F-35's Engine Problem Solved Out by 2024?
Modifications to the cooling system of the F-35's overheating avionics/electronics compartments and to meet the additional electricity needs of the new weapons and sensors to be acquired with the Block 4 version are considered mandatory.
F-35 Block-4 Modernization
The fifth-generation F-35, which is best described as a 'low-visibility stealth aircraft designed to perform missions while avoiding enemy radar', is a flying mission computer. Thanks to the mission computer, which has a total of 24 million lines of software code in the background, the F-35 fighter jet fulfills the missions expected of it.
The operating software of the F-35 is being improved with new versions called blocks. Each time a block/version is upgraded, new software capabilities are added to the aircraft in the new block.
In this context, the Block-4 software version is planned to be commissioned in the near future. Block 4 is the name given to the current modernization program for the F-35 platform. With the currently planned final software version Block-4, it is aimed that the users of the aircraft will have a brand new war machine in terms of operations. With the Block-4 version, which is expected to allow the highest level of use of avionics systems, the aircraft's mission systems will be further upgraded.
The Block 4 version also includes the integration of a new radar to replace the APG-81. The AN/APG-85 radar, developed by Northrop Grumman and expected to be ready for flight tests by 2025, is expected to become the standard radar used on all F-35s following the tests.
There has never been an aircraft that provides as much situational awareness as the F-35. Situational awareness of the pilot is one of the biggest advantages for air combat. For this reason, along with the radar, advanced DAS (six infrared cameras and processors mounted on the outside of the aircraft) and EOTS (targeting system) systems that increase situational awareness will be integrated into the aircraft, doubling the performance of the sensors on the aircraft and increasing the capabilities of the F-35 in general. Block-4 will also provide nuclear weapon capability to the aircraft of the countries that request it.
The development/integration cost of the Block-4 version is estimated at approximately 10.8 billion dollars, excluding the engine. This is expected to bring an additional burden of approximately 3 million dollars per aircraft. As in the case of the F-16s, each time a new version is integrated, the countries that use the aircraft also have to bear this additional cost.
Engine and Cooling System Modification
The F-35 is a single-engine aircraft. The aircraft's Pratt & Whitney-built F135 turbofan engine has a rated thrust of 28,000 lbs. at military idle and 43,000 lbs. (191 kN) with the afterburner engaged. This engine is known as the most powerful engine ever developed and deployed in fighter jets in the world today. Even as it stands, it allows the F-35 to fly at Mach 1.2+, the super cruise speed. The development process is expected to take several years and the new engine version is expected to be commissioned in 2028/2029. This will save 30% fuel for F-35 users, while increasing engine power by 10% and increasing engine displacement from 43,000 pounds to 47,300 pounds.
Meanwhile, the main problem with the F135 engine used by the current F-35 is that it runs twice as hot as designed. In order to provide adequate cooling for the avionics systems, as well as to achieve the desired weight-to-efficiency ratio, the engine must run at high performance at all times. This leads to continuous overheating of the engine, which in turn leads to metal fatigue and shortens the lifespan of the engines. In this context, modifications in the cooling system of the aircraft's overheating avionics/electronics compartments, as well as meeting the additional electricity needs of the new weapons and sensors to be acquired with the Block 4 version, are deemed imperative.
In fact, the F135 engine, the world's most powerful engine in its class, is insufficient for the F-35. The design and production of a new engine for the F-35 was on the agenda. General Electric Aerospace's XA100, a new engine based on adaptive engine technology, was being considered in this context. However, cost and time pressures led the Pentagon to prioritize upgrading the existing F-135 engine over the new engine. At the center of the engine upgrade is the engine core, called the ECU (Engine Core Upgrade).
According to the Pentagon's roadmap, Pratt & Whitney will continue to be the sole source for engine upgrades, unless there is a major change in the coming years. Accordingly, P&W will start the engine upgrade program in mid-2024 and will complete it in 2031.
The Engine Core Upgrade aims to provide more power and cooling capacity to the F-35 without requiring the replacement of existing F135 engines with a new design. The high weapon capacity, new sensors, and sensors and systems for advanced electronic warfare and target recognition capabilities to be gained with the F-35 Block 4 require more power than the aircraft's current state, making it necessary to address cooling problems. In this context, the Honeywell-made power and thermal management system PTMS (Power and Thermal Management System) used in F-35s needs to be modified together with the ECU.
Conclusion
The need to upgrade the F-35 engines is driven by the need to support improvements in Block 4 weapon and sensor systems, in addition to addressing existing problems. The new Block 4 systems will require more electrical power and more cooling. In addition to providing additional power, the F135 engine modernization is expected to provide a solution to the aircraft's current heating problem.
Meanwhile, the Pentagon considers upgrading the existing F135 engine sufficient for now. This means that the option of developing an adaptive engine, which many experts say is the F-35's real need, has been shelved for now. However, it has been leaked to the media that there is talk in US defense industry circles that this decision will be reconsidered in the 2030s and that a step will be taken to continue with the new engine, especially in the F-35B. It is likely that by the time the sixth-generation fighter jet, the NGAD, is ready in the mid-2030s, the corresponding engine will also be ready. It is understood that GE's XA100 adaptive engine technology will be a solution in this sense. I believe that the progress made for the NGAD engine will eventually be a gain that will be reflected in the F-35 engine (similar to the AESA SABR version of the radar). I believe this is why the Pentagon has closed the door to any other pursuit than simply upgrading the existing PW-built F135 engine for the Block 4 version.
References
Raif BİLGİN, “F-35'lerin Soğutma Sistemlerinde İyileştirme Gerekiyor”, STRASAM, 8 Haziran 2023, https://strasam.org/savunma/havacilik-ve-uzay-sanayii/f-35lerin-sogutma-sistemlerinde-iyilestirme-gerekiyor-2040
Hüseyin FAZLA, “F-35 Savaş Uçağının Artıları ve Eksileri Nelerdir? F-35 Programının Halletmesi Gereken Sorunlar: Bölüm-5”, STRASAM, 17 Ocak 2023, https://strasam.org/savunma/havacilik-ve-uzay-sanayii/f-35-savas-ucaginin-artilari-ve-eksileri-nelerdir-f-35-programinin-halletmesi-gereken-sorunlar-bolum-5-1569
Stephen Losey, “Pratt to start receiving F-35 engine upgrade contracts in early 2024”, Defensenews, 29 November 2023, https://www.defensenews.com/air/2023/11/28/pratt-to-start-receiving-f-35-engine-upgrade-contracts-in-early-2024/
