eVTOL Firefighting Platform

A Tethered eVTOL Platform for High-Rise Firefighting and Rescue Operations

Document Version: 1.0
Date: March 2026

Executive Summary

This proposal outlines the development of an electrically powered Vertical Take-Off and Landing (eVTOL) platform specifically designed for high-rise firefighting and rescue operations. Current firefighting apparatus, including aerial ladder trucks, are physically limited in their reach, rendering them ineffective for fires occurring above approximately 100 meters. Conventional helicopter operations near burning high-rises are hampered by smoke ingestion, rotor vulnerability, and limited hover endurance.

The proposed solution addresses these limitations through three core innovations:

1. Tethered Ground Power Delivery: The vehicle is powered continuously from a ground-based mobile generator via a lightweight, high-voltage DC tether, eliminating the endurance constraints of onboard batteries.
2. Minimalist "Barebone" Airframe: The vehicle is designed as a purpose-built, high-power-density workhorse, stripped of all non-essential weight (e.g., conventional seating, non-structural fairings) to maximize payload capacity for personnel and equipment.
3. Passive Thermal Protection: A water-cooled "exo-dermis" layer on the airframe utilizes the latent heat of vaporization of water to protect the structure and critical components from extreme fireground temperatures, potentially allowing limited incursions into the thermal envelope.

This project aims to develop and demonstrate a scaled prototype, proving the core technologies and operational concepts required for a future full-scale manned rescue vehicle.

1. Problem Statement & Rationale

Modern urban firefighting faces a critical capability gap. High-rise building fires present a unique and deadly challenge:

• Reach Limitations: Aerial ladder trucks are typically limited to heights of 100 meters or less, leaving occupants of taller buildings inaccessible from the exterior.
• Internal Access Compromised: Fire often breaches stairwells and elevator shafts, the primary internal access routes, trapping victims above the fire line and endangering firefighters attempting internal assault.
• Conventional Helicopter Limitations: Traditional helicopters cannot safely hover close to a burning building for extended periods. Rotor blades are vulnerable to impact with the structure, turbine engines are susceptible to flameout from smoke ingestion, and hover endurance is strictly limited by fuel.

There exists a clear and present need for an external, agile, and persistent rescue platform capable of operating at any altitude, in the immediate vicinity of a high-rise fire, to extract victims and deliver firefighters to otherwise unreachable locations.

2. Project Objectives

The primary objectives of Project are:

1. Develop a Proof-of-Concept Tethered Power System: Design, build, and test a ground-based power generation and tether management system capable of delivering 600 kW of continuous DC power to an altitude of 300 meters using a 3000V DC lightweight composite cable.
2. Design and Fabricate a Scaled "Barebone" eVTOL Airframe: Construct a 1/3rd scale, unmanned prototype airframe embodying the minimalist, high-power-density philosophy, with an integrated water-cooled skin test section.
3. Validate the Thermal Protection System: Quantify the effectiveness of the water-cooled "exo-dermis" in protecting structural elements from radiant and convective heat flux representative of a high-rise fire.
4. Demonstrate Coordinated Multi-Vehicle Tether Management: Prove the concept of using smaller, tethered support drones to offload the weight of the main power cable at altitude, enabling extended operations with a lightweight main vehicle.
5. Produce a Validated Engineering Framework: Deliver a comprehensive set of design guidelines, performance models, and safety protocols for a future full-scale manned rescue vehicle.

3. Technical Approach & Innovation

3.1 High-Voltage Tethered Power System

Initial calculations demonstrate that a 600 kW system at 1000V DC would require a tether weighing over 650 kg, severely compromising vehicle payload. However at 3000V DC, reduces current to 200A and enabling a dramatic reduction in conductor size.

• Conductor: Aluminum alloy, sized for 200A continuous current with a 3% voltage drop over 300m (~115 mm² estimated).
• Cable Construction: A custom-designed, dual-core cable incorporating:
  • XLPE insulation rated for 3.6 kV DC.
  • An integrated Kevlar strength member to bear the tensile load of the cable's own weight.
  • A flame-retardant, abrasion-resistant outer sheath.
• Estimated Tether Weight (300m): ~380 kg total (both cores, with insulation and strength member).
• Ground Station: A mobile, diesel-powered generator (800 kVA) feeding a solid-state 3000V DC power supply. An automated, tension-controlled drum system will manage cable deployment and retrieval in coordination with the vehicle's flight controller.

3.2 Minimalist "Barebone" eVTOL Airframe (Scaled Prototype)

The scaled prototype will be a purpose-built, uninhabited aircraft with the following characteristics:

• Configuration: Coaxial contra-rotating rotors enclosed within a protective duct/guard rail. This configuration maximizes thrust-to-weight ratio, eliminates the need for a tail rotor, and the duct provides critical blade strike protection against the building.
• Propulsion: High-torque, outrunner BLDC motors utilizing Neodymium magnets, powered by the 3000V DC tether via onboard switched mode power supply.
• Airframe Construction: A welded 4130 chromoly steel or 7075 aluminum space frame, providing a rigid chassis for component mounting while minimizing weight. All non-structural fairings will be eliminated. The "cockpit" area will be an open frame with minimalist standing provisions and integrated harness attachment points.
• Target MTOW (Scaled Prototype): 500 kg (including tether share and test payload).

3.3 Passive Water-Cooled Thermal Protection System

This system is designed to allow the vehicle to survive the extreme thermal environment of a fire.

• Concept: A porous outer layer ("exo-dermis") bonded to the primary airframe structure. This layer is saturated with water.
• Operation: Incident heat flux causes the water to vaporize, absorbing energy at a rate of 2.26 MJ per kg of water vaporized (latent heat of vaporization). As long as the water supply is replenished, the structure's temperature cannot exceed 100°C.
• Scaled Prototype Implementation: A test section of the airframe (e.g., a landing skid or a section of the space frame) will be equipped with this system. Instrumented with thermocouples, it will be subjected to controlled radiant heat sources to validate the thermal model and quantify water consumption rates.

3.4 Coordinated Tether Management via Support Drones

To prevent the main vehicle from bearing the full weight of the 300m tether, a system of smaller, autonomous support drones will be employed.

• Concept: At intervals of approximately every 75-100 meters, a support drone will attach to and support the tether. These drones will be powered from the same ground generator via taps on the main tether.
• Control: The support drones will operate in a coordinated "daisy chain," using sensors and inter-drone communication to maintain position and tension, effectively creating a lightweight, aerial cable support structure. This offloads the majority of the tether's weight from the main rescue vehicle, restoring its full lifting capacity for personnel and equipment.

4. Project Phases

Phase 1: Feasibility & Detailed Design

• Finalize system architecture and specifications.
• Detailed design of the 3000V DC tether, ground station, and power electronics.
• Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) of airframe, rotors, and thermal protection system.
• Procure long-lead items (motors, SiC components, custom cable samples).
• Deliverable: Preliminary Design Review (PDR) package.

Phase 2: Component & Subsystem Fabrication

• Fabrication of the scaled prototype airframe.
• Assembly of ground power station and tether management system.
• Development and programming of support drone prototypes.
• Bench testing of power electronics and motor controllers.
• Deliverable: Critical Design Review (CDR) package.

Phase 3: Integration & Ground Testing

• Full integration of all vehicle systems.
• Tether integration and ground-based tension testing.
• Thermal protection system testing under controlled radiant heat panels.
• Tethered thrust stand testing (vehicle secured).
• Deliverable: Test report and safety certification for flight.

Phase 4: Flight Test Campaign

• Low-altitude tethered hover tests (vehicle lifting minimal tether weight).
• Incremental altitude increases, culminating in a 300m tethered hover.
• Demonstration of coordinated flight with support drones.
• Demonstration of emergency disconnect and safe descent on backup battery.
• Deliverable: Final test report, validated performance models, and a comprehensive technology roadmap for a full-scale manned vehicle.

5. Risk Assessment & Mitigation

Risk Category	Specific Risk	Probability	Mitigation Strategy
Technical	Tether weight higher than modeled	Medium	Over-specify ground station power; design airframe with modular ballast to adjust for actual tether weight. Use conservative design factors.
Technical	Thermal protection system ineffective or consumes water too rapidly	Medium	Conduct rigorous ground-based testing in Phase 3; design the system with modular water tanks to adjust capacity; explore alternative or hybrid coolants.
Safety	Tether failure during flight	Low	Incorporate a secondary safety tether or an automatic, parachute-assisted emergency descent system triggered by loss of power/tension.
Programmatic	Scalability to manned vehicle proves more complex than anticipated	High	This is the primary reason for the scaled prototype approach. The project's explicit goal is to retire technical risk and provide a validated roadmap. The final report will clearly outline the challenges and required investments for the next phase.

6. Expected Outcomes & Impact

Successful completion of Project will deliver:

1. A Demonstrated Capability: A flying prototype proving the feasibility of high-power, high-altitude tethered flight for persistent aerial operations.
2. Validated Engineering Data: Openly published data on high-voltage tether design, thermal protection system performance, and coordinated multi-drone tether management, benefiting the wider engineering community.
3. A Clear Roadmap to a Life-Saving Solution: A detailed, technically grounded plan for the development of a full-scale manned rescue vehicle.

7. Conclusion

This eVTOL project offers a technically grounded path toward solving one of the problems in urban firefighting. By combining a high-voltage tethered power system, a minimalist high-power-density airframe, and a passive thermal protection layer, this project will lay the groundwork for an aerial rescue vehicle capable of operating where no current asset can go. 

The proposed scaled-prototype approach is the prudent and necessary first step to retire technical risk and pave the way for a full-scale, life-saving manned platfom.

© Ly Sandaru.

Reference :  https://projectsdesandaru.blogspot.com/2023/11/electrically-powered