Fifth Gen Flight Test

July 27, 2015

The pace of testing the three F-35 strike fighter variants is nearing its peak. The program is the priority flight-test program at Edwards AFB, Calif., and gets first dibs on its tankers, ranges, ground control, and bandwidth. Even so, the pressure is on from military services anxious to field the jets and from Congress to hurry up and prove the multiservice fighters ready for combat.

Testing the F-35, however, is unlike any previous program—even its stealthy, fifth generation F-22 stablemate—because of the program’s size, its international nature, the astonishing array of capabilities jammed into it, and the unprecedented amount of concurrency built into the project.

With only 60 percent of development completed, the Marine Corps expected to declare initial operational capability with the F-35B in July. With a modern fighter, that is unprecedented.

“There’s … a lot of political pressure [and] visibility on it,” said Lt. Col. Andrew Allen, commander of the F-35 Integrated Test Force, in a recent interview.

Will it be everything they want? That’s relative, Allen said.

“To have a service willing to declare IOC well before we’re done developing the aircraft, … I think, speaks

positively about the health of the program and where we are right now,” he asserted.

More, More, More

The Marines will have a basic air-to-air and air-to-ground capability with the F-35B in the 2B configuration. Later software builds will add additional capabilities such as more weapons, more sensor fusion, and more electronic warfare options.

“Any fighter pilot, any service, … you always want more,” Allen said, and he expects that flight testing of software updates and upgrades will probably go on “for decades.”

The F-35s—there are nine test aircraft at Edwards, supported by more than 1,000 people—rub shoulders at the base with just four F-22s, which continue to prove out updates and improvements to that system.

Steve Rainey, Lockheed Martin’s chief F-22 test pilot at Edwards, offered caution about the pace of F-35 testing in a recent interview. A longtime veteran of the aircraft, Rainey was the first USAF pilot to fly the Raptor, headed the test program while in the Air Force, and was Boeing’s chief F-22 test pilot before coming over to Lockheed Martin.

Recalling when the F-22 program was under the congressional microscope and under pressure from Pentagon leaders to speed up flight test, Rainey warned that F-35 testers “have to start worrying about ‘the push.’?” In the surge to get the F-22 on track, he said, USAF leadership put the test force on a seven-day-a-week flying schedule, working 12-hour shifts, without enough people. Predictably, they got tired and made some mistakes,

Rainey asserted.

In one test hop, “we almost put a guy in the dirt” because the simulator didn’t predict the forces the jet would encounter under a specific negative-G maneuver, and neither pilots nor engineers anticipated the situation, resulting in a close call.

Although the workweek was later reduced to six days, Rainey said there was a significant exodus of experienced flight and ground crews after 15 months of the F-22 testing surge, hurting the program and causing further delays.

With “people pushing really hard, you can do that for a while, but you have to recognize the repercussions,” Rainey said. “If you keep doing it forever, you’re going to lose people. We did. Good people decided to leave the [Combined Test Force] when it got really tough.” He said the same problem could affect the F-35. “Ops tempo is always the killer.”

Allen did not complain about the pace of F-35 testing, saying he has the needed manpower, facilities, and aircraft to do the job, but he did urge patience, noting numerous times that an enormous amount of flight sciences and mission systems testing remains to be done.

“In 2014 we overflew our goal of testing sorties,” he said, flying 704 hops when 666 were planned, “so getting the aircraft to work and get airborne is not a limiting factor at all. We have a fully trained and qualified team that is very much capable of operating at max capacity for long periods of time, and our throughput and our capability is definitely not a hindrance to … accomplishing the test program.”

The overflying wasn’t necessarily a good thing, though, Allen noted. The extra sorties had to be flown because there were more software drops than anticipated, requiring extra tests to maintain the schedule.

The mix of aircraft in Allen’s test force includes six F-35As, two F-35Bs, and one F-35C: respectively, the conventional takeoff version, the short takeoff/vertical landing model, and the carrier-capable version. Although there are differences in how they fly, their mission systems are identical, and a mission systems test can be flown with whatever jet is ready to go next.

Flight sciences is the bread and butter of flight test: It defines the aircraft’s performance envelope, its ability to handle stress and loads, vibration and flutter, and how it behaves under unusual circumstances or in odd configurations and in air refueling. While flight sciences on the F-35B with 2B software is done, Allen said there’s still a lot to do with the F-35A and C models and quite a bit more testing to do on mission systems. Much of the flight sciences work being done now concentrates on carrying external loads with a variety of weapons, in

different and asymmetric combinations, to explore as many conceivable contingencies as possible.

Allen said the F-35 is “incredibly stable,” and “I don’t know if I want to admit this, … but it’s incredibly easy to fly. It’s not necessarily easy to employ, but it is easy to fly.”

He said pilots don’t spin-test the F-35 because it won’t spin. “We do departure [from controlled flight] resistance, and then recovery from intentional departures,” he said. “We try to put it out of control and see how it behaves,” but for the most part, pilots don’t have to do anything to recover the airplane; it largely rights itself. Even at very high angles of attack—extreme nose-up attitudes while the jet is moving straight ahead—“the jet’s stable,” Allen said.

The F-35 has a dizzying number of capabilities, he said, and they all have to be tested and refined.

“There’s probably buttons on your [TV] remote, and you … probably have no idea what they do, right? It’s the same concept. There’s just so many things that this aircraft will eventually be able to do.”

A typical day adds up to about three test flights, but they require a phenomenal amount of planning, coordination, assets, and conditions—such as tankers, controllers, chase aircraft, ranges, and weather, to name just a few—that must all line up to make a successful mission.

In addition to envelope expansion, the F-35 is actually put through its paces, dropping ordnance, exercising its electronic warfare, and even flying “against” F-16s, though the Vipers are usually targets and not dogfight adversaries. Even live shots are made, against subscale target drones. Weapons drops are performed both to make sure the ordnance separates safely from the jet and also to ensure the F-35’s accuracy. This constitutes an “end-to-end check” that “the kill chain can be completed, from a weapons perspective,” Allen explained.

Ability to Execute

The F-35 has been flown in concert with E-3 AWACS, F-15Es, Navy F/A-18s and E-2Cs, and in interoperability testing with the British Typhoon and ground-based tactical air controllers. However, these are all systems and compatibility tests. Tactics are developed at Nellis AFB, Nev.

Delays to testing are usually associated with things not being in a software drop that were expected, Allen said. “Our ability to execute is very dependent on the product that we received.”

In the case of the extra missions flown last year, the software “either didn’t perform to the level it was supposed

to, or [as] advertised, … so we were a little less efficient on the amount of test we could accomplish on each sortie.” But the ability to fly those extra missions means that “our maintenance effectiveness and the sustainability of the aircraft here at Edwards have greatly improved.” Edwards has the most experienced maintainers of any unit flying the F-35, he said, and many have been with the program since its inception. The CTF has had the first look at every software version.

Two years ago, when Allen came to the job, F-35s were available for test about 50 percent of the time, and now “it’s improved to where it stays on the schedule and we fly an effective sortie … between 60 and 70 percent” of the time. “So it’s much improved, and that’s nothing to make light of.” Besides the skills of the maintainers, “the supply chain is always going to continue to improve and grow.” Moreover, test maintainers have direct access to the engineers and experts who designed the systems. “We have a little more at our fingertips, … more expertise, here,” to make sure flight tests happen on schedule.

Broadly, Allen said the F-35s are meeting contract specifications, although “expectations may be a different discussion.” In its stability, ability to fly at high angle of attack, and departure resistance, it does very well and has performed “better than expected,” Allen said. The F-35 does “exceptionally well” at instrument approaches and as a stable communication-navigation platform, without the need to reset the computers.

The software pieces are tested individually to make sure they work alone—radar, electronic warfare, sensors, targeting system—and then “we start to add things together,” such as how the radar works with the software fusion engine, with electronic warfare, and the Distributed Aperture System that allows the pilot to see 360 degrees in darkness.

“We go out and in a repeatable manner … try to employ the aircraft in the way that we think it will be employed in the near future. And we make assessments on how well it does in each individual mission,” such as offensive or defensive counterair or interdiction.

Ultimately, they “roll everything up in a ball and do more integrated, big-­system-level testing. But that’s all after we’ve done all the building-block tests up … to that graduation-type exercise.”

One of the challenges of flight testing the F-35 is that it will be used by three different services, whose pilots grew up in different communities and have different ideas of “how something should be displayed,” Allen observed. Display and data management preferences will be different for a pilot coming from an air-to-air system, like the F-15C, versus a mainly air-to-ground system, like the Harrier, and there will be differences in how suitable the pilots think the presentation is. But “we’re not going to develop three different versions of the mission system software,” Allen stated.

Allen, who was also an F-22 test pilot, said the software stability is far more advanced than it was on the F-22 at a similar stage.

Testing the F-22

The F-22 program, which produced 187 combat-capable jets, remains a high-profile presence on the Edwards flight line. Test director Rainey said that although the F-22 program wrapped up development a few months before the jet became operational in late 2005, flight testing has continued since then and will carry on for the foreseeable future.

Two kinds of changes are tested on the F-22: updates—which are corrections of problems—and increments, which are increases in capability, usually in the form of new weapons, sensor changes, or electronic warfare enhancements.

The F-22s that flew missions into Syria last year “were Increment 2 jets,” Rainey said. “That’s so long ago I barely remember doing the testing. That’s how long it takes to get these things fielded and supported.”

The biggest increment so far has been 3.1. It “allowed us to use sensors that were previously passive … in an active way. By coupling that with multiple Raptors, it helps us identify where a threat is.”

Increment 3.1 added a synthetic aperture radar to the F-22, allowing it to perform almost as a mini-JSTARS, but behind enemy lines. It also added the Small Diameter Bomb, giving the F-22 more of an air-to-ground capability besides its initial Joint Direct Attack Munitions. So the F-22 now has even more “knock the door down” capability to penetrate, suppress enemy air defenses, perform surveillance, and escort attacking aircraft “through that hole we just knocked down,” Rainey said.

“In a way … we’re replacing 12 airplanes with a four-ship of Raptors,” he said.

Now the force is testing Increment 3.2, broken up into A and B installments. It adds the new AIM-120D AMRAAM radar missile, the AIM-9X heat-seeking missile, data transfer improvements, and “some other air-to-air capabilities I can’t talk about,” Rainey noted.

The CTF also tests unprogrammed improvements. One example is a sliding panel that covers holes in the wing when fuel tanks and their pylons are jettisoned, restoring the Raptor’s stealth. It works, but Air Combat Command has yet to decide whether to acquire the improvement for the fleet.

A mandated upgrade is an automatic Ground Collision Avoidance System, directed after an accident that killed an F-22 pilot. The system uses a “line in the sky” method that commands a fly-up of the airplane if it’s getting too close to a selected altitude. Flight testing showed that if a pilot forgot to reset the fly-up altitude after coming from a higher altitude terrain to a lower one, it could cause problems. “What if you’re in formation” when that happened, Rainey asked.

Now, if the jet is diving at less than 10 degrees and 60 degrees of bank, the GCAS will warn the pilot of an impending fly-up six seconds before it happens. The line in the sky is not ideal, but using a terrain-based model—Rainey called it preferable—was deemed too difficult to manage on the F-22’s computer arrangement.

The F-35 program has already learned from the experience and went with a terrain system.

After update 3.2B, future F-22 improvements will be called tactical mandates, Rainey said. Some of these are already in the pipeline: methods for the F-22 to talk stealthily with the F-35 and also with fourth generation fighters such as the F-15 and F-16.

The CTF has four airplanes, one of them in “flyable storage” at Edwards and used as a maintenance trainer. There are 330 people in the test force; eight are pilots. Rainey said he plans about two sorties a day, but they are not necessarily all test flights. Some are proficiency hops for the pilots.

Even though some maintainers have been reassigned, Rainey said “we still probably have more expertise and longevity than … the fielded units.”

Why were those cuts made

“Cost. Everything is about money. The more money we can save at the CTF, that’s more money the [system program office] has, to spend on operating the airplane.”

The F-35 is often mischaracterized by people who simply see it as a replacement for the F-16, AV-8B, or F-18, Allen said. “That’s selling this aircraft short.” The F-35, he said, will be applicable “across the full spectrum of combat,” from a “Day One” attack against a heavily defended target to “Day 365 of doing an urban close air support mission.” Allen asserted that “I don’t know another aircraft out there that can be [as] effective across the full spectrum of operations.”

Although the F-35 is not there yet, he said, “I fully believe” the program will deliver on its promises. “We can have a common platform that can operate in a language we can speak among the services and between partner nations, which is a huge capability to have, … no matter what the mission.”

On the spectrum of “crawl, walk, run, … we’re starting to run,” he said.