🎓 Lesson 2
D2
UAV Platforms: Fixed-Wing vs VTOL vs Multirotor Tradeoffs
UAV platforms are flying robots used in mining—fixed-wing planes fly fast and far, VTOLs take off/land vertically like helicopters but fly efficiently forward, and multirotors hover precisely but don’t go far or fast.
🎯 Learning Objectives
- ✓ Analyze tradeoffs among endurance, spatial resolution, and operational flexibility across fixed-wing, VTOL, and multirotor UAV platforms for mine surveying tasks
- ✓ Calculate platform-specific mission efficiency (km²/hour per kWh) using published sensor, battery, and aerodynamic parameters
- ✓ Design a platform selection matrix for a given mine site (e.g., open-pit vs. steep-walled quarry) based on terrain slope, required GSD, and regulatory airspace constraints
- ✓ Explain how propulsive efficiency (thrust-to-power ratio) and lift-to-drag ratio govern platform viability in high-wind, high-altitude mining regions
📖 Why This Matters
In modern mine surveying, choosing the wrong UAV platform wastes time, compromises data quality, and risks regulatory noncompliance. A multirotor may capture 2 cm GSD orthomosaics of a stockpile—but fail to map a 5 km² pit in one flight. A fixed-wing may cover that area in 45 minutes—but crash attempting to inspect vertical highwalls. VTOL bridges this gap—but at higher cost and complexity. Understanding these tradeoffs isn’t theoretical: it determines whether your drone program delivers ROI, meets MSHA/ICAO compliance, or gets grounded during monsoon season.
📘 Core Principles
Flight physics drives platform performance: fixed-wing UAVs leverage lift-to-drag (L/D) ratios >10–15 for efficient cruise, but require minimum takeoff speed (~12–18 m/s) and landing clearance. Multirotors achieve L/D ≈ 1–2—they trade efficiency for agility, enabling stationary imaging and low-speed inspection (<3 m/s), but suffer exponential power demand above 8 m/s. VTOL platforms decouple takeoff/landing from cruise: tilt-rotor designs maintain rotor efficiency in hover while transitioning to wing-borne flight (L/D ~9–12); lift+cruise architectures use dedicated rotors for VTOL and separate wings/propellers for forward thrust—enabling 30–50% longer endurance than multirotors at similar payload. All platforms must satisfy mine-specific constraints: Class G airspace rules (FAA Part 107 / EASA STS-01), 120 m AGL altitude limits, wind tolerance (>12 m/s gusts common in arid pits), and EM interference from blasting networks.
📐 Mission Efficiency Index (MEI)
Mission Efficiency Index quantifies usable survey output per energy unit—critical for comparing platforms across real mine conditions. It integrates ground sampling distance (GSD), flight speed, swath width, battery energy, and system overhead.
Mission Efficiency Index (MEI)
MEI = (v × w × 3600) / (E_usable × 10^6)Quantifies survey coverage per unit energy (km²/Wh), enabling objective platform comparison under mission constraints.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| v | Cruise or average flight speed | m/s | Effective forward velocity during data acquisition phase |
| w | Effective swath width | m | Ground width imaged per pass, accounting for sidelap and sensor FOV |
| E_usable | Usable battery energy | Wh | Total battery capacity × (1 − system overhead fraction) |
Typical Ranges:
Fixed-wing (mine survey): 0.015 – 0.025 km²/Wh
VTOL (mine survey): 0.008 – 0.014 km²/Wh
Multirotor (mine survey): 0.002 – 0.005 km²/Wh
💡 Worked Example
Problem: Compare two platforms surveying a 2.5 km² copper pit: (A) Fixed-wing (WingtraOne GEN II): cruise speed = 18 m/s, GSD = 3.2 cm @ 120 m AGL, swath width = 240 m, battery = 1080 Wh, system overhead = 25%. (B) Multirotor (DJI Matrice 350 RTK + P1): max speed = 5 m/s, GSD = 2.1 cm @ 60 m AGL, swath width = 80 m, battery = 560 Wh, overhead = 35%.
1.
Step 1: Compute effective survey rate (km²/h) = (speed × swath width × 3600) ÷ 1,000,000 → A: (18 × 240 × 3600)/1e6 = 15.55 km²/h; B: (5 × 80 × 3600)/1e6 = 1.44 km²/h
2.
Step 2: Adjust for battery usable energy: A: 1080 × 0.75 = 810 Wh; B: 560 × 0.65 = 364 Wh
3.
Step 3: Calculate MEI = (survey rate) ÷ (usable Wh) → A: 15.55 ÷ 810 = 0.0192 km²/Wh; B: 1.44 ÷ 364 = 0.00395 km²/Wh
Answer:
Fixed-wing MEI is 4.9× higher than multirotor. For this site, fixed-wing completes the mission in one 42-min flight (13.2 km²/h × 0.7 h = ~9.2 km² covered); multirotor requires 7+ flights—increasing risk of data misalignment and weather interruption.
🏗️ Real-World Application
At Newmont’s Boddington Mine (Western Australia), survey teams replaced DJI Inspire 2 multirotors with Quantum Systems Trinity F90+ VTOL for highwall monitoring. The pit’s 45° slopes and 3.2 km² footprint made multirotor operations unsafe and inefficient (12 flights/week, 4.2 hr total flight time). The VTOL reduced flights to 2/week, cut total flight time to 1.8 hr, and improved GSD consistency from ±1.8 cm to ±0.4 cm by eliminating manual pilot altitude adjustments. Crucially, its 1.2 m/s wind tolerance margin enabled reliable operation during 10–14 m/s afternoon gusts—where multirotors were grounded daily per site safety protocol (Boddington SMS Procedure DRN-SUR-007 Rev. 4).