P1: Nitrous at Balls in '08

Airframe Design Notes

Notes on carbon-fiber airframe tube construction

Last Update, 7/10/07 by Stephen Daniel

Design Goals:

  • 4" tubing, pieces up to 28" long
  • light weight
  • smooth finish
  • moderate cost
  • capable of super-sonic flight

Fabric Supplies:

  Material Width Price per Yard  Supplier
4.1oz Uni Tape 2" $1.77 Soller Composites
6 oz 3K Plain Weave 39" $26.73 Soller Composites
6 oz 3K Plain Weave 50" $30.99 Soller Composites
5.5oz, 4HS Weave 30" $20.28 Mr. Fiberglass
5.7oz, Plain or 2x2 Twill Weave 50" $46.50 Mr. Fiberglass
11 oz, carbon uni tape 13" $10.71 Mr. Fiberglass
5.7 oz 3K TOW 42" $58.40 (on sale) The Composite Store
5.7 oz 3K TOW 50" $75.75 The Composite Store
3 oz carbon uni tape 11.5" $19.50 The Composite Store
0.2 oz carbon tissue 35.5" $15.95 The Composite Store

Current Thoughts

  • Current plans call for the motor to be exposed, i.e. no airframe tubing over the motor. This means that the longest piece of tube we need to fabricate is perhaps 28 inches.
  • I had been assuming that in order to use uni-directional CF I would need to buy a 12.5" wide unidirectional tape. However, I see no reason why I cannot put a number of narrower pieces next to each other.

  • I propose to build the airframe tubing with these layers:
    • Inner most layer will be PML 3.9" craft phenolic. This layer provides shape and takes compressive loads.
    • Each end of the tube will be wrapped in a single layer of 4.1 oz 2" uni tape. This will help stabilize the ends against wear and zippering.
    • Next layer will be a single layer of Soller's 4.1oz unidirectional CF. I will set this up by wetting the tube with a thin layer of epoxy and then lay out out 7 strips of 2" CF tape down the length of the tube. This will cost about $21 for the CF.
    • Next layer will be a single wrap of Soller's 6 oz 3K plain weave. This will cost about $10.
    • All of this will be wetted out with Mr. Fiberglass slow cure epoxy.
    • To make the finish nice I will wrap the entire tube in .005" mylar before curing.
    • Curing will involve heat-shrink tape to tighten everything down, then curing in Mike Harris' tube oven.
  • The fin can will sit directly on the motor casing's thrust ring. Fabrication thoughts:
    • Use a piece of 4" aluminum tube as the mandrel.
    • The fin can will be perhaps 8" long.
    • Primary goal is strength without stretching. I plan to build it out of 3 wraps of Soller's 6 oz plain weave CF. A wrap of 2" of uni tape will be applied at each end, between the first and second layer.
    • Finish will be with peal-ply to provide a good surface for the fin roots to adhear.

Materials Selected


  • 50" Soller plain weave
  • 2" Soller uni tape

Fin Can -- presumed to be 8" long

  • 13" of Soller plain weave for the three layers (leaves 25" x 13" scrap)
  • 26" of Soller uni tape for the tube end wraps
  • 30" of uni tape plus scrap plain weave to stiffen the fins

Aft tube -- presumed to be 24" long (worst case)

  • Use the 25" by 13" scrap from the fin can
  • 26" of Soller uni tape for the tube end wraps
  • 14' of uni tape for the bottom layer

Foreward tube -- presumed to be 36" long (worst case)

  • 13" of plain weave (no usable scrap)
  • 26" of uni tape end wraps
  • 21' of uni tape for the bottom layer

Net Order

  • 1 yard of 50" plain weave
  • 44 feet of uni tape (however, the price break makes it cheaper to order 50')