EXACT Turbofan LH2 Hybrid

The D250-TFLH2-MHEP-2040 is an innovative short-range aircraft. Developed for entry into service in 2040, the aircraft features the use of liquid hydrogen (LH2) as an energy source to power a Mild Hybrid Electric Propulsion (MHEP) system.

This system combines two gas turbines with fuel cells, allowing more efficient use of fuel, particularly on shorter flights. This reduces energy consumption and improves sustainability.

It is powered by liquid hydrogen (LH2), providing a clean energy alternative that supports the sustainable operation of the aircraft. To improve aerodynamic performance, the design incorporates foldable wingtips, allowing greater efficiency while still fitting within the 36-metre gate limit at airports. The carbon fibre reinforced polymer (CFRP) wing structure reduces the weight of the wings, improving overall performance and efficiency.In addition to these technologies, the aircraft uses an all-electric on-board system architecture, further boosting energy efficiency. The design range is shorter than that of many current short-haul aircraft, at 2800 kilometres, balancing energy consumption while still covering over 85% of the short-haul market.

This aircraft concept represents a significant step towards the future of aviation, combining novel- technologies with a focus on sustainability, efficiency, and the ability to meet future market needs.

The most important differences to today’s short-haul aircraft are:

Mild-Hybrid-Electric-Propulsion (MHEP) architecture consisting of two gas-turbines and fuel-cells instead of a conventional gas-turbine propulsion
Liquid hydrogen (LH2) as main energy carrier
Foldable wingtips to increase the aerodynamic efficiency
Reduced wing mass and higher wing-spa through carbon fiber reinforced polymer (CFRP) wing structure instead of aluminum
All-electric on-board system architecture
Reduced energy consumption at comparable missions through shorter design-range (from 2800 kilometres to approximately 4600 kilometres) while still covering most of the short-range market (>85%)
Reduced energy consumption per passenger by an increased passenger capacity

Advantages

⬆️ High climate impact reduction potential
⬆️ Potentially economically advantageous compared to aircraft operated with synthetic kerosene
⬆️ Low primary green electric energy requirements
⬆️ Less energy consumption at the majority of missions (short distances below 1000 kilometres) compared to an LH2 powered aircraft without the MHEP-system
⬆️ The combination of this design range (2,800 kilometres) and design passenger capacity (250) is the sweet spot for single-aisle short-range hydrogen aircraft in terms of energy efficiency. Longer design ranges would require more tank volume and therefore longer fuselages, reducing efficiency for the more relevant shorter missions. There would also be significant challenges in terms of landing gear integration and fuselage structure. A possible solution would be to switch to a twin-aisle configuration, which would further increase fuel consumption. In general, the definition of the design mission, which defines the available range flexibility and the most relevant operational missions (usually much shorter), is more sensitive for LH2 compared to kerosene powered aircraft.

Challenges

➡️ Global implementation of LH2 might be challenging
➡️ Rather high uncertainties of the cryogenic storage and processing systems in mass, volume, production costs, maintenance efforts and lifetime
➡️ Economically challenging if LH2 costs not sufficiently low compared to sustainable aviation fuel. One of the rare major advantages of LH2 compared to SAF are the lower energy carrier production costs. In case LH2 is just slightly cheaper than SAF, the economical drawbacks of other costs are more dominant.
➡️ The integration of the MHEP-system could be associated with risks

Project & Partners

The aircraft was designed in the DLR-project EXACT as one of the most promising future aircraft concepts with the potential to reduce climate impact drastically while being economically viable. It was designed to enter into service in 2040.

Outlook

The detailed integration of the MHEP system into the aircraft and the electric motors in the gas turbine will be studied in detail in future. Furthermore, synergies with the on-board systems as well as advantages in gas turbine design should be investigated in detail.

Key Characteristics

Name	Unit	Value
Design Range	NM (km)	1500 (2778)
Design Passenger Capacity	-	250
Design Cruise Mach Number	-	0.78
Entry into Service Year	-	2040
Take-off-Field-Length	m	1900
Approach Speed	kts (CAS)	140
Propulsion Architecture		MHEP (Turbofan / Fuel-Cell)
Energy Carrier		Liquid Hydrogen
Max. Take-Off Mass (MTOM)	t	82.7
Operating Empty Mass (OEM)	t	55.4
Max. Landing Mass	t	81.5
Maximum Fuel Mass	t	3.6
Max. Payload	t	25
Wing Span (unfolded)	m	42.0
Wing Span (folded)	m	36.0
Distance to alternate Airport	NM	200
Loiter Time	min	30
Contingency	-	3%
Max Operating Altitude	ft	41000
Min. Climb Rate	ft/min	300
Passenger Seats Abreast	-	6
Block-Energy (@ Design Mission)	GJ	312.9
Block-Energy (@ Evaluation Mission, 500NM)	GJ	125.4
Block-Energy per Pax and NM (@ Design Mission, high density)	MJ/PAX/NM	0.834
Block-Energy per Pax and NM (@ Evaluation Mission, high density)	MJ/PAX/NM	1.003

Mass Breakdown

Payload-Range Diagram

Technical background information

The Mild-Hybrid-Electric-Propulsion (MHEP) Architecture

The MHEP system consists of two turbofan engines for main power and polymer exchange membrane (PEM) fuel cells for off-design operation, both powered by LH2. The idea is to replace the gas turbine power with the fuel cell during low-power and off-design phases (taxiing, descent). In order to be able to fly these phases on fuel cell power alone, the on-board system must also be powered by the fuel cell. The gas turbine achieves high efficiencies at high power levels and high power settings, as well as high gravimetric power densities. The fuel cell, on the other hand, provides high efficiencies also at low power levels and especially at low power settings, but has rather low power densities. The MHEP architecture combines the advantages of these two power sources and reduces energy consumption, especially for shorter missions.

Cabin layout

Cabin cross-section

Key Characteristics

Research Category	Future Concept
Entry into Service	2040
Passengers	250
Range (km)	2778
Wing Span (m)	42
Maximum Take-Off Mass (t)	82.7
Cruise Mach Number	0.78
Cruise Speed (km/h)	832.7
Energy Carrier	LH2
Energy Consumption	13.6
Total Installed Power (MW)	41.6

Downloads

CPACS Parametrisation

Geometry

Technical data sheet