F-22 Raptor Flight Test
The demonstration and validation (dem/val) phase of the program began on October 31, 1986 and cumulated with an intensive flight test program at the Air Force Flight Test Center at Edwards AFB, Calif. in late 1990. In just over three months of flight testing, the two YF-22 prototypes demonstrated maximum mach number, supercruise (supersonic flight without afterburner), high angle of attack (high alpha) maneuverability, aerial refueling, and thrust vectoring. This flight testing helped substantially in reducing risk going into the current Engineering and Manufacturing Development (EMD) phase.
The supercruise capability was demonstrated on both aircraft using different sets of engines (General Electric YF120 GE 100 and Pratt Whitney YF119 PW 100). The high angle of attack work accomplished by the YF-22 was impressive and gave the team high confidence in the F 22's stability and flight controls.
A total of 74 flights were flown on the two YF-22s for a total of 91.6 hours. After contract award in July 1991, another 39 flights totaling 61.6 hours were subsequently flown on the Pratt & Whitney powered number two prototype in a follow on dem/val flight test effort.
Although the team built and flew the prototype YF-22s and gained quite a bit of knowledge about the technologies involved, there have been some significant changes in the design for the production F-22s. The YF-22 and the F-22 are similar in shape but there are a number of differences not immediately apparent to the uninitiated observer. The external geometry of the F-22 changed significantly from the YF-22 prototype. Specifically, the wingspan was increased, the wing leading-edge sweep was decreased, the vertical tails were reduced in area and moved aft, and the horizontal-tail surfaces were reconfigured.
Externally, the wing sweep has been reduced 8 degrees (from 48 on the prototype to 42 degrees on the F-22). The canopy has been moved 7 inches and the inlets have been moved aft 14 inches to increase the pilot's visibility. The wing trailing edge and horizontal stabilator shape have been changed for low observability reasons, as well as structural strength and aerodynamic refinements. The prominent vertical tails of the prototype have been reduced in size by approximately 20 percent. As a result of the rapid pace of the dem/val program, the team designed the vertical stabilizers of the YF 22 larger than was necessary in order to avoid potential spin problems. When the spin problems never materialized, the airframe designers could reduce the size of the vertical tails of the F-22 to make the aircraft more aerodynamically efficient and reducing drag and weight.
Internally, the F-22 has all new subsystems based on the prototype's approach, built to an 8,000-hour service life. While the YF-22s were essentially engine and airframe demonstrators, the F-22A has complete sensor and weapons capability. The aircraft is fully self-contained for starting and can use its auxiliary power unit to perform most maintenance tasks.
The number one YF 22 prototype was taken to Andrews AFB, Md., in 1991 where it was a part of the Air Force's Stealth Week informational display for Congress. The aircraft was then brought to the then Lockheed Aeronautical Systems Company in Marietta, Ga., where it was used as an engineering mockup. In March 1997, the YF-22 was shipped to Nellis AFB, Nev., where it was part of the Air Force's 50th Anniversary Celebration in April. In the summer of 1997, the number one YF-22 was retired to the Air Force Museum at Wright Patterson AFB, Ohio.
The number two YF 22 prototype was used in the follow on flight test program in late 1991 and early 1992. Returning to Edwards after a test flight, the YF 22 experienced a series of pitch oscillations, and with the landing gear retracted, the aircraft hit the runway, slid, and burned. Although no longer flightworthy, the external damage was later repaired, and the YF-22 was airlifted to the Rome Air Development Center at Griffiss AFB, N. Y., where it received representative F-22 wings and empennage and is still being used to validate aircraft antenna patterns. Final disposition of the number two YF-22 has not yet been determined.
Flying a specially configured F-16, test pilots completed tests on the first block of flight control laws for the F-22 in 1996, more than a year before first flight of the actual aircraft.
The flight control laws (the complex set of computer instructions that keep a modern fighter aircraft flying) for the F-22 were programmed in the Variable Stability In flight Simulator Test Aircraft (VISTA), a highly modified, one of a kind F-16D that, through a sophisticated control system, can emulate the flight characteristics of another airplane in flight.
A total of 21 sorties totaling 26.8 hours were flown in the NF 16D (the official designation for the VISTA aircraft) in two test sessions.
The first test session was devoted to comparing the baseline flying qualities of the F-22 to proposed or potential changes in the aircraft's pitch and roll control characteristics for landing, air refueling, and formation flying.
The second phase focused on two aspects of F-22 flying qualities. The first aspect was how the control laws performed during an engine failure, and separately, two different failures of the hydraulic system, including a dual hydraulic failure that resulted in the loss of use of one horizontal tail, one rudder, an aileron on one wing, and a flaperon on the other wing.
The second aspect considered the effects of not accurately achieving the predictions of the F-22's aerodynamics and structural characteristics. The so-called 'parameter variation' test flights allowed for relatively large changes to be made in the F-22's stability and flight control power.
In smooth air, the various failures and parameter variations were almost indistinguishable from the baseline F-22. In more severe winds and turbulence, some differences could be noted but the aircraft remained well behaved and respectable landings could be made even with a badly degraded aircraft as a result of the simulated dual hydraulic failure.
The overall results of the VISTA tests were excellent.
The F-22 Flying Test Bed (FTB), a modified 757, is used by Boeing to integrate and flight test the F-22 air dominance fighter's highly integrated avionics. Boeing has the lead for testing the F-22's avionics system in the current Engineering and Manufacturing Development (EMD) program.
The test bed sports an F-22 forward fuselage (built by Lockheed Martin in Marietta, Ga.) installed on the 757's forward pressure bulkhead. The structure houses the Northrop Grumman/Texas Instruments AN/APG 77 multimode radar designed for the F-22.
A second modification is the installation of a sensor wing on the crown of the fuselage immediately behind the flight deck. Electronic warfare (EW) and Communication/Navigation/Identification (CNI) sensors are mounted directly on the sensor wing, which is designed to simulate the sensor positioning found on the F-22's wings. The configuration provides high fidelity data and allow the test bed to emulate the sensor capabilities of the F-22 in realistic, real time operations.
The nose modification was completed late 1997 at Boeing's Wichita, Kan., facility with in flight radar testing to begin shortly thereafter. Boeing installed the sensor wing in late 1998.
Internal modifications to the 757 include structural supports for the special nose and sensor wing structure and the installation of unique electrical power, liquid cooling, and instrumentation systems. Avionics racks, test stations racks and seating for more than 25 technicians are located in the FTB cabin.
Based in Seattle, the FTB wasused to conduct in flight tests of the F-22 mission avionics system, in addition to the radar, starting in late 1998.
A government/contractor integrated test team was formed for the preparation, planning, conduct, and reporting of the F-22 Flight Test Program. This integrated test team is composed of personnel from the Air Force Flight Test Center (AFFTC) at Edwards AFB, Calif.; the Air Force Operational Test and Evaluation Center (AFOTEC) headquartered at Kirtland AFB, N. M.; Air Combat Command (ACC), the ultimate user of the F-22, headquartered at Langley AFB, Va.; Pratt & Whitney; the F-22 System Program Office (SPO) at Wright Patterson AFB, Ohio, and the Lockheed Martin Boeing team. This organization is defined as the F-22 Combined Test Force.
The various personnel and organizations functioning as the CTF have responsibility for:
- Estimating the scope of the air vehicle flight test program;
- Organizing the test team to accomplish assigned tasks;
- Determining and obtaining sufficient resources (budget, schedule, materiel, facilities, and personnel) for successful accomplishment of the flight test program;
- Develop planning and documentation that adequately describes the flight test program;
- Conduct the flight test program in a safe, efficient, and effective manner, and
- Report the flight test program status, accomplishments, significant problems, and results.
Given the geographical locations of the various organizations involved, the CTF did not initially exist as a fully co-located entity. The CTF functions as a virtual co-located entity by using methods such as frequent face-to-face meetings and video teleconferencing.
Fully co-located operation of the CTF commenced with delivery of the first Engineering and Manufacturing Development F-22 (the aircraft identified as company number 4001) to Edwards AFB in October 1997.
The combined test force started at about 290 people and built to a maximum of 650 in 2001. Initially the CTF comprised a 60/40 percent mix of contractor and Air Force personnel. As testing progressed, the mix shifted to 50/50. The organization was commanded by an Air Force officer, with a contractor deputy. The internal organization is built around the Integrated Product Teams (IPTs) that produce the flight test "product"-data.
The Airworthiness IPT is permanent at Marietta, Ga. and is responsible for taking the F-22s from manufacturing through initial ground tests, first flight, air worthiness, and ferry to Edwards.
The Air Vehicle IPT is responsible for all tests on the first three aircraft while the Avionics IPT does the same for the six avionics test aircraft. All other participants support these IPTs so that test pilots receive their assignments from flight operations but work directly for the IPT when conducting flight tests.
The major objective of the CTF during this phase is to determine the various Integrated Product Team (IPT) requirements and to insure that they are consistent with published plans and are fully traceable to Contractual Product Specifications, or are required to measure the Military Utility of the F-22 Weapons System.
From these requirements, detailed Test Information Sheets (TIS) are written from which the actual content of the test program can be verified, required supporting resources (such as instrumentation, data processing, personnel, facilities, equipment, etc.) can be identified, and documented methods and processes of operations can be defined.
Flight Test Requirements Working Groups (FTRWGS) are set up to execute the test planning process. The FTRWG responsibility and location were determined based on the Lockheed Martin Boeing assignment of Product and/or Technology IPT design responsibility. This enhanced communications between the various Product personnel and the Test IPT personnel, particularly in the early stages of test requirements identification.
The working groups are generally divided by disciplines. The groups had to decide what had to be tested and who are the people who were doing the tests.
The working groups remain intact throughout the test program, and are responsible for the test conduct, data analysis, and reporting for their particular technical discipline.
Each of the nine F-22s to be built in the Engineering and Manufacturing Development (EMD) phase is dedicated to flight test, and each of these aircraft is heavily instrumented to record flight test data.
Unlike past aircraft development programs, the Flight Test IPT was brought in at the very beginning of the F-22 program. On other aircraft, flight test was normally brought in after the aircraft was built and had to integrate flight test instrumentation where it could find room to put it. On F-22, Flight Test worked closely with the aircraft's designers, and the instrumentation was incorporated in the original aircraft design and is installed as the aircraft is being built.
With the instrumentation installed as the first F-22 entered final assembly, Flight Test was able to start telemetering data to the Flight Test Control Room in Marietta, Ga., in order to begin checking out the data processing system.
A large orange box with flight instrumentation flew in the F-22's right hand main weapons bay. The box, called the instrumentation data acquisition package, acquires data from more than thirty remote units scattered around the airplane. The box contains a high-speed data recorder that retains all the flight data. It also encrypts and transmits selected parameters back to the mission control station on the ground via two antennas on the aircraft. The instrumentation box stays with the airplane for its entire flight test life.
The flight test data processing requirements are split into real time data collection for safe and efficient test conduct and post flight data processing. The Air Force is responsible for the real time collection, while the contractor team is responsible for the post flight processing.
A test correlation software program called Test Plan is used by the team to maximize the data collected on each test flight. Developed by G&C of San Juan Capistrano, Calif., Test Plan is expected to increase flight test efficiency and lower testing costs.
By using this software to plan a specific test mission, flight test managers were able to determine if other tests requiring the same test conditions and aircraft configuration can be piggybacked on to the planned flight. The program can match up data points that were originally scheduled to be gathered months apart and compare the resultant flight plan against any known limitations of the particular test aircraft.
The program is also of benefit in daily flight test data management. The program would indicate what was flown on a given day, and whether that data was acceptable.
The Flight Test IPT put emphasis on training. Most flight test programs rely mostly on on the job training to train the control room personnel, but formal training for the controllers and pilots separately began in November 1996.
Personnel were identified by name and discipline for who was going to be in the control room in Marietta when training started. This reinforces the idea that the controllers are the pilot's 'eyes and ears' on the flights.
Four training sessions were held at the Vehicle System Simulator (VSS) at Fort Worth (see VSS in the Other Testing section). The first run was basic tasks and responsibilities; the second session introduced anomalies (or glitches) into the scenario, but the controllers and pilot were told what situations would be coming up; in the third and fourth sessions, the team ran the first flight profile, but anomalies were introduced at unexpected times. A fifth session would be conducted from the Mission Control Room in Marietta and would be a full dress rehearsal of the first flight using an F-15 as a stand in for the F-22 and F-16s as chase aircraft.
The first flight was preceded by a series of taxi tests. The tests were 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 was also thoroughly checked during these ground tests.
First flight of the first aircraft took place on September 7, 1997 from Dobbins ARB in Marietta, Ga., with F-22 Chief Test Pilot Paul Metz at the controls. Flying chase on the first flight was fellow contractor pilot Jon Beesley in one F-16 and Maj. Steve Rainey, who was the first Air Force pilot to fly the F-22, in a second F-16 chase plane.
The three aircraft taxied onto the runway. The two F-16 pilots took off first and started a slow 360-degree turn back towards the runway. Metz held the F-22 on the runway, making final instrumentation checks with the mission control room team.
Metz released the brakes, simultaneously easing the twin throttles to military power with his left hand. The Pratt & Whitney F119 PW 100 engines spun up, and the F-22 started down the runway. At about 140 knots, Metz pulled back slightly on the sidestick controller with his right hand. The aircraft rotated and took off. The landing gear remained down as the F- 22 climbed, and Metz pointed the aircraft to the north.
The most impressive feature of the first flight was the F- 22's rate of climb. Even though the Raptor climbed with its landing gear down, the F-16 chase aircraft had a tough time keeping up with the F -22, as the F119 engines produced a tremendous amount of thrust. The airplane climbed out fast at around a twenty-five-degree pitch angle in military power. The steep climb angle is a function of wanting to maintain a constant velocity under a fixed power setting.
The airplane reached 15,000 feet in less than three minutes. Once at that altitude, Metz leveled off and then cycled the engines through a series of power changes. The engine afterburners were not used during the first flight. Metz took the airplane to a maximum angle of attack of fourteen degrees.
All along, Metz evaluated the handling qualities of the F-22. Handling qualities describe the feel of an airplane. 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 just under one-hour flight, Metz raised the landing gear and took the F-22 to 20,000 feet, the maximum altitude for the flight. At this altitude, he went through more engine transients and evaluated the cruising performance before descending. On his way down, Metz flew 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 finished with the landing gear once again lowered for two simulated approaches at 10,000 feet. Metz then made his final approach. The F-22's main gear touched down first. Metz aerobraked to slow the aircraft to about 100 knots. The nose lowered and Metz applied the brakes to bring the aircraft to a full stop.
The first flight lasted just under one hour. During its flight, the F-22 reached a maximum speed of 250 knots and a maximum load of three Gs (three times the force of gravity).
Metz flew three times around a triangular route that took him about forty miles north from Dobbins to the Rome, Ga., area, and then northwest from Dobbins into Alabama. This route was carefully coordinated with Atlanta's Hartsfield International Airport to deconflict with commercial traffic.
All of the test flights at Marietta are designed to confirm the basic airworthiness of the F-22. These test flights are designed to clear a basic flight envelope roughly equivalent to a commercial airliner's in order to ferry the aircraft to Edwards.
After the first flight and two or three additional airworthiness flight tests in Marietta, the F-22 (Aircraft 4001) went through several months of further preparation and ground testing before it flew again.
Engines as well as control surfaces and weapon bay doors were removed and the aircraft was placed in a large test frame. The aircraft was then pushed and pulled using jacks and hydraulic pistons to simulate air loads encountered in flight. The deflections of the airframe were 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 ground testing, the F-22 is put back together and sent to the coatings facility in Marietta where it received a final paint job. After painting, the airplane went through ground vibration tests in Marietta to measure its structural dynamic characteristics. These tests were necessary for expanding the flight envelope in subsequent flights at Edwards.
Ground tests were 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.
After the F-22 completed this ground preparation and test, test flights further expanded the flight envelope to meet the parameters that were required to ferry the aircraft to Edwards. These flights also made use of the flutter excitation system. Beesley took the aircraft up to 40,000 feet and 325 knots.
The first F-22 flew several times at Marietta before flying to Edwards in October 1997. The last of these flights qualified the airplane for aerial refueling at altitudes of 20,000 and 30,000 feet. The F-22's flying qualities, emergency breakaway procedures, refueling boom clearance, and fuel transfer rates were evaluated in these aerial refueling flights.
Whereas the testing at Marietta ensured that the F-22 can be ferried safely, the test program at Edwards focused on determining that the F- 22 does what it promises. Its performance will be 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 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 EMD flight test program calls for establishing a long term average of approximately 12 flights per month on each test aircraft.
The first F-22 completed about 100 flights before the second airplane (Aircraft 4002) took off for the first time in mid 1998. After a few flights in Georgia, the second aircraft was ferried to Edwards where it was 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 were 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'ss infrared signature.
The first flight of the third aircraft, or Aircraft 4003, was not much different from the first flight of 4001. The aircraft flew a profile similar to that flown by Aircraft 4001 on its first flight, but the landing gear was raised right after takeoff.
Aircraft 4003 was unique in other ways. It was the first F-22 to have an internal structure that is fully representative of the production aircraft and it was used to perform demonstrations to 100 percent of the loads. Aircraft 4003 was the first used to test the operation of the M61A2 cannon. It was also used in acoustic surveys at Edwards. In these surveys, the engines were 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 would never take off. The aircraft stayed 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.
In steps, the static test article is taken to the aircraft's load limit first; that is, the design limit of the structure. In the 'ultimate test' the structure was taken to 150 percent of its load limit. Successful completion cleared Aircraft 4003 to demonstrate maximum loads in flight.
All of the test results are used to update structural models, also called finite element models (FEMs). 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 by '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. The airframe was put through two lifetimes to evaluate its basic durability. It was then subjected 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. 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.
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.
Before any software ever flies on these aircraft, it is thoroughly tested on the ground in Seattle in Boeing's Avionics Integration Laboratory (AIL) and in the air in 757 Flying Test Bed (FTB). All of the software and hardware goes through the integration lab for Aircraft 4004 and later flight test aircraft. This work includes the full weapon system integration as well.
Aircraft 4004 through 4009 fulfill a number of functions - testing of the Communications, Navigation, and Identification (CNI) system, Electronic Warfare (EW), radar integration with missiles and the M61A2 cannon, JDAM releases, and low observables testing. Flight testing of the dedicated avionics aircraft runs approximately 35 months from the first flight of Aircraft 4004 in 1999 to the end of EMD in 2002.
All of the aircraft are configured the same, so any aircraft can be used to collect data for a specific mission, which made scheduling much more efficient.
At the end of EMD, Aircraft 4001 went into flyable storage at Edwards. Aircraft 4003 was the primary functional aircraft, used for testing any non avionics modifications or changes to the airframe. Three aircraft were kept flying for follow on avionics testing, primarily the proposed Block 4 avionics software that included helmet mounted cueing, AIM 9X integration, and Joint Tactical Information Distribution System (JTIDS) send capability.
The F-22's design evolved over the course of EMD. As one example, Aircraft 4003 had a single piece forward fuselage keel, which on 4001 and 4002 were made up of 70 separate pieces and had to be assembled. All necessary improvements and changes were incorporated in Aircraft 4008 and 4009, so they were essentially production quality aircraft.
Those two aircraft, along with the first two true production aircraft (4010 and 4011) were the four aircraft the Air Force used for Initial Operational Test & Evaluation (IOT&E).
During IOT&E, AFOTEC operated the aircraft as an operational unit would. The aircraft were also maintained by Air Force crew chiefs and flight line maintainers.
Dedicated IOT&E ran from mid 2002 until early 2003. At the end of IOT&E, AFOTEC filed a report to Congress attesting to the worthiness of the F-22 to enter full production.
The F-22 Flight Test program consisted of the nine aircraft built during the Engineering and Manufacturing Development (EMD) phase of the program. The nine aircraft were flown approximately 2,500 flights covering over 4,500 test hours in EMD.
|4001||September 1997||Flying qualities, flutter, loads, and high angle of attack; Avionics Block 1 configuration|
|4002||Summer 1998||Propulsion, performance, and stores separation|
|4003||Summer 1999||Flying qualities, flutter, loads and JDAM integration; Avionics Block 2 configuration|
|4004||Fall 1999||Integrated avionics, CNI, observables testing|
|4005||Winter 2000||Integrated avionics, radar, CNI, and armament|
|4006||Late Spring 2000||Integrated avionics and observables testing; Avionics Block 3 configuration|
|4007||Late Summer 2000||Integrated avionics and air vehicle performance|
|4008||Winter 2001||Integrated avionics and observables*|
|4009||Spring 2001||Integrated avionics and observables*|
As of FY03, only one flight test aircraft incorporated the structural modifications and special instrumentation needed to enable the flight envelope to be fully cleared to its airspeed, altitude, and G-load design limits. This situation posed a schedule risk in clearing the required flight envelope prior to IOT&E. Additionally, all operational test aircraft currently have multiple operating limitations, including the aircraft intended to be production representative and available for operational testing. Successful conduct of IOT&E requires an adequate flight envelope and unmonitored flight clearance (without control room support to monitor loads/stresses during maneuvers typical of visual "close-in" air combat).
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