Five Reasons Buying An All-New Engine For The Air Force’s F-35 Fighters Is A Real Bad Idea

Over the last decade, the Pentagon’s F-35 fighter has progressed from controversy to acclaim. With more than 800 fighters delivered to three U.S. military services and nearly a dozen allies, the stealthy, single-engine aircraft is now widely recognized as the future of tactical air power.

That status is due in no small part to Pratt & Whitney’s F135 engine, an afterburning turbofan that is by far the most powerful, reliable propulsion system ever to equip a tactical aircraft. The F135 has already supported three upgrades of the fighter’s airframe and payload, and is capable of supporting yet another aimed at giving the aircraft greater reach, lethality and survivability.

However, the engine has never been significantly upgraded since its inception over 20 years ago. Although it is capable of providing the additional power and cooling needed to support further aircraft improvements, that would require the engine to run hotter—which in turn would require more frequent maintenance.

A more sensible approach would be to upgrade the engine in tandem with the airframe, an option that is eminently feasible given F135’s built-in growth margin and modular design. Pratt & Whitney, a contributor to my think tank, has proposed an “enhanced engine package” to do precisely that, focused mainly on providing the system with a new core.

This should be a simple story of how the world’s dominant fighter will evolve to keep up with emerging threats.

However, the path forward has been confused by an ill-conceived proposal to develop new engines for the Air Force’s variant of F-35. The new engine would be based on research funded by the Air Force in an effort called the Adaptive Engine Transition Program—research that was intended to design an engine that could be more fuel-efficient and powerful while still masking its thermal “signature.”

The concept was reasonable enough, and with additional years of investment it might eventually have yielded a highly capable engine. However, the Pentagon has already embarked on development of an even more advanced next-generation engine, and the so-called adaptive solution would cost much more to produce and field than simply upgrading the F135.

Air Force Secretary Frank Kendall has recently cited the high cost of developing such an engine—equivalent, he says, to the price of 70 F-35 fighters. But there are more compelling reasons to avoid buying an all-new engine for the Air Force’s F-35 fighters. Here are five of them.

Technical risks would slow fighter modernization. It takes a long time to design and develop a new fighter engine, particularly one that promises world-class performance. The adaptive engine is expected to weight a thousand pounds more than the F135, so it can’t simply be “dropped” into the fighter the way a modified F135 would be.

Integrating a completely new engine into a preexisting airframe would entail extensive engineering challenges, some of which could not be anticipated in advance. By the time engineers were sufficiently confident in the engine’s performance to ramp up production, it would be “late to need” as they say in the Pentagon—in other words, not available in time to support other modernization objectives. It thus would be a drag on the overall program.

The cost of operating fighters would balloon. Secretary Kendall figures it would cost $6 billion to develop the new engine, three times what it would cost to upgrade the F135. But that would just be the beginning—the Air Force would then need to procure the new engine and sustain it in service. It would require a new supply chain, new maintenance procedures, and a host of other add-ons to existing infrastructure.

Since the Air Force already has hundreds of F135s in the active force and it is by no means clear the sea services would want to pursue a new engine for their own fleets, the prospect would be for two different engines taking the place of a single common engine across the joint force—each with its own unique support requirements. We know this is likely, because even if the new engine could be made to fit in Navy versions of F-35, it definitely will not fit in Marine variants. Imagine the cost and complexity such diversity entails across a 50-year service life.

Allies would be left behind. The money-saving potential of fleet commonality extends far beyond America’s joint force. The F-35 program was conceived to have a global sustainment system that would generate major economies of scale, and that applies to the engine as well as the airframe. However, although most of the overseas partners in the program are purchasing the Air Force variant of the fighter, none has signaled interest in substituting a new engine for the F135.

Many of these partners are eager to upgrade their fighters with new weapons, improved sensors, agile software and the like, but they expect to obtain those benefits without paying for a new engine. It is implausible that they would be willing to start over with a new engine, and all the logistical complexities that entails, when a simple upgrade of the F135 would support all of the fighter’s envisioned enhancements for the foreseeable future.

Money would be diverted from other priorities. The U.S. Air Force is straining to modernize a fighter fleet that has become the oldest in its history. It is also trying to acquire (1) a new bomber, (2) a new tanker, (3) a new airborne warning plane, (4) a new trainer, (5) a new intercontinental ballistic missile, (6) a new nuclear cruise missile, and (7) a host of advanced conventional munitions. And that’s before we even get to space systems. The service’s modernization budget is stretched to the limits of what is doable.

Against that backdrop, it makes little sense to embark on development of a new fighter engine when the existing system still has growth potential and research on a next-generation engine has already commenced. Any attempt to introduce an adaptive engine into the F-35 will drain billions of dollars away from other modernization priorities at a time when threats are multiplying.

No meaningful gain in performance would be achieved. Since the F135 is already capable of supporting planned improvements to the aircraft and modifications of the engine would minimize any maintenance impacts, the benefits of an all-new engine would be confined entirely to the propulsion aspects of performance. An adaptive engine would likely offer significant fuel savings and an incremental gain in power, but those benefits would be eclipsed by the huge cost burden of developing, producing and sustaining a new propulsion system.

The absence of enthusiasm for buying a new engine among the sea services and overseas partners implies that they do not see performance gains commensurate with the price. Quite the opposite: introducing additional complexity into a weapons program that is already one of the most ambitious in history would just make life more difficult for warfighters. The Air Force should stick with an engine that has proven its safety and reliability, rather than leaping into the mare incognitum of unproven technology.