Bob Perovich’s C-57D Hull Assembly part 4

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This hull construction has been challenging, but I have the methods all figured out. The solutions are simple, and low cost. Polar Lights really did a great job on the engineering of this model, although it does not appear so at first glance. The alternative would have been a 2 piece fiberglass casting, which would be very expensive. Due to the shape of the hull, and the flexible nature of styrene, some reinforcement is necessary, and fairly easy to do. The fiberglass kit is about $9, and another $5 or $6 for all the other parts.

There are some structural limitations with this kit that require us to do some custom work…

  • The lower hull has 6 landing wells, with panels to close the alternating 3. The closed panels do not connect well to the hull, so we have to do some custom work to get a flush mount, and add strength.
  • The bottom hull center is flat by design, and supports the entire weight of the model on the lower bubble ring. By itself, the stock hull may sag due to insufficient structural strength.

This is not bad engineering on the part of Polar Lights. Styrene plastic is flexible, which is good for models because it does not break easily. The hull is huge, and the bottom section if flat, so it is hard to attain structural strength using styrene alone without a convex surface. To add strength, we will need to use cross members and composite materials. (Plastic beams and fiberglass cloth.)

Closed Landing Wells

1. Remove part of the top of the closed landing wells. Leave 1 inch near the center, where the mating pins are.

2. Build “hard points” to connect inside the landing wells, so we can mount the panel flush.

3. Attach brass rods to the outside hull across the closed landing wells using silver duct tape.

4. Flip the hull over, and insert Panel 45 from inside. The brass rods will hold the panel flush against the hull.

5. Place the hard points against the side of the landing well, and rest them on top of Panel 45.

6. Glue the hard points to the inside landing well, but NOT to the lower Panel 45. These hard points will later allow us to glue Panel 45 in position with a flush mount.

7. Remove the brass rods.

8. Glue Panel 45 in position.

9. Glue more plastic beams in position against the side well and Panel 45 for extra strength.

10. Use 2 part epoxy putty to fill the gap between the lower bubble ring and Panel 45. (use masking tape to cover the lower bubble ring!)

Bottom Hull Center Fiberglass Sections

  • There are 12 sections to be fiberglass reinforced, 6 sections adjacent to the closed wells, and 6 sections adjacent to the open landing wells.
  • The two sets are treated differently, so it is recommended to do this with two applications.

 

Bondo Fiberglass Repair Kit No. 420

Six Closed Well Cloth Sections

Note: If the fiberglass sections will not hold in place, then rough sand both surfaces, and glue them back in with epoxy glue. This may happen if you do not use enough resin on the cloth.

bperoc57d-12bondo

bperoc57d-07clothstencil

bperoc57d-8clothtrace

bperoc57d-09cloth

1. These photos show the fiberglass stencil, the cloth, and the cut reinforcement piece.

bperoc57d-10reinforce

2. Place the fiberglass cloth in position,

3. Do this to all 6 sections, and lay them in place.

4. Mix about 1 1/2 ounces of resin with hardener.

bperoc57d-11fiberglas

5. Soak 1 cloth section in the resin, and let the excess drip off. (Do not use a blotter! The cloth should be sloppy looking)

6. Lay the cloth into position, and tuck it down. (The resin should not quite overflow the landing section. Excess can be ground off later.

7. Do the remaining 5 sections.

Six Open Landing Wells Cloth Sections

These 6 sections have landing gear glued to them, so we must not cover the notches with resin. Mark off about 5/16 inch square over the landing gear notch, and leave the end of the masking tape sticking out in the landing well.

After about 10-20 minutes, the resin should form a hard gel. Take a razor knife and cut the resin along the borders of the masking tape, then pull up the masking tape. The resin piece will be removed.

After the landing gear are glued in, the notches can be filled with epoxy putty

Bob Perovich

Part 5 shows the interior of the model