Charged EVs | Fraunhofer IISB develops 750 kW hairpin winding traction motor for hybrid-electric regional aircraft, achieving 8 kW/kg
Fraunhofer IISB has developed a 750 kW permanent-magnet traction motor for hybrid-electric regional aircraft, hitting 8 kW/kg power density through a combination of thin-lamination electrical steel, hairpin windings and direct oil-spray cooling.
The machine uses NO15 (0.15 mm) electrical steel—a thin-lamination grade that reduces eddy current and AC losses at high rotational speeds—to support the 8 kW/kg target in a 94 kg package.
| Spec | Value |
|---|---|
| Rated power | 750 kW @ 65 °C oil coolant |
| Rated speed | 21,000 rpm |
| Torque | 350 Nm |
| Power density | 8 kW/kg |
| Weight | 94 kg |
| Dimensions | D 250 mm × L 600 mm |
| Electrical steel | NO15 (0.15 mm) |
| Cooling | Direct oil spray |
| Winding | 4×3 phase hairpin, 4 independent sections |
The stator uses a 4×3 phase hairpin winding arrangement with four electrically decoupled sections, each driven by its own inverter. Distributing the windings this way improves fault tolerance: a failure in one section doesn’t take down the others. Hairpin windings also allow higher current density in the slot and better thermal contact with the stator core than conventional round-wire coils. Direct oil spray cooling manages the resulting heat load, enabling rated power at 65 °C coolant temperature.
The motor is Fraunhofer IISB’s contribution to Project AMBER, a Clean Aviation EU program targeting a ~2 MW hydrogen fuel cell hybrid-electric propulsion system for regional aircraft. The architecture is a parallel hybrid, pairing the IISB motor/generator with Avio Aero’s Catalyst advanced turboprop engine. GE Aerospace is also part of the consortium. AMBER targets at least 30% CO₂ reduction at entry into service compared to 2020-era regional aircraft.
The motor was developed entirely at Fraunhofer IISB—concept, CAD, manufacturing, assembly and validation—in accordance with aerospace standards.
Source: Fraunhofer IISB
