One of the programs that’s causing excitement among military aircraft observers is the adaptive engine (AE) effort which is intended to be applied to the F-35 and the next generation aircraft.
What kinds of benefits are being sought? From Wikipedia,
The AETP [Adaptive Engine Transition Program] goal is to demonstrate 25% improved fuel efficiency, 10% additional thrust, and significantly better thermal management.
From Wiki, here’s a brief description of the technology and hoped for benefits:
The XA100 is a three-stream adaptive cycle engine that can adjust the bypass ratio and fan pressure to increase fuel efficiency or thrust, depending on the scenario. It does this by employing an adaptive fan that can direct air into a third bypass stream in order to increase fuel economy and act as a heat sink for cooling; in particular, this would enable greater use of the high speed, low altitude part of the F-35 envelope. The increased cooling and power generation also enables the potential employment of directed energy weapons in the future. When additional thrust is needed, the air from the third stream can be directed to the core and fan streams. In addition to three-stream adaptive cycle configuration, the engine also uses new heat-resistant materials such as ceramic matrix composites (CMC) to enable higher turbine temperatures and improved performance. According to GE, the engine can offer up to 35% increased range and 25% reduction in fuel burn over current low-bypass turbofans.
Currently, the F-35A has an unrefueled range in the region of 1,350 miles, which would be increased to around 1,800 miles with the new engine. [ed. 33% increase]
So, to sum up, what are the benefits? From the above description, we see claims of :
- 25% fuel efficiency
- 35% increased range
- 10% additional thrust
- Better thermal signature management
On the other hand, what do we know about developmental programs? Well, with 100% historical certainty, we know that developmental programs always overpromise and underdeliver. Thus,
- Costs always increase
- Schedules always slip
- Claimed capabilities are never met
- The new technology will be vastly more complex and less reliable then the preceding technology
In addition, the claimed benefits are obtained only under perfect conditions. For example, the claimed increase in range is only if the engine is used under ideal conditions for the entire distance. In reality, no aircraft is going to cruise under perfect, maximum economy conditions for an entire mission. Therefore, the increase will be significantly less than claimed.
So, combining the three factors of claims, historical reality, and realistic operating conditions, what would more realistic benefits be?
- 15% fuel efficiency
- 20% increased range
- 5% additional thrust
- Slightly better thermal signature management
Even those are likely on the optimistic side!
We don’t know the costs but, like any cutting edge technology, they’ll be eye-watering. Now, let’s combine the more realistic benefits with the massive costs, greater complexity, and lower reliability that goes hand-in-hand with greater complexity and ask ourselves, are the benefits worth the cost, complexity, and lower reliability (reduced aircraft readiness/availability)?
Given that aircraft readiness rates are already in the toilet, is introducing an even more complex and less reliable engine really a step in the right direction?
Are we sure this isn’t a case of pursing a technology for its own sake rather than for any actual gain in combat effectiveness? In fact, let’s think about combat effectiveness.
Fuel efficiency is a cost savings but is not a direct improvement to combat effectiveness. Similarly, increased range may offer some improvements in flexibility of operational planning or loiter time but is not really a direct improvement to combat effectiveness. Thrust, on the other hand, can enhance combat effectiveness but not significantly in the small amount we’re talking about. Thermal signature reduction also offers a direct improvement to combat effectiveness but the degree of improvement is unquantified and will likely be minor.
Without a doubt, gains in thrust (even small gains), fuel efficiency, and range are all nice to have. No one would argue with them or turn them down … if they were free. However, as with any new, cutting edge technology, they most certainly will not be free in terms of dollars, time, or reliability. There will be staggering prices to be paid.
Consider the examples of the LCS, Zumwalt, F-35, and Ford. All promised huge gains but the reality is that the gains have been non-existent to minimal and, in some respects, have resulted in decreases in combat effectiveness while incurring horrific costs and massive schedule delays. Do we really think that never before done adaptive engines will be the breakthrough technology that will achieve all its goals and do so affordably? Only a fool would believe that.
So, again, is it worth it?
I would suggest, no.
An adaptive engine will, without a doubt, result in staggering costs, increased complexity, decreased aircraft readiness and minor improvements mainly financial and logistic in nature. Are the improvements worth the cost and problems? K.I.S.S. rules the battlefield. Is a more complex and less reliable engine the way to follow the K.I.S.S. mandate?
We also need to consider the implication for war. When the war with China comes, we’ll need lots of engines. The more complex the engine, the fewer we’ll be able to produce and the longer they’ll take to make. During war, it’s better to have a simpler engine that meets 80% of the performance needs and can be quickly and easily produced than to have complex engines that are difficult to make and cannot be produced in the required quantities.
China is coming for us and we need to reorient our thinking to wartime production requirements instead of long, drawn out, unaffordable, complex peacetime requirements. The adaptive engine appears to be more of a business case than a combat case.
Wikipedia, “General Electric XA100”, 14-Apr-2022,
The Drive website, “F-35s Could Get New Engines As Soon As 2027”,Thomas Newdick & Joseph Trevithick, 11-Dec-2021,