Scratch El Cheapo Pyramid Original Design / Scratch Built

Scratch - El Cheapo Pyramid {Scratch}

Contributed by Dick Stafford

Manufacturer: Scratch
(Contributed - by Dick Stafford - 06/09/08)

Brief:
This is a simple mid-powered pyramid that flies on either one 29mm motor and/or three 24mm motors. The finishing matches the construction materials--'el cheapo'.

Construction:
The parts list:

  • four carrugated cardboard triangles, 12" base and 13.75" sides
  • plywoods square, 4" x 4"
  • one 3.25" 29mm tube
  • three 3.25" 24mm tubes
  • 1/4" lug
  • lead shot
  • duct tape

I started by attaching the cardboard triangles to form a pyramid. These were attached with epoxy and the joints were covered (hidden) with duct tape. The motor support plate was a scrap piece of 1/4" plywood. Before this was attached, I located the motor tube locations and drilled a hole for the lug. As the plate was epoxied into place, I measured the distance to each corner to make sure it was even. To find the location of the launch lug hole in the top of the pyramid, I dry-fit a 1/4" lug and used a rod to start a hole. I finished the hole with a hobby knife. After the lug was attached, I cut it flush to match the angle of the pyramid's side.

The theoretical CP of a pyramid is 1/3 of its height up from the base. I added lead shot to get the CG ahead of this point (as best as I could estimate). I now know from Bruce Levison's analyses that the CP is probably behind the bottom due to base drag effects.

Finishing:
There was no real finishing. To keep with the pyramid theme I found on on-line hieroglyphic translator and drew the various characters with felt-tipped markers (very high class). The 4 sides say:

  1. Beware all who enter here
  2. El Cheapo Pyramid of Death
  3. No BATFE (shown in one photo)
  4. Miscellaneous characters (shown in another photo)
  5. Flight:
    This rocket has flown once on a G38 and once on three E9s. The G38 flight was nice and smoky with the low pressure area at its base clearly visible. The E9s made for a slow boost and the rocket seemed to stop abruptly at burn-out. In both cases, the pyramid fell nose first slowly to the ground.

    Summary:
    This was a simple, inexpensive, and fast build. Everyone who likes saucers, pyramids, etc. should build one. Not necessarily exactly like this one. You can even paint it :)

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