Axter Aerospace propulsion hybrid system AX-40S – Aerokurier Magazine

Additional performance at takeoff and fully electric operation in case of shutdown of the internal propulsion engine. That’s what AXTER Aerospace promises with the hybrid AX-40S engine.

What is the use of a hybrid engine in aeronautics? Reduce emissions of fine particles and carbon dioxide are relevant dimensions.

For the Spanish startup AXTER Aerospace, the increase in safety that an additional electric motor can offer was the decisive argument to develop a hybrid engine for the aeronautical sector. With the first model realized of the AX-40S with an electric motor of 30 kilowatts (40 horses) for the engines Rotax 912 and 914, it was possible to fly during 7 minutes being propelled only by the electric motor fed with batteries of lithium. This first test was carried out with the Light Aircraft Tecnam P92J. In a version already made for customers with the Technam P2004 with variable pitch propellers, it provide 12 minutes to the pilot for landing in case of conventional engine failure.

And what’s the use? The two founders of AXTER Miguel Suárez and Daniel Cristóbal have investigated in detail the statistics of air accidents, after having worked for 8 years in Airbus projects, before venturing into the development of hybrid engines. The aeronautical engineer Miguel Sánchez and the electrical engineer Daniel Cristóbal want to reduce the sad balance of 71 deaths per year in Europe and in the US caused by engine failure during the flight. The hybrid system now provides pilots a break after the shock of an engine failure, which allows them to act without stress and in a relaxed manner.

The Spanish government considered the project worthy of subsidizing and provided a start-up capital. The company CT Engineering Group of Madrid-Getafe, provider of engineering services for companies such as Airbus, Dassault or ATR, joined the project as a strategic partner. Jesús Prieto, the CEO with affinity to the aeronautical sector, has a company with more than 1500 employees, which supported AXTER by making available their simulation software using the finite element m

ethod and structure determination systems. For the design of the power electronics, the University Carlos III of Madrid contributed its knowledge in the field.

The hybrid system already patented by AXTER is the first step towards more efficient systems, until reaching the one hundred percent electric propulsion. It aims to obtain permits for experimental aircraft, Light Sport Aircraft (LSA) and Very Light Aircraft (VLA) and even aircraft of the CS-23 to CS-25 categories. Even with VLAs, which are allowed to take off with a maximum weight of 750 kilograms, there should be no problems with the additional weight of the hybrid system.

The AX-40S was implemented as the most reasonable input variant for use in LSA and Experimental aircraft, where Rotax engines dominate. The AX-40S has already obtained the operating license from the Spanish air certification agency.

The Axter system can be mounted on four different points of the Rotax 912/914. The frame is part of the system. The crankshaft is coupled to the electric motor by an automatic clutch, which is manufactured by Endrax in Slovenia especially for AXTER. The electric motor can be connected when the pilot deems it convenient. In case of motor failure, the electrical motor will continue working uncoupled of the main motor. During the flight the batteries can be recharged with the combustion engine as long as the electric motor is used for the takeoff and ascent phase.

At the Casarrubios del Monte aerodrome southwest of Madrid, which has an asphalt track of 950 meters and is frequented by Madrid’s aviation followers, Miguel Sánchez demonstrates the efficiency of the AX-40S taking off with and without electric motor. All this at 2050 feet of altitude and summer weather conditions with temperatures hovering around 35 degrees.

Under standard conditions the use of the hybrid system decreases the takeoff distance of the Tecnam P92J (with 600 kilograms of maximum takeoff mass) from 200 to 145 meters. In the altitude and density of the air of Casarrubios del Monte the difference is even greater. Unlike the piston engine, the electric motor doesn’t lose power with higher altitude and density.

In the 100% electric mode the P92J-Hybrid with a speed of 135 km / h continues to climb to 200 feet per minute. To prove it, Miguel Sánchez turns off the Rotax.

The additional power of the hybrid system during takeoff and ascent is more relevant in Hot-and-High situations as well as short take-off runways (with tall grass or hill). On the other hand, the electric motor can be used under normal conditions to decrease  the use of the conventional motor and thus reduce the noise emission. In this way airports with limited use due to noise can be reused.

On the descent to runway 26 of the Casarrubios aerodrome, Rotax is again used. The wild and rugged landscape of the landing area is imposing. In the case of a conventional engine stop the electric motor could allow a safe landing. In this situation there would be too little height to use the integral rescue system.

Starting and connecting the electric motor only requires turning a rotary knob on the instrument panel, as long as the main switch is ON. The display informs about the most important power parameters. For the malfunction alarm there are different LEDs in the prototype instrument panel.

No major changes were necessary in the P92 to install the hybrid system. The additional mass of the frame (0.9 kg), the coupling (5 kg) and the electric motor (12 kg) together with the compensation of the controller (6 kg) and the batteries (20 kg), which are mounted behind the seats , they do not displace the center of gravity. The forward propeller shift doesn’t have a negative influence on different flight configurations either.

More than 200 hours of test flights have demonstrated the ability of the AXTER AX-40S system to obtain the flight license. Including also flights from Seville in torrid heat conditions typical of Andalusia with temperatures around 45 degrees, in which the cooling system of the electric motor has proven its effectiveness.

With the use of the hybrid system, AXTER engineers have obtained advantages that are difficult to ignore for flight schools, saving on fuel as well as reducing maintenance costs through the lower use of the Rotax in the landing phase. Electric propulsion and  the coupling are maintenance free. Pilots using the hybrid system score points against neighboring airports or aerodromes, with lower CO2 emissions.

The complete package is easy to assemble, is manufactured in Getafe and currently costs 18,700€ plus taxes and shipping costs. Miguel Sánchez explains that this only includes production costs.

After the development, obtaining of the license and the start-up of the production, AXTER now wants to start the commercial exploitation of the AX-40S. The second aircraft is already being equipped with the hybrid system. Two specimens are going to be sent to the University of Cranfield in Great Britain where electric propulsion will be used in drone research.

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