Antares climbs even higher with Saft lithium-ion batteries

Citation

(2003), "Antares climbs even higher with Saft lithium-ion batteries", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 2. https://doi.org/10.1108/aeat.2003.12775baf.009

Antares climbs even higher with Saft lithium-ion batteries

Antares climbs even higher with Saft lithium-ion batteries

Keywords: Lithium, Power supply, Sailplanes

It is believed that a switch to Saft high energy rechargeable lithium-ion batteries will enable Antares, the self-launching sailplane with a retractable electric motor and propeller, to reach an altitude of 3,000 m in powered flight (Plate 1). This is an improvement of around 1,100 m over the maximum height achievable by the prototype, powered by nickel metal hydride (Ni-MH) batteries.

The Antares concept has been developed in Germany by Lange Flugzeugbau GmbH as the "motorglider of the future" with a high performance, almost silent, and environmentally friendly propulsion system. This consists of a brushless 42 kW (56 hp) electric motor with external rotor, power electronics, rechargeable batteries and a slowly-revolving pusher propeller with a diameter of 2 m.

Plate 1 A switch to Saft high energy rechargeable lithium-ion batteries will enable Antares, the revolutionery self-launching sailplane with a retractable electric motor and propeller, to reach an altitude of 3,000 m in powered flight

For take-off and powered flight the motor and propeller unit is extended above the wing. For soaring, the pilot simply pulls a lever and the complete propulsion unit retracts into the fuselage to improve the sailplane's aerodynamic efficiency.

The Antares prototype was designed around an Ni-MH battery system, which enabled it to climb under power to a height of around 1,890 m. However, in the quest for even greater performance the design team decided to switch to Saft's VL lithium-ion cells, which were originally developed for hybrid and electric vehicle applications to pack as much power as possible into a lightweight and space efficient package. These cells have a nominal capacity of 39 Ah and a nominal voltage of 3.6 V, enabling a significant increase in power for Antares from a battery which is 30 per cent lighter.

The Antares battery system comprises 72 VL41 M cells in series, providing a nominal voltage of 260 V. The total weight of the battery is around 76 kg, which represents some 13 per cent of Antares' maximum all-up weight (including pilot, parachute and water ballast) of 600 kg.

Production versions of Antares will be limited to a maximum take-off power setting of 42 kW. This will provide an average climb-rate of 4.3 m/s, enabling the motorglider to reach 1,000 m (twice the height achieved by a good winch launch) in 4 min. The battery system can provide around 13 min of duration at maximum power, which will take Antares to over 3,000 m. Even in no lift conditions, from this height the motorglider will take an hour and 40 min to glide back to earth.

Charging

The Saft lithium-ion battery system is fitted with an electronic control management system for the monitoring of charge and discharge voltages, as well as temperature, and takes 8 h to charge at 220 V. A charger is fitted onboard the Antares to allow for cross-country travel.

The VL cells are capable of up to 1,500 charge/discharge cycles, and in this application are expected to have a service life of around 11 years.

The motorglider

The development of this new motorglider would in itself have been a big challenge. But Lange Flugzeugbau wanted more. With innovative ideas and a new, evolutionary and technologically advanced concept, it wanted to create the glider of the future.

Propulsion system

The aircraft developed by Lange Flugzeugbau is said to have a high performance, almost silent propulsion system, plus an optimal gliding performance. Comfortable and simple handling, exceptional reliability, maximum safety, low maintenance costs and simple service are other features attributed to this glider. The company believes that with these features, along with the elegance of a beautiful aircraft, it has recreated the fascination of gliding.

The brand new developed and patent pending propulsion system of the Antares is said to be the heart, or better yet, the soul of the concept. Lightweight, high performance and ecological batteries, a brushless 42 kW external rotor electric engine, new power electronics and a large, slowly rotating propeller were developed into one system, tailor made together with an optimised configuration for the Antares. For the first time a complete propulsion system had been developed and completed exclusively for one special motorglider.

The results are stated to be high climb rates (approx. 4.6 m/s; 905 ft/min), very high service ceiling (>3,000 m and >9,850 ft in calm air) and almost absolute silence.

According to Lange Flugzeugbau, great performance is one side of this new and patent pending propulsion system–Reliability, safety and simple handling the other. Due to the system characteristics, the electric engine already claims high safety in operation. Using a well tuned brushless external rotor engine, is said to give an extra service safety.

Relatively few, but high quality parts give a minimum failure risk. Compared to internal combustion engines, the Antares propulsion system is stated to have very little vibration. This avoids wear and tear problems and offers the prospect of greater reliability.

All the propulsion system functions, i.e. extension and retraction, propeller adjustment as well as power regulation are gently and manually controlled by the patent pending "One Lever Control".

Maintenance of the propulsion is thought to be of very low cost, a complete contrast to conventional aero engines.

Aerodynamics

The desire of every pilot: very good climbing characteristics, excellent glide ratios even at high speeds, optimum thermaling performance, and overall very pleasant handling characteristics, are claimed. This aerodynamic layout is the result of an ambitious research project. Developed over many years, a completely new motorglider design took shape. Its aerodynamic outline was designed entirely as one piece.

All possibilities for optimisation are thought to have been addressed.

Wing geometry

An extremely slender super ellipse describes the outline of the Antares wing. This geometry allows us to reach the theoretical minimum of induced drag. This is the value for the untwisted elliptical wing. The unpleasant flight characteristics of the untwisted elliptical wing, however, are said to have been avoided by the Antares design. Relatively long airfoil chord lines in the outer wing section team up with winglets to provide forgiving stalling characteristics. The winglets reportedly allow a further reduction of the induced drag by 5 per cent. Thereby, the induced drag of the 20 m Antares wing reaches only 95 per cent of the value for fully elliptical wing of the same wingspan.

Airfoils

Nine different airfoils, fine tuned onto each other, provide minimum pressure drag and friction drag. The laminar flow extends to 95 per cent chord of the lower wing surface. As a result, high speeds can reportedly be flown at previously unachieved gliding performances – the airfoils leave the low drag bucket characteristic of laminar flow only after airspeeds of 116-128 knots (210-230 km/h, depending on wing loading and wingspan).

Detail perfection/fine tuning

Antares possesses a sufficient wing area, adapted to the needs of a motorglider. This, together with a high aspect ratio of 32, is said to guarantee excellent climbing characteristics in thermal flight.

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  Wing and winglets have been developed as a single unit. The advantages of the winglets are used to their full extent in perfect harmony with the wing.

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  The compact electric engine allows us to realise a fuselage shape with an aerodynamically optimal contraction ratio behind the cockpit. This results in a further drag reduction.

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  Usual aerodynamic losses at the wing-fuselage junction are minimised through a careful design of the mid-fuselage section, and through the use of specifically designed wing airfoils close to the fuselage.

Comfort

The manufacturers consider that comfort is more than just convenience: the individually adaptable sitting technique offers a pleasant sitting position for every pilot. And more especially during long flights helps counter tiredness and fatigue. Comfort is thereby an important contribution to active safety.

Landing gear suspension

The specially designed Antares landing gear suspension and the large 5 in. wheel offers a high comfort standard for taxiing as well as during take off and landing.

Steerable skid wheel

Free and easy taxiing on the ground is possible with the steerable skid wheel and wingtip wheels. Low taxi speeds require just minimum battery power.

Rigging aid

The rigging aid, specially designed considering the weight of the Antares wing, reduces the effort and rigging time to an easy minimum.

Portable charger

As described earlier, as an option for cross-country tours a portable charger has been designed, which is integrated inside the fuselage.

Safety

With regards to safety, Lange Flugzeugbau explains that the entirely new developed Antares design offered the possibility to give safety a high priority. Passive as well as active safety systems are said to be the key components of the integrated concept. With know-how and materials developed in the FIA Formula 1, the company reports that the Antares cockpit has been designed to incorporate a survival zone.

The cockpit

According to Lange Flugzeugbau the front fuselage is divided into two entities: the nose is designed to work as a crash element. It absorbs a great deal of the damage in the event of an impact. To integrate this element, the fuselage has been elongated – without causing aerodynamic drawbacks. The company reports that the survival space adjoining the crash element was reinforced with new size stringers and spars to be able to withstand even high velocity impacts.

The landing gear

Besides the usually comfortable suspension, the Antares landing gear is equipped with energy absorption elements. These elements regulate impact forces by controlled deformation: an important protection device against widely known spinal injuries resulting from stalled landings.

Active safety

In designing the aircraft the company reports that it looked at active safety measures to counteract dangers from the outset and to avoid accidents beforehand. With these criteria in mind, the entire layout of Antares was developed:

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  a very large cockpit canopy to allow best possible all round visibility for the pilot,

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  the easy handling of the propulsion system with its unique single-lever operation – patent pending. Errors or warnings are given optically and acoustically, and

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  last but not least the general system safety inherent to the electric propulsion system is, without doubt, a key contribution to active safety.

For further details contact: Saft Industrial Battery Group. Tel: +33 1 49 93 17 69; Web site: www.saftbatteries.com. Lange Flugzeugbau GmbH. Tel: +49 (0) 6332. 9627-0; Fax +49 (0) 6332. 9627-19; E-mail: info@lange-flugzeugbau.com