Assumptions:

  1. The fuselage is constructed as a hollow 3D printed shell laminated with fiberglass on each side: $[45/core/-45]$
  2. A 50/50 resin to fiber ratio is assumed: $W_{glass}=W_{epoxy}$
    1. Thus the weight of the laminate ($W_{lam}=W_{glass}+W_{epoxy}$), can be taken as: $W_{lam}=2W_{glass}$
  3. A composite ‘super factor’ of 1.50 is applied to the weight of the laminate to account for manufacturing inconsistencies
  4. A blanket factor of 1.10 is applied to account for the weight of filler, paint, and other coatings. (ie, assumed to be 10% of the overall mass)

*Both the composite ‘super factor’ and blanket factor are subject to change based on experimental results

Derivation:

  1. The estimated mass of a 3d-composite fuselage section is given as the weight of the 3D print and the weight of the composite laminate, multiplied by the blanket factor of 1.10 to account for the mass of paint, filler, and other coatings [Assumption 1]

    $$ \begin{equation} W_{fusesec,approx}=1.10*[W_{3DP}+W_{lam}] \end{equation} $$

  2. The estimated mass of the 3D printed section is taken from the mass estimated by the slicer software

    1. Assuming the use of Bambu Lab’s ASA-Aero as the standard filament,

    $$ W_{3DP}=W_{ASA} $$

  3. Estimated mass of a single ply composite laminate is given by the weight of the glass cloth and epoxy resin:

    $$ W_{lam}=W_{glass}+W_{epoxy} $$

    1. Given a 50/50 resin to fiber ratio [Assumption 2], the laminate weight is:

      $$ W_{lam}=2W_{glass} $$

    2. Weight of the glass cloth $W_{glass}$ is derived from the weight of the cloth per unit area, multiplied by the surface area of the laminate:

      $$ W_{glass}=A_{surf}*W_{glass/area} $$

    3. Applying the above to our fuselage, the weight of the glass on the outer surfaces of the fuselage is driven by the cloth weight $W_{glass/area}$ and the surface area of the outer fuselage section $A_{surf,fusesec}$:

      $$ W_{glass}=A_{surf,fusesec}*W_{glass/area} $$

    4. For simplicity, the inner surface area of the fuselage is taken to be equivalent to the outer surface area. Thus, the mass of the glass cloth for both the outer and inner fuselage is:

      $$ W_{glass}=(2*A_{surf,fusesec}*W_{glass/area}) $$

  4. Thus, mass of the composite laminate, factoring in the ‘super factor’ [Assumption 3], is:

    $$ W_{lam}=1.5[2*(2A_{surf,fusesec}W_{glass/area})]\\W_{lam}=1.5(4A_{surf,fusesec}*W_{glass/area}) $$

  5. We can now estimate weight of a fuselage section given a slicer estimated weight for the 3D printed shell and the outer surface area of the fuselage section; equation $(1)$ can now be expressed as:

$$ \boxed{W_{fusesec,approx}=1.10*[W_{ASA}+1.5*(4*A_{surf,fusesec}*W_{glass/area})]} $$

Example:

A 3D-composite fuselage section is constructed with a shell printed of ASA-Aero filament, laminated with a single layer of 2.74oz/yd^2 fiberglass on the inner and outer walls. The outer surface area of the fuselage is 85 in^2, and the slicer estimates the section to weigh 0.176 lbs.

Given Data: