Cardinal and a helicopter, as well as other airplanes. The French company Citroën developed a rotary-powered helicopter in the 1970s. In Germany in the mid-1970s, a pusher ducted fan airplane powered by a modified NSU multi-rotor rotary engine was developed in both civilian and military versions, Fanliner and Fantrainer. At roughly the same time as the first experiments with full-scale aircraft powered with rotary engines, model aircraft-sized versions were pioneered by a combination of the well-known Japanese O.S. Engines firm and the then-extant German Graupner aeromodelling products firm, under license from NSU. The Graupner model Wankel engine has a chamber volume Vk of 4.9 cm3, and produces 460 W at 16,000 min−1; its mass is 370 g. It was produced by O.S. engines of Japan. Rotary engines have been fitted in homebuilt experimental aircraft, such as the ARV Super2, a couple of which were powered by the British MidWest aero-engine. Most are Mazda 12A and 13B automobile engines, converted for aviation use. This is a very cost-effective alternative to certified aircraft engines, providing engines ranging from 100 to at a fraction of the cost of traditional piston engines. These conversions were initially in the early 1970s. Peter Garrison, a contributing editor for Flying magazine, has said that "in my opinion … the most promising engine for aviation use is the Mazda rotary." The sailplane manufacturer Schleicher uses an Austro Engines AE50R Wankel in its self-launching models ASK-21 Mi, ASH-26E, ASH-25 M/Mi, ASH-30 Mi, ASH-31 Mi, ASW-22 BLE, and ASG-32 Mi. In 2013, e-Go airplanes, based in Cambridge, United Kingdom, announced that its new single-seater canard aircraft, will be powered by a rotary engine from Rotron Power. The DA36 E-Star, an aircraft designed by Siemens, Diamond Aircraft and EADS, employs a series hybrid powertrain with the propeller being turned by a Siemens electric motor. The aim is to reduce fuel consumption and emissions by up to 25%. An onboard Austro Engines rotary engine and generator provides the electricity. A propeller speed reduction unit is eliminated. The electric motor uses electricity stored in batteries, with the generator engine off, to take off and climb reducing sound emissions. The series-hybrid powertrain using the Wankel engine reduces the weight of the plane by 100 kg compared with its predecessor. The DA36 E-Star first flew in June 2013, making this the first-ever flight of a series-hybrid powertrain. Diamond Aircraft state that the technology using rotary