Installing The Wing Ribs; Installing The Beam Webs And Web Blocks - Model Airways CURTISS JN-4D JENNY Instruction Manual

Since the wing ribs have undercamber, jig
shims are required to correctly locate the
beam flanges at their proper angles. The
shims are laser-cut parts.
The leading edge is a rectangular spar and is
deeper than necessary so it can sit directly on
the plan without any shim strips. Pin the
leading edge to the plan first. Later, when the
wings are removed from the building board,
the leading edge will be rounded to its cor-
rect shape.
Next, lay a 1/32"-thick shim just behind the
leading edge in way of each rib. This will
hold the ribs off the work surface to allow for
the thickness of the cap strips. Also, lay a
1/32"-thick shim under the trailing edge.
Both of the 1/32" shims can be short pieces
in way of each rib or a long strip.
Laser-cut jig shims, W24, are used to hold
the beam flanges at the correct height and
angle. It is suggested that these shims be laid
just to one side of each wing rib rather than
under it, so you can still see the rib locations
on the plan. Pin the shims to the plan. Note
that there are only enough of the laser-cut
parts to build one wing panel at a time. If you
want to build more, you must make your
own additional shims.
Lay down the lower beam flanges and pin
them on top of the jig shims.
illustrates the setup. Out near the wing tips,
both of the beam flanges must be tapered as
shown on the plans. Also, the flanges are
angled toward the wing tips outboard of the
last full-size rib. Consequently, you can take
the flanges during this step only out to the
full-size rib and then add the remaining
portion of the flanges when you do the wing
tips (to be discussed later).
Option:
The small lower stringer at the mid-
dle of the wing ribs could also be installed
along with the beam flanges. Refer to Para-
graph 6 for a discussion on the stringers.
When pinning the flanges (and the
Note:
stringer if the option is chosen) to the shims,
use one of the full-length lightened ribs to
check the fit as you go. The front end of the
rib will butt against the leading edge, and the
bottom slots in the rib must fit the lower
beam flanges (and stringer).

3. Installing the Wing Ribs

Position and glue each wing rib to the leading
edge, and to the front and rear beam lower
flanges (and the center stringer if this option
is used). Use pins if necessary to hold the ribs
vertically at each location
(Figure 1-3)
The short ribs at the trailing edge, W7, can
be installed now, or wait until the trailing
edge is in place.
4. Installing the Beam Webs
and Web Blocks
With the ribs in place add the webs at the
front and rear beams. The top of the webs
must be shaped so they are flush with the
bottom of the slots for the upper flanges.
Glue the webs to the lower flanges and to
each rib. illustrates the basic
Figure 1-4
3/32" X 3/16"
LEADING
1/32" SHIM
LOWER BEAM FLANGES
Figure 1-2
THIS SHOWS OPTION WITH
REAR WEB SHOWN
.
(FRONT SIMILAR)
webs between ribs. Variances are as follows:
A.
The webs between the inboard two ribs
are the same thickness as the flanges.
This thick web supports the fake hinge
pins that connect the lower wings to the
fuselage and upper wings to the center
section. For the model, drill a hole in the
ends of each web for inserting a fake
hinge made of steel rod. The inboard ribs
FIG. 1-2 WING RIB JIG SETUP
EDGE
JIG W24
1/32" X 1/32" STRINGER
(OPTION – INSTALL NOW)
1/32" X 3/32" FRONT
1/32" X 1/8" REAR
FIG. 1-3 INSTALLING THE WING RIBS
W24 OFFSET FROM RIBS
FIG. 1-4 INSTALLING BEAM WEBS
8
TYPICAL WING RIB
1/32" SHIM
PINS
BEAM WEB –
1/32" FRONT WEB
3/64" REAR BEAM
5/64" IN WAY OF
AILERONS
already have a laser-cut guide hole (more
on this later).
B.
The rear web outboard where the ailerons
are located is a continuous piece and is set
flush with the aft side of the flange. Like
the flanges, the beam webs outboard of
the last full depth rib are not installed at
this time. They will be done with the wing
tip construction per Paragraph 5.