This article appeared in the January 1997 issue of Code One Magazine.

"Raptor flight check."

The radio call comes from Paul Metz, the Lockheed Martin test pilot sitting in the cockpit of the first F-22 off the production line. His sleek gray airplane idles between two orange-and-white F-16s. All three aircraft await takeoff on the ramp at the end of the runway at Dobbins Air Reserve Base in Marietta, Georgia.

"Two," responds Jon Beesley, another Lockheed Martin test pilot sitting in the F-16 to the left of the F-22.

"Three," responds Maj. Steve Rainey, a USAF test pilot sitting in the other F-16.Metz requests permission to take off.

"Dobbins Tower, Raptor One flight of three, ready. Airborne pickup."

"Raptor One, you are cleared for takeoff," the tower replies. "Airborne pickup approved."

The three aircraft taxi onto the runway. The two F-16s take off first and start a slow 360-degree turn back towards the runway. Metz holds the F-22 on the runway, making final instrumentation checks with his mission control team.

The next radio transmissions come from Beesley, approaching about a mile behind Metz. As his aircraft nears the waiting F-22, Beesley times his radio calls to coordinate the F-22's takeoff with his approach.

"Thirty seconds."

"Ten seconds."

"Release brakes... Now."

Metz releases the brakes, simultaneously easing the twin throttles to military power with his left hand. The Pratt & Whitney F119 engines roar to life, and the F-22 hurtles down the runway. At about 140 knots, Metz pulls back slightly on the sidestick controller with his right hand. The aircraft rotates and jumps into the air. The crowds cheer as the F-22, with landing gear down, climbs steadily north.

This entire first flight scenario, except for the cheering crowds, will be enacted many times before the F-22 actually takes off for the first time in late May of this year. "We began practicing the profile for the first flight last August," explains Metz, who is training the flight team for the initial flights of the first F-22. "The work last summer was to refine the first flight profile and to develop the communication and coordination with the mission control room personnel."

Subsequent training for the first flight involves about nine major practice sessions in Fort Worth in a smaller version of the real mission control room in Georgia. "We can simulate an entire test mission in Fort Worth," Metz says. "We are practicing everything from starting the engine through landing. We want to familiarize the first flight team with the mission control room and with all the procedures associated with the flight tests."

The practice sessions in Fort Worth are conducted in the F-22 Vehicle System Simulator, more affectionately called the Iron Bird. The facility allows the F-22's subsystems and all of their associated hardware and control software, including flight controls, to be tested under realistic flight conditions on the ground. Metz flies the Iron Bird from a simulated cockpit in the facility. A flight test team in the mission control area in the next room monitors the flight. Members of the flight test team are subjected to a number of scenarios in later practice sessions to make sure they know how to respond appropriately to a variety of expected and unexpected events.

The last three of these practice sessions before the first flight are conducted in Marietta, Georgia, not far from the runway at Dobbins. "The first two of these latter training sessions are simulations," says Metz. "They consist of verbal communications between the pilots and the mission control team." The third session is a detailed dress rehearsal of the first flight. "In it," Metz says, "I fly an F-15 as a surrogate F-22. Two F-16s piloted by Beesley and Rainey provide chase. All participants are involved, down to the level of having ground photographers on the runway shooting the takeoff, processing the film, and getting Air Force approval for releasing the photos."

That rehearsal and the real first flight last approximately one hour. The F-22 will fly three times around a triangular route that takes it about forty miles north and northwest from Dobbins. Two flight test support F-16s borrowed from Edwards AFB, California, chase the F-22. Beesley's F-16 is the primary chase aircraft. Rainey's F-16 carries a photographer in the rear seat and performs as a backup for the primary chase.

According to Metz, the most impressive feature of the first flight will be the F-22's rate of climb. "This airplane is not going to take off like a cargo plane," he says. "Even though we're climbing with the landing gear down, the F-16 chase is going to have a tough time keeping up with the F-22. The F119 engines produce a tremendous amount of thrust. The airplane will climb out fast at around a twenty-five-degree pitch angle in military power."

The steep climb angle is a function of maintaining a constant velocity under a fixed power setting. "As a safety precaution," Metz explains, "we want to limit engine transients as much as possible until we gain some altitude. So we're leaving the engine at a military power setting as long as we can. We also have to keep the airplane below a given maximum speed for the climb. These two factors combine with some very powerful engines to produce an impressive angle of climb-even with the gear down, which creates a lot of drag. The takeoff will be an excellent display of the F-22's raw performance."

The airplane reaches 15,000 feet in less than three minutes. Once there, Metz levels off and then cycles the engines through a series of power changes. (The afterburners are not used during the first flight.) He also takes the airplane to an angle of attack of fourteen degrees-the maximum for the first flight. All along, he evaluates the handling qualities of the F-22. "Handling qualities describe the feel of an airplane," Metz explains. "An airplane that requires little pilot effort or is easy to maneuver, land, fly formation, aerial refuel, or dogfight another fighter is said to have good handling qualities."

About midway through the one-hour flight, Metz raises the landing gear and takes the F-22 to 20,000 feet, the maximum altitude for the flight. At this altitude, he goes through more engine transients and evaluates the cruising performance before descending. On his way down, Metz flies formation on Beesley's F-16 to determine the F-22's handling qualities during relatively demanding piloting tasks-what pilots refer to as "high gain" flying.

The profile finishes with the landing gear once again lowered for two simulated approaches at 10,000 feet. The F-22 makes its final approach with Beesley's F-16 flying alongside. The F-22's main gear touches down with a squeak of the tires. Metz aerobrakes to slow the aircraft to about 100 knots. The nose lowers and Metz applies the brakes to bring the aircraft to a full stop. The crowds cheer again.

During its flight, the F-22 reaches a maximum speed of 250 knots and experiences a maximum load of three g's.

"The profile of the first flight may not look like much, but the flight is more than historically significant," explains Keith Lyles, the flight test team lead for the first aircraft.

"The flight itself is a big step in delivering an operational airplane to the customer. All the systems in the aircraft are working together for the first time in the air, and we are collecting a lot of information from the flight as well as establishing an initial flight envelope."

Lyles and about two dozen other engineers will be staffing the control room during the first flight. The room is located in a large hangar near the flight line in Marietta. "We will be monitoring what we call safety of test parameters during the flight," Lyles says. "We're watching things like air speed, fuel flows, structural loads, and hydraulic pressures." These parameters relate to specific sensors-the test boom on the nose of the aircraft, fuel meters, and strain and pressure gauges-that provide aircraft information not available to the pilot.

"We will be monitoring readings from a lot of instrumentation," Lyles continues. "A typical instrumented F-16 allows engineers to monitor a subset of about 350 total parameters. We can monitor about 2,500 parameters on an instrumented F-22. And we can record every parameter at all times during the flight."

Advances in technology have made it easier to monitor and sort through more data. The highly integrated nature of the F-22's systems makes such monitoring essential. The extra parameters result in a more refined structural computer model of the aircraft as well.

All of the test flights at Marietta are designed to confirm the basic airworthiness of the F-22. "These test flights basically fill all the squares for getting the airplane to Edwards AFB in California for additional testing," explains Metz. "We fly the airplane in Marietta to gain enough confidence in its flying qualities and reliability to take it to Edwards."

The first flight is preceded by a series of taxi tests. The tests are used to evaluate the aircraft's nosewheel steering, the braking system, and the operation of the arresting gear at various speeds up to 110 knots. The instrumentation system on the aircraft is also thoroughly checked during these ground tests.

"The taxi tests are also the first basic shakedown of the airplane," Lyles says. "The airplane is running on its own power and moving for the first time. We run the engines in the airframe before these flights, but the aircraft is static for these initial engine runs. Furthermore, the taxi tests, especially at higher speeds, tell us if the air data system is working properly. We are also watching all of the subsystems associated with hydraulics and fuel."

After the first flight and two or three additional airworthiness flight tests in Marietta, the aircraft goes through several months of further preparation and ground testing before it flies again. Engines as well as control surfaces and weapon bay doors are removed and the aircraft is placed in a large test frame. The aircraft is then pushed and pulled using jacks and hydraulic pistons to simulate airloads encountered in flight. The deflections of the airframe are measured by strain gauges attached to hundreds of locations inside and outside the airplane. The strain gauges are calibrated with known loads so they can gather accurate load data on the airplane in flight.

After this testing, the F-22 is put back together and sent to another facility in Marietta where it receives a final paint job. After painting, the airplane goes through ground vibration tests in Marietta to measure its structural dynamic characteristics. These tests are necessary for expanding the flight envelope in subsequent flights.

Ground tests are also performed on the airplane's flutter excitation system. This system sends commands to the flight controls to oscillate or vibrate any of the control surfaces on the airplane while it is flying. The system can induce controlled pulses that simulate atmospheric turbulence and other disturbances. Like plucking a banjo string, the flutter exciter causes the aircraft structure to vibrate. The damping, or dying out of the vibrations, is measured to ensure that the structure is free from flutter-a large amplitude vibration that can be destructive. The system makes certain that the aircraft is structurally stable throughout its flight envelope.

Beesley flies the first flight after the airplane completes these intervening ground preparations and tests. His flights further expand the flight envelope to that required to ferry the aircraft to Edwards. These flights also make use of the flutter excitation system.

Beesley takes the aircraft up to 40,000 feet and 325 knots. He also shuts down and then restarts the engine and the auxiliary power unit in the air. These tests ensure that the engines will restart should they die or flame out during some of the aggressive high angle-of-attack and high-speed tests later in the program.

The first F-22 is scheduled to fly six to eight times at Marietta before flying to Edwards in October 1997. In the last of these flights, Rainey qualifies the airplane for aerial refueling at altitudes of 20,000 and 30,000 feet. The aircraft's flying qualities, emergency breakaway procedures, refueling boom clearance, and fuel transfer rates are evaluated in these aerial refueling flights.

"Aerial refueling is mostly basic formation flying," Rainey explains. "It involves constantly putting a lot of inputs into the stick to make slight adjustments-more of that 'high-gain' flying Metz performs in the first flight. We're confident that we won't encounter any surprises. We've done a good job with the aerodynamic models and predictions with the flight control laws and a good job replicating those laws in the handling qualities simulator. We have also verified them in flight in the F-16/VISTA."

Rainey is also in the cockpit when the F-22 heads to Edwards. A KC-135 tanker and two safety chase aircraft accompany him on this non-stop flight. The route takes the aircraft over eight states in a little over four hours. A backup three-leg route without aerial refueling takes the aircraft from Marietta to Fort Worth to Holloman AFB in New Mexico and then to Edwards.

Whereas the testing at Marietta ensures that the F-22 can be ferried safely, the test program at Edwards focuses on determining that the F-22 does what it promises. Its performance is measured at all altitudes, speeds, g loadings, and angles of attack. The flight test program concentrates on flying the F-22 to the edges of its flight envelope. The airplane breaks the sound barrier about five weeks after arriving at Edwards. The F-22's flying qualities are evaluated under a variety of conditions, including flight with the weapon bay doors open. The aircraft also flies with external stores. The program calls for about three flights per week at Edwards.

"Expanding a flight envelope as large as the F-22's takes a lot of effort," Rainey explains. "This airplane has no limit on its angle of attack. What that means is that we can fly to a post-stall condition and still control the airplane. The F-22's large tail surfaces and thrust-vectoring engines provide a lot of post-stall control authority. The velocity vector may be pointing straight down, but we can put the nose of the airplane wherever we want it. That ability is a revolutionary step in fighter aviation."

The first F-22 completes about 100 flights before the second airplane takes off for the first time with Beesley at the controls. After two or three flights in Georgia, the second aircraft is ferried to Edwards where it is used for high angle-of-attack testing and, later, for testing weapon separations from the internal bay. Before ejecting weapons from the internal bay in the air, weapons are ejected from the bay with the aircraft on the ground.

This ground testing covers AIM-120 ejections from the main bay as well as pylon and store ejections from the various wing stations. The aircraft is also used for testing the performance of the propulsion system and for evaluating the F-22's infrared signature.

The third aircraft, or Aircraft 4003, is slated to be flown for the first time by Boeing's test pilot Chuck Killberg. "The first flight of Aircraft 4003 won't be that different from the first flight of 4001," explains Killberg, who will have flown the first two F-22s well before that flight. "The aircraft will fly a profile similar to that flown by Aircraft 4001 on its first flight. However, I will raise the landing gear right after takeoff.

"Aircraft 4003, though, is unique in other ways," Killberg adds. "It is the first F-22 to have an internal structure that is fully representative of the production aircraft. So we will perform demonstrations in it to 100 percent of the loads." Aircraft 4003 is the first to test the operation of the cannon. It is also used in acoustic surveys at Edwards. In these surveys, the engines are operated at various power settings from idle through maximum power to obtain data on the resulting structural effects and potential physiological effects on maintenance personnel.

The fourth and fifth F-22s to roll out of the Marietta factory will never take off. The aircraft stay in Marietta for static load testing and fatigue testing. (While the flying F-22s are referred to as Aircraft 4001, 4002, 4003, etc., the two non-flying F-22s are designated 3999 and 4000.) Static loads testing on Aircraft 3999 begins after the airplane is placed into a static testing fixture. The fixture allows loads to be applied to various parts of the airplane at varying degrees to test its structural strength under highly controlled and closely monitored conditions. Generally, these loads are applied to simulate loads experienced in actual flight.

"Our work is sequenced to support flight tests," explains Ed Kelley, the structures manager for developmental and verification testing for the F-22. "We test loads on the ground before they are tested in the air. We go through all the load cases to limit load first, that is, the design limit of the structure. Then we perform what are called ultimate tests in which we take the structure to 1.5 times its load limit. We perform these ultimate tests before we fly the flight test airplanes to their limit."

All of the test results are used to update structural models, also called finite element models. These models are representations of the airplane that break down its structure into discrete mathematical units called elements. The model is used as a basis for all structural analysis.

For fatigue testing, Aircraft 4000 is placed in a test fixture similar to the one used for static loads tests. The airframe is then loaded in many cycles over long periods of time to simulate stresses associated with expected operational use. "This testing evaluates the durability of the airframe," Kelley adds. "We are essentially flying it on the ground in a flight-by-flight manner around the clock." The airframe accumulates a lifetime of stresses in about eight months of this testing. Kelley and his coworkers put the airframe through two lifetimes to evaluate its basic durability. They then subject it to two more lifetimes of extended fatigue and damage tolerance testing.

"Fatigue relates to how long it takes to form a crack, which affects when the F-22 is required to go through its initial inspection," Kelley explains. "Damage tolerance is related to crack growth rates, which are used to determine inspection periods for the aircraft."

Fatigue testing takes about two and a half years. Afterwards, the airframe is completely disassembled and thoroughly inspected for any cracks not detected during the tests.

Beginning around the year 2000, F-22s roll out of the factory at a fairly regular rate-about one every other month. The biggest jump in technology comes with Aircraft 4004. It and subsequent aircraft have a full suite of avionics and software. In some respects, this airplane represents the first "real" F-22 because it contains all of the avionics that allow the pilot to use aircraft sensors to locate, target, and shoot enemy aircraft.

"The first three aircraft blaze the way for 4004 by flying to maximum speeds, g loads, and angles of attack for the first time," Metz says. "These flights make sure the airplane has the strength and flying qualities throughout its envelope. Aircraft 4004 begins the task of verifying that the sophisticated sensors and other avionics work within that flight envelope."

Before any software ever flies on an F-22, it is thoroughly tested on the ground in Seattle in Boeing's Avionics Integration Laboratory and in the air in Boeing's Flying Test Bed. "Our primary purpose is to reduce risk and to find problems," explains Bruce Ammerman, manager of the lab. "This program is unique in the extent it uses ground testing. The highly integrated nature of the airplane makes such testing essential. It's much cheaper to find and fix problems in the lab than it is on the airplane."

All of the software and hardware goes through the integration lab for Aircraft 4004 and on. "This work includes the full weapon system integration as well," Ammerman continues. "We use actual missiles, without warheads and propulsion systems, as part of this effort."

The Flying Test Bed begins flying well before Aircraft 4004 comes off the production line. It is used primarily to integrate aircraft sensors. The aircraft, which happens to be the first flight test Boeing 757, carries the forward fuselage of an F-22 on its nose and a sensor wing on its crown. The aircraft also contains a simulated F-22 cockpit for pilot-in-the-loop testing. The nose structure houses the Northrop Grumman AN/APG-77 radar designed for the F-22. The sensor wing contains electronic warfare equipment and communication, navigation, and identification sensors.

Interestingly, the F-22 contractor team used the same 757 to successfully demonstrate sensor fusion during the demonstration/validation phase of the F-22 program. "The modified 757 is our dynamic sensor fusion test bed," Ammerman explains. "We test the sensors on the ground under static conditions. Targets may move, but the sensors themselves don't. But sensors, such as radars, behave differently when they are moving. So we use the 757 to investigate that subset of issues peculiar to dynamic conditions." The airplane is also used to integrate the full suite of sensors for the first time.

"What we are doing with the first three airplanes has been done in individual pieces before," Rainey explains. "We have done supercruise with the prototypes. We have done fly-by-wire flight controls with several aircraft. We have done thrust vectoring and post-stall maneuvering with the YF-22 and with the MATV/F-16. But the integrated avionics truly separate the F-22 from any aircraft flying.

"The F-22 has the most advanced avionics combined with outstanding flying qualities, high pitch rates, post-stall capabilities, supercruise, incredible agility, rapid acceleration, internal weapons, and with a very high degree of stealth," Rainey continues. "What happens after that first flight will be truly amazing."