Section B Chapter 3
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ROUTED TYPE WING RIBS
Most common used tools: Horizontal belt sander or large bench-mounted disc
sander (9-12”), jigsaw, and laminate router.
** Note: A hand-held disc sander or vertical belt sander will be extremely difficult
to use to obtain smooth contours.
** Pro's of routed ribs - quicker to build and apply finish
Con's of routed ribs - 7lbs. heavier per set and more expensive material.
** The recommended material for routed ribs is 1/4" Birch 12 ply plywood.
"Horizontal" belt sander.Clamped in place
with a wood wedge against the motor casing
underneath. BE SURE it is set at 90 degrees
to the ribs being sanded
Please read Truss Type Ribs chapter 2 before building routed ribs as many of
the instructions apply here as well.
This chapter will build the rib profile patterns and the upper and lower wing ribs
per the dimensions shown on the plans sheets 8 and 9.
Step 1
Layout the rib patterns on 1/2" MDF using either:
a) Carbon paper between the rib pattern and the mdf or;
b) Drawing the rib profile using the print dimensions.
Step 2
6 **patterns will be needed, upper and lower full size ribs, upper
and lower tip ribs and upper and lower aileron ribs. Cut out the
patterns using a band or jigsaw. Leave approx. 1/8" material on the
OD for final contour sanding on the horizontal sander or disc
sander.
** After the main ribs are completed [stations 2 ¼ thru 57 ¼] the patterns are
modified to make the short ribs in front of the ailerons ribs [stations 68 ¼ thru 101
¼] .
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** Double check the
distance between spar
centers shown on the
plans. The main rib and
tip rib distance must be
the same!
** Figure A below shows the layout of the routed rib in comparison to the truss rib
profile. The solid lines are the truss rib; the broken lines are the routed rib profile.
Figure A
Step 2
The upper and lower "cap strip" should be 1/2" thick. The vertical
cap strip as shown on the plans should be 1" thick on your pattern.
Measured 1/2" left and right from the cap strip center as shown on
the plans. The necks adjacent to the spars are ½” (except the
shorter wing ribs, which are ¼” aft of the rear spar as per rib outline
on the plans ). There are no diagonals in the routed rib patterns.
Drag wire clearance is already achieved with routered ribs.
Step 4
Drill starter holes in the corners on every section to be discarded.
These will be the starter holes for the jigsaw.
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Step 5
With a jigsaw,
cut out the
sections to be
discarded leaving
approx. 1/8"
of material past
the pattern
line to be routed
out.
Step 6
½” mdf blocks are tacked/screwed to
the bench, surrounding the template,
effectively locking it in position.
Temporarily tack/screw 1/2" mdf
guide boards right on the pattern
cutout lines as shown at the left, tack
or screw the boards to the mdf bench
blocks.
Using a router pattern bit similar to
the one shown in section W, page 2,
figure B, except with the guide
bearing on the top of the bit, set the
cutter depth so the bearing is riding
against the mdf guide boards and the
bit is cutting the template.
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Step 7
Repeat step 6 to clean up every cutout area on the pattern ribs.
All the pattern ribs are completed 
Step 8
Using the templates, layout all the ribs needed on the 1/4" plywood
(grain lengthways). Run a pencil line around the templates and in
each aperture.
Step 9
Cutout the outline of all the ribs with a band or jigsaw leaving
approx 1/8”. Drill starter holes in the apertures and remove with the
jigsaw, again, leaving 1/8” for the router to clean up.
Step 10
Temporarily attach the ¼” ply to the template using finish nails,
small screws, double sided tape, etc. Install the router pattern bit
with the bottom mounted bearing, adjust the cutter height and
proceed to cut completely around the ID and OD of the rib
Step 11
Repeat step 10 until all the ribs are finish profiled.
** The 6.5-degree sweepback in the upper rib spar openings will be filed in
at wing assembly
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Step 12
With step 11 completed modify the upper and lower rib patterns at
the rear spar location and build the short ribs following steps 8 thru
11 above.
Step 13
The spar opening corners are radiused due
to the nature of routing. These need to be
squared up using a sharp chisel. If your
chisel is NOT sharp, you may crack the
thin ¼” neck! You can also use a jigsaw
with a fine metal cutting blade to achieve
the same result
Aileron ribs at various
stages of build.
Pattern matched to
print and attached to
table
Rib cutout attached to
pattern with router bit
starter holes drilled.
Laminate trimmer
router in the
background.
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The end result: