RTX‘s [RTX] engine subsidiary Pratt & Whitney said that it has established firewalls between its F135 Engine Core Upgrade (ECU) for the Lockheed Martin [LMT] F-35 fighter and the Enhanced Power and Cooling System (EPACS) design effort by another RTX subsidiary, Collins Aerospace, for a new Power and Thermal Management System (PTMS) for the F-35.

Honeywell‘s [HON] Torrance, Calif., plant builds the F-35 PTMS, which supplies main engine start and auxiliary and emergency power needs, in addition to 30 Kilowatts of aircraft cooling, but the F-35 Joint Program Office (JPO) and industry representatives say that the current PTMS needs an upgrade or replacement to accommodate the cooling requirements of new weapons and sensors for Block 5 of the F-35, which is to field after 2030, and possibly for Block 4.

“The JPO is in the early stages of determining next steps for PTMS modernization,” Jen Latka, Pratt & Whitney’s vice president of F135 programs, wrote in an Aug. 15 email through Pratt & Whitney public affairs. “We will support them in their efforts as required. The JPO asked us [in] mid-June 2023 not to share any information on ECU with potential PTMS providers because it could turn into a competitive effort. Based on this request, Pratt immediately developed and implemented a mitigation plan that includes firewalls between our Pratt ECU and Collins EPACS teams to avoid conflicts of interest. We respect the JPO’s desire for a fair competition on PTMS.”

Collins Aerospace said at June’s Paris air show that the company had conducted a lab test in Windsor Locks, Conn., of the EPACS  (Defense Daily, June 28). Collins Aerospace said that EPACS will provide “more than twice the current cooling capability to support additional growth beyond Block 4 and is expected to provide enough cooling capacity for the life of the aircraft.”

EPACS includes a Collins Aerospace air cycle system, electric power generator and controller and an auxiliary power unit (APU) by Pratt & Whitney. The F-35 now has Honeywell’s GTS130 APU.

Jill Albertelli, president of Pratt & Whitney’s military engine business, has said that “the F135 ECU paired with an upgraded PTMS can provide 80KW [kilowatts] or more of cooling power for the F-35, which will exceed all power and cooling needs for the F-35 through the life of the program.”

Honeywell said that it has been working with Lockheed Martin and the F-35 Joint Program Office to lend up to 17 kilowatts more of cooling for the F-35 for a total of 47 kilowatts of cooling on the Block 4 F-35.

The addition of 17 kilowatts of cooling includes two kilowatts to be fielded in PTMS next year under the F-35 Continuous Capability Development and Delivery effort. The two kilowatt improvements include “optimizing the cold liquid loop architecture and increasing the ability to use the jet’s heat sinks via the thermodynamic cycle,” Honeywell said.

From Honeywell’s standpoint, the 17 extra kilowatts may be enough extra cooling for the sensors and weapons on F-35 Block 4, while Block 5 after 2030 will likely require additional incremental changes like additive or other advanced heat exchangers to give the fighter 60 kilowatts to 80 kilowatts of cooling. The requirements for Block 4 and Block 5 thus far are not firm.

Honeywell has said that its PTMS was a factor in Lockheed Martin winning the Joint Strike Fighter competition in 2001, as the company says that PTMS is 1,000 pounds lighter than conventional, non-integrated power systems.

In May, a Government Accountability Office (GAO) report highlighted a lack of bleed air and said that the F-35 will need a new or improved PTMS to accommodate future weapons and sensors on the aircraft (Defense Daily, May 30). The question appears to be when.

Honeywell has lamented the lack of collaboration it has had with Pratt & Whitney to improve Honeywell’s existing F-35 PTMS.

“We haven’t talked to Pratt & Whitney at all,” Matt Milas, president of Honeywell’s defense and space business, said in an Aug. 14 virtual interview. “I’ve been reaching out to them to try and get some sort of connection going. We don’t have any contractual relationship so there’s not really anything that we can work with them on, but I’ve been engaging with the JPO to try and get access to the F135 data so that we can look at what else we can do.”

Milas said that replacing, rather than upgrading, the existing F-35 PTMS, which is integrated in the F-35’s electrical and life support systems, is like “doing heart surgery” and that a new PTMS could cost $3 billion (Defense Daily, Aug. 14).

“The thing with the [May] GAO report is that it put all the blame on bleed [air],” he said. “But there’s a lot of things that can cause engines to have reliability issues, and I think the report was too far biased towards just focusing on bleed but not on the other things. There have been a number of quality concerns over the years.”

“There are things that we can do to reduce the amount of bleed air required by the PTMS, and it would be nice if Pratt & Whitney would reach out and ask to collaborate and work together on some of those solutions that could help improve the reliability of the engine, but I think that largely it’s been, ‘Blame the PTMS. The engine’s fine,’ ” Milas said.  “You’d think that if I had a teammate that was causing my components to have issues, I’d be reaching out to them, saying, ‘Hey, this bleed air is a real problem for my engine. What else can you do?’ But we haven’t had any of that sort of conversation.”

Latka wrote in the Aug. 15 email that Honeywell has not approached Pratt & Whitney on an upgrade to the existing F-35 PTMS.

“Honeywell has not approached Pratt & Whitney asking for help with their PTMS upgrade plans,” per Latka. “This makes sense because there is no direct contractual relationship between Pratt & Honeywell, and we therefore cannot collaborate without explicit JPO direction, which has not been given.  Honeywell is a subcontractor to Lockheed Martin on the Air Vehicle prime contract with the JPO, and all PTMS activities including propulsion integration fall under the Lockheed contract.”