Bd-5j

[Gil]

The following is the culmination of the BD-5J design and interim mold design and fabrication.

The plug (gray fuselage shape) consists of a built up lacquered chip board card model coated with wall board compound and shaped with various tools till fair. It was then sealed with thinned lacquer followed by multiple iterations of primer, spot glaze, sanding and repeat cycles.

The half mold box is made from corrugated cardboard and a triple layer of chip board. The chip board separator is held to the cardboard with acrylic modeling paste which also seals the sides of the cardboard.

The plug was then inserted half way into the mold box and held fast with plasticine modeling clay. The inside of the mold and the plug surface were then brushed with a mixture of Vaseline thinned with paint thinner followed by heating with a heat gun to flow the mixture onto the surface. This dissolves any brush marks that might show in the casting.

A thin mixture of Durhams Water Putty was then poured into the prepped side of the mold. The mold was then jarred repeatedly to surface any air bubbles in the Water Putty and left to set overnight.

Removing the mold from the mold box consisted of using a spatula down the sides all around the periphery of the mold till the sides were free. The modeling clay holding the plug on the bottom side was removed. The mold box was then placed with the molded part side down. The plug was then gently pressed down till the mold was freed from the mold box. The mold is being allowed to dry for an additional two days.

The opposite side will be done in exactly the same way over the next several days...,

Where's this going? Stay tuned and you'll find out...,

+Gil

[Sakrison]

A generous and trusting friend of mine once offered to let me fly his BD-5 (not the "J" version) around the patch. I've flown lots of different aircraft, including a warbird or two, but as I looked at that sleek, cocky little bird sitting on the ramp, I asked myself, "Self, how long do you think it will take you to hurt yourself in that airplane?"
The little voice that sits on my shoulder said, "About 150 yards."

They are fun to watch, but I have yet to fly one. It's better to be down here wishing you were up there than up there wishing you were down here.

Nose up, wings level, and pointy end forward,
--David

[Gil]

David,

The BD-5 has a reputation for being a dangerous aircraft. The J's reputation is even worse. The reason for choosing it as a subject was for the nice looking fuselage and even though it's made of aluminum it has the look of fiberglass with no noticeable surface discontinuities. This is the reason behind this design thread. How do you make this kind of surface using only paper?

+Gil

P.S. I think you could of gone further than a 150 yards..., 153 maybe?

[Sakrison]

Originally Posted by Gil

David,

The BD-5 has a reputation for being a dangerous aircraft. The J's reputation is even worse. The reason for choosing it as a subject was for the nice looking fuselage and even though it's made of aluminum it has the look of fiberglass with no noticeable surface discontinuities. This is the reason behind this design thread. How do you make this kind of surface using only paper?
+Gil

I think it's a great subject for a paper model and I'm looking forward to building it in 1/33 scale--much safer and saner than trying to fly one.

Originally Posted by Gil

P.S. I think you could of gone further than a 150 yards..., 153 maybe?

Maybe . . . but I doubt it.

[Gil]

David,

It's a tad larger than 1:33 at the moment..., more like 1:10. The large size was selected due to its being a nice number for the model, namely 12 inches...,

+Gil

[Gil]

Just had to try a quickie shell made using the half mold.

It consists of a staggered double layer of 80# card stock. The first layer was laid into the mold after soaking in warm water for a few minutes. The second layer was laid in staggered to the first layer to overlap the seams. Thinned PVA was applied to the secondary pieces before laying in. The shell was then burnished into the mold.

I tried vacuum bagging the structure but didn't have the right bag to pull it off (a thin vegetable bag from the grocery store). I laid the original plug somewhat back into the mold to hold the pieces in place. A small muffin fan was placed to blow air over the layup and left to dry.

Below is the result of this process. The gaps were caused by not being careful about the overall layup and the fact that not all the segments glued the first time and some had to be redone (sound familiar?).

The results aren't terrible but then again they aren't all that blindingly good either. I think that this method works rather well for compound surfaces although the method isn't the goal of this project...,

+Gil

[Gil]

From one many....,

The above thought struck home as the following shell was being assembled. Really amazing what lurks in your mind when you have a mold to work with. A shell using the "piece cut" construction method was given one last try before moving on to the next phase.

Regular chip board (0.5 mm) was used to make all the outer pieces of the shell. The inner shell, or "the glue tabs", uses 80 # card stock. The chip board pieces were soaked in warm water, laid into the mold and pressed to the form. The "glue tabs" were then coated with PVA and laid in so as to overlap the chip stock pieces. A cotton bag filled with sand was placed into and over the mold as a surface clamp before the entire assembly was placed in a drying oven and left to dry at 105 degrees F. Some of the print lines don't line up. This is due to their being on the downside of the chip board. The major concern was with attaining good seam alignment. This is easily overcome by using mirrored pieces.

The dried structure shrank lengthwise by approximately 3 mm. The shell also showed a definite tendency toward springing open which bowed the shell lengthwise. The solution was to add 5 mm strip stock to the edges and build up two layer "formers" as seen in the second photo. The formers are easily laid in and create a surprisingly rigid structure. All reinforcing is accomplished with the shell reinserted into the half mold. The entire assembly was then painted with thinned sanding sealer lacquer (nitrate dope is preferred). The chip board absorbed some of the remaining mold release agent (Vaseline) which shows lighter in the images due to the low penetration of the sanding sealer.

Overall, this is an easy process once the initial trials and tribulations of making a female mold are out of the way. Laying up a fuselage shell is easy and a straight forward process producing predictable results. It does require precision cutting on the assembly pieces but that's part of the craft. The last photo shows the two axis curvature to good effect. I think this method to be highly recommended to builders of small ship models and modern nuclear submarines...,

The real discovery is the ease in which the formers and other strengtheners can be applied to the shell. The all up weight is 18 grams...,

+Gil

[Gil]

The piece molded shell was prepped for painting with clear acrylic gesso. This is an artists paint that fills in the weave of the canvas and creates a toothed surface for improved paint adhesion. One important point arose during the sanding process. For some reason I used the wrong side of the chip board for the exterior surface. It has a diamond pattern on the surface and requires a large amount of sanding to remove it. The other side is a nicely calendered surface which is the one that should be used.

The prepared shell was painted with white gloss acrylic. Three layers were required to completely hide the surface beneath. The NASA duct was painted flat black for effect. The last image shows the internal structure inserted to support the canopy edges. Some pretty creative former patterns can be realized using this method including geodetic.

This completes the piece molded shell part of the project. It works fairly well and can be used to develop shell molds and the attendant shells for a number of models where a smooth compound curved hull is required. The resultant shell is both light and strong. Besides it looks fairly good. The negative side is the amount of preparatory work required to make the mold. A lot of time was spent filling and sanding due to using the wrong side of the chip board but even so it was still required. Cutting all the pieces and getting everything aligned in the mold is also a time consuming task.

The next phase will replace all the pieces with one piece of paper...,

+Gil

[Leif Ohlsson]

Exquisite and beautiful result, both exterior and interior. There must be some features of this procedure that could be utilized by ordinary modelers as well. What would a "half-baked" procedure look like?, I wonder.

Leif

[popala]

Wow Gil, you never cease to amaze...