US environmental project Green Flight International is planning a cross-country biodiesel flight in April or May as a prelude to a round-the-world trip.
The transcontinental flight will involve the same ex-military Aero L-29 Delfin trainer used by Green Flight to make the first biodiesel-fuelled jet flight in October 2007. But the team is planning to use a Bombardier Learjet 25 for the round-the-word flight.
Green Flight founder Douglas Rodante says final Federal Aviation Administration concerns must be addressed before the agency approves the cross-country flight. The remaining issue, he says, is the build-up of soot on fuel nozzles and combustor walls in the L-29's Motorlet M701 engine. "We have satisfied cold flow concerns, but others have cropped up, including viscosity."
Produced from recycled vegetable oil, the biodiesel Green Flight is using is not a jet fuel. The Soviet-era L-29 was chosen for demonstration flights because its engine was intended to use multiple fuels, including diesel. Its fuel pump is designed to heat the fuel to overcome cold flow issues, says Rodante.
The major issue with the Learjet round-the-world flight will be keeping the biodiesel warm at altitudes above 40,000ft (12,200m). "If we go 100% biodiesel, we will need energy to keep the fuel warm. A mix [with conventional fuel] may not need much modification," says Rodante.
Green Flight also plans to test an alternative biofuel in another ex-military aircraft. A biodiesel processed as a jet fuel, it "is not yet on the market, but is significantly less expensive and doesn't compete with food crops", he says.
With the L-29 flights laying the groundwork, "we are not on a timeline for the Learjet flight," he adds. "It is one step at a time. Our first concern is safety."
Source: Flight International
