Snecma Continues Open Rotor Aircraft Engine Tests

The Open Rotor type aircraft engine, a futuristic concept with counter-rotating high-speed propellers, underwent a new series of tests i...

The Open Rotor type aircraft engine, a futuristic concept with counter-rotating high-speed propellers, underwent a new series of tests in mid-July in the large S1 wind tunnel operated by French aerospace research agency Onera in Modane, Savoy region.

These tests used a 1/5 scale model that enabled engineers to check out several types of propeller pairs. Carried out within the scope of the European research program Clean Sky (a partnership between the European Commission and the aviation industry), this latest series of tests focused on the engine's low-speed aerodynamic and aeroacoustic performance.

 Results were promising according to Marc Doussinault, propeller module manager at Snecma.

"This was the third series of tests for the setup we have dubbed HERA (hélice rapide, the French acronym for "high-speed propeller), which is dedicated to maturing the design of the open rotor's counter-rotating propellers," explained Marc Doussinault.

"The test rig comprises two compressed air turbines, each driving one propeller. We performed two different test series, one using the baseline propeller pair, which had already been tested, the other 
with a new configuration reflecting the architecture selected for the target engine. This configuration allows the propellers to rotate at different speeds, giving the engine greater operating freedom and enhancing both aeroacoustic and aerodynamic performance. The tests proceeded smoothly, without any major problems. We used a number of different settings, giving us a complete profile of the propeller pair's acoustic and aerodynamic performance."

Based on this data Snecma's teams were able to validate the design codes and better understand the physical phenomena involved in reducing propeller noise – especially reducing vortices around the blade tips and the wake intensity.

According to Marc Doussinault, this latest series of tests settled a number of issues concerning the Open Rotor's acoustic performance. "Noise has always been the major problem with the Open Rotor. But we have made a lot of progress in this area, and today we demonstrated that we can meet the new noise standards for certification," he added.

Full-scale propeller tests planned in 2015. The Open Rotor engine still has a long way to go before entering service, perhaps in 2025-2030. A new series of tests is already scheduled for September-October 2013, also using Onera's wind tunnel in Modane.

But as Marc Doussinault explains, "This time it will be a high-speed test, since we want to demonstrate the engine's potential for reducing fuel consumption. Our objective on the Open Rotor is to reduce fuel burn by 25 to 30 percent compared with the CFM56 – and we are very confident we can reach this goal."

Tests using full-scale propellers are slated for 2015 on the test stand in Istres, southern France. The demonstrator will be based on a gas generator (core) from the M88, the engine powering the Rafale fighter.

These tests will be used to characterize the performance of full-size blades made of a 3D woven composite, like the fan blades on the LEAP commercial aero-engine, now under development. In turn, this means that the blade design will have to be frozen very shortly.

"We will start manufacturing the molds in early 2014, then we will need nearly a year to produce the first blades," notes Marc Doussinault.

Snecma will then have another 15 years or so to develop the complete Open Rotor engine and show that it is ready to power aircraft in revenue service.