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EAA AirVenture Oshkosh RSS Feed Pipistrel seeks a three-peat in CAFE Green Challenge

By RANDY DUFAULT
Pipistrel
PHOTO BY STEFAN SEVILLE

Come this September the 2011 CAFE Green Flight Challenge competition will select a winner as it has twice before in this contest to advance technology that reduces general aviation’s carbon footprint.

Twice before aircraft from Slovenian manufacturer Pipistrel took those crowns.

Pipistrel fully expects their 2011 entrant to be that crown: a dual fuselage, electric powered, four seat aircraft they call the Taurus G4.

“Pipistrel reviewed the rules and decided in our opinion that it would have to be an electric aircraft in the competition if it would have a chance to be successful,” said Michael Coates, master distributor for Pipistrel USA. “And it would have to have four seats to take advantage of the rules.”

He added, “The simplest way of doing that was to use the existing Taurus G2 aircraft, which is a two seat self launched glider that we’ve made just over a hundred of already.
“The obvious thing was to use an existing fuselage structure and an existing wing structure, and graft them together.”

Rules for the competition require the airplane to achieve a two-hour duration at 100 mph, with a 30-minute reserve.

Economy must be equivalent to at least 200 passenger miles per gallon.

Pipistrel staff are not saying what they expect performance to be—other than their expectation of scores at least double the absolute minimum.

A design deja vu
The G4, on display at Pipistrel’s booth just west of Exhibit Hangar B, evokes memories of the U.S. Air Force’s post World War II F-82 fighter, which connected two P-51 Mustangs into a single, twin engine, two fuselage aircraft.

Pipistrel’s example differs from the F-82 configuration in that it mounts a single motor on the structure connecting the two fuselages.

Plus the motor is electric and, according to Coates, at 200 hp the most powerful single electric mill ever on an aircraft.

Liquid cooling will keep motor temperatures under control.

“It’s not just a matter of taking model technology and scaling it up,” said Tine Tomazic, Pipistrel’s technical coordinator for the project. “There are different safety aspects and different control aspects.

“It’s very different than a model airplane made bigger.

An electromagnetic personality
“The motor control is full digital as well as the avionics are full digital. That is an attempt to make all the systems on the airplane robust against electromagnetic interference.

“Most people don’t know that when you build electric airplanes the motor will emit [electromagnetic interference], the controller will emit, and the cables in there are huge antennas.

“So you have to be careful where you route things.”

“When you put it on full power your compass starts to swing, your radio does funky things…so in the process of development the wiring harness was made differently and now it is just about perfect. The electromagnetic interference is now less than with a typical [gas engine] installation.”

Tomazic and his team created the entire airplane: structure, electronics, and power, from, as he says, “zero to hero” in exactly four months.

Rapid prototyping techniques and computer analysis all contributed to the quick build.

Roughly 95 percent of the 75-foot span structure is constructed from carbon fiber, with the remaining 5 percent Kevlar.

The weight of things to come
“Basically this configuration weighs on the order of 35 percent of its takeoff mass,” Tomazic said. “The payload is tremendous.

“We are talking about a payload that is almost 2,000 pounds and the gross weight of the airplane is around 3,600 pounds.

“Without the batteries and the passengers it is really, really light. This is something that we’ve never done before.”

Flight tests will commence immediately following EAA AirVenture and are expected to be complete, with the aircraft ready to compete, in mid-August.

Purpose built for the competition and for other development needs, the Taurus G4 will never be a production aircraft.

However, Pipistrel does expect to leverage much of the developed technology in a new, four seat aircraft now under development.

The efficiency of that design should be another crowning achievement.

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