Bombardier has begun flight testing of a second, larger, unmanned demonstrator of a mixed-wing concept aircraft, expanding an effort the company says could inform the design of a large-cabin business jet. radically different in the future.
Earlier this year, the Montreal-based manufacturer unveiled the “EcoJet demonstrator” program and said it was testing the design in flight using a model airplane.
Bombardier says early flight test results prompted it to continue the program using a larger unmanned demonstrator.
“We flew a much larger model, with a wingspan of 20 feet,” Bombardier research and technology director Benoit Breault told FlightGlobal at the International Aerospace Innovation Forum in Montreal on Tuesday. September 6.
The latest model is about 20% the size of a large-cabin business jet, he adds. The previous demonstrator is about 1.2–1.5 m (4–5 ft) long.
Bombardier believes the radical new shape could deliver a significant reduction in emissions and fuel consumption. “With just changing the shape of the plane today, we believe we can reduce [emissions] 17% to 20%,” says General Manager Eric Martel.
Bombardier emphasizes that EcoJet is not a development program but an effort to understand the design.
“There’s no rush at Bombardier right now,” Martel said. “Eventually we have to develop the next plane…I have people working on it today.”
Breault says the cabin of a mixed-wing aircraft would be too low for a smaller jet like a mid-size Challenger, but perfect for the large-cabin sector, in which Bombardier now competes with its Global series.
Mixed-wing aircraft are hybrids, sharing characteristics of traditional designs and ultra-efficient “flying wings,” says NASA, which has studied the concept.
While traditional aircraft have wings mounted above or below a cylindrical fuselage, Bombardier’s EcoJet has a wide, non-cylindrical fuselage that curves gently to wings extending from the fuselage itself . “The wingline is much taller than what you… see on normal airplanes today,” says Breault.
Instead of a T-tail, EcoJet has a U-tail with two horizontal and two vertical stabilizers. It has two engines mounted on top of the rear fuselage.
The shape means that the fuselage generates 20 to 30 percent of the total lift, compared to 5 to 10 percent for a traditional plane, Breault explains. This means the wings can be made smaller, reducing weight and drag, and therefore requiring less thrust and fuel, he adds. This is how Bombardier achieves fuel savings estimated at 20%. He says the design could use traditional turbofan engines or new propulsion systems.
Many hurdles remain, but the aircraft maker says it has solutions to the technical and certification challenges. “We haven’t found anything that kills the concept,” says Breault.
The EcoJet project comes as aircraft manufacturers face immense pressure to reduce carbon emissions, a daunting challenge given the energy needs of business jets.
Breault says Bombardier has met its initial flight test goals for the smaller model, but will continue to use this aircraft to evaluate technologies before moving them to the larger demonstrator. However, the company declines to say where it is carrying out test flights, or provide details on funding or timing, saying progress is dependent on test results. It has partnered in the program with unnamed Canadian universities.
The mixed wing body concept was developed decades ago and has been studied extensively. It has gained attention in recent years after Airbus said it was studying the concept.
Breault says technical challenges have kept the design mainstream. He cites the complexity of the flight controls and says the location of the U-tail and the wing require “completely different control laws”.
“Common knowledge of such an aerodynamic shape, in the world of flight science, has not been explored much,” he says. “The stall [speed] of this vehicle is going to be uncharted territory for Bombardier.
Additionally, non-cylindrical fuselages are more difficult to pressurize, which tends to require more structural reinforcement, which adds weight.
There are barriers to manufacturing. Unlike cylindrical fuselages, which can be lengthened or shortened by removing sections, mixed wing-body designs are more difficult to stretch or shrink due to their non-linear fuselages, Breault explains.
This creates challenges because aircraft manufacturers invariably build families of aircraft around base variants, allowing them to extract maximum value from a massive investment.
But Breault says Bombardier has found a “solution” to that problem, without giving further details.
“We think we have sophisticated ways to make the economy work,” he says. “I take the liberty of believing…I’m going to put one into service before I retire.