against the
inside corner of the tank.
Adding the Tank Baffle
- The arm on the fuel level sensor has to be bent and shortened
so it will swing from one stop to another and just touch the bottom
or top of the tank at the same time. Van's sells a "right" and
"left" side sensor which differ only in the hole pattern in the
flange; there will be a mark on the box to indicate which one
goes on which side.
- You may also want to calibrate your gauge-sensor pair at this
point. Connect the gauge to the sensor and power it with about
14 volts such as from a car battery with the engine running. If
the gauge does not read exactly full and empty as you move the
arm full up and down, you may be able to bend the stops on the
sensor so it will.
- Hold the fuel level sensor up to the rear edge of the root rib
at about the level it will sit in the access plate. Make sure
you have it right side up; in this position the arm will swing
to a straight-up position before you bend it. Bend the arm down
carefully to avoid any stress being placed on the arm bearing.
When it is bent to the point where it goes up and down by the
same amount before hitting the sensor stops, find the point on
the arm that will be a float radius above the bottom and below
the top when the arm is moved from stop to stop. At that point
bend the arm so the lower end will be at a right angle to the
rest of the arm, parallel to the bottom, and parallel to the root
rib. Put the float on this part of the arm and cut off the excess,
leaving about 3/16" protruding from the float. Put a washer on
the end of the arm and then swage (flatten) the end of the arm
to hold the washer and float on.
- Put the sensor body through the access plate hole, making sure
it is aligned for vertical movement of the arm. Mark the sensor
mounting holes on the access plate. Pull out the sensor and drill
the marked locations #19 or 11/64" and deburr. You will also need
to notch the access plate to clear the protrusions and rivets
which attach the fuel sender body cover to its flange, and to
radius the edges of the hole in the access plate so they don't
dig into the sender body or prevent the flange from seating fully
on the access plate. Mount platenuts for the fuel sender screws
on the inside of the access plate (the drawings do not show these;
they are necessary if you want to be able to remove the fuel sender
without removing the access plate).
- Make a cork gasket out of the same thin cork used for the access
cover gasket; the gasket supplied with the sender is too thick
and may loosen up in time. Put the sensor back in with the cork
gasket and secure with #8 screws, putting a small amount of Pro-Seal
under each screw head. Then put a small amount of Pro-Seal on
the inside to fill the gap between the access plate and the sender
- Bend the arm if necessary to insure that the arm travels from
stop to stop as well as reaches the top and bottom of the tank.
- Remove the access plate from the end rib.
Sloshing the Tank
- Mix up a batch of Pro-Seal about the size of a golf ball. Spread
it in a solid strip on the skin where the baffle will mate with
it, but stopping just past the rivet holes; don't put any farther
back where the screw holes are. Put a solid strip on the flanges
of the outside ribs, but just a patch around the rivet holes on
the inside rib flanges. Put an extra blob where the outside ribs
and the skin meet. Spread it on the mating surfaces of the baffle.
Put the baffle in place and secure with clecos in every other
- Install the AD-41H closed-end pop rivets in the #30 holes that
attach the baffle to the ribs, then install the rest of the rivets.
- Clean all the excess Pro-Seal off the skin flanges and the baffle
flanges; otherwise it will stick to the wing. Either clamp the
skin securely to the baffle with enough pressure to squeeze out
the excess Pro-Seal or cleco the tank to the wing using the #30
holes. Let it sit for at least a day or two.
Testing for Leaks
- Many but not all builders slosh the tank to ensure a good seal.
If you were very careful with the cleaning and the Pro-Seal you
will not have to. You can always go back and do this later if
leaks develop. See the procedure below for checking for leaks.
- After a week (longer if the weather is cold), you are ready to
slosh the tank. If you want to continue with other tasks, leave
the tank on the wing and go to the next section to do the bottom
skins. Then after a week slosh the tanks and cleco them back on
- Take the tank off the wing. Seal the access plate hole with a
piece of truck inner tube or something similar. Put a 1/8" pipe
plug in the drain hoe to seal it. Remove the inverted fuel system
flop tube if installed and plug that hole. Pour a quart of slosh
into the tank through the filler hole using a funnel. Put the
filler cap in and rotate the tank slowly in every direction so
the slosh will reach every nook and cranny. Keep the tank sealed.
- A slight pressure will build inside the tank from the evaporation
of the solvent; this will force the slosh into any holes which
may be present. After a few minutes loosen the filler cap to relieve
the pressure but don't remove it. Drain the slosh through the
drain hole. Rotate the tank so all the slosh has a chance to work
its way out. Blow air through the vent line to clear out any slosh
that got in it. Remove the filler cap and clean it.
- Check the outside of the tank for evidence of significant leaks.
If any are seen, wait a few days and slosh again.
- Do not put gasoline in the tank for at least several weeks.
Install the access plate with just the cork gasket. Put a little
Pro-Seal or fuel line sealer under the head of each screw. Secure
a balloon over the fuel pick-up fitting. Put the tank drain valve
in the drain hole, sealing the threads with a fuel line sealing
material borrowed from your A? mechanic or a small amount of Pro-Seal
(don't worry, it doesn't harden up and prevent later removal).
Inflate the balloon through the vent fitting. Brush soapy water
or leak detecting compound over all the rivets and joints. If
there is a leak around the fuel filler cap tighten the nut on
it. tanks.doc 1/14/95 Frank Justice
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