After Pratt & Whitney’s F135 Engine Core Upgrade solution was chosen by the USAF to enhance the F-35’s powerplant ahead of the highly anticipated Block 4 configuration, Khalem Chapman spoke with the firm about the progress being made and the benefits it will bring to not only the Lightning II family, but also future sixth-generation fighters.
After spending a year deliberating the future of its Adaptive Engine Transition Program (AETP), the USAF ultimately decided against the continued development of new-generation adaptive cycle engines for the fifth-generation F-35A/C Lightning II multi-role stealth fighter families in a move that was confirmed by Air Force Secretary Frank Kendall during a budget briefing on March 10, 2023.
The $4bn+ AETP project saw both GE Aviation and Pratt & Whitney (P&W) developing competing powerplants – the XA100 and XA101, respectively – using a bypass air system to achieve gains in overall efficiency, thrust, and to meet the additional power and cooling demands of the highly anticipated Block 4-standard versions of the F-35. Before the plug was pulled on the project, the two engines achieved improvements of 30% in fuel efficiency and at least 10% in thrust, when compared to the fighter’s current P&W F135 powerplant.
Despite the cancellation of AETP, the USAF will still push forward with providing a suite of upgrades for the F-35’s existing F135 afterburning turbofan, while pressing forward with developing more advanced engines for its sixth-generation fighters under the Next Generation Adaptive Propulsion (NGAP) programme. Meanwhile, the upgrades to the current F135s in use has fallen to the powerplant’s original equipment manufacturer, P&W, which will deliver the necessary improvements to the engine to meet the requirements to restore the engine to full life and provide additional power and cooling for the advanced F-35 Block 4 aircraft and future capability upgrades.
Known as the F135 Engine Core Upgrade (ECU) – which is the only option that can be applied to all three unique variants of the F-35 family – P&W now embarks on a quest to validate these requirements for the Lightning II’s highly anticipated Block 4 upgrade, while also reducing overall lifecycle costs. AFM recently spoke with P&W regarding its mission to modernise the F-35’s propulsion system.
AFM: For how long has P&W been working on the F135 ECU, what progress has recently been made on the programme and what are the overall benefits that the upgrade will bring to the wider F-35 family?
P&W: We have been developing a series of upgrades to the F135 for years to ensure it remains the most advanced fighter engine in the world. Currently, P&W has 600 employees fully dedicated to this effort and our progress in the preliminary design phase is going very well.
The ECU is the current iteration of those upgrades which will restore the engine to full life while increasing the power and cooling capacity needed to fully enable Block 4 and beyond capabilities for the F-35. P&W was selected by the US Department of Defense (DOD) to modernise the F-35’s propulsion system in 2023.
The ECU is the only F-35 propulsion modernisation solution that is compatible with all variants of the F-35 and will be available to all F-35 customers. Importantly, the ECU will deliver the additional vertical lift capabilities the short take-off and vertical landing (STOVL)-configured F-35B needs to conduct future missions with new weapons systems.
AFM: How far is P&W along in developing and testing the F135 ECU and when is the first ECU-equipped F-35 scheduled to be first fielded operationally?
P&W: We are on track to complete preliminary design work and begin the preliminary design review (PDR) with the DOD in the first half of 2024, then proceeding to the detailed design phase in mid-2024. This schedule will deliver the first F135 ECU-powered F-35 to the warfighter in 2029 and provide meaningful capability by the end of the decade.
AFM: Described as the ‘most cost-effective, lowest-risk propulsion modernisation solution for the F-35’, how will the ECU build and improve on the Lightning II’s baseline F135 powerplant and how will it complement the type’s Block 4 configuration?
P&W: The ECU will provide additional engine bleed air, additional horsepower extraction for electrical power generation, and lower fuel system heat generation to support the increased Power and Thermal Management System (PTMS) requirements needed for the weapons and systems included in Block 4 and future block upgrades. The ECU will also meet full life requirements and deliver higher bleed air than today’s engine fleet and incorporates an updated duty cycle with more cycles than the original F135 design while providing greater resistance to Calcium Magnesium Aluminium Silicate (CMAS).
AFM: How has P&W leveraged both digital and adaptive technologies to develop the F135 ECU and how will this benefit the integration process when operational F-35 units start to go through the modernisation process?
P&W: Today’s F135 engine uses adaptive technologies in its full authority digital engine control (FADEC), which means it leverages digital computing to change aspects of the engine’s performance based on real-time data. This is one of the critical technologies that makes the F-35B’s STOVL capabilities possible. In addition to improving the engine through ECU, we’ll also insert additional adaptive enhancements to the digital engine control. Specifically, we’ll be introducing new hardware and software capable of delivering 10x greater processing capabilities. This will improve the F135’s ability to further utilise adaptive control laws, allowing the F-35 to better optimise its mission throughout the flight envelope.
AFM: How will the F135 ECU be made available to global F-35 customers and will the new engine be installed as part of the production process for customers who are expected to receive their first F-35s after 2030?
P&W: The ECU is a variant-common upgrade that will be available to all F-35 operators. Because ECU is a targeted upgrade with engine changes limited to the power module, F-35s will either have the ECU upon delivery, or the ECU can be retrofitted post-delivery.
AFM: How will the F135 ECU and the digital/adaptive technologies used to develop the upgrade be used to feed into future powerplants for future fifth- and sixth-generation fighter platforms?
P&W: The F135 ECU is actually leveraging investments from the Navy’s Fuel Burn Reduction programme and other advanced engine development programmes. Because of this, many of the aerodynamic designs and technologies that make up ECU have already been designed, demonstrated, matured and tested. This is common practice in the industry and we are looking forward to continuing further advanced technology development through the sixth-generation NGAP programme, which is inheriting many of the learnings from AETP.
AFM: What work is P&W currently doing on developing a sixth-generation propulsion system for NGAP and how has the F135 ECU informed such developments thus far?
P&W: In addition to the ECU, we have also been focused on further development of adaptive engine technology for sixth-generation fighters. While the innovative technology progresses, that work is based on the adaptive technologies currently demonstrating superior performance on fifth-generation fighter engines, such as our F135. The USAF’s investment in the AETP has also proven invaluable as we are flowing technology and architecture learnings from that programme into our NGAP offering as well.
Our offering for the NGAP programme is highly classified, but we have completed a digital PDR, which signals the progress we are making on our design. In 2024, we will continue to advocate for robust funding for sixth-generation propulsion development in the FY25 Department of Defense’s Budget to not only support critical platform milestones and warfighter readiness, but also to prevent a premature down select. The USAF intent is to appropriately resource a competitive programme through detailed design. FY25-28 funding enables competitive prototyping through prototype testing.
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