Heart Aerospace's X1 Battery-Electric Demonstrator Flies 27 Minutes, but ES-36 Airline Design Still Needs Turbines

On August 12, Heart Aerospace flew its X1 demonstrator for 27 minutes from Plattsburgh International Airport in New York. The aircraft weighed more than 25,000 pounds, had a 106-foot wingspan and put more than a megawatt through its electric propulsion system while taxiing, taking off, climbing, maneuvering and landing. There were no hydrogen tanks, fuel cells or gas turbines aboard as propulsion backup. For those 27 minutes, batteries flew a machine roughly the size of the regional aircraft Heart eventually wants airlines to operate.

That makes Heart’s current commercial design more interesting, because the ES-36 still carries gas turbines. Its two propellers are permanently driven by electric motors, but turbogenerators make electricity when the mission extends beyond what Heart considers practical to supply from batteries alone. The important question is not whether the ES-36 is “really electric,” but why an aircraft that has demonstrated battery-electric flight still needs liquid fuel and how quickly that fuel-burning portion of the mission can shrink as batteries improve.

I modelled that moving boundary in Heart Flew on Batteries. Its Airliner Still Needs Turbines., the full TFIE Strategy Briefing analysis. The paid assessment includes the route-energy model, battery-density scenarios, Jet A and SAF comparisons, regional-jet and turboprop references, contrail sensitivities and the auditable workbook behind the results.

Heart’s design history helps explain how it reached this point. The original ES-19 was a straightforward battery-electric regional aircraft concept. In 2022 Heart replaced it with the 30-seat ES-30 and added turbogenerators, creating a series hybrid in which fuel powered turbines, the turbines drove generators and electric motors turned the propellers. In 2024 the company changed direction again, moving to two battery-electric propellers plus two conventional turboprops. That avoided some series-conversion losses but left the aircraft carrying two complete propulsion architectures. The ES-36 reverses that choice: two nacelles, two propellers, electric motors permanently driving both, and turbogenerators supplying electricity when batteries alone cannot cover the mission.

The reason is easier to understand when power and energy are separated. Takeoff and initial climb require several megawatts, but only for relatively short periods. Cruise requires less instantaneous power but has to continue for much longer. Batteries are exceptionally good at delivering high power, which X1 demonstrated at regional-aircraft scale. Liquid hydrocarbons remain exceptionally good at carrying large quantities of energy without becoming prohibitively heavy. Heart’s current architecture lets both technologies operate where their present strengths are greatest.

Heart currently puts the battery-electric commercial range of the ES-36 at about 200 kilometres, while the hybrid architecture is intended to provide substantially greater fleet range. That distinction matters because airline aircraft are not bought for a single optimized city pair. They need to handle weather, diversions, repositioning, schedule disruptions and different routes while remaining useful across a network. An aircraft capable of flying short sectors without burning fuel but retaining longer-range capability is operationally easier to integrate than one confined to the shortest missions.

The climate value changes with route length. At short range the aircraft can avoid onboard fuel combustion altogether. As distance rises, the turbogenerators supply progressively more of the energy, and the comparison increasingly becomes one between a series-hybrid propeller aircraft and conventional regional aircraft that are already quite efficient. That last point matters because replacing a regional jet is a much easier climate proposition than replacing a modern turboprop. Regional jets generally burn considerably more fuel on comparable short routes, while efficient turboprops already exploit the aerodynamic advantages of propeller propulsion at regional speeds.

This makes the ES-36 more interesting than a simple electric-versus-fossil comparison. Electrification and lower-carbon liquid fuels are separate levers. A short flight may draw heavily or entirely from batteries, while a longer one increasingly depends on liquid fuel. The carbon result then depends not only on distance but on grid electricity, the fuel pathway and what aircraft the ES-36 displaces. Those distinctions are important enough that headline range alone tells relatively little about the aircraft’s climate performance.

Battery improvement could move that boundary substantially over the operating life of the aircraft. Heart has not publicly disclosed the production ES-36 battery chemistry, pack capacity or installed specific energy, and cell-level energy-density announcements should not be confused with certified aircraft battery systems. An aviation battery needs adequate power as well as energy, along with cycle life, thermal management, containment and certification-level safety. A cell that stores more energy per kilogram but cannot deliver enough takeoff power does not automatically extend practical electric-aircraft range.

That caveat is also what makes Heart’s architecture strategically interesting. Aircraft remain in service for decades, while battery packs can be replaced several times during that period. A conventional turboprop does not become progressively more electric when battery chemistry improves ten years after delivery. The ES-36 potentially can, because its propellers are already driven electrically. Better future batteries could displace generator operating hours without another fundamental change in how thrust is produced.

Heart’s progression from the ES-19 through two different ES-30 architectures to the ES-36 is a long experiment in locating the boundary between battery power and liquid-fuel energy. Today Heart places that boundary near 200 kilometres for battery-only commercial missions. Better batteries can push it outward, provided gains in watt-hours per kilogram arrive with adequate power, life, safety and complete-system performance. Until then, the turbines give airlines the range flexibility needed to use the aircraft before batteries can cover every mission.

The full TFIE Strategy Briefing analysis quantifies how battery and generator energy shares change with distance, tests higher-energy-density battery scenarios, compares the ES-36 with turboprops and regional jets under Jet A and selected SAF pathways, and includes the underlying workbook.