FSAE RW Internal Structure Project - Documentation in Progress

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Introduction

The goal of this study is to compare the stiffness-to-weight performance between two RW mainplane internal structure concepts: sandwich panel reinforcement (Clifford) and spar reinforcement. We will see if the sparred design can yield weight loss that is worth the added manufacturing complexity, while maintaining the same if not higher stiffness. The study will be based off of the RW mainplane geometry/load from last year. This document records the study uptill IDR for the most part. Since IDR, I moved onto the updated 2026 RWMP geometry and more detailed strength/deflection analysis, which will be recorded in another document. 

Sparred Concept Design

Spars

  • We chose to chop up the ribs to keep the spars continuous, because it is harder to maintain spanwise rigidity​
  • Carbon fiber C-channel for spars​
  • Maximize area moment of inertia while keeping the crosssections a continuous profile for ease of layup​
  • Goes around the ribs for maximum area of contact foradhesives​
  • Manufacturing will be discussed in later slides​

Ribs 

  • 4 ribs
    • Two for endcap inserts, two for strut connection
  • Full length ribs doesn't make a lot of sense anymore
    • It is chopped into segments due to spars
    • The parts in front of and behind the spars have no mechanical connection to the 
      mounting points except adhesives
    • Mainly for supporting the leading/trailing edge

3D Printed Leading/Trailing Edge Support

  • Full length rib replaced with 3D printed supports
    • It solves leading edge crushing from stagnation point
    • Help maintain slot gap at the trailing edge
    • Less weight V.S. aluminum
    • More area of contact for adhesives V.S. aluminum
    • Easy to iterate
    • Potentially help accounting for tolerance stack-up within the assembly

Manufacturing plan

  • Spars
    • 3D print the spar mold in pieces with alignment features
    • Preliminary deburring + sanding
    • Epoxy+dowel pin together
      • In retro - get actual dowel pins or threaded rods, cutting bolts as dowel pin is suboptimal
    • VARTM with chassis tool carbon and high temperature epoxy
      • In retro - We had to constantly heat up the epoxy with heat gun to lower the viscosity in order for it to flow properly for VARTM. This shortens the curing time but seems like it is still more than enough for the infusion process. Maybe a heating blanket can be a better tool for this? It would be nice if we can find high temperature resin with lower viscosity at room temp. Peter Zhao Recommends FibreGlast System 4600
  • Airfoil
    • Duratec the mold surface to fill gaps and fill corners
    • Applied mold sealer - Easycomposite S120

Sandwich Panel Concept Design

  • Largely the same as last year
  • The design was cleaned up a little
  • [0/45/0] 0.25" core SYM lower surface + [0/45/0] upper surface

Weight Calculations

RW MP Trade Study Weight Tracker.xlsx

Sparred Concept FEA Analysis

ACP setup

Good tutorial on ACP:

To simplify the ACP process, I created a creo part file with only the surfaces I will be doing ACP on. Remember to check on which side are the plies laid up on to ensure that the parts are indeed the right geometry. You can change which side to lay up on by flipping the direction of the oriented selection set in ACP. 

Loads & Boundary Conditions

For this study I used force data from last year's WBPJ file. It is just two forces loaded onto the top surface and the bottom surface, with fixed support at the strut mounting holes. 

 

Sandwich Panel Concept FEA Analysis

ACP setup

Remember to do named selection for the upper and lower surface of the airfoil respectively so that you can set them to different stackups and solid bodies. Only the lower surface has core. 

Loads & Boundary Conditions

Data

As shown by the weight calculator, the sandwich panel design with [0/45/0] 0.25" core SYM lower surface + [0/45/0] upper surface will end up with similar weight with 10 ply spar + 3 ply surface. I believe that the design with less deflection out of the two can end up with less weight when targeting the same stiffness target. 

Sparred design: 

Sandwich panel design: 

maximum surface deflection

maximum mounting point deflection

Sparred design

6.17mm 

15.55mm

Sandwich panel design

3.37mm

7.04mm

 

Conclusions

We are seeing deflection numbers are nearly halfed with the sparred design, which gives me confidence that such design is worth pursuing for this year's new RW geometry. 

Next Step

Bond analysis, bolt sizing, ply schedule optimization and sheet metal sizing will be done on the new RW geometry with updated loads. 

SS Dump for Future Organization

 

 

 

 

 

  

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