# Reasoning Chain

## Dimension 1: Radio Transparency

### Fact Confirmation
Carbon fiber composite provides 30-52 dB electromagnetic shielding across UHF to X-band (Fact #3). This means a carbon fiber structural element blocks 99.9% to 99.999% of RF energy passing through it. S2 fiberglass is radio-transparent — standard radome material with dielectric constant ~4.4 at 8.5 GHz (Fact #4). The ACASIAS project proved that CFRP ribs in a GFRP panel create measurable electromagnetic interaction zones (Fact #14).

### Reference Comparison
**Approach A (S2 FG + CF stiffeners)**: The FG skin areas are fully RF-transparent. However, carbon stiffeners running through the fuselage create discrete RF shadow zones. Any antenna placed near or behind a CF stiffener will experience 30-50 dB signal degradation in that direction. This constrains antenna placement — antennas must be positioned in FG-only zones between stiffeners. For a UAV with multiple antennas (C2 link, video downlink, GPS, telemetry, ADS-B), this creates a spatial planning challenge. The stiffener geometry defines "forbidden zones" for antenna placement.

**Approach B (pure GFRP, Shark M)**: The entire fuselage is RF-transparent. Antennas can be placed anywhere inside or on the fuselage without material-induced signal blockage. GPS, C2, video, telemetry antennas have no placement constraints from the airframe material. This is confirmed by Shark M's operational success with 180 km communication range and EW resistance (Fact #6).

### Conclusion
Pure GFRP has a clear advantage for radio transparency. The hybrid approach is workable but requires careful antenna placement engineering. For a reconnaissance UAV operating at long range (100+ km) in EW-contested environments, unconstrained antenna placement is a significant operational advantage.

### Confidence
✅ High — supported by quantitative RF data, aerospace project (ACASIAS), and field experience

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## Dimension 2: Radar Transparency (Stealth)

### Fact Confirmation
GFRP is inherently dielectric and transparent to radar waves (Fact #5). Carbon fiber, while not as reflective as metal, is conductive and reflects/scatters radar energy. The PD-2/Shark design philosophy explicitly leverages "fully composite airframe + absence of large metal parts" for "low radar visibility" (Fact #1).

### Reference Comparison
**Approach A**: Carbon stiffeners create discrete radar-reflective structures inside the airframe. While individually small, their regular geometric pattern could create a detectable radar signature at certain angles — essentially a grid of conductive elements acting as a partial radar reflector.

**Approach B**: Pure GFRP is essentially invisible to radar (the signal passes through). Radar cross section comes only from metallic components (engine, servos, connectors) and the payload, not the airframe itself.

### Conclusion
For military reconnaissance in contested airspace, pure GFRP provides a stealth advantage. Carbon stiffeners slightly increase radar detectability. The magnitude depends on stiffener geometry and radar frequency, but the principle is clear: less conductive material = lower RCS.

### Confidence
⚠️ Medium — the magnitude of RCS increase from stiffeners vs pure GFRP is not quantified; the principle is sound but the practical significance depends on adversary radar capabilities

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## Dimension 3: Parachute Landing Impact Survivability

### Fact Confirmation
From solution_draft05: parachute landing impact energy ranges from 190 J (calm) to 762 J (8 m/s wind) to 1,499 J (12 m/s wind) for an 18 kg UAV. S2 glass fiber with cross-ply layup absorbs impact energy effectively with no penetration (Fact #9). Carbon fiber fails in a brittle manner — sudden delamination and fiber fracture (Fact #7). BVID in carbon fiber reduces structural integrity without visible signs (Fact #7). Fiberglass bends/deforms rather than cracking (Fact #8).

### Reference Comparison
**Approach A (S2 FG + CF stiffeners)**: The FG skin absorbs belly landing impact well — it will dent, flex, and possibly crack locally but without catastrophic failure. However, if impact loads are transmitted to CF stiffeners (which they will be, since stiffeners carry structural loads), the CF elements may suffer BVID. This internal damage is invisible but weakens the structure progressively. After multiple parachute landings, CF stiffeners could accumulate micro-delaminations that are detectable only via ultrasound or tap testing.

**Approach B (pure GFRP)**: The entire structure responds to impact by flexing and absorbing energy. Damage is typically visible (cracks, dents, whitening of the resin). No hidden BVID in brittle elements. The structure degrades gracefully — visible damage allows timely repair/replacement.

### Conclusion
Pure GFRP is significantly better suited for repeated parachute landings. The key advantage is not just better single-impact performance, but the absence of hidden damage accumulation in brittle carbon elements. For a UAV expected to land on a parachute hundreds of times, this is critical.

### Confidence
✅ High — supported by materials science (CF brittleness is well-documented) and field evidence (Shark M's 50,000+ hours with parachute landings)

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## Dimension 4: Cumulative Damage and Inspection

### Fact Confirmation
Carbon fiber BVID requires non-destructive testing (ultrasound, Lamb wave techniques) to detect (Fact #7, #13). Fiberglass damage is generally visible — cracking, whitening, deformation (Fact #8, #12). Field inspection of FG requires visual inspection; field inspection of CF stiffeners requires ultrasonic equipment.

### Reference Comparison
**Approach A**: After each parachute landing, operators should theoretically inspect CF stiffeners for BVID. In field conditions (battlefield, remote area), ultrasonic inspection is impractical. This creates a reliability risk — the aircraft may fly with undetected internal damage.

**Approach B**: Visual inspection sufficient. Operators can see damage and decide whether to fly or repair. Simple tap-test can detect larger delaminations. No special equipment needed.

### Conclusion
Pure GFRP provides much simpler damage inspection, which is critical for field operations. The inspection advantage compounds over the UAV's lifetime — hundreds of landings, each requiring either a quick visual check (GFRP) or an NDT scan (hybrid with CF).

### Confidence
✅ High

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## Dimension 5: Weight Efficiency

### Fact Confirmation
Carbon fiber density ~1.5-1.6 g/cm³ vs fiberglass 2.46-2.58 g/cm³ (Fact #10). CF is ~5× stiffer per unit weight. CF stiffeners achieve similar structural performance to pure CFRP with hybrid approach (Fact #15). Stiffener optimization achieves 60.9% stress reduction (Fact #16).

### Reference Comparison
**Approach A**: CF stiffeners provide excellent stiffness at low weight. A few hundred grams of CF stiffeners can replace kilograms of FG stiffening. This is the primary reason for using the hybrid approach — to achieve the required wing/fuselage stiffness without the weight penalty of all-FG construction.

**Approach B**: Must compensate for lack of CF stiffness with more FG material. This means thicker skins, more internal FG ribs, or geometric stiffening (corrugations, foam sandwich). Results in a heavier airframe for equivalent stiffness. Shark M achieves 14.5 kg MTOW with pure GFRP — so it works, but the user's UAV at 18 kg MTOW with heavier payload (Viewpro Z40K + electronics) may benefit from the weight savings of CF stiffeners.

### Conclusion
Hybrid approach has a clear weight advantage. For a reconnaissance UAV maximizing endurance, every 100g saved translates to ~2-3 minutes additional flight time. If CF stiffeners save 300-800g vs equivalent pure GFRP stiffening, that's 6-24 minutes additional endurance. This is meaningful but not dramatic.

### Confidence
✅ High — materials properties are well-established; the magnitude estimate depends on specific structural design

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## Dimension 6: Material Cost

### Fact Confirmation
CF cloth is 5-10× more expensive than FG cloth per m² (Fact #11). In the hybrid approach, only stiffeners use CF — perhaps 10-20% of total composite material by area.

### Reference Comparison
**Approach A**: Moderate cost increase. If total FG material cost for an airframe is ~$300-500, adding CF stiffeners might add $100-300 for the CF material itself, plus slightly more complex layup procedures.

**Approach B**: All-FG, minimal material cost. Simplest manufacturing.

### Conclusion
The cost difference is moderate, not dramatic. The hybrid approach costs more but not prohibitively so for a military UAV.

### Confidence
✅ High

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## Dimension 7: Field Repairability

### Fact Confirmation
FG/epoxy field repair requires no specialized training or vacuum equipment (Fact #12). CF repair is more complex, requiring specialized knowledge and ideally autoclave/vacuum bagging (Fact #13).

### Reference Comparison
**Approach A**: If the FG skin is damaged, field repair is straightforward. If a CF stiffener is damaged, field repair is significantly harder — the operator may need to fabricate a CF patch, which requires proper layup, vacuum bagging, and controlled cure. In practice, a damaged CF stiffener in the field likely means the UAV is grounded until returned to base.

**Approach B**: All damage is FG, all repairs are FG. Personnel with average manual skills can perform field repairs with epoxy and FG cloth patches.

### Conclusion
Pure GFRP is much better for field repairability, especially in expeditionary/forward-deployed scenarios. This matters for the user's military use case.

### Confidence
✅ High

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## Dimension 8: Proven Operational Track Record

### Fact Confirmation
Shark M has 50,000+ operational hours with parachute landings in combat (Fact #17). The user has direct operational experience confirming radio transparency (Fact #6). The hybrid S2 FG + CF approach is unproven for this specific application.

### Reference Comparison
**Approach A**: Novel design, not combat-proven. Introduces CF stiffeners which are new variables in the parachute-landing reliability equation.

**Approach B**: Combat-proven in the most demanding environment possible (active warfare with EW, harsh conditions).

### Conclusion
Pure GFRP has massive advantage in proven reliability. This cannot be understated — a combat-proven material system that demonstrably works for this exact mission profile (long-endurance reconnaissance, catapult + parachute, EW-contested) is extremely valuable evidence.

### Confidence
✅ High
