section 1 - lower wing - direct drive · pdf filesection 1 lower wing ... y with the spar...

Chapter 2

Section 1

Lower Wing Materials: 16 - 3/32” x 4” x 48” balsa sheets 4 - 8-32 blind nuts 4 - 4-40 blind nuts 2 - 8-32 x 2-¾ cap screws 2 - 8-32 x 1-¾ cap screws 6 to 7 - 1/8” carbon rods 4 - Wing strut mounting posts Parts: Aileron servo wire extensions: 48” - 1 36” - 2 24” - 1

Begin by setting up a perfectly flat building table. Check for flatness in all

directions, including diagonals, using a good straight edge. The table must have minimum dimensions of 24” by 100”. With care, the wings can be built on a shorter table, but they will have to be carefully repositioned to work on each half separately.

Install 2, 8-32 blind nuts into each of the R3 ribs. Make sure to make one left

and one right by installing the nuts into opposite sides of each rib. You will have to fashion a plywood spacer so the nuts do not protrude out of the back side of the ribs.

The inside of the left R3 rib showing the 8-32 blind nut and R2 positions.

The outside of the R3 rib showing the R4 position.

Rear outside of the left R3 rib. Glue the R2 ribs to the inside of each R3 rib (side that has the blind nuts). Glue

the R4 ribs to the outside of the R3 rib. In each case, line up the aft edges of the spar notches…the front edge of the notches will be staggered slightly.

Bolt the rib assemblies you just fabricated to the frame assembly using 2, 8-32

by 2-¾ bolts in front and 2, 8-32 by 1-¾ bolts in the rear.

Front plate and R1 installation. Install and glue the front plate, using care not to bond the ribs to the frame.

Install the R1 rib in the center of the front plate. Tack scrap wood to the top of

the ribs to hold them in this position. You will need to use several pieces to ensure the ribs will not shift when removed from the frame. Be careful not to glue the ribs to the frame.

Set the frame aside while you work on the wing skins.

Fabricate two strut mounts. Each mount requires 2 strut mount ribs and the

appropriate strut mounting blocks. The strut mount blocks have been shaped to the contour of the top of the wing. Be sure to get the front and aft - and left and right mounts in their proper positions. The sanded side will go up - or to the outside of the ribs. The front mounts must be even with the front of the rib spar notches. The aft mounts must be even with the trailing edge of the ribs. Make

certain to make a left and right assembly that are mirror images of each other.

Once the mount blocks are glued in place, gusset the bottom of the blocks using

½” balsa gusset stock and thick CA. The ½” square balsa spars have 18 degree bevels on their inside edges. Glue

the spar halves together to form an upper and lower set. Using an x-acto knife, continue the Grooves through the center of the joined spar halves to the opposite side.

Glue the two ½” square balsa splice joiners to the center of the two spars. Do

this over wax paper on the table to ensure the un-notched side of the spars are flat when finished.

Join the 3/32” balsa sheets to form the leading edge sheeting. You will need 4

panels that are 6” wide by 52”. End splice sheets as necessary by using at least a 60 degree angle. These splices should be located closest to the wingtips when

the wing is assembled. Sand the sheeting on a flat surface to eliminate the visible glue joints.

Trim the Leading edge sheeting to match the plan. Trim the long edges with a

straight edge to ensure they are perfectly straight. It is alright if the final width is slightly less than the 6” shown, in order to achieve straightness. Use the rib template to measure the 9 degree end angles.

Note: the 50-5/8” dimension must be exact, as this will set the size of the wing later.

Lay one of the completed spars on wax paper. Place one of the completed

leading edge sheets in position against the spar. Align the inside edge of the sheet with the center point of the spar and with the angle in the proper direction. The edge of the sheeting assures the angle and straightness of the spar.

Working your way from the center outward, glue the sheeting to the front of the

spar using thin CA. As you work your way, be sure the sheeting and spar are flat against the table and butted against each other before adding the glue. This joint will be part of the outside of the wing, so a nice fit is important.

Repeat with the other side of the spar. Do NOT glue the two leading edge sheets

to each other at the center. With the spar assembly still held flat against the table, insert the 1/8” round

carbon rods into the groove as follows: 1. Take a 48” rod and insert it into the groove on the right side of the spar. The

rod should extend to the left of the center line so it just exits the front of the left spar side. Press the rod all the way to the bottom of the groove for its full length.

2. Take another 48” rod and sand an 18 degree angle in one end. Insert the rod into the left spar groove so the bevel you sanded is flush against the first rod you inserted. Make sure the rod is inserted all the way to the bottom of the groove.

3. Squirt enough thin CA along the entire length of the rods to wet the rods on both sides of the groove.

4. Cut another carbon rod into two 24” lengths. Install these into the spars as described above, but this time insert into the left side first, so the rod overlaps the others at center and extends to the front of the right side of the spar.

5. Sand an 18 degree bevel on the second 24” rod and install it into the right side spar so it butts against the other one at center.

6. Make sure the second layer of rods are inserted all the way down against the first layer.

7. Squirt thin CA into the groove to saturate the second layer of rods. For the 212cc model, cut another rod into 12” lengths, and install these into the

notches as done previously. Be sure to alternate the overlap at center as you have been doing.

Clean any excess glue from the top of the notches and use kicker to cure the

glue. Repeat the above steps for the other spar assembly.

Carbon rods installed in spar notches - note overlap at center.

Fashion the two aft wing skins to match the pattern using 3/32” x 4” x 48” balsa

sheeting. Sand both sides on a flat table to smooth the glue joints.

Glue one of the skins to one of the leading edge assemblies using the same

technique you used for the leading edge sheets. This will now be the bottom of the wing. Do NOT glue the top skin to the other spar at this time. Trim the spar ends to be even with the wing skins.

Pin the spar to the work table to keep it from shifting.

Lower wing spar and skin assembly. Mark the rib locations on your skin assembly as follows:

1. Mark the centerline at the joint of the leading edge skins and perpendicular to the spar splice joiners.

2. Start from the outer tips of the spar and measure to the outside of each rib. Make all measurements from the front of the spar.

3. Mark the measurements on the front, top of the spar according to the plan. 4. Repeat the measurements on the trailing edge of the aft wing skin.

Position the fuselage frame assembly - with the center rib section still attached -

into place on the bottom wing skin. Check alignment from both wing tips. When certain it is perfectly centered, tack the ribs in place on the spar with thin CA. Lift the skin so it is flush to the ribs and glue with thin CA.

Positioning mount ribs on skin assembly.

Remove the wing mounting bolts and separate the frame from the center ribs.

Tack the ribs in place along the spar at the positions you marked. They are all

mounted at a 9 degree angle to the spar, with the exception of the R5 rib, which is at a 3 degree angle. Use the marks you made to align the standard ribs. Use the aft wing skin aileron cutout to set the angle of R5.

When satisfied with the rib positioning, glue them to the wing skin aft of the

spar. Do NOT glue forward of the spar yet. Slide the wing trailing edge jig under the rear of the wing skin. The trailing

edge of the ribs should be even with the forward edge of the jig. The inside edge of the jig goes under the R5 rib, but no farther towards the center of the wing. Pin in place.

Using a straight edge to position jig under the wing skin. Slide the center jig so the aft edge is even with the trailing edge of the center

ribs. Pin in place. Shape and install the 3/8” square balsa leading edge in place. Sand the inside

end to mate against R3. Also sand the top and bottom edges before installing so they match the size of the rib notches.

Lift and glue the leading edge sheeting to the ribs using thin CA. You will have

to trim the sheeting at the center from R3 inward to achieve a fit around the ribs and front plate.

Trim the lower leading edge sheeting that protrudes above the leading edge.

Fit and glue the shear webs on top of the spar and between the ribs using thick

CA. The webbing must be centered on the spar so it fully covers the carbon rod grooves.

1. Use ½” web in the center of the wing out to the first standard rib. 2. Use 3/8” web from the first standard rib to the 4th standard rib. 3. Use ¼” web from for the remainder of the wing.

Assemble the servo boxes.

1. Lay the parts out for each of the four boxes. The plate with the larger bolt hole goes to the bottom. Determine the orientation of these plates and install 4-40 blind nuts from the bottom side of the bottom plate. Lock the nuts in place with a square of glass cloth and thin CA.

2. The two inner boxes use the servo rib reinforcement for the outer side. The two outer boxes use the side of the strut ribs for their outside.

Leave the side of these boxes open for now. 3. Glue the boxes with thin CA.

Trial fit the boxes and mark their locations on the wing skin. The outer box

is part of the strut rib. The inner box mounts to the inside of the second standard rib from the inside of the wing. Make certain the rear edge of the boxes are aligned with the wing skin.

Sand the wing skin under the servo box locations to a 5 degree angle so the skin

will lay flat against the bottom of the adjacent ribs when the boxes are installed. The skin will be about 1/32” thick when you are finished.

Glue the boxes in place against the ribs

Fit and install the 3/8” balsa trailing edge between the servo boxes.

Use the trailing edge stock to fashion two aft spars to the center section of the

wing. Trial fit the upper spar in place. Make cutouts for the forward wing cutout tabs.

Make sure it fits flush on top of the shear webs and ribs. When happy with the fit, remove the spar again.

Remove all pins that will be covered by the leading edge sheeting. Use weights to maintain the lower spar flat against the table.

Glue the upper spar in place. Use slow CA so you have time to apply glue to

the ribs and webs before setting it in place. Use ample weight on the spar to ensure the wing will remain straight. Only glue the leading edge sheeting from the spar to about half way to the leading edge.

Now is the time to run your wiring to the servo boxes. Secure as necessary to

the ribs. The wires will exit the wing through the upper aft skin just outside the frame side. This will be between the frame and fuselage side. It is recommended that all the wires exit through a single hole on one side, as this will make wing assembly easier when the plane is complete.

Trial fit the upper aft wing skin. Once again, mark and sand a 5 degree bevel

into the skin where the servo boxes contact it. Make cutouts for the rear wing mounting tabs. Trim and sand the lower wing skin in the center, and bevel with sandpaper so the upped skin will lay over the top of the trailing edge in this area.

When satisfied with the fit, remove any remaining pins and glue the aft skin in

place using slow CA. Apply an even weight load to the skin while it dries. Remove the wing from the table and turn it over so it rests on the mounting

tabs. Glue the front of the top leading edge sheeting as follows:

1. Place ½” square by 48” long balsa sticks under the spars to lift the wing up so it no longer rests on the fuselage mounting tabs.

2. Place ½” square by 48” long balsa sticks under the aft wing jig strips and position them under the trailing edge of the wing as before.

3. Hold the wing flat against the table using weights as required. 4. Working from the center of the wing out, lift the leading edge sheeting

up against each rib one at a time. Drip thin CA so it runs along the rib and bonds the sheeting. Repeat for each rib location.

5. Go back to the center of the wing and gently pull the sheeting flush against the leading edge spar and bond with thin CA. Work on about 6 inches at a time, allowing the glue to dry and then moving to the next segment until the entire sheet is bonded to the leading edge spar.

Remove the weights from the wing. It is now structurally complete. Trim the remaining leading edge sheeting that extends beyond the front of the

wing. Using 3/32” balsa sheet scrap, trim and cap the lower leading edge sheeting at

the front of rib R1. Sand the wing to shape. The leading edge should be rounded. The trailing edge

should remain sharp. The wingtips should have a very small radius on the edges.

Lay .56oz glass cloth over the top of the wing between the wing mounting tabs.

Wet this with thin CA to harden. This is the area of the wing that is exposed to the muffler heat, so the cloth will protect it.

Cutout the strut mount holes and install the 3/8” aluminum strut mounting

posts. Screw them in until the last thread is even with the surface of the wing.

section 1 - lower wing - direct drive · pdf filesection 1 lower wing ... y with the spar...

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