Wing Rib Preparation
by Frank Justice
Marking the Rib Stations
Making a Fluting and Rivet Location Guide
- Hang up drawing #10 in the work area where you can see it easily.
You will be using it for most of this process.
- Separate the ribs by type. Using drawing 10 as a guide mark station
numbers 1 through 14 starting at the root end, and the wing side
(right, left), on each main rib. If you have the ribs that re
factory-notched for the spar flange strips, make sure the deepest
notches get the lowest numbers. Mark the leading edge ribs that
line up with a main rib as 14 through 9 and mark the inboard one
that doesn't as A. Mark each tank rib 6 through 1. Note that not
all ribs on a side face the same way. Since you will be cleaning
and possibly priming these later, one of those sets of numbers
and letters that you tap with a hammer is a great time saver.
Be sure to make any such marks as lightly as possible and not
near any edges where stresses are concentrated. Lacking this you
can put small round notches in the edge of the flanges that go
against the spar using a rat-tail (round) file Put one mark for
left and two for right, then farther down put one mark for the
inboard rib, two for the next, etc.
- Debur the edges of the flanges.
- Bend all of the flanges to where they are approximately perpendicular
to the face of the ribs.
This section describes another fixture you can make that you don't
have to have but will save a little time and prevent misalignment;
then it will save the people you loan it to (or yourself when
you build your second RV) about two hours of time and worry. You
can also do the same things but on your benchtop if you prefer.
Rivet Holes for Mating with Spars
- At one end of a 12" x 48" x 1/2" or larger work board draw the
outline of one of the W-409 leading edge ribs, including the tooling
holes. Draw a line through the tooling hole marks extending to
the far edge of the board. Using a square remark the rear edge
line exactly perpendicular to the tooling hole line. Lay a main
rib of the same orientation (right, left) over the line so that
its tooling holes lay directly over the line and its forward flange
lies right at the perpendicular line. Draw the outline of the
main rib and its tooling holes.
- Precisely locate and drill 3/16" holes at the tooling hole locations
and centered on the line between them. Cut the heads off of AN470AD6-12
rivets and drive them into the four holes, leaving about 1/4"
- Mark the locations on the outline where the leading edge and main
skin edges will meet at the spar; these are 1" back from the forward
end of the main rib (from drawing 21) rather than right at the
ends of the ribs. Then mark the locations for the rivets on the
outline as follows using SK-46, 48, 49, 50, and 51 as a guide.
See also drawing 21 to get another perspective. The location of
the first main rib rivets is 1/4" rearward of the skin line mark.
On the top side the rearmost rivet is about 7/16" past the rear
of the rib and on the bottom side about 3/8" inside the rear (this
is where the rear spar flanges are). The first rivets at the trailing
edge of the leading edge skin are actually on the main rib; the
second ones are 1/2" forward of the edge of the leading edge rib
except on the three inboard ribs where they are 3/4" forward of
the edge. Lay a rib on the pattern to place the location of the
forward-most rivet on the leading edge ribs; note that the W-409
rib noses are slightly different from the W-408 noses, but it
may be possible to get the same pattern to work for both.
- You must decide at this point whether you want to take advantage
of the 2" spacing allowed for pop rivets in the wing walk area
and if so whether you want them in the top or bottom skin. See
the construction manual for the different skinning techniques.
It is possible to do these skins with all driven rivets with only
a little extra effort, and these instructions define that technique.
If you definitely want to avoid pop rivets, or if there is any
doubt about what you want to do, use 1 1/4" spacing instead of
2". Now mark the rest of the rivets between the end ones.
- Put V-shaped marks halfway between each of the rivet marks to
indicate flute points.
- One at a time place those ribs that go on the pattern with their
flange side up and flute to make them lie flat.
- Place a pair of ribs of the opposite orientation onto the tooling
hole pins flange side up and mark their outline. Lay one of the
fluted (or marked) ribs upside down on this pattern and use it
to mark these fluting locations. Then use this pattern to flute
the rest of the ribs.
- On another work board (or the same one if large enough) draw an
outline of a T-603 tank rib and a T-404 tank rib. SK-47 is not
very useful here except to show the spacing. On the outlines mark
the ends of the long flanges and put a mark 5/16" in from these
to indicate the first rivets. Then mark the rest of the rivet
locations. On the T-403 ribs (the heavier end ones) the rivets
are 3/4" apart. On the T-404 ribs the rivets are 1" apart. Flute
- Make sure that there is no twist in the ribs, especially the leading
edge and tank ribs. Finish making the flanges perpendicular to
the face of the ribs. If necessary re-bend the flanges that touch
the main spar so they line up with the line perpendicular to the
tooling hole line, then recheck the straightness.
- Make lightening holes in the leading edge and main ribs if they
did not already have them. Do not do the tank ribs.
- Straighten the flanges on the two W-625 short ribs.
Make hole-marking templates as follows:
Aileron Bellcrank and Reinforcing Ring Clearance Cutouts
- Cut a strip of thin piece of aluminum scrap about 1" wide and
7- 19/32" long. Make a line of five small holes in the strip (whatever
size suits your marking method) 1" apart and 5/16" from one edge
of the strip, with the third hole in the center.
- Cut another 1" wide strip 3-3/4" long. Make a line of four holes
1" apart as before, but with the first hole 1/4" from one end
of the strip. On both sides of this strip write "rib bottom" and
draw an arrow from the note toward the end of the strip where
the hole is 1/4" from the end.
- Mark the holes on the main-spar edge flanges of all the main ribs
by holding the rib web and the longer template down on the work-board
and centering the template on the flange. They will be spaced
right and meet the minimum edge-distance (1/4").
- Set aside the ten main ribs that go in the wing walk area (the
five lowest station numbers on each side). Find the next four
ribs on each side (numbered 6 thru 9) and use the shorter template
to mark the outer two holes and the one middle one closer to the
indented flange. Mark all four holes on the rear of the remaining
main ribs. Note that the hole that is 1/4" from the end of the
flange is at the corner where the rib has an indentation to clear
the rear spar flange; this is the "bottom" of the wing.
- Drill #40 all the marked holes in the main ribs.
- Place a leading edge rib (not the tank ribs) with its corresponding
numbered main rib on the rivets in the workboard (the work board
pins will normally make the skin edge flanges line up well enough
to make a fairly smooth curve). Drill #40 through the main rib
holes into the leading edge rib. Repeat for all of the leading
edge rib/main rib pairs. The innermost leading edge ribs, numbered
A, have no corresponding main rib; use any of the main ribs as
a template for those two.
Tank Rib Cutouts
- On both the main ribs for station 73.5 make the 3/4" -wide cutout
between the two lightening holes where the aileron bellcrank goes.
See drawing 19. The location and dimensions of this cutout are
not critical at all.
- Do not do this step if you have the predrilled wing skins: Cut
out the flange and about 1/16" into the web part on the lower
edge of the rib to allow room for the bottom skin access plate
reinforcing ring; the cutout starts 6 3/4" from the leading edge
of the rib and ends 8 5/8" from the leading edge. See drawing
Cutouts for Wiring Conduit
- There are two ways to make the tanks; standard and inverted-flight.
The inverted-flight version is necessary if you plan to do aerobatics
involving extended inverted attitudes or negative G-forces. For
simple rolls and loops the inverted-flight version is not required.
The following directions are for the standard tanks which are
easier to build. The inverted-flight version has a flap on the
large hole at the bottom of the inboard-most inside rib to keep
the fuel from flowing toward the wingtip during maneuvers, a flop
tube fuel pickup located near the leading edge instead of a fixed
tube located on the access plate, and a different placement of
the fuel level sensor to keep it out of the way of the flop tube
fuel pickup. These changes are shown mainly in the photographs
in the construction manual; the flop tube is shown on drawing
- Make the five holes in each of the eight T-404 (thinner material)
tank ribs as shown at the top of drawing 18. Make the cutouts
on the thicker inside end ribs (station 22.0) as follows: Drill
a 7/16" hole as shown for the vent line elbow (location not critical).
Take out all of the larger lightening hole, including the reinforcing
Now is the best time to plan for a conduit through the wings that
will allow you to push wiring through for lights or antenna cables.
CPVC pipe (the tan stuff for hot water) 1/2" diameter from a building
supply store works well; it will hold two RG58 antenna cables
and some wire. Van's sells flexible conduit for this purpose which
is slightly lighter and flexible; hence it cannot chafe on the
ribs when the wing flexes but it may be harder to pull wires through.
Thin-wall aluminum tubing could also be used. To make the conduit
have a straight run drill holes in all the main ribs about 2 1/4"
back from the spar and 1 1/2" down from the topskin flange to
accommodate the tubing. Some builders prefer to put their conduit
in front of the main spar to avoid having to route all of the
wiring over or through the spar inside the fuselage; this will
require a sharp bend at the tank-leading edge junction, not condusive
to easy pulling of wires. Cutouts to Clear Spar Flange Strips
A notch must be cut out of some of the ribs to clear the main
spar flange strips. This is already done in more recent kits.
Make the notch clear the strips by about 1/16" but it is not necessary
to follow the contour where a tapered strip is on top of a full
width strip. Be sure to radius the inside corner. Be careful in
deciding which ribs to notch and by how much; hold each rib up
to its proper location on the correct side of the spar, and don't
get confused by the leading edge rib that doesn?t have a corresponding
main rib. Making Reinforcing Angles
Making Bellcrank Support Angles
- Cut 24 pieces of 3/4" x 3/4" x .062 (1/16)" angle 7 5/8" long.
Cut two more pieces 7 1/2"; mark these "first leading edge rib".
Along the centerline of one side of each drill five holes #30
per drawing 20; the holes are 1 3/4" apart and the end holes are
5/16" from the end. These are for the main and leading edge ribs
where they are notched to clear the flange strips.
- Take four of the angles and mark them as 11 left, 11 right, 12
left, and 12 right. Clamp each to the leading edge rib of the
same designation in the location shown for them in drawing 10
(rib stations 93.5 and 103.5). The side with the holes goes against
the rib. Mark through the holes in the rib flange onto the angle.
Remove the angles and drill 1/4" at these marks. (These are clearance
holes for the blind rivets that are used to hold these ribs to
Deburr, Clean, and Prime
- If you have bought the predrilled wing skins, do not do this step;
it is not necessary to cut the main rib since a reinforcing ring
is not needed: Cut two pieces 2 1/2" long. In one side drill three
holes #30 per drawing 21, 7/8" inches apart. These are to reinforce
the main rib where the flange is cut out for the bellcrank access
hole reinforcing ring. Note that drawing 19 shows these as 2 1/2"
long whereas drawing 19a (the one that shows the newer bellcrank
support gussets) shows them as 2" long. Either will work.
- Cut two pieces 6 15/16" long. In one side drill four holes #30
per drawing 19, 5/16" and 1 1/4" from each end. These hold one
end of the bellcrank support angles.
- Cut four pieces of 3/4" x 3/4"x .125 (1/8)" angle 9 1/2" long.
In one side of each drill holes #30 1/4" and 1 1/4" from each
end. On the other side of two of the angles drill #30 at a point
6 7/16" from one end and 5/16" from the edge. Clamp each of these
angles to the one of the remaining two angles, against the side
that is not drilled. Drill through both angles with a 1/4" drill
using the #30 hole as a guide. See drawing 19. You can also taper
these angles as shown in the photographs in the construction manual
to lose a few ounces of weight.
Building the Aileron Bellcrank Bracket on Rib 73.5
- Since the rivet holes in the ribs will be enlarged later there
is no need to fully deburr them now. Deburr the other holes and
- Carefully round off the noses of the leading edge and tank ribs,
especially at the notches. The skin will be pulled tight here
and any defect will show in the finished wing.
- Prime everything except the tank ribs. Put an especially heavy
coat on the noses of the leading edge ribs.
Wing Jig Setup
- Place the three previously prepared angles on main rib #9 as shown
in drawing #19 and drill through the holes into the rib. Drill
through the rearmost holes of the horizontal angles into the vertical
- Trim the rib web as necessary to give access to the back side
of the rivets that hold the two horizontal angles to the vertical
angle. Rivet this assembly together.
- Place the short piece of angle that reinforces where the rib flange
was cut out to clear the access plate reinforcing ring. The angle
should be 7/16" in from the skin line so it will clear the nutplate
that will be on the access plate reinforcing ring. Drill through
its three holes into the rib and rivet it on.
Drilling the Rib Attach Rivet Holes in the Main Spar
- Set up the wing jig as described in the construction manual. Use
108" (for an RV-6) as the spacing between the inside surfaces
of the uprights if possible to allow best work access without
getting excessive sag in the spar. The spacing between the inside
edges of the crossarms should be no less than 105" (for an RV-6).
The skins will extend 1/2" past the main spar flanges at the outboard
end, so the crossarm to which the spar jigging tab is clamped
must be notched so you will have the full tab to clamp onto. The
upper crossarms need to extend at least one foot from the uprights
and the top side should be about four feet from the floor.
- Note to RV-4 and -3 builders- since there is more skin on the
-4 and the -3 (narrower fuselage) the jig posts and crossarms
need to be farther apart. 117 inches for the distance between
the uprights and 114 for the spacing between the crossarm edges
will work. Actually, these same numbers will work for an RV-6
since the spar is very rigid at the inboard end.
- Some builders prefer to build both wings at the same time to avoid
having to figure out everything and making the same mistakes twice.
This is not as important when using these directions. There should
be at least four feet between the two spars to allow plenty of
working room. At least one builder put long cross-arms on one
set of posts to do both wings. He used a spacing of 24 inches
between the spars but recommends using at least 30 inches.
The following procedure assumes that the holes in the spar are
not in the exact locations where the drawings say they should
be, as is sometimes the case with the pre-drilled spars. If you
ordered the predrilled wing skins this will not be a problem.
It adjusts the rib position as necessary to center the location
of the bolt holes in the rib reinforcing angles. If the spar holes
are not precisely located then you will not be able to predrill
the skins according to the dimensions in the construction manual
sketches. None of the ribs needs to be precisely located to the
drawing dimensions except where the ends of the pre-cut outboard
skins lie; the inboard edges of the leading edge and outboard
main skins (two-piece) must completely cover the rib flange at
their inboard edge and still overhang the outermost rib by enough
to attach the wingtip (one-half inch in plans, 5/8 is better).
On the leading edge side of the spar (the side with the doubler)
measure from the outboard end of the spar flange (not the jigging
tab) and mark a point 54 1/2" in toward the root. The end of the
flange is where the outside edge of the outermost ribs will be
located later. The mark should be 3/8" past an empty bolt hole.
If it is off more than !/8", either trim some more from the spar
flange or place a new mark on the spar as the outer rib edge location,
whichever is appropriate. This new location will be used as the
reference for placing the rest of the wing components. Do the
same on the trailing edge side of the spar at a point 62 1/2"
in for the main skins joint rib.
Mounting the Rear Spar
- Set the main spar on a table, trailing edge (large flange side)
up. Using drawing 10 mark the locations of the main rib webs on
the spar. Use the outboard end of the spar flange (or the mark
made in the previous step), 126.0", as your reference and the
location of the web of rib #14. Since the drawing dimensions are
all to the inboard side of the rib, add 5/8" for those ribs that
have their flanges pointing toward the root (#14, 4, 3, 2, and
1). Also mark which direction the flanges go for each one.
- Place the main spar in the jig with the large flange down and
roughly level it.
- At the outboard end of the spar put the #14 main rib in place
(with its web lined up with the end of the spar flanges or the
mark and its flanges toward the root, then move it inboard about
1/8" to give a little more room to attach the tip to the skin
later). Clamp some fairly stiff aluminum strips to the rib flanges
to make them align themselves exactly with the spar flanges; the
skin surface will not come out smooth if you don't. Drill #40
through the rib flange holes into the spar. Cleco the leading
edge rib on also.
- Do the next rib (#13) in the same way, with its web lined up with
your marks on the spar, flanges toward the outboard end.
- The third leading edge rib in (#12) gets a reinforcing angle,
and there are two bolts attaching the ribs to the spar in addition
to the rivets through the flanges. To insure that the rib gets
placed so the bolt hole is in a good location on the angle, do
the following steps. On the leading edge side mark the location
of the centers of the bolt holes onto the spar flanges so you
can see them with the angles in place. Place the angle over the
holes with the hole centers in the middle of the flat area and
the upright side toward the root. Shift the angle if necessary
to make it perpendicular to the spar flange. Make sure that the
bolt holes in the angle will not be so close to the upright side
that a nut or washer on the bolt will dig into the angle corner.
Mark on the spar along the edge of the angle. Mark the angle through
one of the bolt holes in the spar and drill this hole #12 in a
drill press. Put the angle back on the spar with a bolt through
the hole and a clamp on the other end, making sure the angle is
perpendicular to the spar flange using a square. Carefully drill
the other bolt hole in the angle through the spar. If you are
worried about enlarging the bolt hole in the spar you can find
a piece of tubing in a hobby store that will fit snugly inside
the bolt hole and over a smaller drill for making a pilot hole.
Put a bolt in this hole.
- Clamp the leading edge rib to the spar and angle, making sure
the rib flange lines up evenly with the spar flange on both sides.
Drill #40 the rivet holes onto the spar through the rib. Make
sure the nose of this rib is lined up with the noses of the other
leading edge ribs, and then drill #30 through the angle into the
rib. Remove the angle and cleco the main rib in place. Drill #12
through the spar into the main rib.
- Repeat for ribs #11 and 10, making sure you use the angles previously
marked for those ribs.
- Do the same for rib #9, but note that the reinforcing angle goes
on the opposite side of the leading edge rib. For this reason
there are no bolt holes to drill in the corresponding main rib.
Use the angle marked "first leading edge rib".
- Drill the leading edge rib A (at station 71.5, the one with no
corresponding main rib) and its angle to the spar as above.
- Position each of the rest of the main ribs on the spar one at
a time, aligning the reinforcing angle with the bolt holes as
before, and drill the bolt and rivet holes as before. Pay close
attention to the orientation of each rib and angle on it as shown
in drawing #10 (angle on opposite side from flanges, and flanges
toward the wingtip except #4 and lower).
- Lay the rear spar next to the main spar with the outboard ends
lined up. Mark the final position of the main rib webs onto the
front side of the rear spar.
- Disassemble and debur.
- Rivet the angles to the ribs with the shop heads on the side where
the rib flanges are to make later operations easier, except where
it might dig into the lightening hole reinforcing ring.
- Cleco the leading edge ribs with angles to the spar. Clamp the
angles to the flange strips and drill the angles #12 through the
- Remove the leading edge ribs, turn the spar over, and do the same
for the main ribs, including the ones which have no angles but
still get bolt holes (#10 thru 12). This will be easier to do
if the spar is placed at least temporarily on the jig.
- Place a main and leading edge rib together to the spar; drop bolts
in the holes and then put two clecos in; enlarge the rivet holes
to #30. Repeat for the rest of the pairs, removing each as you
finish. Also do the inboard leading edge rib.
- Put the rest of the main ribs on the spar one at a time aligned
with bolts. Enlarge the rivet holes to #30.
- Drill the innermost two leading edge ribs of the left wing only
for the pitot tube passage as shown in drawing #20. The holes
are 7/16" in diameter, 1 1/2" from the top side of the rib, and
through the reinforcing angle as close as possible to the spar
attach flange as possible with just enough room to put a bushing
through the hole.
Final Wing Jig Alignment
- Cleco on the leading edge and root main ribs and clamp the rear
spar to them using the marks placed on the spar previously. Clamp
the rear spar to the jig.
- On the root rib drill #30 through each flange strip into the rib
flange. Drill one hole between these two through the doubler plate,
the rear spar web, and on through the rib flange.
- Drill #30 through the four holes in the outboard rib into the
rear spar; continue on toward the root by drilling through the
rib flange holes into the spar.
- At the wing-walk area ribs drill through the flange strips into
the rib flanges. At the second rib drill one hole between these
two through the doubler plate, the rear spar web, and on through
the rib flange. At the third, fourth, and fifth ribs drill one
hole between the two through the rear spar web into the rib flange.
- Remove the rear spar from the ribs and jig. Deburr all the holes.
Reinstall the rear spar, and drop bolts in the main spar-to-rib
holes for those ribs that use them.
- Countersink all the rear spar holes for the outboard rib. This
is so rivets there will not be in the way of the outboard aileron
hinge bracket. (See drawings 16 and 21)
wingribs.doc 11/24/94 Frank Justice
- Place supports under the rear spar at two points to keep the main
spar from bowing. Carefully level the main spar in both directions
while adjusting the supports to keep it straight.
- Run a piece of thread through each of the two alignment holes
in the main spar and the rear spar; tape the end of the thread
at the main spar and tie a 10-32 nut to the other end just below
the rear spar. Clamp the rear spar to the jig so that both threads
hang through the center of the rear spar alignment holes.
- Clamp both spars securely to the jig.
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