Overall Design Concept for a Medium-Lift Fixed-Wing Observation UAV Platform
1. Introduction and Design Objectives
This chapter presents the conceptual design of a fixed-wing unmanned aerial vehicle (UAV) optimized for short-to-medium endurance, low-altitude observation missions carrying a 10 kg payload. The platform is powered by a Zenoah 26cc gasoline engine. The reduced endurance requirement of 60 minutes allows for a smaller fuel load, lighter airframe, and more compact overall dimensions while still providing sufficient loiter time for many practical observation missions. This design represents an optimal balance between mission capability, aircraft simplicity, and ease of prototyping for doctoral research.
Core Design Specifications:
- Maximum Payload: 10 kg (observation equipment and mounting structure)
- Mission Type: Low-altitude optical/infrared reconnaissance and surveillance
- Endurance Requirement: 60 minutes at cruise power with full payload
- Powerplant: Zenoah G260PUH or G260RC 26cc gasoline two-stroke engine
- Fuel: Gasoline (pre-mixed with oil at typical 25:1 to 50:1 ratio)
- Airframe Configuration: High-wing fixed-wing monoplane
- Cruise Speed: 70-90 km/h (approx. 19-25 m/s)
- Stall Speed: < 45 km/h (target for safe low-speed observation)
- Operational Ceiling: ≤ 2000 m
2. Weight Budget and Fuel Calculation (60-Minutes Endurance)
| Component | Weight (kg) | Notes |
|---|---|---|
| Payload (Observation Equipment) | 10.0 | Gimbal + support systems |
| Engine (Zenoah 26cc) | 1.8 – 2.1 | Using G260PUH as baseline |
| Fuel for 60 minutes | 1.0 – 1.4 | Gasoline: ~0.72 kg/L × 1.4-2.0L |
| Airframe Structure | 4.5 – 5.5 | Further weight reduction possible |
| Control Systems & Avionics | 0.8 – 1.2 | Servos, receiver, flight controller |
| Landing Gear | 0.5 – 0.8 | Fixed taildragger configuration |
| Estimated MTOW | 18.0 – 20.0 kg | Further reduced from 20-22 kg |
Fuel Calculation Revisited: With lower MTOW, the engine operates at an even lower cruise power setting. A 20-25cc two-stroke gasoline engine at reduced cruise power (40-50%) may consume only 12-15 ml/min. For 60 minutes: 60 min × 13.5 ml/min = 810 ml (0.8 L). With generous reserve: 1.4-2.0 L tank (1.0-1.4 kg fuel) .
3. Aircraft Dimensional Specifications (Scaled for 60-Minute Endurance)
With MTOW reduced to approximately 19 kg, all lifting surfaces can be scaled down further while maintaining excellent performance.
3.1 Wing Design
| Parameter | Value (60-min, 10kg) | Value (90-min, 10kg) | Change |
|---|---|---|---|
| Wing Area | 1.7 – 1.9 m² | 2.0 – 2.2 m² | -15% |
| Wingspan | 3.5 – 3.8 m | 3.8 – 4.2 m | -8% |
| Root Chord | 0.50 – 0.55 m | 0.55 – 0.60 m | -9% |
| Tip Chord | 0.32 – 0.37 m | 0.35 – 0.40 m | -9% |
| Mean Aerodynamic Chord (MAC) | 0.42 – 0.46 m | 0.45 – 0.50 m | -8% |
| Airfoil Selection | Clark Y or NACA 4412 | Same | No change |
| Dihedral | 3° – 5° | Same | No change |
| Wing Loading | 10.0 – 11.0 kg/m² | 9.5 – 10.5 kg/m² | Slightly higher |
Justification: With MTOW reduced to 19 kg (average) and wing area of 1.8 m², wing loading = 10.6 kg/m². This is still well within the acceptable range for low-speed flight and ensures excellent handling characteristics.
3.2 Fuselage Dimensions
| Parameter | Value (60-min, 10kg) | Value (90-min, 10kg) | Change |
|---|---|---|---|
| Fuselage Length | 2.3 – 2.6 m | 2.6 – 2.9 m | -11% |
| Fuselage Width (max) | 0.28 – 0.32 m | 0.30 – 0.35 m | -8% |
| Fuselage Height (max) | 0.32 – 0.37 m | 0.35 – 0.40 m | -8% |
| Nose Length (from firewall) | 0.30 – 0.35 m | 0.30 – 0.35 m | No change |
| Payload Bay Dimensions | 0.25 × 0.25 × 0.35 m | 0.25 × 0.25 × 0.35 m | No change |
| Fuel Tank Bay | 0.15 × 0.15 × 0.20 m | 0.18 × 0.18 × 0.25 m | -44% volume |
Justification: The fuselage length scales with the reduced wingspan. The payload bay remains unchanged as it is driven by the 10kg sensor package dimensions, not by fuel volume. The fuel tank bay is significantly smaller due to the reduced fuel requirement.
3.3 Horizontal Tail (Stabilizer) Design
| Parameter | Value (60-min, 10kg) | Value (90-min, 10kg) | Change |
|---|---|---|---|
| Horizontal Tail Volume Coefficient (c̄_h) | 0.45 – 0.55 | Same | No change |
| Tail Arm (L_h) | 1.2 – 1.3 m | 1.3 – 1.5 m | -11% |
| Horizontal Tail Area (S_h) | 0.25 – 0.32 m² | 0.30 – 0.40 m² | -20% |
| Horizontal Tail Span | 1.2 – 1.5 m | 1.4 – 1.7 m | -14% |
| Horizontal Tail Root Chord | 0.22 – 0.26 m | 0.25 – 0.30 m | -12% |
| Horizontal Tail Tip Chord | 0.13 – 0.16 m | 0.15 – 0.18 m | -13% |
| Horizontal Tail Airfoil | Symmetrical (NACA 0010) | Same | No change |
| Elevator Area | 20-30% of S_h | Same | Proportional |
Calculation: S_h = (c̄_h × Wing Area × MAC) / L_h. Using c̄_h = 0.5, Wing Area = 1.8 m², MAC = 0.44 m, L_h = 1.25 m → S_h = (0.5 × 1.8 × 0.44) / 1.25 = 0.317 m².
3.4 Vertical Tail (Fin) Design
| Parameter | Value (60-min, 10kg) | Value (90-min, 10kg) | Change |
|---|---|---|---|
| Vertical Tail Volume Coefficient (c̄_v) | 0.03 – 0.04 | Same | No change |
| Tail Arm (L_v) | 1.2 – 1.3 m | 1.3 – 1.5 m | -11% |
| Vertical Tail Area (S_v) | 0.15 – 0.20 m² | 0.18 – 0.24 m² | -17% |
| Vertical Tail Height | 0.35 – 0.45 m | 0.40 – 0.50 m | -12% |
| Vertical Tail Root Chord | 0.25 – 0.30 m | 0.28 – 0.35 m | -11% |
| Vertical Tail Tip Chord | 0.13 – 0.17 m | 0.15 – 0.20 m | -13% |
| Vertical Tail Airfoil | Symmetrical (NACA 0010) | Same | No change |
| Rudder Area | 25-35% of S_v | Same | Proportional |
Calculation: S_v = (c̄_v × Wing Area × Wingspan) / L_v. Using c̄_v = 0.035, Wing Area = 1.8 m², Wingspan = 3.65 m, L_v = 1.25 m → S_v = (0.035 × 1.8 × 3.65) / 1.25 = 0.184 m².
4. Summary of Key Dimensions (10kg Payload, 60-Minute Endurance)
| Component | Dimension (60-min) | Dimension (90-min) | Reduction |
|---|---|---|---|
| Wingspan | 3.5 – 3.8 m | 3.8 – 4.2 m | ~8% |
| Wing Area | 1.7 – 1.9 m² | 2.0 – 2.2 m² | ~15% |
| Mean Aerodynamic Chord | 0.42 – 0.46 m | 0.45 – 0.50 m | ~8% |
| Fuselage Length | 2.3 – 2.6 m | 2.6 – 2.9 m | ~11% |
| Horizontal Tail Area | 0.25 – 0.32 m² | 0.30 – 0.40 m² | ~20% |
| Horizontal Tail Span | 1.2 – 1.5 m | 1.4 – 1.7 m | ~14% |
| Vertical Tail Area | 0.15 – 0.20 m² | 0.18 – 0.24 m² | ~17% |
| Vertical Tail Height | 0.35 – 0.45 m | 0.40 – 0.50 m | ~12% |
| Fuel Tank Capacity | 1.4 – 2.0 L | 2.2 – 2.8 L | ~36% |
| Estimated MTOW | 18 – 20 kg | 20 – 22 kg | ~10% |
5. Performance Characteristics with 60-Minute Endurance
The reduced endurance and MTOW provide excellent performance margins:
| Parameter | 60-min Design | 90-min Design | Improvement |
|---|---|---|---|
| Power-to-Weight Ratio | ~110-125 W/kg | ~100-110 W/kg | +10-15% |
| Climb Rate | Very good | Good | Enhanced |
| Takeoff Distance | < 25-35 m | < 30-40 m | Reduced |
| Fuel Efficiency | Excellent (lower cruise power) | Good | Improved |
| Structural Margins | Very high | High | Safer |
| Handling Qualities | Highly responsive | Responsive | Enhanced |
| Prototyping Complexity | Lower (smaller, lighter) | Moderate | Easier build |
6. Design Implications and Opportunities
The 60-minute endurance design offers several practical advantages for doctoral research:
- Simplified Prototyping: The smaller, lighter airframe (3.5m wingspan, 18-20 kg MTOW) is easier and cheaper to construct, transport, and test. It can potentially be built in a standard workshop and transported in a pickup truck or trailer.
- Reduced Fuel Costs and Handling: The smaller fuel tank (1.4-2.0 L) means less fuel to purchase, store, and handle during testing. This simplifies logistics and reduces operational costs.
- Enhanced Safety Margins: The higher power-to-weight ratio provides excellent climb performance and go-around capability, increasing safety during flight testing.
- Flexibility for Additional Payloads: If desired, the 5 kg reduction in fuel load (compared to the 90-min, 15kg design) could be reallocated to:
- Larger fuel tank (if longer endurance is later desired)
- Redundant systems for research into reliability
- Additional sensors or experimental equipment
- Heavier, more robust airframe for durability
- Ideal for Proof-of-Concept: The 60-minute endurance is sufficient for most proof-of-concept flight testing, allowing multiple flights per day without the need for extended refueling or cooling periods.
- Zenoah 26cc Engine Suitability: At 18-20 kg MTOW, the Zenoah 26cc engine provides approximately 110-125 W/kg, which is ideal for this class of aircraft. The engine will operate comfortably at lower power settings during cruise, enhancing reliability and longevity.
7. Design Validation and Next Steps
The 10kg payload, 60-minute endurance design represents an optimal balance for doctoral research—sufficiently challenging to demonstrate engineering competence, yet practical enough for successful prototyping and flight testing.
Key Research Areas:
- Engine-Airframe Matching: Characterizing the Zenoah 26cc engine’s performance at reduced power settings with the 18-20 kg airframe.
- Vibration Isolation: Developing effective isolation for the 10kg sensor payload from the two-stroke engine vibrations.
- Structural Optimization: Achieving the 4.5-5.5 kg airframe weight target using hybrid steel/wood/composite construction.
- Flight Testing Program: Validating 60-minute endurance, handling qualities, and sensor performance.
Subsequent Practical Work:
- CAD modeling with updated 60-minute endurance dimensions.
- Structural analysis (FEA) of the scaled-down airframe.
- Engine bench testing to confirm fuel consumption at 40-50% power settings.
- Prototype construction using lightweight hybrid construction techniques.
- Flight test program culminating in a 60-minute endurance demonstration flight.
8. Comparison with Existing Platforms
This design compares favorably with existing 10kg-class observation UAVs:
| Platform | Payload | Endurance | Powerplant | Wingspan | MTOW |
|---|---|---|---|---|---|
| This Design | 10 kg | 60 min | Zenoah 26cc | 3.5-3.8 m | 18-20 kg |
| Bramor PPX | 4 kg | 3 hours | Electric | 4.1 m | 16 kg |
| UX5 | 1 kg | 90 min | Electric | 1.6 m | 2.9 kg |
| DT-26 | 6 kg | 2 hours | Gasoline | 4.2 m | 22 kg |
This design occupies a unique niche: high payload fraction (50% of MTOW is payload) combined with practical endurance in a compact, easy-to-manage airframe.
References
- Zenoah G260PUH 26cc Petrol 2-Stroke Engine Specifications. JPerkins.com
- GWAIHIR Senior Design Project, Kennesaw State University, 2025
- Resende, G.J. “A proposal of tail and control surfaces design.” Universidade Federal de Uberlândia, 2019
- Bramor PPX UAV Specifications. C-Astral Aerospace
- Trimble UX5 UAV Specifications. Trimble Navigation
- DT-26 UAV Specifications. DeltaQuad UAV
- Raymer, D. P. Aircraft Design: A Conceptual Approach. AIAA Education Series.
- Anderson, J. D. Fundamentals of Aerodynamics. McGraw-Hill.
- Sadraey, M. H. Aircraft Design: A Systems Engineering Approach. Wiley.