Schweizer TG-3 ~ 1/3-scale model by Peter Goldsmith (Build Thread by JimD)

[JimD]

Time to flip the fuselage structure over and build on the bottom. We used bricks and hardwood sticks to support the fuselage. We did a dry run parts placement and then built the wheel well assembly. This assembly is built in a way that keeps it true and forms a good starting point for the lower fuselage construction.

[JimD]

Building fore and aft from the wheel well structure:

[JimD]

Adding more pieces!

[JimD]

Peter includes a Delrin tow release block and servo mount tray for the tow release servo. The position of the tray requires a low profile servo like the recommended Spektrum A6220.

[JimD]

Rudder servo mount:


Wheel well surround sheeting:



Don't forget to run the elevator servo extension wires back inside the fuselage before covering! We like to make our own extensions and use color coded wire to distinguish between right and left elevator extensions.

[JimD]

Wing mounting/fuselage side sheeting.

Laminate parts making sure you have a left and right side.







Note that these 1/8" thick plywood sides do not fit in flush with the surrounding stringers and bulkheads. They stick out about 1/32"...this is because of the way the 1/32" thick plywood fuselage sides join up with the wing mounting area.

[JimD]

Here you can see how the 1/32" plywood sides fit up to the 1/8" wing mount sides.

[JimD]

Building the wings

The way Peter has designed the wing structure, it is not necessary to build over the plans. As a matter of fact, it is best that you DO NOT build over the plans!!!

Each rib has a tab on the front and rear that fits into a slot in the leading and trailing edge laser cut parts. The shear webbing is laser cut to the exact size needed between each rib. The parts set the spacing between the ribs and the notches in the top and bottom of the ribs set the spacing between the main spar and the drag spar. Trying to build over the plan would only confuse how these parts fit together.

The airfoil is such that the ribs sit flat on the building surface from the main spar to the trailing edge. The key to building the wings is having a flat and true work surface. The finished wings are about 8-1/2' long, so unless your building board is longer than 8', a bit of the wing is going to overhang. This is really not a problem.

Our workbench is 24" wide x 8' long. It is covered with a sheet of Homasote sound board that is easy to pin into. Establish a straight line the length of the work surface with a perpendicular line at one end.

The 48" main spar basswood will require two joints in order to extend the necessary 8-1/2'. We made 1-1/4" overlap scarf joins.

The first rib is not perpendicular to the worksurface (but all other ribs are). The slant of this first rib is set by the laser cut shear webs that fit between the first and second ribs.

Cover your work surface with wax paper or similar non-stick material. Place the main spar on the reference line and pin it as needed to keep it perfectly aligned with the reference line on the workbench. Place the first two ribs and shear webs onto the spar and place the rear bottom piece of the drag spar under these ribs. Dry fit everything to see how the parts fit together. We placed a row of T-pins along the line drawn at one end of the main spar reference line. These pins keep the bottom edge of the first rib aligned with the reference line.

Take your time to get these parts in place and to fully understand how they fit together. If done correctly, the rest of the wing is super easy to build out straight.



Add the laminations and wing attachment blind nut to each root rib. Be sure to make a right and a left side.



Glue the blind nut in place so it can not come apart inside the wing later. The shear web for the drag spar is 1/4" thick plywood and it has the additional job of holding the steel wing anti-rotation pin. Inserting this steel pin through the root rib and into the shear web adds additional strength to the interlocking of these parts. We glued the 1/4" thick plywood shear web to the bottom shear web before adding the ribs and starting the wing build proper.




Time now to glue R1 and R2 to the spars and set the spacing and slat of R1 with the shear webs. Note the steel anti-rotation pin. Also note the building triangle to check the alignment of R2 relative to the main spar. Use whatever your favorite tools and weights are to lock these parts in place until the glue sets.



The main spar shear webs in the first four rib bays form a slot for the wing tube to slide into. Make sure your lay these parts out to understand how they are positioned because this is a critical step. From this point, building the rest of the wing goes quick and easy.





Now we are off to the races placing the shear webs, then a rib, then the shear webs, then a rib...

Make sure the ribs seat fully down over the spars and make sure that the whole structure aft of the main spar stays flat on the worksurface.



Add the leading edge strip the front of the ribs (note that the bottom edge of this strip sits flush against the work surface). Cut pieces from the balsa stick provided the same length as the shear webs and fit these pieces in from the trailing edge using the plan as a reference for this placement. Note that the spoiler and aileron servos are mounted sideways through specific ribs. Best to add the reinforcement laminations before placing these ribs.

[JimD]

The inboard (approximately 4') section of the wings is constant cord and constant thickness. The outboard (approximately 4-1/2') section tapers along both the leading and trailing edge. The thickness also tapers. Note that the bottom of the wing is flat along the main spar from the root to the tip. The top of the wing tapers downward from the transition between point between the inner and outer sections toward the tip. This is important to note when adding the top main spar.

There is a double rib at the transition point between the inner and outer sections. We placed the first main spar scarf joint at this double rib location. The double rib is split into a front and a back half. Shear web Sh8 extends through the rib bays to either side of this double rib and acts to reinforce the spar joint. In addition, a piece of the main spar basswood stock is cut to extend through these same two bays and in glued to the top of the lower main spar to further reinforce this joint.




Here is the outer main spar scarf joint detail.

[JimD]

Once all of the ribs are in place, the top main spar and top drag spar can be added. The slotted leading and trailing edge laser cut balsa pieces can also be added. These balsa LE and TE parts get sanded to follow the contour of the ribs.

Add the 1/32" plywood cap along the trailing edges, the inboard 1/32" sheeting, and the spoiler surround. Note how these parts overlap the main spar slightly.











Next add the inboard 1/32" plywood sheeting. We used Speed Bond and hot iron technique.







Then add the laser cut 1/32" plywood rib cap strips.

[Swiss1]

That's a lot of work in one day Jim

[JimD]

Instant glue ;-)

[JimD]

Once all 1/32" sheeting and caps strips are added to the top of the wing, it can be flipped over and the bottom sheeting and cap strips added.

Next step is to build the ailerons (which are in two sections each driven by its on servo). The wing is used to help hold parts in alignment. Place the 1/32" plywood bottom skin in position and set the aileron leading edge on the skin and push hinge pins through holes to align everything. Use scrap sheeting to set correct spacing. After a dry run test fit, place a strip of wax paper between the wing and aileron parts. Glue on the leading edge using the hinge pins to hold in place. Then add ribs along the laser etched lines on the bottom skin. Sand the leading to the slope of the ribs, glue in the "donuts" at the hinge pin locations, and glue on the top 1/32" skin.

[JimD]

Use a scrap piece of hardwood stick to help hold the top wingtip skin level with the top of the wing.



Add the triangular ribs under this 1/32" plywood top skin. Next, hold the bottom skin in place and mark it (note that it is oversize on purpose). Cut of excess and glue in place to finish wingtip.

[JimD]

Decided to use this scheme.



Peter send his graphics info to Callie Graphics and they can be duplicated for your build if you so desire. I made a few additions to Peter's graphics package to match the plane I am modeling, and Callie did a great job as usual.

Our model has Silver UltraCote on the fuselage and Cub Yellow UltraCote on the wings. White, True Red, and Corsair Blue for the rudder.

[JimD]

We used Tamiya XF-53 Neutral Grey Acrylic Paint for the cockpit area and used the supplied instrument panel.