# Validation Log

## Validation Scenario 1: Parachute Landing in 8 m/s Wind (200th landing)

### Expected Based on Conclusions

**Approach A (S2 FG + CF stiffeners)**: UAV lands at 9.2 m/s resultant velocity, 762 J impact energy. FG belly skin absorbs initial impact — possible crack, repairable with field patch. CF wing spar stiffeners experience shock loading. After 200 landings, accumulated micro-delamination in CF stiffeners is possible but invisible without NDT. The stiffeners might be at 70-90% original strength without any visible indication. Operator has no way to know without ultrasonic inspection.

**Approach B (pure GFRP, Shark M style)**: Same impact conditions. FG belly absorbs impact — same crack/dent pattern. FG internal stiffening ribs absorb shock by flexing. Any damage is visible (cracking, whitening). After 200 landings, operator can visually assess the entire airframe and decide to replace worn components. No hidden degradation.

### Actual Validation
The Shark M has performed thousands of such landings in operational service. The design is validated by 50,000+ hours of combat operations. The hidden damage accumulation scenario (Approach A) is a real engineering concern documented in aerospace literature (BVID in CFRP is a well-known problem).

### Counterexamples
- Approach A could be validated if CF stiffeners are designed with high safety margins (oversized stiffeners that tolerate some delamination). This adds weight, partially negating the weight advantage.
- Some carbon fiber structures are designed for crash energy absorption (automotive) — but those are single-use absorbers, not reusable structural elements.

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## Validation Scenario 2: Long-Range Communication at 150 km, EW Environment

### Expected Based on Conclusions

**Approach A (S2 FG + CF stiffeners)**: C2 antenna inside fuselage. If antenna is placed between CF stiffeners (in FG-only zone), signal passes through FG skin with minimal attenuation. If antenna is near a CF stiffener, signal degrades by 30-50 dB in that direction → potential link loss. Requires careful antenna integration engineering during design.

**Approach B (pure GFRP)**: C2 antenna placed anywhere inside fuselage. 360° RF coverage through fuselage. Signal attenuated only by FG dielectric properties (minimal). The Silvus radio modem in Shark M achieves 180 km range through the GFRP fuselage.

### Actual Validation
Shark M demonstrates 180 km range with confirmed EW resistance. The user's direct experience confirms radio transparency. Shark M's Silvus-based communication system operates at full capability through the GFRP airframe.

### Counterexamples
- The hybrid approach can achieve good RF performance if stiffeners are designed to avoid antenna zones. Many military UAVs use carbon fiber with external antennas successfully.
- If antennas are mounted externally (on wings, tail boom), the fuselage material is less critical for RF performance. However, external antennas are vulnerable to parachute landing damage and increase drag.

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## Validation Scenario 3: Weight-Critical Endurance Mission

### Expected Based on Conclusions

**Approach A (S2 FG + CF stiffeners)**: Lighter airframe by 300-800g. At 18 kg MTOW, this translates to larger battery or more fuel → 6-24 minutes additional endurance. For a 7-8h mission, this is 1-5% improvement.

**Approach B (pure GFRP)**: Heavier airframe. Must compensate with slightly reduced payload or accept lower endurance. Shark M achieves 7h at 14.5 kg MTOW with pure GFRP — the user's UAV at 18 kg MTOW has different payload requirements.

### Actual Validation
The weight difference is real but modest relative to total system weight. Shark M proves that 7h endurance is achievable with pure GFRP. The question is whether the user's heavier payload (Viewpro Z40K vs Shark's USG-231) makes the weight savings from CF stiffeners more critical.

### Counterexamples
- If the user can meet endurance requirements with pure GFRP, the CF stiffeners are unnecessary complexity
- Weight savings might be achievable through other means (optimized FG layup, foam sandwich cores, lighter internal components) without introducing CF

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## Review Checklist
- [x] Draft conclusions consistent with fact cards
- [x] No important dimensions missed
- [x] No over-extrapolation
- [x] Conclusions actionable/verifiable
- [x] Field evidence (Shark M) validates pure GFRP approach
- [x] Weight trade-off quantified with reasonable estimates
- [ ] Note: Exact weight penalty of pure GFRP vs hybrid cannot be determined without detailed structural analysis of specific airframe geometry
