A top US Air Force technologist confirms the potential exists after 2013 to greatly improve the fuel efficiency of the F-35 Joint Strike Fighter engine by inserting a third bypass airstream.
Air Force Research Laboratory (AFRL) studies have affirmed the upgrade is technically feasible, albeit complex and expensive, says Larry Burns, programme manager for the versatile affordable advanced turbine engines programme.
By engaging the third bypass airstream during cruise, the engine can adapt the ratio of the airflow bypassing the core in flight. A higher bypass ratio reduces speed, but increases fuel efficiency dramatically during cruise flight.
AFRL is developing the potential upgrade under the adaptive versatile engine technology (Advent). The AFRL last week selected Rolls-Royce to build and test a full-scale engine demonstrator on the ground in early 2013.
General Electric, meanwhile, will develop a separate Advent core, but budget cuts prevented a second, full-scale ground test programme.
Advent technology has often been linked to the cancelled Next Generation Bomber programme. Burns, however, calls that a misconception. Instead, Advent is developing a suite of technologies that can support any of several potential next-generation programmes, including for fighters, bombers, airlifters and spyplanes, Burns says.
It is unlikely that a new centreline engine could be inserted into a current aircraft, such as an F-35, Burns says. But key Advent components, such as the third bypass airstream, would be available for retrofit on current engines, he adds.
Retrofit engine programmes are "few and far between", Burns says, but the potential fuel savings over the 20-year life of the aircraft could justify the investment.
The AFRL has explored such opportunities by commissioning "vision studies" by the major airframers - Boeing, Lockheed Martin and Northrop Grumman.
The potential advantages of Advent technology have been raised in the debate over the future of the General Electric/Rolls-Royce F136 alternate engine. The GE/R-R team has argued that one of the reasons to preserve funding for the embattled F136 is Advent, since rival Pratt & Whitney has been excluded from the programme.
P&W officials have responded that the Advent technology could be applied to any engine, including the baseline F135 engine for the F-35. Burns also adds that Lockheed's vision studies have commissioned P&W to continue designing Advent upgrades.
The AFRL launched the Advent programme to achieve a step-change in the fuel-efficiency performance of turbofan technology, which had seemingly reached an innovative plateau more than four decades after it was introduced with the GE TF33.
Source: Flight International
