# Comparison Framework

## Selected Framework Type
Concept Comparison + Decision Support

## Compared Approaches
- **Approach A**: S2 Fiberglass + Carbon Fiber Stiffeners (hybrid, as selected in solution_draft05)
- **Approach B**: Pure Fiberglass Composite (inferred Shark M approach — GFRP, no carbon elements)

## Selected Dimensions

### Primary (directly requested by user)
1. Radio transparency (communications: 900 MHz, 2.4 GHz, 5.8 GHz)
2. Radar transparency (stealth / low RCS)
3. Parachute landing impact survivability
4. Parachute landing cumulative damage tolerance

### Secondary (engineering trade-offs)
5. Weight efficiency (strength-to-weight, stiffness-to-weight)
6. Structural stiffness
7. Material cost
8. Field repairability
9. Proven operational track record
10. Hidden failure modes

## Initial Population

| Dimension | S2 FG + Carbon Stiffeners (Approach A) | Pure GFRP (Approach B, Shark M) | Factual Basis |
|-----------|---------------------------------------|--------------------------------|---------------|
| Radio transparency | Mostly transparent (FG skin is RF-transparent); carbon stiffeners create localized RF shadow zones; antenna placement must avoid CF elements | Fully transparent — entire fuselage passes RF; antenna placement unconstrained | Fact #3, #4, #5, #6, #14 |
| Radar transparency | Mostly transparent; CF stiffeners reflect radar → slight increase in RCS compared to pure FG | Fully radar-transparent (low RCS by transparency) | Fact #5, #14 |
| Impact survivability (single event) | FG skin absorbs impact well; CF stiffeners may crack/delaminate under localized impact; BVID risk in CF elements | FG absorbs impact, bends rather than cracks; no brittle CF elements; simpler damage profile | Fact #7, #8, #9 |
| Cumulative damage tolerance | FG skin handles repeated impacts; CF stiffeners accumulate micro-damage that is hard to detect | All-FG structure: damage is visible, cumulative tolerance is good, easier inspection | Fact #7, #8, #13 |
| Weight efficiency | Better — CF stiffeners provide stiffness at lower weight than equivalent FG stiffening | Heavier — must use thicker FG skins or more material to achieve same stiffness | Fact #10, #15, #16 |
| Structural stiffness | Higher — CF stiffeners ~5× stiffer per unit weight than FG | Lower — FG is more flexible; adequate for Shark M class but may need design compensation | Fact #10, #15 |
| Material cost | Higher — CF cloth is 5-10× FG cost; only stiffeners are CF, so total cost increase is moderate | Lower — all FG, significantly cheaper material cost | Fact #11 |
| Field repairability | FG skin: easy field repair; CF stiffeners: harder, needs specialized knowledge to repair | All components field-repairable with basic skills and epoxy patches | Fact #12, #13 |
| Proven track record | Not yet built/tested | 50,000+ operational hours, 1,200h maintenance-free, combat-proven | Fact #17 |
| Hidden failure modes | CF stiffener BVID after impact — invisible internal damage reduces strength | None specific to material; pure FG damage is generally visible | Fact #7, #13 |
