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Pipistrel Taurus G4 Completes Oshkosh Test Hops

First flight imminent for NASA Green Flight Challenge entrant

By Fareed Guyot, Manager – Electronic Publications, EAA 388642

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

Pipistrel
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.

Pipistrel
The mid-day heat off the pavement enhances the mysterious look of this electric-powered aircraft. Photos by Steve Cukierski

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August 11, 2011 – The Pipistrel Taurus G4 is one step closer to its first flight after making four test hops at Wittman Field in Oshkosh Thursday. 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.

The aircraft has already made some test hops in Europe but its first flight and aircraft certification will take place 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 a bigger propeller (6.5 feet), giving more efficiency and performance at altitude that is close to that of a turbo-normalized piston engine.

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 come together in less than five months.”

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