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Old 08-24-2011, 07:29 PM
luke strawwalker's Avatar
luke strawwalker luke strawwalker is offline
Join Date: Dec 2007
Location: Needville and Shiner, TX
Posts: 5,860
Default BT-80 based Saturn V/ "Saturn I-F"

Hi all...

Well, after finishing the Dr. Zooch SLS last week, I thought I'd dust off some projects that have been partially finished. Last summer, while at the MIL's in Indiana, I turned a transition out of pink house insulation foam for a BT-80 based Saturn V. Didn't take long to figure out that a BT-80 based Saturn V, with a BT-60 based S-IVB third stage, would be perfectly "in scale" with the Dr. Zooch Saturn I/IB's I bought (but have yet to assemble.) In fact, I was playing with the idea a good while back and bought an extra pair of SLA adapter transitions, SM tubes, and CM BPC nosecones from Dr. Zooch on a big kit order. One has been sitting in the box awhile, and the other on the BT-60 S-IVB for "inspiration". So, having turned the transition and then the project 'stalling out' at the end of last summer, I decided to get back to work on it.

First off, I decided that the foam, while an excellent core for the transition, wasn't quite tight enough or really as strong as I'd like for a transition. I turned one end slightly undersize and that also complicated things, so I took a page out of the Tim Van Milligan Rocketry Workshop vids and added a tube coupler to each side (after sanding down the side that wasn't undersize so the coupler could slip over) The transition itself was made by cutting an appropriately sized "blank" from pink foam, doubled up to make the blank bigger than the diameter of the finished BT-80 transition base. A little quick work with Peter Alway's "Rockets of the World" and a calculator gave me the correct scale factor (roughly 1/152) and dimensions for the transition. Wrap a dowel in sandpaper and sand a half-round slot in each block of foam, then using epoxy or other NON-EVAPORATIVE CURING adhesive (IE NOT white glue, yellow glue, or other 'water solvent' type glues (of course they have to be FOAM SAFE AS WELL) glue the two blocks around a dowel. Once dry, cut the block down to the approximate size (octagonal) and tighten it up in the chuck of a drill (homemade lathe I built, using a $14 Harbor Freight drill for power) and turn the transitiond down to size using progressively finer grits of sandpaper.

Once the transition had the couplers glued on, I did a bit of experimenting with an online transition maker and came up with the appropriately sized transition, trimmed the pattern out of printer paper, trimmed it to final fit, and then traced it onto cardstock and cut it out. Using an old ball-point pen that no longer works and a piece of cardboard (or old mouse pad if you have a spent one) I "embossed" the corrugations in the cardstock transition by eye. Since it's on a conical part, the corrugation lines all have to 'intersect' at the center point of the transition, so this is probably better done before cutting it out, using a steel ruler through the center point as a guide for the corrugation lines as they're embossed onto the cardstock transition. Remember they have to be embossed from the INSIDE of the transition. I also added another "dividing line" halfway between the upper BT-60 end of the transition and the lower BT-80 end, using a drafting compass, to guide painting of the interstage roll pattern later on. The handy transition tool on the web also prints markings for both three and four fins if the transition is used as a tail cone, which makes it VERY easy to lay out the proper roll pattern on the transition. Simply go over the lines with a ruler and pencil to make the lines fully visible and where they intersect with the "halfway mark" you put on the transition earlier with the drafting compass establishes the roll pattern. Once the transition is marked, cut out, embossed, test fitted, and glued up, it's then ready to glue over the foam transition core. Some final trimming pretty much finished it off. I added a paper "ring" about 1/8 inch wide to the top of the BT-80 coupler tube at the transition base to make a positive step "shoulder" to keep the transition from going too far into the tube, especially under the gee forces and drag pressure of flight. I topped this thin paper ring with a decorative ribbed paper "wrap" to smooth the blend with the corrugated transition wrap above.

Next is the F-1 engine fairings. After some more calculations with the "Rockets of the World" photocopy 'worksheet', I determined that BT-55 was pretty darn close to the correct size for the fairings. Going back to the online transition tool, I printed off a "tranistion" which was basically a paper cone... the transition tool wouldn't accept "0" as a 'custom tube size' so I put "0.010 inches" as the upper tube diameter, and it worked... it printed out an cone with a TINY circle at the upper end which I then subsequently ignored in cutting out the fairing patterns. Again, since the fairings are a HALF circle, you cut the pattern in half using the "second fin line" halfway around the circumference of the cone. Next, emboss the pattern similarly to how was done with the upper stage tranistion, but this is a bit more difficult since ALL the corrugations would converge at the point. It's best to end every other one about 3/8 inch or so from the fairing "tip", or even every 2 for each 1 that goes all the way to the tip. This makes a neater looking fairing. Next, the four transitions are glued to the outside of a BT-55 tube, using white glue and set aside to dry...

Here's the completed transition, on top of the S-II stage tube

More later! OL JR
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