Ejection Seats: A Necessity for Safe eVTOL Prototype Development and Flight Testing

The world is witnessing a surge in the development of new aircraft concepts and prototypes, driven by companies eager to exploit the advantages of electric propulsion and energy storage. Leading this charge are eVTOL (electric Vertical Take-Off and Landing) aircraft, which utilize distributed propulsion systems and often employ tilt mechanisms to achieve vertical flight. Numerous companies are developing eVTOL airframes, including Archer, Joby, Vertical Aerospace, Supernal, and Lilium.

eVTOL aircraft featuring a DEP (Distributed Electric Propulsion) System

These companies are rapidly iterating their designs, all with the goal of piloted flight for their prototypes. This marks a significant moment in aviation history—the first time in over 50 years that we've seen such a rapid emergence of new aircraft prototypes and the first genuinely new aircraft type to be developed in a similar period.

However, a concerning trend is emerging: the vast majority of these companies seem to deem it unnecessary to provide their pilots with robust escape systems. This article will examine why this is a critical oversight, exploring the challenges of eVTOL escape and arguing for the necessity of ejection seats in these experimental aircraft.

Why is an Escape System Necessary?

eVTOL aircraft represent a new frontier in aviation, bringing with them a unique set of uncertainties and potential failure modes. While aircraft designers strive for reliability, no engineer can guarantee an aircraft will never crash. Pushing the boundaries of technology inevitably leads to unforeseen challenges and occasional failures. eVTOL aircraft are complex systems, blending flight control and avionics with experimental propulsion, energy storage, and lightweight composite structures. As history has repeatedly shown, complex systems can result in complex and unpredictable failure modes.

eVTOL aircraft crashes are possible, and as more and more begin flying are ever more likely to happen.

The development of the Bell XV-15 tilt-rotor aircraft, the precursor to the V-22 Osprey, provides a compelling example. Recognizing the inherent risks of this new technology, engineers equipped the XV-15 with a Martin-Baker ejection seat to provide a means of escape for test pilots. The development of eVTOL aircraft mirrors this situation, as we are venturing into similarly uncharted territory with novel aircraft configurations and technologies.

eVTOL manufacturers often cite high reliability standards as justification for not requiring pilot escape systems. They argue that their aircraft are designed to achieve extremely low failure rates. However, it is crucial to remember that reliability calculations are theoretical until validated by extensive real-world testing. Reliability predictions can, and often do, prove inaccurate, especially given the lack of historical data for the complex systems used in eVTOL aircraft.

Furthermore, several eVTOL prototypes have unique flight characteristics that differ from conventional aircraft. This could invalidate traditional failure mitigation strategies like gliding or autorotation, further increasing the need for a reliable escape system. The inclusion of such a system is an acknowledgment that unforeseen circumstances can occur during flight testing. Prioritizing pilot safety should be paramount, and test pilots should be provided with a robust means of escape in the event of system failure or loss of control.

The Challenges of eVTOL Escape

eVTOL aircraft present unique challenges for escape systems. Operating at low altitudes and speeds, with the potential for high sink rates in failure cases, these aircraft create a demanding environment for pilot safety. The limited time available for escape in such scenarios is a critical concern.

Traditional aircraft recovery systems, like pilot-worn parachutes or whole-aircraft recovery parachutes, rely on sufficient altitude and airspeed to function effectively. In low-altitude, low-speed situations common in eVTOL operations, these systems become ineffective. There's simply not enough time for deployment and inflation, let alone for the aircrew to safely egress the aircraft.

This challenge is compounded by the complexity of eVTOL control and propulsion systems. Distributed Electric Propulsion (DEP), while potentially more resilient to individual component failure, introduces intricate flight control and avionics systems. Any malfunction within these systems could lead to rapid loss of control, further complicating escape procedures. This vulnerability, coupled with the aircraft's typical operating conditions, necessitates escape solutions that can function effectively in these constrained circumstances.

Evaluating Escape System Options

Given that these are prototype aircraft, and the need for an escape system will hopefully diminish as the technology matures, it makes sense to consider existing technologies rather than developing bespoke solutions. Three main options exist: pilot-worn parachutes, aircraft recovery parachutes, and ejection seats.

Pilot-worn parachutes, while offering benefits like low complexity, cost, and weight, are ultimately unsuitable for eVTOL aircraft. Their long deployment time, manual operation, and the need for an efficient escape route pose significant challenges in time-critical emergencies. Additionally, safe escape with a parachute generally requires more altitude than is available in many eVTOL failure scenarios. The risk of the pilot colliding with the aircraft during egress is also a major concern.

RCAF pilot climbing into his aircraft with his parachute fitted.

Similarly, aircraft recovery parachutes, while attractive due to their ability to recover both pilot and airframe, also face limitations in the context of eVTOL operations. Like pilot-worn parachutes, they require significant altitude and time to deploy effectively. This is problematic for low-level eVTOL flights where emergencies can occur rapidly and close to the ground. Moreover, they don't offer a means of escape for the pilot alone. In scenarios like a battery fire, the pilot would still need a separate parachute, adding complexity and risk. Finally, the potential for entanglement with the airframe and the need for bespoke systems for heavier eVTOL aircraft further diminish their suitability.

An example of an aircraft recovery parachute in action.

In contrast, ejection seats offer a proven and reliable solution for pilot escape in challenging VTOL environments. Their rapid deployment and ability to function in a variety of dynamic situations make them uniquely suited to the demands of eVTOL prototype testing. They can rapidly and safely egress the pilot from the aircraft in a range of dynamic conditions. Importantly, "zero-zero" ejection seats allow for safe escape even from extremely adverse situations, such as a complete loss of control at extremely low altitudes (less than 200ft).

S-3 Viking Ejection Test at China Lake.

However, ejection seats also present significant development and operational challenges. They are complex systems that rely on pyrotechnic components requiring regular replacement and specialized maintenance. This complexity translates to high costs and potential challenges with the availability of seats and components. As "defence" hardware, there may also be hurdles related to import and export regulations. Integrating ejection seats into an airframe is a complex process with stringent requirements, demanding expensive and complex testing to demonstrate functionality. Furthermore, the regulatory framework surrounding the civil use of ejection seats remains underdeveloped.

Despite these challenges, ejection seats remain the only escape system that can reliably protect aircrew in eVTOL prototypes across their entire flight envelope. No other system offers the same level of performance, especially in low-altitude, low-speed emergency scenarios where rapid escape is critical.

Conclusions

The rapid development of eVTOL aircraft presents a unique opportunity to revolutionize aviation. However, it's crucial to prioritize pilot safety, especially during the experimental phases of prototype development. While ejection seats come with their own set of challenges, they remain the only escape system that can reliably protect aircrew in eVTOL prototypes across their entire flight envelope. eVTOL manufacturers must seriously consider incorporating ejection seats into their prototype aircraft to ensure the safety of the test pilots who are pushing the boundaries of this exciting new technology.