The US Air Force is moving ahead with plans to develop a sixth-generation fighter jet engine based on technological improvements achieved through an ongoing effort to produce a power plant for a future long-range bomber.

In a request for information released 19 August, the air force said it plans to release a final request for proposals for the adaptive engine transfer programme (AETP) in the first quarter of fiscal year 2015, “notionally December 2014.”

AETP is aimed at finding mature engine technologies that will feed into an engineering and manufacturing development program, according to Pentagon documents. The eventual goal is to design, build and test a 45,000lb-thrust-class fighter engine “suitable for further development and ultimate installation into combat aircraft.”

The programme is a direct follow-on to the Air Force Research Laboratory’s adaptive versatile engine technology (ADVENT) programme. General Electric and Rolls-Royce North America developed engines that meet the 25 percent efficiency metric under ADVENT.

GE currently has a full ADVENT engine in testing that is designed for a “bomber application,” says spokesman Matt Benvie. Northrop and a Boeing-Lockheed Martin team are expected to compete for the LRS-B contract that will be awarded in spring 2015.

GE and Pratt & Whitney in 2012 scored contracts under the follow-on adaptive engine technology development (AETD) programme. AETD will produce a fighter engine core based on ADVENT technologies by 2016 that incorporates ceramic matrix composite material to improve heat tolerance and acceleration.

AETP will further mature the core’s heat tolerance and mate the core with an adaptive fan. The effort will conclude with a full-engine test either on a ground test bed, aboard a Lockheed Martin F-35 or in an “unnamed flight test application,” Benvie says.

“We are doing work as if AETD leads directly into AETP,” he says. “We’re maturing and incorporating more and more of these higher-temperature capability technologies so you can drive more power and fuel efficiency.”

Adaptive engines incorporate three airflow pathways through the jet engine to increase fuel-burn efficiency without increasing its diameter and therefore the size and design of the fighter. Current engines take in air in two ways: through the core and “bypass” air that creates efficient thrust by flowing around it. The larger the intake, the more efficiently thrust is generated. But fighter jet engines are limited in size because an increase in intake diameter has third order effects on the aircraft’s drag, radar signatures and other attributes.

At cruising speeds, the third air intake pathway is used to increase the amount of bypass air around the engine’s core, which boosts propulsive efficiency. It can also be directed through the core to increase the total volume of air intake, which increases the exhaust jet velocity.

Pentagon scientists have estimated the engine technology could increase fuel efficiency by 25% to 30%.

In its fiscal year 2015 budget submission, the air force requested a $1 billion investment over the next five years in next-generation engine technology development. AETP is scheduled to last through 2019.

But the service’s proposed budget ignores the likelihood that sequestration-level budget cuts will again go into effect in fiscal year 2016. Unless lawmakers either repeal sequestration prior to fiscal 2016 or enact relief measures, the law automatically will excise about $600 billion from the Pentagon’s budget over the following five years.

An April Defense Department report bluntly states that the adaptive engine program would be “eliminated” by such reductions.