gps-denied-onboard/_standalone/UAV_frame_material/01_solution/solution_draft04.md

Solution Draft (Rev 04) — Launch & Recovery Assessment

Assessment Findings

Old Component Solution	Weak Point	New Solution
No launch/recovery method specified	Aircraft cannot operate without a defined takeoff/landing approach	Two viable options analyzed: Quad VTOL (recommended for field ops) or Catapult + Parachute (recommended for maximum endurance)
Y-3 tricopter VTOL (user proposed)	Zero motor redundancy, tilt servo failure risk, no production platforms use Y-3	Quad (4+1) VTOL — industry standard used by DeltaQuad, YUAV Y37, WingtraOne
YUAV Y37 listed as 17-20 kg MTOW	Product page confirms TOW 22-26 kg; 10 kg empty weight with VTOL system	Corrected Y37 specs: TOW 22-26 kg, empty 10 kg (with VTOL), 4+1 config, $16,900 PNP
18 kg MTOW design (Draft 03)	Cannot accommodate VTOL within 18 kg — VTOL system adds 2.5-3.2 kg	Option A: raise MTOW to 21-22 kg for VTOL variant; Option B: keep 18 kg for catapult variant

Product Solution Description

Two platform variants from the same S2 FG airframe, optimized for different operational needs:

Variant A — Quad VTOL (recommended for forward/mobile operations): Scaled-up modular S2 FG fixed-wing with 4+1 quadplane VTOL. Wingspan 3.8m, MTOW 21-22 kg. 4 dedicated VTOL motors on carbon fiber tube booms + 1 pusher for cruise. Separate VTOL battery (12S 5500 mAh). Endurance 6.5-7.5 hours. Launches and recovers from any 5m × 5m flat area. No ground equipment needed.

Variant B — Catapult + Parachute (recommended for maximum endurance from established bases): Same S2 FG fixed-wing, no VTOL hardware. Wingspan 3.8m, MTOW 18 kg. Pneumatic catapult launch (ELI PL-60 class). Parachute recovery (Fruity Chutes 20 kg bundle). Endurance 8-8.5 hours. Requires 108 kg catapult system and 8m launch space.

VARIANT A — QUAD VTOL (4+1)
┌───────────────────────────────────────────────────────────┐
│                                                           │
│   VTOL Motor 1              VTOL Motor 2                  │
│     (front-left)              (front-right)               │
│     ⟐ 15" prop               ⟐ 15" prop                  │
│      \                        /                           │
│       \     CF tube boom     /                            │
│        \                    /                             │
│    ┌────────────────────────────┐                         │
│    │   LEFT     FUSELAGE   RIGHT│                         │
│    │   WING     [VTOL bat] WING │                         │
│    │   1.9m     [Cruise    1.9m │                         │
│    │            batteries]      │       Pusher motor      │
│    │            [Payload]  ─────┤────── ⊕ (cruise)        │
│    └────────────────────────────┘                         │
│        /                    \                             │
│       /     CF tube boom     \                            │
│      /                        \                           │
│     ⟐ 15" prop               ⟐ 15" prop                  │
│   VTOL Motor 3              VTOL Motor 4                  │
│     (rear-left)               (rear-right)                │
│                                                           │
│   Motor booms: CF tubes (narrow, minimal RF impact)       │
│   Boom-wing joints: aluminum brackets with S2 FG layup    │
└───────────────────────────────────────────────────────────┘

VARIANT B — CATAPULT + PARACHUTE
┌───────────────────────────────────────────────────────────┐
│                                                           │
│    ┌────────────────────────────┐                         │
│    │   LEFT     FUSELAGE   RIGHT│                         │
│    │   WING     [Parachute WING │                         │
│    │   1.9m      bay + hatch]   │       Pusher motor      │
│    │            [Cruise    1.9m │                         │
│    │            batteries]      │       ⊕ (cruise)        │
│    │            [Payload]  ─────┤───────                  │
│    └────────────────────────────┘                         │
│                                                           │
│   No motor booms = cleaner aerodynamics                   │
│   Parachute bay with spring-loaded hatch (top/bottom)     │
│   Catapult carriage mounting rails on belly               │
└───────────────────────────────────────────────────────────┘

Why Not Y-3 (Tricopter)?

The user asked specifically about Y-3 (3-motor) VTOL. After research, Y-3 is not recommended for this application:

Factor	Y-3 (Tricopter)	Quad (4+1)
Weight saving vs quad	~400g less	Baseline
Motor redundancy	Zero — any motor failure = crash	Partial — single motor loss survivable
Yaw control	Tilt servo on rear motor (mechanical failure point)	Differential thrust (no moving parts)
Production platforms using this	None found in 15-25 kg class	DeltaQuad, YUAV Y37, WingtraOne
ArduPilot support	Supported but less tested	Well-tested, widely deployed
Hover stability	Lower (3-point, asymmetric)	Higher (4-point, symmetric)

The 400g weight saving (~2% of MTOW) does not justify the reliability and redundancy loss. For a $15,000-17,000 aircraft in a conflict zone, motor redundancy is critical.

Architecture

Component: Launch & Recovery System

Solution	Weight on Aircraft	Ground Equipment	Endurance	Landing Precision	Cost (airborne)	Cost (ground)	Deployment Speed	Fit
Quad VTOL (recommended for field ops)	+3.0-3.2 kg	None	6.5-7.5h	1-2m	$1,000-1,500	$0	< 2 min	✅ Best for mobile ops
Catapult + Parachute (recommended for max endurance)	+0.95 kg	108 kg catapult	7.5-8.2h	50-200m drift	$925	$15,000-25,000	5-10 min	✅ Best for endurance
Catapult + Belly landing	0 kg	108 kg catapult + 200m strip	8-8.5h	On strip	$0	$15,000-25,000	5-10 min + strip	⚠️ Needs flat terrain
Y-3 VTOL	+2.5-2.7 kg	None	7-7.5h	1-2m	$800-1,200	$0	< 2 min	❌ Reliability risk

Component: VTOL System (Variant A — Quad)

Component	Specification	Weight	Cost
VTOL motors (×4)	T-Motor MN505-S or equiv., ~5-6 kg thrust each on 15" prop	880g total	$400-600
VTOL ESCs (×4)	40A BLHeli_32 or equiv.	320g total	$120-200
VTOL propellers (×4)	15" folding (fold for cruise to reduce drag)	200g total	$60-100
Motor booms (×4)	Carbon fiber tubes 20mm OD, 400mm length + aluminum brackets	700g total	$150-250
VTOL battery	12S 5500 mAh LiPo (dedicated)	700g	$120-180
Wiring + connectors	12AWG silicone, XT60 connectors	180g	$30-50
VTOL system total		2,980g	$880-1,380

Component: Catapult System (Variant B)

Component	Specification	Weight/Size	Cost
Pneumatic catapult	ELI PL-60 or equivalent	108 kg (2 cases)	$15,000-25,000 est.
Catapult carriage	Custom for UAV fuselage, quick-release	~2 kg (stays on ground)	Included or $500 custom
Belly mounting rails	Aluminum rails on fuselage for carriage attachment	~150g on aircraft	$50

Component: Parachute System (Variant B)

Component	Specification	Weight	Cost
Fruity Chutes FW bundle 20 kg	IFC-120-S Iris Ultra + pilot chute + deployment bag + Y-harness	950g	$925
Servo-actuated hatch	Spring-loaded door on fuselage top/bottom, triggered by autopilot	80g	$30
Recovery system total		1,030g	$955

Updated Weight Budgets

Variant A — Quad VTOL (21 kg MTOW)

Component	Weight (kg)	Notes
Airframe (S2 FG, 3.8m, reinforced for VTOL loads)	6.0-7.0	+0.5 kg structural reinforcement at boom attach points
Wing joints (aluminum 7075)	0.35	Same as Draft 03
Motor (800W cruise) + ESC + prop	0.65	Slightly larger to handle higher MTOW
Wiring, connectors (cruise)	0.45	Same as Draft 03
VTOL system	2.98	4 motors, 4 ESCs, 4 props, booms, VTOL battery, wiring
Platform subtotal	10.4-11.4
Payload (cameras + compute)	0.89	Same as Draft 03
Cruise battery (4× Tattu 6S 33Ah)	8.86	Same as Draft 03
Total	20.2-21.2

Conservative: 11.4 + 0.89 + 8.86 = 21.15 kg (at 21 kg MTOW — tight) Optimistic: 10.4 + 0.89 + 8.86 = 20.15 kg (0.85 kg margin)

To fit 21 kg MTOW: reduce to 3× cruise battery packs (6.65 kg, 2198 Wh) → total 18.9-19.9 kg → endurance ~5.5-6.5h. Or accept 22 kg MTOW → endurance ~6.5-7h with 4 packs.

Variant B — Catapult + Parachute (18 kg MTOW)

Component	Weight (kg)	Notes
Airframe (S2 FG, 3.8m)	5.5-6.5	Same as Draft 03
Wing joints (aluminum 7075)	0.35	Same
Motor (700W cruise) + ESC + prop	0.6	Same as Draft 03
Wiring, connectors	0.45	Same
Catapult belly rails	0.15	Aluminum mounting interface
Parachute system	1.03	Chute + hatch mechanism
Platform subtotal	8.1-9.1
Payload (cameras + compute)	0.89	Same
Cruise battery (4× Tattu 6S 33Ah)	8.86	Same
Total	17.9-18.9

Conservative: 9.1 + 0.89 + 8.86 = 18.85 kg (slightly over 18 kg; accept 19 kg MTOW or trim airframe) Optimistic: 8.1 + 0.89 + 8.86 = 17.85 kg (fits within 18 kg ✓)

Endurance Comparison

Variant A — Quad VTOL

MTOW	Battery Config	Usable Energy	Cruise Power	Endurance (practical)
21 kg	4× 6S 33Ah (2930 Wh)	2344 Wh	~310W	7.0-7.5h
22 kg	4× 6S 33Ah (2930 Wh)	2344 Wh	~330W	6.5-7.0h
20 kg	3× 6S 33Ah (2198 Wh)	1758 Wh	~295W	5.5-6.0h

Cruise power increase vs Draft 03: higher MTOW (21-22 vs 18 kg) + ~3-5% additional drag from VTOL booms.

P_cruise (21 kg) = (21 × 9.81 × 17) / (17 × 0.72) × 1.04 = ~310W (including boom drag penalty)

Variant B — Catapult + Parachute

MTOW	Battery Config	Usable Energy	Cruise Power	Endurance (practical)
18 kg	4× 6S 33Ah (2930 Wh)	2344 Wh	~275W	8.0-8.5h
19 kg	4× 6S 33Ah (2930 Wh)	2344 Wh	~285W	7.5-8.0h

Parachute adds ~1 kg but no aerodynamic penalty (stowed internally).

Summary

Variant	MTOW	Endurance	vs Draft 03 (8-8.5h)
A: Quad VTOL (4 packs)	21-22 kg	6.5-7.5h	-12-20%
A: Quad VTOL (3 packs)	20 kg	5.5-6.0h	-30-35%
B: Catapult + Parachute	18-19 kg	7.5-8.5h	-0-6%
B: Catapult + Belly	18 kg	8-8.5h	0%

Cross-Validation Against YUAV Y37

The Y37 is the closest production reference for our VTOL variant:

Parameter	YUAV Y37	Our Variant A (Quad VTOL)	Delta
Wingspan	3.7m	3.8m	+3%
Empty weight (with VTOL)	10 kg	10.4-11.4 kg	+4-14% (S2 FG heavier than carbon)
MTOW	22-26 kg	21-22 kg	Similar
Battery energy	2700 Wh	2930 Wh	+9%
Endurance (1 kg payload)	8.5h	~7h (est. at 0.89 kg payload)	-18% (S2 FG weight penalty)
Material	Full carbon	S2 FG + CF spar	S2 FG is ~2-3 kg heavier
RF transparent	No	Yes	Our advantage
Price (PNP)	$16,900	~$11,000-14,000 (DIY)	18-35% cheaper

The 18% endurance gap between Y37 and our Variant A is primarily due to the S2 FG weight penalty (~2-3 kg heavier airframe). If RF transparency is not required, a carbon airframe would close this gap.

BOM Cost Impact (5 UAVs)

Variant A — Quad VTOL

Category	Total (5 UAVs)	Per UAV	vs Draft 03
Draft 03 baseline	$77,481	$15,496	—
VTOL system hardware	$5,000-7,000	$1,000-1,400	+$1,000-1,400/unit
Structural reinforcement	$750	$150	+$150/unit
Larger cruise motor/ESC	$250	$50	+$50/unit
Variant A total	$83,481-85,481	$16,696-17,096	+$1,200-1,600/unit

Variant B — Catapult + Parachute

Category	Total (5 UAVs)	Per UAV	vs Draft 03
Draft 03 baseline	$77,481	$15,496	—
Parachute systems (×5)	$4,775	$955	+$955/unit
Catapult (ELI PL-60, ×1)	$15,000-25,000	$3,000-5,000 (amortized)	+$3,000-5,000/unit
Belly rails + hatch mech.	$500	$100	+$100/unit
Variant B total	$97,756-107,756	$19,551-21,551	+$4,055-6,055/unit

Key insight: VTOL is cheaper per fleet. The catapult is expensive one-time equipment that only amortizes well over large fleets (20+ UAVs).

Recommendation Matrix

Operational Scenario	Recommended Variant	Rationale
Mobile forward operations (changing locations, no established base)	A: Quad VTOL	No ground equipment, instant deploy from any flat area, precision recovery
Fixed base operations (airfield or prepared area available)	B: Catapult + Parachute	Maximum endurance, no VTOL dead weight, lower per-unit complexity
Mixed operations (both scenarios)	A: Quad VTOL	VTOL works everywhere; endurance trade-off (6.5-7.5h vs 8h) is acceptable for operational flexibility
Maximum endurance priority (>8h critical)	B: Catapult + Belly	Zero weight penalty; but needs 200m landing strip
Budget-constrained fleet (5 units)	A: Quad VTOL	$83-85k total vs $98-108k for catapult variant

Risk Assessment (New Items for Draft 04)

Risk	Impact	Probability	Mitigation
VTOL motor failure during hover landing	Aircraft loss ($17k)	Low	Quad config allows single-motor-out survival; redundant ESC power feeds
VTOL boom attachment failure on S2 FG	Boom separation → crash	Low	Aluminum through-bolt brackets; static load test to 5× hover thrust
Catapult malfunction	No launch capability	Low	Carry spare seals and Makita batteries; ELI PL-60 is simple design
Parachute deployment failure	Aircraft loss + ground damage	Very Low	Dual deployment triggers (autopilot + RC manual); pre-flight chute check
Wind drift on parachute recovery	UAV lands in inaccessible area	Medium	Select recovery area with margin; GPS tracking; contingency recovery team
VTOL adds drag → endurance less than calculated	Endurance only 6h instead of 7h	Medium	Folding VTOL props reduce cruise drag; boom fairing; accept margin
S2 FG structure insufficient for 21-22 kg VTOL loads	Structural failure	Low	Full FEA analysis; static wing load test at 3.5g; boom attachment cycling test

Testing Strategy (Additions for Draft 04)

VTOL-Specific Tests (Variant A)

• Hover stability test: 60-second hover at 21 kg, measure motor temps and vibration
• Transition test: full transition from hover to cruise and back, measure altitude loss and energy
• Single-motor-out test: kill one VTOL motor at 30m altitude, verify safe emergency landing
• Boom attachment cycling: 200× VTOL power-on/off cycles, inspect boom joints for fatigue
• VTOL battery endurance: verify 2+ full VTOL cycles (takeoff + landing) on single charge
• Drag measurement: compare cruise power with VTOL booms vs clean airframe

Catapult-Specific Tests (Variant B)

• Catapult launch: 10 consecutive launches, verify consistent exit speed and UAV integrity
• Launch acceleration: measure g-forces on airframe and payload during catapult stroke
• Parachute deployment: 5 test deployments at various speeds and altitudes (min 50m AGL)
• Parachute reliability: 20 pack-deploy cycles, verify consistent opening
• Landing impact: verify payload cameras survive 4.6 m/s descent impact

References

1-57: See Draft 03 references (all still applicable)

Additional sources: 58. YUAV Y37 product page (updated specs): https://www.airmobi.com/product/yuav-y37-3700mm-vtol-fixed-wing-uav-pnp/ 59. YUAV Y37 engineering blog: https://www.airmobi.com/yuav-y37-a-new-standard-in-long-endurance-vtol-fixed-wing-uavs/ 60. DeltaQuad Evo TAC specs: https://docs.deltaquad.com/tac/vehicle-specifications 61. DeltaQuad Evo VTOL takeoff: https://docs.deltaquad.com/tac/flight/quick-takeoff/vtol-takeoff 62. ELI PL-60 pneumatic catapult: https://eli.ee/products/catapults/pl60/ 63. Fruity Chutes FW bundle 20 kg: https://shop.fruitychutes.com/products/fixed-wing-recovery-bundle-44lbs-20kg-15fps 64. Robonic pneumatic launcher advantages: https://www.robonic.fi/advantages-of-pneumatic-launch/ 65. Starlino power-to-thrust analysis: http://www.starlino.com/power2thrust.html 66. T-Motor U13II specs: https://store.tmotor.com/product/U13-v2-KV130-Power-Type-UAV-Motor.html 67. Belly landing research: https://www.scientific.net/AMM.842.178 68. Aeromao Talon belly landing: https://aeromao.com/2018/10/18/talon-fully-autonomous-belly-landing/ 69. SCL bungee launcher specs: https://uascomponents.com/launch-and-landing-systems/bungee-catapult-scl2 70. UkrSpecSystems SCL-1A: https://ukrspecsystems.com/uascomponents/bungee-uav-launching-system-scl-1a 71. VTOL weight penalty research: https://hal.science/hal-03832115v1/document 72. VTOL configuration endurance comparison: https://mediatum.ub.tum.de/1462822

Related Artifacts

• Previous drafts: solution_draft01.md through solution_draft03.md
• Research artifacts: _standalone/UAV_frame_material/00_research/UAV_frame_material/