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) (Scratch) El Cheapo Pyramid

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.

(Scratch) El Cheapo Pyramid 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. (Scratch) El Cheapo Pyramid

    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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