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F-22 Raptor Design

The F-22 will be in service for more than 25 years, or more than 40 years from the time of what was then called the Advanced Tactical Fighter dem/val contract was awarded in 1986.

Projecting that far into the future is difficult and one can get an idea of the magnitude of the challenge by comparing the best U. S. air dominance fighter of 1940, the P-51, with the F-4 25 years later. In that time, speeds had quadrupled and weapons and sensors were unlike anything available to the World War II pilot.

Perhaps most importantly, this 25 year leap occured with a revolution in fighter aircraft - the conversion from propellers to jet power. These relatively rare revolutions are marked not by incremental improvements, but rather, profound new directions in design. All of the aircraft from this revolution on would follow the new 'branch' or would be hopelessly outclassed.

It would have been ludicrous in 1945 to argue that the P-51 was the only fighter the U. S. would need for the next 25 years, but in 1945 few people could imagine just how far the science of flight would progress, or the impact of the switch from props to jets. Yet the aircraft designer of today is being asked to make a similar leap.

The F-22 Approach

Rather than a brute force approach with better thrust to weight engines, lower wing loading, sustained or instantaneous turn performance, maximum speed, maximum altitude, or post stall, high angle of attack (AOA) maneuvering; and faced with the realities of reduced defense budgets and fewer fighters in the future, the F-22 team established three basic guidelines for a fighter slated for operations in an uncertain future:

Exploit Information

Deny Information to the Enemy

Overwhelming Lethality

The F-22 is designed to exploit information, that is, to gather information from many sources and then process that information into a simple, intuitive picture of the tactical situation for the pilot.

The F-22's airframe and avionics architecture is specifically designed to provide these capabilities without locking the design into any particular use of equipment or capabilities available in 1997.

The F-22 is also designed to deny the enemy information on where the F-22 is and what it is doing.

If fewer numbers of fighters are to be built, then they must be overwhelmingly lethal compared to the aircraft of today. This level of dominance was hinted at during Operation Desert Storm where fewer aircraft, using precision munitions, accomplished greater destruction of military targets in a shorter period that in previous American wars.

If a similar level of lethality can be attained in an air dominance fighter, then fewer aircraft would have a far greater impact in the air battle.

In short, in a future air battle, with American lives at risk, there is no interest in that battle being a fair fight. The U. S. must win quickly, decisively, and with minimal casualties.

The Key: An Exponential Increase in Computer Power

To design an airplane that embodies these characteristics means moving beyond traditional design approaches. The common thread to making the 25 year leap, answering the government's challenge of making the F-22 twice as effective as the F-15, solving the technical and organizational challenges of running the program, and implementing the three points of the F-22 design approach lies in the extensive use of computers.

The exponential explosion of computer technology in the last 10 years has allowed the F-22 team to radically alter every aspect of this program from detailed design through manufacturing, communication, and into the cockpit itself.

To put this into perspective, the computer used in the Lunar Module operated at 100,000 operations per second and had 37 kilobytes of memory. Today, the F-22's main mission computers, which are called Common Integrated Processors or CIPs, operate at 10.5 billion instructions per second and have 300 megabytes of memory. These numbers represent 100,000 times the computing speed and 8,000 times the memory of the Apollo moon lander.

Impossible, Maybe, Probable

In 1986, the IBM 286 computer was just coming into service with the general public. The avionics goals for the F-22 seemed huge and the team's confidence in meeting the computational and information management to the pilot was relatively low.

For instance, a fiber optic transmitter and receiver (FOTR), a part of the display avionics, was roughly the size of half a sheet of paper in 1986. By 1990, that same computational power had been shrunk to the approximate size of today's computer disk, and the team's confidence was increasing.

Today, that same computing power has been packaged into a small device a little bigger than a business card, and size, weight and power requirements for these types of modules continue to drop. Confidence is now high that what was planned for is indeed achievable.

Such a quantum leap in capability has not been limited to the F-22 aircraft itself. Computational power has greatly changed the use of computers in all aspects of the F-22 program from design, through manufacturing, and even the testing of the airplane.

CATIA and COMOK

The computer revolution has changed the detail design process of the aircraft. With IBM Dassault Systemes designed Computer Aided, Three Dimensional Interactive Application (CATIA), the aircraft designer can design the parts of the F-22 as a solid object, not just lines on a flat page.

With COMOK (a team developed computer mockup simulation), the designer can visualize every aspect of the design including complex routing for wires, tubes, and cables. There is no hard mockup of the F-22.

These computer programs allow the design engineer and the manufacturing engineer to look inside the structure before it is built.

More than just a visualization, the computer data that creates these images are precisely stored design measurements that can be transferred, again by computers, between the team's locations in Marietta, Ga., Fort Worth Texas, Seattle, Wash., and West Palm Beach Fla., and East Hartford, Conn. and supplier locations all around the country.

Parts of the aircraft fit remarkably well when received in Marietta, where final assembly takes place, even though no master tool was sent to trial-fit the pieces.

The F-22 Design

The design of the F-22 addresses the challenge of air dominance in two ways, one traditional and one non traditional.

The traditional and most obvious approach to dominance is to create highly advanced machinery in the form of an aircraft with (1) better speed, (2) better turning performance, (3) better weapons, or (4) specialized technologies, such as stealth.

The most publicized and most revolutionary technology for aircraft is stealth. Stealth makes an object become very difficult to detect by sensors such as radar, heat seekers (infrared), sound detectors, and even the human eye. While not invisible, the F-22's radar cross section (RCS) is comparable to the radar cross sections of birds and bees. Compared to other current fighters, the F-22 is much more difficult to detect. (See Stealth section for slightly more detail).

Supercruise and Agility

The traditional design approach stresses increases in aerodynamic performance, and the F-22 emphasizes two technologies. Supercruise is the term given to the capability of sustaining supersonic speeds for long periods of time.

Conventional fighters, while capable of supersonic flight, can only sustain these speeds for relatively short periods as the result of excessively high fuel consumption using afterburner. The F-22 can cruise supersonically without afterburner and, therefore, can sustain these speeds for long periods.

The question could be asked "So what?". The enemy must react to any intruder and that reaction time to detect, aim weapons, and launch, is severely reduced when the intruder is moving fast. At supercruise speeds, the F-22 (and its pilot) becomes less vulnerable to enemy missiles and aircraft simply because they cannot react fast enough.

Agility is the ability of the F-22 pilot to point and shoot with his aircraft, pirouetting, and facing the enemy with his weapons at all speeds. The F-22 pilot can maintain control of the aircraft at speeds as low as that of a Piper Cub or at very high supersonic speeds.

The fighter pilot is able to do whatever he wishes with the F-22, without fear of loss of control, loss of thrust or aircraft structural overstress. Specifically, this has resulted in an unlimited angle of attack (AOA) capability for the aircraft's basic combat configuration (for example, all internal carriage of weapons and no external stores). There are no AOA limiters, and, most importantly, no restrictions on flightpath. The pilot can run the airplane out of speed and maneuver in the post stall regime with integrated flight controls and thrust vectoring. The F-22 responds smoothly to the pilot and can change flight condition at his command.

First, all the traditional limitations seen in flight manuals have been coded into onboard computers. For example, some components (such as landing gear and air refueling doors) have speed limits. The pilot is never prevented from exceeding those limits. If the pilot exceeds a limit, either intentionally or unintentionally, he gets a message with an aural warning to tell him that a limit is being exceeded. In addition to overspeed warnings to the pilot, the flight control system provides load limiting for all pilot inputs as a function of aircraft gross weight.

Second, the flight control system provides automatic load limiting for all pilot inputs as a function of aircraft gross weight. The pilot gets the maximum performance the aircraft is capable of achieving at any time when full roll, pitch or yaw commands are used. The pilot can 'yank and bank' all he wants without fear of 'hurting' the airplane.

Avionics

Avionics share as large a part in the success of a fighter as the ability to maneuver and fly fast, or to "turn and burn". F-22 avionics reflect the quantum leaps in computer technology in the last 10 years. "Integrated" means that the F-22 can take information from many sources, compare that information and determine a single, consistent picture of the world around the pilot. In addition to these external inputs gathered by the F-22's own sensors, several F-22's can exchange information by means of the aircraft Inter/Intra Flight Data Link (IFDL) and additional information can be gathered from off board sensors like E 3 Airborne Warning and Control System (AWACS) aircraft and satellites.

Integrated avionics have some unusual characteristics. The F-22 has no radios, navigation gear like TACAN or Global Positioning System (GPS) or Instrument landing System (ILS) or even a radar in the traditional sense.

The Common Integrated Processor modules have the ability to emulate any of the electronic functions through automatic reprogramming. For example, if the CIP module that is acting as radio dies, one of the other modules would automatically reload the radio program and take over the radio function. This approach to avionics makes the equipment extremely tolerant to combat damage as well as flexible from a design upgrade point of view.

The aircraft's avionics architecture remains flexible to accept future upgrades without having to design and retrofit new hardware to the fighter.

The Non-Traditional Design Approach

There is also a non-traditional design approach that was used for the F-22. The non traditional approach was driven by the reality of smaller military budgets, fewer aircraft, and a requirement to make those few aircraft far more lethal than their predecessors.

In World War II, the U. S. Army Air Corps downed 15,798 aircraft in day air to air combat. Those kills were made by only 7,306 of the approximately 35,000 fighter pilots in combat. Of that number only 1,284 were aces. In other words, only 21% of the fighter pilots shot down other aircraft and only 3.6% were aces. In the Korean War, similar results occurred for the dedicated fighter pilots. There, 4.8% of the pilots were aces but they got 38% of all kills.

The F-22 team reasoned that a smaller force could be far more lethal if the percentage of fighter pilots who achieve combat kills could be increased significantly from the historical averages of 10 to 20%.

"Human Potential" Design Concepts

These engineering concepts were formalized in the F-22 design process by defining three basic design criteria for the pilot:

Eliminate "housekeeping"

"Carefree abandon" flying qualities

Maximize information, minimize data

This elimination of "housekeeping" design criteria was driven by the desire to off load the pilot from the many system operations that have classically taken a significant portion of the pilot's attention in the cockpit.

The question was asked, "Why should an airplane be any more complex to operate than your car?" Is there really a need for "all those little switches, knobs and dials in the cockpit?" Like a car, the basic approach was to make the operation of the F-22 a true "kick the tires and light the fires" machine. All switches, even the most traditional functions, had to earn their way into the cockpit.

It became apparent that computers and Built In Testing (BIT) could replace much of the traditional pilot "housekeeping". Interestingly, the pilots did not drive this capability.

The Crew Chief Got There First

Maintainers were included early in the design process for the F-22, and they quickly established a strong foothold. To improve maintenance turnaround, the maintainers insisted on extensive self diagnostics and BIT capability for the various subsystems.

As a result, virtually every piece of hardware in the aircraft either does its own health checks or reports when it has failed. There are more than 15,000 fault reports that can be made on the basic engine and airframe and another 15,000 fault reports available for the avionics. Most of these are low level fault reports that do not result in warnings, cautions, or advisories to the pilot or degrade the operation of the F-22.

It was reasoned that if the airplane knew so much about itself, then that capability could be leveraged to help the maintainer and the pilot.

Tactician not Housekeeper

The idea was to relieve the pilot of the bulk of system manipulations associated with flying and allow him (and now her) to do what a human does best - be a tactician. Using the power of the onboard computers, coupled with the extensive maintenance diagnostics built into the F-22 by the maintainers, that workload has been significantly reduced.

Aircraft startup and taxi are excellent examples of harnessing the power of the computer to eliminate workload. There are only three steps to take the F-22 from cold metal and composites to full up airplane ready for takeoff. The pilot places the battery switch ON, places the auxiliary power unit (APU) switch momentarily to START and then places both throttles in IDLE. That's it.

The engines start sequentially right to left, the APU then shuts down, all subsystems and avionics are brought on line and BIT-checked, the necessary navigation information is loaded and even the pilot's personal preferences for avionics configuration is read and the systems are tailored to those preferences. All of this happens automatically with no pilot actions other than the three steps. The airplane can be ready to taxi in less than 30 seconds after engine start.

To reduce pilot workload in flight, the F-22 incorporates a unique caution and warning system called Integrated Caution, Advisory, and Warning (ICAW) system.

ICAW messages normally appear on the 3"x4" up front display (UFD) just below the glare shield. A total of 12 individual ICAW messages can appear at one time on the UFD and additional ones can appear on sub pages of the display.

Two aspects of the ICAW display differentiate it from a traditional warning light panel. First, all ICAW fault messages are filtered to eliminate extraneous messages and tell the pilot specifically and succinctly what the problem is. For example, when an engine fails, the generator and hydraulic cautions normally associated with an engine being shutdown are suppressed, and the pilot is provided the specific problem in the form of an engine shutdown (ENG SHUTDN) ICAW message.

More than two years of detail design by pilots and engineers has gone into the filtering logic of the ICAW system and an extensive test of the system occur in the Vehicle System Simulator (VSS) or 'Iron Bird' and the avionics labs. .

In addition, the success of the Army's RAH 66 Comanche helicopter's ICAW system that uses a similar filtering approach gives the F-22 team confidence in the fundamental soundness of the design.

Another feature of the ICAW system is the electronic checklist. When an ICAW message occurs, the pilot depresses the checklist push button (called a bezel button) on the bottom of the UFD and the associated checklist appears on the left hand Secondary Multi-Function Display (SMFD).

If multiple ICAWs occur, their associated checklists are selected by moving a pick box over the desired ICAW and depressing the checklist button. Associated checklists are automatically linked together so that if an engine failure occurs, the pilot would not only get the checklist for the engine failure procedure in-flight but also the single engine landing checklist. The pilot can also manually page through the checklists at any time from the main menu. This is particularly handy when helping a wing man work through an emergency.

"Carefree Abandon" Flying Qualities

The second design principle is really an extension of the philosophy for the cockpit itself. "Carefree abandon" translates into the ability of the fighter pilot to do whatever he wishes with the F-22, without fear of loss of control, loss of thrust, or aircraft structural overstress.

Specifically, this has translated into an unlimited angle of attack (AOA) capability for the aircraft's basic combat configuration (i.e. all internal carriage of weapons and no external stores). There are no AOA limiters, and, most importantly, no restrictions on flightpath. The pilot can run the airplane out of speed and maneuver in the post stall regime with integrated flight controls and thrust vectoring. The F-22 responds smoothly to the pilot and can change flight condition at his command.

Carefree also applies to structural limits on the airplane, and this is handled two ways. First, all the traditional limitations seen in flight manuals have been coded into onboard computers. For example, some components (such as landing gear and air refueling doors) have speed limits. The pilot is never prevented from exceeding those limits.

If the pilot exceeds a limit, either intentionally or unintentionally, he gets an ICAW with an aural warning to tell him that a limit is being exceeded. In addition to overspeed warnings to the pilot, the flight control system provides load limiting for all pilot inputs as a function of aircraft gross weight.

Second, the flight control system provides automatic load limiting for all pilot inputs as a function of aircraft gross weight. The pilot gets the maximum performance the aircraft is capable of achieving at any time when full roll, pitch or yaw commands are used. The pilot can 'yank and bank' all he wants without fear of 'hurting' the airplane.

These flying qualities are backed by more than 8,000 hours of stability and control wind tunnel testing (during the EMD testing phase alone), thoroughly tailored flight control laws, and countless handling quality simulation evaluations - all of which are demonstrated during the flight test program. The design philosophy was established up front, with engineers and pilots working closely together. This dedicated team has worked through numerous design challenges to get the F-22 to where it is, and agrees - flying qualities look good!

Maximize Information, Minimize Data

Everyone who works in an office knows that the inverse of this design maxim is often seen. E-mail, voice mail, and the near compulsive desire to print copies and distribute them to the world often leaves people swamped in data from which we must divine information. The F-22 design team has worked hard to turn this axiom of the computer age around and provide the F-22 pilot with information, while tasking the computer to organize the data and present as coherent information to human occupant.

The cockpit displays are set up to be intuitive to the pilot. Confirmed enemy aircraft are red triangles, friendly aircraft are green circles, unknown aircraft are yellow squares, and wing men are shown as blue F-22s.

One of the original objectives for the F-22 was to increase the percentage of fighter pilots who make 'kills'. The Inter/Intra Flight Data Link (IFDL) is one of the powerful tools that make all F-22s more capable. Each F-22 can be linked together to trade information without radio calls with each F-22s in a flight or between flight. Each pilot is then free to operate more autonomously because, for example, the leader can tell at a glance what his wing man's fuel state is, his weapons remaining, and even the enemy aircraft has targeted. Classical tactics based on visual 'tally' (visual identification) and violent formation maneuvers that reduce the wing man to 'hanging on' may have to be rethought in light of such capabilities.

Targets can be automatically prioritized and set up in a shoot list with one button push. A SHOOT cue in the head up display (HUD) alerts the pilot to the selected weapon kill parameters and he fires the weapons. Both a pilot's and wing man's missile flight can be monitored on the cockpit displays.

Considerable effort has been expended in making the F-22 'user friendly'. The aircraft systems operations are straightforward and simple. The airplane can be flown with carefree abandon, and the tactical situation can be understood and acted upon through intuitive presentations from many sensors.

Synergistic Combined Effects of Stealth, Supercruise, and Integrated Avionics

Looking at how the traditional and non traditional elements of the F-22 add up, synergistic effects like these can be seen.

A conventional fighter is equal to, or, in some cases, less capable, than the best enemy fighters. In mock combat with real aircraft or in simulators, it is found that neither enemy or friendly aircraft has the 'edge', or advantage. The enemy sees us at the same time we see him. We both fire at the same time and both airplanes go down or, in the exact military language, we have 'parity'.

Parity is neither politically or militarily acceptable. Politically, because the U. S. can never build the numbers of fighters to overwhelm an enemy by sheer force of numbers (the so-called 'bludgeon' approach to war) and because Americans abhor any losses of its fighting men and women.

Militarily, 'parity' violates the most basic of tenets - attack with overwhelming superiority, which is the capability that the F-22 would provide.

Three Tools

The pragmatic way to determine the capability of the F-22 would be to send it into a full scale war and see how it does. That would be effective, but clearly isn't practical.

The trick is in using three program tools and the power of the computer to simulate war, yet are credible representations of the 'real world'. Three tools currently exist to create that 'crucible of war' evaluation.

Once reserved for hobbyists, war gaming has become a sophisticated, computer based simulation that allows modeling of enemy and friendly weapons and tactics. The advantages are obvious. Once modeled, virtually unlimited numbers of aircraft, missiles, guns, and radars can be added to hypothetical scenarios.

The F-22 can be flown through this computerized combat zone at relatively little cost and over a short period of time. Many scenarios can be explored and statistical results obtained. More than 10,000 of these runs can be made per day. To date, more than 1,000,000 simulator 'battles' have been fought using this tool. Of course, these still remain models of reality and they do not include human operators of the F-22 and the enemy equipment.

The F-22 program uses two simulators, one in Marietta, Ga., and the other in Fort Worth, Texas, to study the effectiveness of the F-22 using real pilots. These simulators combine some of the advantages of war gaming (the large number of enemy aircraft, defenses, and targets) with the variability and unpredictable nature-of the human operator.

In the Air Combat Simulator (ACS), up to 12 F-22 pilots flying simulated F-22s and enemy aircraft can fight each other. Ground controlled intercepts can be directed by four human operators, and the computers can model as many as 80 other aircraft and 80 surface to air missiles can join in this air battle.

While a step closer to reality, the ACS still uses a model of the F-22 and, except for the 16 human operators, all other airplanes and defenses are computer models of what human operators would do. (See ACS in the Other Testing section).

Flight Test

The F-22 represents the real world and, as such, the sensors, the aircraft's performance, its stealth, supercruise and, most importantly, its pilot's performance, would be what would really enter the combat fight. Unfortunately, it is not possible to actually test the F-22 against a large numbers of enemy aircraft and defenses as is done in the Ops Analysis and ACS. The approach that is being used in the F-22 program is to verify or validate the Ops Analysis and ACS predictions using the results from the F-22 flight test program.

Synthesis of the Tools

The three tools represent a spectrum of decreasing battlefield complexity but an increasing involvement of humans and real hardware. Interestingly, no single tool can be used to ascertain F-22 effectiveness as each is, in some unique way, 'limited'. The problem is one of establishing a credible simulation of warfare.

To do this, several simplified scenarios are flown in each of the three tools and results compared. The Ops Analysis and ACS simulations are 'tweaked' until they match the real F-22's capabilities. With a level of confidence established that the simulations represent the real F-22, the confidence that results from the more complex war scenarios in the ACS and Ops Analysis are credible.

Flight Test Program

The flight test program was the first look at the real F-22. 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. Externally, the wing sweep has been reduced eight degrees (from 48 on the prototype to 42 degrees on the F-22) and the canopy has been moved forward seven 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.

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-22's 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 (APU) to perform most maintenance tasks.

In addition to a screwdriver and wrench, the F-22 maintainer would also carry a laptop sized computer. The maintainer accesses the F-22 by a laptop sized computer called a Portable Maintenance Aide (PMA) that can read and record aircraft consumables like fuel and oil, but can also control aircraft systems during maintenance, as well as upload new Operational Flight Programs (OFPs), computer software to run the aircraft. (See PMA in the Supportability section).

There are nine single seat F-22As in the basic EMD test program. First flight is scheduled to take place from Dobbins ARB in Marietta, Ga. followed by six to eight airworthiness flights prior to the ferry flight to the Air Force Flight Test Center at Edwards AFB, Calif. The test program runs for five years and consists of approximately 2,700 flights and 7,800 hours.

The first three F-22 aircraft are essentially engines and airframes and do not have the full up tactical avionics and sensors. They were used for envelope expansion, structural loads, propulsion, and weapons, and other flight test areas such as high AOA flights and arresting gear tests.

The remaining six F-22s are interchangeable avionics test aircraft. The avionics suite matures through four stages or 'blocks' of avionics, however, each of the six avionics aircraft all carry the same configuration of avionics at the same time. This allows any airframe to be used for any avionics test and not lose a test flight maintenance down days or modifications on a particular airframe.

The combined test force (CTF) 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 progresses, the mix shifted to a 50/50 mix The organization is be 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.

Air Dominance for the 21st Century

The history of air power shows that there are periods of incremental evolution and refinement of a basic configuration, as was seen in the first fifty years of flight where the propeller driven airplane was refined to its ultimate expression in World War II fighters.

At some point, however, a truly revolutionary breakthrough occurs that overshadows current aircraft and leads to a new period of evolution and refinement of this revolutionary change. The jet engine represents that first revolutionary jump. The F-22 Raptor represents the next revolution in aircraft development.

Interestingly, this revolution is not as visual as the jump from prop to jet, but it would just as profound. The explosion of computer capability now turns warfare into a war of exploiting information and denying it to the enemy. This information would make the F-22, and all other new weapons of war, a leap ahead of current weapons.



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