In a more environmentally conscious world where cutting aviation emissions is of increasing importance, propellers may be staging a comeback
Propfans will be cleaner and more fuel-efficient | Science & technology
GE, an American engineering group, and Safran, a French company then called Snecma. The pair are now developing a new version, which they reckon could reduce fuel consumption and CO2emissions by more than 20% compared with the best jet engines currently in use. And the new propfan will be capable of running on unconventional sources of energy, such as synthetic aviation fuel, hydrogen or a hybrid-electric system. Flight tests are scheduled for 2025.
The newpropfan differs from older designs in various ways. Like the engines on theAN-70, it will sit under the wings, with an open fan at the front. Unlike theAN-70’s engines, though, it will use a single rotating open-fan. It does have a second ring of blades immediately behind the front fan, but these do not spin. Instead, they act as vanes that guide the flow of air backwards. The new arrangement is less complicated than the older one, and should be easier to maintain.
The new propfan is also lighter, which itself saves fuel and hence emissions. This is not just because the fan housing has been eliminated. The thrust reverser—which on a conventional jet engine uses a series of deflectors to slow an aircraft once it has touched down on the runway—has also gone. Instead of deflectors, the pitches of both the rotating blades and the static vanes can be adjusted on the new propfan to reverse its thrust. headtopics.com
One problem with propfans, though, is noise. This was particularly high inside the cabin of the modifiedMD-80. The combination of a single ring of blades, and advances in acoustic design should let the engine meet current and anticipated noise regulations, says
CFM.There has been concern about what would happen if a propfan blade broke off. A conventional jet engine is designed to contain a breakaway blade within the fan housing. With no such housing, there is nothing to stop such a breakaway striking the aircraft’s fuselage or wing, with potentially catastrophic results. That could mean parts of the aircraft near the open blades will need to be reinforced.
The best thing, though, is to stop the blades breaking in the first place. For that, new materials will help. One legacy of theMD-80 propfan was the pioneering use of extremely strong blades made from carbon-fibre composites. This technology has progressed, and the fan blades in jet engines and the propellers of modern turboprops are now routinely made from composites. These blades are proving their durability by safely notching up millions of flight hours, says a spokeswoman for
CFM.Mounting the propfans under the wings of an aircraft is more in keeping with the way modern airliners are built. It also makes maintenance and safety checks easier. However, the consortium says it can producer a “pusher” version if an aircraft-maker wants to design a plane with its engines at the rear, like the old headtopics.com
MD-80.New aircraft designs are in the works, but the two main builders of airliners, Boeing and Airbus, have yet to commit themselves to any big, new projects.CFMhopes the propfan will be a contender for a new generation of short- and medium-haul aircraft, although it could be used on large wide-body aircraft, too. If flight tests go well, in a decade or so travellers might find the aircraft they are boarding is once again powered by propellers.
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