We still can make ten decibels of progress

We were not returned in a wind tunnel for a long time, smiles Vincent Garnier, Director of Snecma research and technology. Modelling enough us so far to develop the developments of our engines. But the study of the next generation for 2020 requires a technological failure. "In recent weeks, the engine manufacturer engineers return to the fundamentals of aerospace development. Several concepts of new civil engines have begun tests in wind tunnels of the Russian Institute of the Tsagi, under a European programme of research. Year-end evaluations will continue in the largest wind tunnel in the world to the French centre of Modane of Onera (). In 2010, other means of testing will be involved. "Our goal is to stop end of 2010 a base configuration", explains Pierre Thouraud. These upstream tests will ask them only 1 to 2 million euros per year, a significant fraction of the 200 million annually spent by Snecma in R & d. General Electric partnered with Nasa on the same subject and other motorists, such as Pratt & Whitney and Rolls-Royce, also work there.

"The race for 2020 is launched", it warns at the engine manufacturer. Because reactors from the aircraft of the 21st century will most look to these cylinders under tower to which it was accustomed for decades. Challenge engines little consumers, engineers are asked to think big. Pierre Thouraud is near researchers at Onera that have carte blanche to be creative. For the moment, the engine manufacturer is given as the basis for starting the revolutionary fast propeller briefly studied concept during the last oil crisis.

This so-called configuration "non-shrouded fan" favoured by Snecma aims to persuade Boeing and Airbus to adopt it for their future more aircraft of 100 seats. The formula seeks to hybridize the propeller and the reactor by retaining their respective qualities while jolts their defects. It is the fan of the reactor, to equip it with two rows of coaxial blades placed below the machine. Freed of its envelope, the fan can take very important dimensions, 4 meters in diameter, and more complex forms.

Bold engineering

The timing of the blades can also vary depending on the speed, as the Turbo. These engines allow then to exceed the traditional ceiling of speed of the propellers, less than 500 km/h, while retaining their frugality. Snecma hopes up to 30 of reduction in consumption from the CFM56. Or that the progress made in thirty years by the sector. This bold engineering is technically equivalent to get very high rates of dilution, a crucial parameter of the reactors. It defines the ratio between the flow of cold air stirred by the blower (80 of the thrust) and the flow of air that passes through the warm parts of the engine. The generation of the CFM56 has a rate of 5 to 1, while the Leap-x developing nearly 9 to 1. Non-keeled blowers wrested outright rates of 40 to 1. Today, advances in materials and aerodynamics give enough confidence to designers to address such failures. Remains a problem of size that has always handicapped propellers: noise produced by the fan is more suppressed by the shroud but can "flourish" freely to the ears of the residents of airport. Experts worry especially that this type of engine produces more sounds low frequencies than the reactors, which increases the arduous nature of the nuisance. At low frequencies, propulsion noise may also make problematic cruise phases. The engine thus find themselves trapped between the fight against the greenhouse effect and the fight against noise. The first has become the public enemy world number one, the second is still cited in surveys as the most exécrée pollution by populations. The engineers are to achieve the same margins reductions in noise for the intermediate generation of the Leap-X. "We still can make ten decibels of progress." "We will enhance our acoustic studies over the next years," insists Pierre Thouraud. Response by 2013 in the first test bench.