August 8, 2021:
The American F-35 program is facing a readiness crisis because of unexpected problems with the F135 engine that powers each aircraft. Because of recent problems with the turbine rotor blades wearing out faster than expected, nearly seven percent of the 665 F-35s delivered as of mid-2021 are out of service because there is an engine shortage caused by so many engines needing repairs. The manufacturer of the F135 has a fix for the problem, a coating for the rotor blades that is being applied to engines that come through the maintenance depots for checkups and fixes to any problems found, as well as dealing with rotor blade failure. The engine shortage and some other problems with an inadequate supply of spare parts has seen about half of F-35s not fully “mission capable.” The additional costs of fixing the readiness problems produced a cost per flight hour of over $35,000, which is substantially more than for the older F-16s and F-15. A new version of the F-15 is being offered with lots of enhancements, one of them being a cost per flight hour about 20 percent less than the F-35. The F-35 manufacturer says it is possible to reduce F-35 cost per flight hour to about $25,000 within five years. That is not very convincing because it will cost a lot to achieve that goal, which was supposed to be available early on at much less development cost. The new problems with the F-135 engines also reduces the mission capable or “readiness for use” rate to under 50 percent.
Many of these problems could have been avoided if the Department of Defense had decided not to save some development expenses by cancelling the program to provide two suppliers of engines. The Air Force insisted that the reliability and performance issues that spurred the earlier “second engine supplier” dispute were not present in the F135 engine used by the F-35. This engine is a derivative of an engine that is already performing well, the F119 that powers the F-22. The F135 has also performed very well in ground and flight-testing in the F-35, so the Air Force didn't believe having a second engine supplier was worth the money. Consequently, no money was requested for the alternate F136 engine program in the 2007 budget, effectively killing the program. However, Britain, a major export customer, was very upset with this decision for a couple of reasons. Firstly, they are contributing over $2 billion dollars of the F-35 development costs, and they weren't consulted about the engine decision. Secondly, the F136 was jointly developed by General Electric and British owned Rolls-Royce. This could be worth billions of dollars in sales for British firms, over a 20-year production run. Fortunately, after pressure from the British and General Electric, Congress restored funding keeping the F136 project going for a while. Eventually the F136 was cancelled because of rapidly increasing F-35 development costs.
The Department of Defense stance on the alternative engine program turned out to be a perfect example of "penny wise and pound foolish". By trying to save money needed to develop and field the F136 it could cost our country billions down the road because of the lack of competition, and shrinking the knowledge and manufacturing base required to design and build military jet engines. In 2021 that proved to be correct.
The original so-called "engine war" started in the 1980's as the Pratt & Whitney (P&W) F100 engine and the General Electric Aircraft Engines (GEAE) F110 went head-to-head for contracts to supply engines for hundreds of F-16 fighters. This conflict continues to this day, as the two firms compete over the engines for the many of the thousands of F-15 and F-16 aircraft still in service.
The original second engine dispute was started by the Air Force in response to manufacturing and reliability problems in the P&W F100, which powered the F-15. The Air Force hoped to use the same engine in the new F-16, but in light of these problems GEAE was asked to develop an alternate engine for the F-16, and the Navy F-14. The GEAE F110 was in production for both the Air Force and the Navy by 1986, and the conflict began. The engine war turned out to be a "win-win" situation for the Air Force, the Navy and the taxpayer. The inherent nature of the competition resulted in both engines being highly reliable, having much improved performance, and costing less. It also provided the U.S with two sources for fighter engines, an important consideration at the height of the Cold War. Another important result of the engine war was that the knowledge and skills required to design and build military engines were maintained and passed on in two companies.
Rotor blades were not the first unanticipated engine problem. Some of these problems were solved quickly and cheaply by applying old (as in 1940s) solutions. During “extreme performance” tests of the F-35 in 2011 it was discovered that when pilots used the afterburner to achieve max speed for more than a few minutes, the engine generated so much heat that the stealth coating near the engine exhaust and tail blistered. This reduced the radar-signal absorbing capability of the entire aircraft. Repairing the damage required special maintenance not available at forward air bases or carriers at sea. The manufacturer developed more heat resistant stealth coating for the aircraft and made some other modifications to the engine exhaust area but that did not completely eliminate the problem.
Such heat damage is not unique and other jets with afterburners have experienced similar problems. The F-35 is unique because of the stealth material that covers the aircraft and contributes much to keeping the aircraft invisible, or difficult for radar to detect. Afterburner speed is meant to be used for achieving extreme speed for short periods of time. It is not used in normal flight not so much to avoid heat damage to the engine exhaust area but to conserve fuel.
A typical modern fighter can cruise at 900 kilometers per hour. The F-35 can cruise faster than that and has a theoretical flying time of three hours but only at speeds that do not uses excessive amounts of fuel to achieve high speeds. Most high-performance fighters obtain their highest speed by having an engine that can increase its fuel consumption enormously for short periods using an afterburner. For example, at cruise speed jet fighters burn .5-.6 percent of their fuel per minute. By kicking in the afterburner, cruise speed can be more than tripled, and fuel consumption increased more than twenty times. At full "war power" (using the afterburner for too long) an F35 can burn 30 percent of its fuel in a few minutes. It can also escape from unfavorable situations using that sudden increase in speed. A less experienced pilot will abuse this war power capability to get him out of one tight situation after another. Once a fighter reaches BINGO fuel (just enough to get home), combat must cease. Otherwise, the aircraft will likely run out of fuel before reaching its base and be just as useless as if shot down by the enemy. It's a common tactic to try and force the other guy into high fuel consumption maneuvers. Eventually he will run low on fuel and try to break away. At this point he becomes desperate and vulnerable.
The F-22 had similar problems with afterburner use, but not as severe as the F-35. The F-22 was designed to supercruise; as in going faster than the speed of sound (Mach 1) without using the afterburner. This is one reason why the F-22 is so much more expensive than the F-35, which can only supercruise at Mach 1.2 (1481 kilometers an hour) for about ten minutes before the afterburner kicks in to sustain Mach speed. This was designed into the F-35 because pilot experience showed that in most cases only short periods of supercruise were required. Using the afterburner consumed too much fuel anyway and was only to be used in an emergency. Most modern air combat is performed at subsonic speeds; usually no more than a thousand kilometers an hour. The F-22 can sustain supercruise at Mach 1.5 for as long as the pilot needs it. Go above Mach 1.5 and the F-22 afterburner automatically starts. Supercruise was all the rage when the F-22 was being designed, so it became a requirement. It turned out to be a very expensive capability that contributed to such a high cost per aircraft that production was halted before 200 were built. Twenty times as many cheaper F-35s are being built.
As a result of the F-35 afterburner heat, problem pilots have been warned not to use afterburners at Mach 1.3 for more than 40 seconds, or 80 seconds at Mach 1.2. This is similar to the use restriction given to pilots of some propeller-driven fighters during World War II. These aircraft, most of them American, were equipped with engines modified to generate much more power (20-100 percent more) for short periods. This was usually set for three to five minutes. The most common boosters were water injection and methanol-water injection. This allowed the aircraft to go faster during emergency situations and was called “War Emergency Power”. Excessive use would damage the engine or even cause the engine to fail. Pilots were warned that if war power were used too long, they would lose the engine. Similar warnings were given to F-35 pilots, who were told that using emergency power for more than a minute would degrade their stealth and possibly reduce engine life.
There was no such simple solution for problems arising from defects in the only engine model available for the F-35. With two suppliers of engines, problems like the current one was usually spotted by one of the engine suppliers early and the other engine supplier was alerted. The Department of Defense, acting on U.S. Air Force advice, believed that such problems were not going to arise because engine technology had advanced to the point that this was no longer an issue. The air force was wrong.