SP-1 Solar Glider Design Log

1. Initial Curiosity: Solar Power & Weight Ratios

Xero began the discussion exploring ultralight solar panels, focusing on commercially viable watt-per-kilogram ratios:

ENGINEERING QUESTIONS:

• What's the lightest watt/kg panel currently on the market?
• Which flexible panels are readily available in bulk (200+ units)?
• How do theoretical lab values compare to commercially deployable solutions?

ENGINEERING DECISIONS:

• Commercial viability prioritized over experimental prototypes
• Weight/power ratio selected as key metric over absolute power output
• Bulk procurement feasibility established as critical requirement

Technical assessment of solar options:

• Commercially available (2025):
  • Sinoltech 500W CIGS: 91 W/kg (panel only)
  • Rich Solar Mega 100 Flex: 45 W/kg
  • Renogy 100W: 42 W/kg
  • Eco-Worthy 130W: 32 W/kg
• Experimental records:
  • MIT fabric cells: 370 W/kg (laminated) or 730 W/kg (freestanding)
  • TMD-based cells: 4,400 W/kg (lab prototype)

Procurement decision: Sinoltech CIGS (91 W/kg) for high-density applications, Rich Solar (45 W/kg) for standard deployments

The first milestone was realizing that commercially available ultralight panels could make aviation-scale solar power feasible when balancing area coverage and weight constraints.

2. Translating to Surface Area & Aircraft Application

ENGINEERING QUESTIONS:

• What are the power and weight per square meter for MIT and commercial panels?
• How do these metrics translate to an actual aircraft wing?
• What percentage of wing area is effectively available for solar coverage?
• What are the trade-offs between experimental vs commercial solar technologies?

ENGINEERING DECISIONS:

• Adopt 10% leading-edge loss for effective coverage area
• Use Top Rudder Solo ultralight as reference airframe
• Evaluate two panel technologies: MIT fabric-backed PV vs commercial CIGS
• Prioritize structural integration of solar panels as wing skin

Power & Weight per Square Meter

Note: MIT technology shows impressive weight efficiency but low power density

Case Study: Top Rudder Solo Ultralight

Reference aircraft: Wing area = 11.3 m² | Effective coverage (90%) = 10.2 m²

Solar Integration Scenarios:

Design Implications & Trade-offs

• Weight vs Power: MIT PV adds minimal weight (0.53kg) but provides low power (194W), while CIGS provides substantial power (1.5kW) at significant weight penalty (17.3kg)
• Structural Integration: Solar panels could replace wing skin material, partially offsetting added weight
• Aerodynamic Impact: Added weight distribution affects CG balance and stall characteristics
• Hybrid Approach: Consider MIT PV for weight-critical areas + CIGS at wing roots for higher power

This analysis revealed the critical design trade-off between cutting-edge weight efficiency and practical power generation capabilities.

3. Aircraft Power Requirements & Solar Coverage Potential

ENGINEERING QUESTIONS:

• What are typical motor power requirements for self-launching motor gliders?
• How do aircraft wing areas compare between ultralights, gliders, and large transports?
• What surface area is practically available for solar coverage on different aircraft?
• How much solar power can be practically generated on large aircraft like the C-130?

ENGINEERING DECISIONS:

• Use Schleicher AS 34 Me and Alisport Silent 2 Electro as reference motor gliders
• Analyze Lockheed Martin C-130 as large transport reference platform
• Apply 90% coverage factor to wings and 100% to fuselage tops
• Compare solar integration scenarios for both MIT and CIGS technologies

Motor Sailplane Reference Data

Note: Motor power used primarily for climb, with gliding during cruise

C-130 Hercules Solar Coverage Analysis

Dimensions: Wingspan 40.4m | Wing area 162m² | Fuselage length 30-35m

Available Solar Coverage:

• Wing upper surface (90% coverage): 146 m²
• Fuselage top surface (3m width × 30m length): 90 m²
• Total available area: 236 m²

Solar Integration Scenarios:

Power Requirement Analysis

• Climb phase: 20-50 kW required for motor gliders (~2-3 kW/m² wing area)
• C-130 with CIGS: 35 kW output could enable solar-assist during climb
• Weight impact: 401 kg represents ~1.5% of C-130's max takeoff weight
• MIT technology: Currently insufficient for primary climb power (4.5 kW vs 20-50 kW required)

Design Implications

• Commercial CIGS panels provide viable solar-assist for climb phases in large aircraft
• MIT technology better suited for auxiliary power or smaller aircraft applications
• Structural integration must consider weight distribution and CG changes
• Hybrid approach recommended: Solar for cruise power, batteries for climb bursts

This analysis demonstrated that solar integration is most practical for cruise power, with batteries remaining essential for high-power climb phases.

3. Dreaming of Ultralights

Xero looked at the Top Rudder ultralight for visual inspiration, asking:

• “If we skin the top of the wing in solar that doubles as structure, what does power output look like?”
• We considered ~10% loss near the leading edge due to shading/angle.

4. Scaling Thoughts: Motor Sailplanes & Heavy Lifters

Discussion expanded to:

• Motor gliders (Pipistrel Taurus, Silent 2) for weight and power benchmarks
• C‑130 as a mental exercise for “cover everything in solar”

This led to the first table of wing area vs power and recognition that slow-climb, solar‑assisted flight was plausible.

5. Visualizing Surfaces

Xero wanted a visual of:

• Wing area scaling
• Power generation with modern and ultralight panels
• Sweet spots for 1‑ and 2‑seat craft

We produced conceptual diagrams showing:

• 10 m and 15 m spans
• Trapezoid / flying wing geometry
• Panel weight vs payload visualization

6. Enter the YF‑23

Xero invoked the YF‑23, realizing its diamond wing offers the perfect combination of solar area and iconic aesthetics:

• Full-size stats: 13.3 m span, ~84 m² area
• Solar coverage: ~75 m² top surface → 12.7 kW peak with modern panels
• MIT ultralight → 27.7 kW peak

ENGINEERING DECISIONS:

• Adopt YF-23 diamond wing planform as baseline configuration
• Strip weapons/sensors to create pure solar platform
• Prioritize visual impact ("God's plane") as key design requirement
• Target 12.7 kW peak power as minimum performance threshold

This was a turning point: SP‑1 would use a scaled YF‑23 wing combining iconic looks with functional solar area.

7. Ultralight Glider Implementation

We translated the YF-23 concept to ultralight/glider specifications:

Structural Approach

• Core materials: Carbon fiber monocoque with foam cores (8-12 kg/m²)
• Alternative: Fabric-covered tubular frames (5-8 kg/m²)
• Solar integration: Direct embedding of panels as structural skin

Scaled Configurations

Performance Characteristics

• Flight profile: Motor sailplane behavior with slow climb and cruise
• Visual signature: "Stealth bomber soaring in silence" aesthetic
• Power management: Solar priority for cruise, battery for climb phases

Design Philosophy

"The planform is the payload" - prioritizing the iconic YF-23 silhouette as a key design requirement while maintaining ultralight glider performance parameters.

Xero formally designated the concept: SP‑1 (Solar Powered‑1), establishing it as a platform where visual impact and solar performance share equal priority.