Murphy's Law: Reviving War Emergency Power

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June 14, 2020: F-35 pilots have a new problem with an old (1940s) solution. 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.

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. However, high-performance fighters obtain their 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; go 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; (less than Mach, 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.

What is old is new again with F-35 pilots given “War Emergency Power”, just like grandpa used to talk about during his time as a P-51 pilot over Europe, fighting Me-109s and, at the end of the war German jet fighters.

This War Emergency Power is not discouraging news for prospective customers for the F-35 because the main attraction is the enthusiasm of those pilots who have flown the F-35. There are a little more than one thousand F-35 pilots (and about ten times as many maintainers who keep the F-35s ready to fly) so far, but that number is rapidly increasing and they all confirm that the F-35 is not just a modern stealth aircraft but incorporates software and a degree of built-in automation that produces a spectacular, easy to use and very effective pilot experience. The F-35 has a large number of sensors, as in receivers for electronic signals, six cameras and a very capable radar, and the fusion of all that data and presentation to the pilot based on the current situation is impressive and makes the F-35 much easier to fly, despite all the additional capabilities it has.

This sort of thing is not a new idea. By the 1990s it was recognized that this new technology (called data fusion) would be a key capability for combat aircraft as well as ships and ground forces. Put simply, it's all about taking real-time vidcam, radar and sensor data plus other information about the battlefield situation (all sorts of databases and reports), and combining it to provide commanders with a better understanding of current operations, preferably in real-time if you are a fighter pilot. Pilots agree that the heart of the F-35 superior capabilities is its software along with the digital communications with other aircraft and troops on the ground.

The F-35 is apparently the best working example of this so far and what is being learned from the F-35 software has become the basis for updated software for older aircraft. But beyond the data fusion, and automatic sharing with other aircraft or systems on the ground, the pilots were impressed about how effective the “pilot assistant” software was. This is another concept that has been around for decades and more frequently installed in new aircraft. These minor advances get reported but never make headlines. But given the F-35s' stealth, maneuverability and sensor/data fusion, most pilots quickly become enthusiastic proponents of the aircraft.

The F-35 software is more complex and omnipresent throughout the aircraft than in any previous warplane. Because of that, it requires a major effort to implement and test any software changes. As a result, some major upgrades are needed to how F-35 software changes are made and how quickly. In wartime this would be essential as otherwise vulnerable aircraft would be grounded when needed most.

As of mid-2020, over 500 F-35s have been delivered, mostly to the U.S. Air Force and Marine Corps. In 2018 alone 133 were delivered and that is expected to rise to 141 in 2020 with additional slight increases in annual deliveries until 2023. By the end of 2020, about 650 F-35s will be in service. Over 4,000 F-35s are expected to be delivered by the mid-2030s with more than 70 percent going to the United States.

The 31-ton F35 is armed with an internal 25mm cannon and four internal air-to-air missiles (or two missiles and two smart bombs) plus four external smart bombs and two missiles. All sensors are carried internally and max weapon load is 6.8 tons. The aircraft is very stealthy when just carrying internal weapons.

Currently, there are orders for nearly 3,000 F-35s. Most of these (1,700) are F-35As for the U.S. Air Force and 500 to foreign customers. Most of the 540 vertical takeoff F-35Bs on order are for the U.S. Marine Corps, and all of the 340 F-35Cs (aircraft carrier version) are for the U.S. Navy and Marine Corps. The F-35B costs about $135 million each and the F-35C about $120 million. This is more than the $90 million F-35A partly because many more F-35As are being built and carrier versions have to be “ruggedized” to handle the harsh treatment received when  making a carrier landing. The air force would call such an event a “hard landing” and pull the aircraft out of service for a thorough checkup for damage. The F-35C is built to regularly survive those hard landings, as well as constant exposure to corrosive saltwater. The F-35B makes gentler landings and can take off like a helicopter thanks to the special engine exhaust system that puts the propulsive jet exhaust under the aircraft. Prices on F-35s are declining as production increases with the F-35A getting as low as $80 million each in a few years.

In 2001 the U.S. believed 5,100 F-35s would be sold but the rising costs and increasing delays drove that down to 3,100 by 2013 and 2,500 by 2018. Now that some F-35s are actually in service (F-35As and 35Bs) and getting good reviews from users, sales are increasing. Or maybe not, because there is a lot still to be discovered about how well the F-35 will do in comparison to the many F-16s, F-15s, F-18s and AV-8s it will replace. The F-35C was supposed to enter service in 2018 but that didn’t happen until January 2020. That has no impact on foreign sales because few, if any, were ever expected for the F-35C.

 


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