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Pipistrel Flies Above Oshkosh

Wittman field sees two first flights in one week

By Fareed Guyot, Manager – Electronic Publications, EAA 388642

The Pipistrel Taurus G4 overhead at Wittman Regional Airport during its first flight August 12. Courtesy: Pipistrel

The Pipistrel G4 is illuminated by the green dot on Runway 27 at Wittman Field in Oshkosh. Photo by Steve Cukierski

The electric motor on the Pipistrel is located in a center nacelle between the twin fuselages. Batteries that power the motor are located in three places throughout the aircraft. Photo by Steve Cukierski

See the photo gallery

August 13, 2011 –The Pipistrel Taurus G4, the first 4-seat electric aircraft in the world, took off Friday morning August 12 from Wittman Field in Oshkosh after making four test hops the day before. The twin-fuselage aircraft was a clear Dead Grass Award winner during AirVenture 2011 and Pipistrel is aiming this one-off design for NASA’s Green Flight Challenge (GFC) that will take place in September.

American test pilot Dave Morss was at the controls to satisfy FAA certification and GFC competition requirements. The G4’s experimental certification will continue in Oshkosh and one other location in the United States before the competition.

The G4 is really two stock Taurus G2 aircraft joined together by a mid-wing that also supports the single motor, can carry four, and, according to Pipistrel, is the biggest, heaviest most powerful electric aircraft to date. The Taurus G4, with its 75-foot wingspan, looks like a glider but is designed to operate like an airplane - one that meets the specific requirements of the GFC, which include a speed of 100 mph or better, ability to complete a 200-mile course in less than two hours, and an efficiency of 100 miles per gallon.

The G4 is designed to carry up to four people; however, there is no limit to the number of passengers a competition aircraft can carry as long as it meets the efficiency requirements. That efficiency will come from several areas. The outboard wing sections and the fuselages come from stock Taurus G2s and along with the mid-wing allows for good span loading that makes it easy to distribute the weight, according to Tine Tomazic, a technical coordinator for Pipistrel’s Research and Development section.

“It’s real light - having two fuselages allows us to distribute the weight of the heavy batteries along the span of the wing,” Tomazic said. “The empty weight is only 35 percent of max gross takeoff weight. The payload is tremendous.”

The batteries are in both fuselages and in the rear of the engine nacelle, which is on the mid-wing in the center of the aircraft. Tomazic said this location means that many different types of propulsion systems can be located here, although they will be using an electric motor for the competition.
“It’s a test bed for different propulsion systems. It also employs a hybrid or conventional engine. The nacelle is designed to accept different engines and motor sizes - It’s much easier to install the powertrain than if it was through the fuselage,” Tomazic said.

The Taurus G4 was designed to fly at 100 knots and stall at 60 knots. The electric motor currently installed uses a geared box variant that provides equivalent to 200 horsepower and is efficient to 95 percent with the controller. Tomazic said the gear box allows for bigger propeller (6.5 feet), giving more efficiency and performance at altitude that is close to that of a turbo-normalized piston engine.

 Making this all work Pipistrel notes was not easy. It was a great challenge even to import the aircraft into the United States because it is powered by 450 pounds of lithium-polymer batteries, which can in certain circumstances be highly flammable. It was also extremely difficult to find an insurance company in the U.S. which was prepared to insure such aircraft. The company also had to find an American test pilot - the FAA requests that the first test flights must be performed by an American test pilot and CAFÉ competition rules also demand an American pilot to fly the aircraft at the race.

Before the GFC was postponed, Pipistrel had been rushing to complete the aircraft in time. When the competition was rescheduled, the company decided to bring it to AirVenture. Tine Tomazic was especially proud of the effort to build the aircraft since it took only five months from concept to completion and only four months to fabricate.

“The project—is really a one-off that you can only do once in a lifetime,” Tomazic said. “It was a joy to see the airplane to come together in less than five months.”

Pipistrel credits the Wittman airport administration and community for allowing them hangar space to prepare for the certification flights.

Pipistrel, founded by CEO Ivo Boscarol, has been producing Light aircraft for 20 years in Slovenia, with more than 1,000 completed overall. Pipistrel aircraft have done very well in previous efficiency competitions, including the 2007 CAFE/NASA Personal Air Vehicle (PAV) Challenge and the 2008 CAFE/NASA General Aviation Technology Challenge Centennial Challenge where the Pipistrel Virus SW claimed victory two years in a row.

Before the start of the NASA GFC competition in September, where the G4 will attempt the third consecutive victory, the aircraft must accomplish 40 hours of test flights under the supervision of the head of the Race team, prof. dr. Jack Langelaan.


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