ProCub Rear Fuselage Assembly Part 2

Picking up where we left off on the assembly of a ProCub Rear Fuselage….

In similar manner, we will glue on each of the remaining rear fuselage bulkheads.  Remember, the placement distances are measured along the centerline, not along the slant edge.

Glue bulkheads 5

Glue bulkheads 7

Glue bulkheads 8 Glue bulkheads 9

After all of the five bulkheads are glued in place, it will look like this.

Glue bulkheads 6

Five bulkheads glued to top plank in rear fuselage. This structure is built upside down. Ensure centering of each bulkhead. Remember to measure the placement down the centerline.

Now it is time to make the hardpoints for the attachment of the rear fuselage.  They are constructed from baltic birch plywood.  The size of each hardpoint is 2″ x 18″ x 12mm; use two pieces of 6mm thick baltic birch plywood for each hardpoint and glue them together using a superior grade of wood glue.

Fuse Attach Hardpoints

Glue the 6mm strips of 2″ x 18″ plywood together, producing 12mm thick hardpoints.

Fuse Attach Hardpoints 2

After cleanup, glue removal and sanding, the hardpoints are ready to install.

Fuse Attach Hardpoints 3

A better fit may be achieved by putting a slight bevel on the inside rear corner of the hardpoint.

Fuse Attach Hardpoints 4

Gorilla glue is used to bond the wood piece onto the plank. Clamp tightly in place while the glue sets!

Now it is time to glue on the side plank of the rear fuselage.  You will want to test fit it first (using helpers and / or clamps) and ensure that the fit is flush.  You may need to slightly trim the bulkheads for a perfect fit using sandpaper and a foam rasp.  After the test fit is perfect, it is time to glue the side plank as shown below:

Fuse Side 2

Gorilla glue applied immediately before placing the side plank. Don’t forget to mist with water.

Fuse Side 4

Side plan being glued. Note weights, clamps and use of pins.

Fuse Side 5

View of gluing process from opposite side, looking inside. Note expansion of Gorilla glue.

Fuse Side 3

Another view of the gluing process. Be careful with the weights and clamps: if the assembly topples off the bench, it would be a very bad day.

In an identical manner, glue on the other side plank.  (Not shown.)

It is time to glue in place the left and right side jigsaw extensions, which were CNC milled from 1″ foam.  At the very rear of the fuselage, where they mate together, you must make a bevel which allows them to symmetrically join together.

Fuse Side 8

Test fitting a jigsaw extension. Note beveling. Note sanding on plank, in preparation for Gorilla glue.

Fuse Side 7

Alternate view of test fit on jigsaw extension.

Fuse Side 10

End view of jigsaw extension gluing. Note use of clamps and weights. Also use pins as necessary to ensure parts don’t creep.

The rudder front square post is glued to the most rearward bulkhead, on the most rearward side.  It is a 36″ length piece of 1″ square aluminum thinwall tubing, and it protrudes 2″ above the bulkhead, as shown in the following photo.  This ensures that it will be merely flush when the remaining bottom plank is glued in place.  Also, you’ll need to cut a hole in the existing plank, so that it can poke through as the assembly overhangs the table.

Front Rudder Post

Front rudder post is glued in place 2″ proud. Glue with Gorilla glue. Clamp well while glue sets.

Front Rudder Post 2

You will have needed to make a hole for the post through the existing plank.

A 1″ hole must be bored in the foam at the location shown in the photo below.  This is done on one side of the rear fuselage only; it is the exit hole for the elevator pushrod.

Elevator Pushrod Holes 2

It is now time to bore out a series of holes which will provide for the elevator push-pull torque tube passage.  It is our plan to eventually include the placement of these holes in the bulkheads, so that you don’t have to do it.  But as of this writing (January 2015) we have not yet programmed the CAD and routing to do that on the bulkheads.  So it has to be done manually by the builder.

Please remember that you are building this rear fuselage assembly upside down, and the objective is to provide a ‘straight shot’ bore hole from the elevator reverser bellcrank to the elevator.  The elevator push-pull tube will pass through this series of holes.

Following are the hole locations which must be drilled into each bulkhead.

Elevator Pushrod Holes 3

Side and down coordinates for first hole in rearward bulkhead. Look at the next two photos as well for help in correlating these numbers!

Elevator Pushrod Holes 9

Center of hole is 1.5″ sideways and 8 3/8″ down.

Elevator Pushrod Holes 10

Another view of same hole. It’s down there.

The other bulkheads are drilled as follows:

Elevator Pushrod Holes 4

Elevator Pushrod Holes 5

Elevator Pushrod Holes 6

Elevator Pushrod Holes 7

After each hole is made, the lineup of holes will look like the following photo.  (Ignore the gorilla glue!)

Bottom Fuse

View of hole lineup in rear bulkheads. Gorilla glue will be applied when it is time to glue the remaining bottom plank.

Now it is time to glue on the remaining bottom rear fuselage plank.  Start by making a hole for the 2″ proud front rudder post.

Front Rudder Post 3

Bottom plank resting on 2″ proud front rudder post. Make a hole for the post in the plank.

Don’t forget surface preparation: sanding, test fitting.  There’s a lot of Gorilla glue to apply, so a helper may be useful.

Bottom plank being glued to rear fuselage.  Use lots of clamps, weights, helpers and pins.

Bottom plank being glued to rear fuselage. Use lots of clamps, weights, helpers and pins.

After the glue sets, remove the weights, pins, clamps from the assembly and turn the assembly over.  It is time to attach the rear rudder post, which is also 36″ long.

In order to do that, the foam must be trimmed.  We’ll mark the trim location by borrowing the partially assembled horizontal stabilizer, setting it in position, and noting the trim spot.

Main Rudder Post

Horizontal stabilizer resting in place for test fit. This helps us find the trim location for the rear foam.

After noting the trim location, we start making a cut using an Exacto saw.

Main Rudder Post 2

Trimming with an Exacto saw, in preparation for gluing the rear rudder post.

Main Rudder Post 3

Another view of the trim in progress.

After some sanding, it is time to glue the rear rudder post in place.  This is done with Gorilla glue, a helper, and lots of masking tape.  Ensure that the post is perfectly flush and square, or your rudder will crooked!!

Main Rudder Post 6 Main Rudder Post 5

To be continued…

One thought on “ProCub Rear Fuselage Assembly Part 2

  1. Working on a 66%cub I used 3/4 radiused alum box tubing fuse and wings complete. ..from full scale plans. It is rc ,100 lb torque servos. JPX 320 engine /37 x 16 prop. ..let me know what your all – up weight is
    ..thanks. .Brent

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