Pratt & Whitney has added power and thermal management upgrades to a list of options available now for the propulsion system for the Lockheed Martin F-35.

If funded by the F-35’s customers, P&W’s Growth Option 2.0 package of upgrades for the F135 engine would support new avionics and systems capabilities planned for the F-35, says P&W Military Engines President Matthew Bromberg.

The unspecified power and thermal management options would add to the thrust and fuel efficiency upgrades that P&W unveiled last year for the F135.

The Growth Option 1.0 package promised to increase thrust by 6-10%, and reduce fuel burn by 5-6%, but so far the joint programme office (JPO) hasn’t funded them, Bromberg says.

Instead, the F-35 JPO has informed P&W that the F-35 requires additional upgrades beyond thrust and fuel efficiency, such as greater electrical power generation to support planned avionics and systems upgrades. As the electric power increases, the F-35’s propulsion system also must be able to absorb a larger volume of heat from the electrical system.

The proposed power and thermal upgrades would be available by 2023, along with the thrust and fuel efficiency improvements, Bromberg says.

Some changes require related upgrades from P&W suppliers. The thrust upgrade for the short takeoff and vertical landing version of the F135, for example, must be matched by a similar improvement from the Lift Fan system. Rolls-Royce, the Lift Fan supplier, has committed to support the upgrade.

Under Growth Option 2.0, however, P&W expects all of the improvements to be limited to the F135. Another key component of the F-35’s power and thermal management system — Honeywell’s integrated power package (IPP) — would not be affected.

How the Growth Option 2.0 fits into the F-35's upgrade plans remains unclear. Late last year, the JPO converted the modernisation plan for the F-35 to a different schedule. Instead of fielding large upgrade packages every two years increments known as Block 4.0, 4.1 and 4.2, the JPO now plans to roll-out smaller capability improvements on six-month intervals under a plan called the Continuous Capability Development and Delivery (C2D2) programme. So far, the JPO has laid out plans for software and sensor improvements in the short-term, but has divulged no commitments to insert engine upgrades.

P&W and GE Aviation are separately working on developing competing versions of a next-generation fighter engine. The Adaptive Engine Transition Programme (AETP) is expected to lead to a competition between the P&W XA101 engine demonstrator and GE's XA102. That engine could be used as a drop-in replacement for the F135 by the mid-2020s, with an adaptive bypass airflow feature that could extend the range of the F-35 as much as 25%. Bromberg declined to provide an update on the status of development and testing of the XA101.