Leading Edge Skin Assembly
by Frank Justice
Read the construction manual section on building the leading edge
skin for additional information.Rib Assembly and Alignment
If you intend to equip your RV for instrument flight, you will
need to install a heated pitot tube. You may find it easier to
mount somewhere in the leading edge rather than on the main spar,
depending on what kind of mounting you can find/make. The best
place in the leading edge is between the two innermost ribs and
just forward of the main spar where space is tight but support
is good. It is suggested that you buy your pitot tube and prepare
a place for it before attaching the leading edge assembly to the
spar, although it is possible to do it later by removing the tank.
Several mail order places sell new pitot tubes but you will either
have to make a mounting bracket or get one from an aircraft salvage
Positioning the Leading Edge Skin
- Lining up the leading edge ribs properly requires some attention
to detail. Misalignment does not affect the strength of the wing,
but it makes it very difficult to get the skin-to-rib rivets close
enough to the middle of the rib flanges for adequate strength
and easy bucking. There are several causes for problems; twist
remaining in the ribs after fluting, rib webs not exactly on a
right angle to the spar long axis, shifting of the ribs as you
put the skin in place, and varying width of the rib flanges. Also
it is difficult to make a straight rivet line along the top side
of the wing where the skin curves more. The following procedure
will minimize the effects of these problems.
- Attach all the leading edge ribs to the spar. Put clecoes in from
the bottom side. Drop bolts in all the bolt holes.
- Mark centerlines on the rib flanges and bring the lines down onto
the top skin and spar flange.
- Make a rib spacing template as follows: On the top side of the
wing place one end of a strip of wood or metal against the leading
edge of the top main skin with the end aligned with the tip edge
of that skin. Mark the position of the centerlines of all the
ribs on it. Place the template on the bottom side of the wing
and do the same; use the tip rib centerline as the reference point
- Secure the ribs vertical to the spar and properly spaced at the
noses. You can cut blocks of wood or plasic pipe to just the right
length and secure them with a piece of wire through the tooling
holes as suggested in the manual. Make sure the spacers do not
hit the raised area of the ribs near the tooling holes or a twist
will be introduced. An easier method is to run 3/16" threaded
rod with large washers on it through the top tooling holes in
the ribs so there is a washer against both sides of every rib.
Use several short rods connected with threaded couplers to save
time in getting the nuts down to the right places. Use washers
no larger than 3/4" outside diameter on the side of the ribs with
the raised area.
- Working on the bottom side of the wing secure the nose end centerlines
of the ribs to exactly the same spacing as the rear edge centerlines
using the bottom side template. Then verify that the rib flange
centerlines on the top side are properly spaced using the top
side template; twist the ribs by hand or re-flute if necessary.
- Make a rivet spacing template for the top of the leading edge
skin by transferring the marks made on the rib layout for fluting
to a strip of aluminum at least 1" wide. At the spar end mark
it "SKIN EDGE" and use the skin joint as the reference point.
Be sure to mark the different position for the first rivet on
the innermost three ribs. If necessary mark alternate positions
for the rivts at the tip in the innermost rib. 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". Make
a similar template for the bottom of the leading edge using the
lower edge of the main spar as the reference point and mark it
- Make five spacer blocks out of 2x2 or 2x4 wood, 7 5/8" long. Tape
these blocks in place under the spar between the large flanges,
about in the center of the gap between the ribs.
- Cut five pieces of the strap material long enough to go completely
around the leading edge skin with about one foot extra. Place
of these straps in the middle of each of the gaps between the
ribs; pull out several of the clecoes holding the main skin on
so the strap can go underneath it. See SK-36. The straps must
go across the wooden blocks previously put in the spar. Later
after the skin is put in place tie the ends of the straps together
with the buckles as shown in SK-36. The buckles should be about
10 inches above the spar on the top side.
Drilling the Leading Edge Skin
- Mark "top" and "bottom" sides of the leading edge skin for easy
reference. The longer side is the top.
- Put some kind of tape that is thin, transparent, and slippery
on the tips of the ribs to allow the skin to slide freely over
them without being scratched. Make sure you can see the centerline
marks through the tape. Place the leading edge skin on top of
the ribs with the top side trailing edge against the main topskin
edge (the straps will hold it there); pull it down loosely with
the strap clamps. Align the outboard edge with the outboard edge
of the main skin.
- Secure the leading edge skin onto the skeleton with the straps.
Mark the positions of the centerlines of the rib flanges onto
the leading edge skin at the trailing edges using the marks previously
made on the spar and topskin. Using the rib spacing template mark
the rib centerline positions near the nose on both the top and
bottom. Mark the positions of the rivets on the bottom side of
the skin using the rivet spacing template.
- Check for any gaps between the leading edge and top skins due
to uneven shearing of the metal. Remove and trim the leading edge
skin edge if necessary.
- Remove the leading edge skin. Draw a line 1/4" up from the trailing
edge on each side of the skin for the skin-to-spar holes.
- Hold the skin up to the wing as a sanity check.
- Using the rivet spacing template mark the positions of the skin-to-rib
rivets on the top side of the skin. Drill the rib rivet holes
#41 or 3/32" at the following locations on both top and bottom:
the ones closest to the spar, the leading edge two, and two more
equally spaced between the leading and trailing edge. Deburr the
- Note: The construction manual suggests drilling all of the holes
before placing the skin, but it is quicker and safer to drill
only a few reference holes at this point. The skin alone is hard
to hold for drilling, and since the ribs must be drilled also
you would have twice as much work.
- Align the rib centerlines with the holes in the skin, Tighten
down on the straps a little at a time while watching to make sure
the centerlines stay visible. Insert the W-623 Joint Plate strip
between the leading edge skin and the innermost rib, with 3/4"
extending past the skin edge. See drawing 19. Line up the strip
so that there will not be a skin rivet through or past its end
in the gap between it and the spar flange. This gap will not cause
- Tighten the straps until the trailing edge of the skin meets the
main skin on the top side and the skin is fairly tight against
the ribs on the top side.
- Mark the positions of the top side skin-to-spar rivets 1/4" in
from the skin edge and lined up with the holes in the main skin
Reposition if necessary those holes where the rivets would be
difficult to buck because of the tiedown bar or stiffener angles
in the spar.
- Drill the top side skin-to-spar rivet holes #41, starting from
the tip end and working inboard. Pull down on the leading edge
of the skin by hand if necessary to keep the trailing edge tight
against the main topskin.
- Drill the first row of skin-to-rib holes working center to ends.
Then drill by rows in the same way up to the leading edge. Put
pressure on the skin next to the drill bit to keep the drill chips
from forcing the skin away and upsetting the alignment.
- If the rib centerlines on the back side are not well aligned with
the pre-drilled holes or the marks on the main skin you can shift
the rivet line and/or reach in and realign the rib centerlines
with the holes.
- Tighten the straps more to make the bottom side trailing edge
meet the line previously marked on the spar or get as close to
it as possible.
- Drill the skin to rib holes starting at the leading edge and working
- Mark and drill the skin-to-spar holes on the bottom side starting
with the ones that line up with the rib lines. Make sure you do
not put holes where you can't buck the rivets. These holes are
1/4" from the edge and 7/8" or less apart.
- Locate the center of the hole for the tiedown ring (presently
hidden by the skin) and drill a small hole. Enlarge the hole a
little at a time and grind one side if it looks like the hole
is not centered. Make sure the final hole is slightly larger than
a 5/16" bolt, then finish the edge with a countersink bit.
Attaching to the Spar
- Remove all of the clecoes from the leading edge skin. Deburr the
outside holes. Remove the straps. Remove the skin and deburr the
inside. Dimple all holes. Clean and prime, at least the inside.
Clean, dimple, and prime the Tank Attach Flange piece on both
- Deburr and dimple the ribs, then remove them from the spar (or
some other order if it suits your tools). Deburr and dimple the
skin attach holes on the bottom side of the spar; countersink
those you can't dimple.
- A cradle of some sort that holds the leading edge securely, leading
edge down, is highly recommended for riveting unless you have
a helper to hold it. This assembly and the tanks are very difficult
to rivet neatly without a holder of some sort.
- Put the ribs in the leading edge skin with the tank attach flange
strip and rivet together. Leave out the second and third ribs
from the root to start with, then put them in after the others
are riveted; this makes it easier to buck the rivets on the first
rib which is very close to the second.
leadedge.doc 9/13/93 (8/17/94 ok) Frank Justice
- If you are using a heated pitot tube install its support between
the innermost two ribs now. (left wing only)
- If you are going to put landing lights in your leading edge it
is easier to do it now.
- Put the leading edge assembly back on the spar held with clecos.
Don't worry about the fact that on the top side the spar holes
are not dimpled yet but the leading edge skin is.
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