Lockheed's F- 117 is the first and only operational stealth aircraft. Its revolutionary design gives it the ability to penetrate dense threat environments with a high degree of survivability, attack high-value targets with extreme accuracy, and serve as a force multiplier, increasing the survivability and effectiveness of conventional forces.

The F- 117 Is the product of over 30 years of stealth-technology development at Lockheed's Skunk Works.

Mention the SR-71 and you think of Mach 3+, high-altitude flight. What most people don't realize is that the SR-71 series, developed in the 1960s, represents the Skunk Works' pioneering efforts in low-observables development. On this program, the Skunk Works first developed aircraft shaping methods, radar-absorbing structural edges, radar-absorbing coatings, and other design features that greatly reduce the SR-7 i's radar signature.

The Skunk Works continued its low-observables technology development and in the 1970s achieved some major breakthroughs.

We developed a computer program called ECHO that enabled us to accurately predict the all-aspect radar signature of an aircraft, taking into account many of the physical radiating phenomena. As illustrated, the ECHO program had the ability to accurately compute the radar signature of an artillery shell. Notice how closely the computed signature matched the measured signature. ECHO and other programs were powerful design tools that enabled us to rapidly evaluate the radar-signature characteristics of a variety of design concepts.

Another key breakthrough was the Skunk Works' development of the faceted-aircraft-shaping concept. Faceted surfaces and straight, parallel edges, when used with advanced radarabsorbing structures, materials, and other design features, enabled Lockheed to develop an aircraft with a low radar signature -significantly better than what had previously been achieved.

Lockheed F-117A - The first and only
operational stealth fighter

The low-observables design capabilities of Lockheed's Skunk Works led to our being competitively selected to develop the "Have Blue" demonstrator aircraft in 1976 under joint sponsorship by the Defense Advanced Research Projects Agency (DARPA) and United States Air Force (USAF). It was the Have Blue program that led to the creation of the colloquial term, "stealth."

Have Blue was a single-seat, subsonic aircraft, powered by twin, nonafterburning engines. Compared to the later F- 117, this technology demon~ strator was quite small:

  • Weight: 12,000 Ib
  • Length: 38 ft
  • Span: 2 2,/2 ft
  • Height: 7/2 ft

There are seven types of observable signatures: radar, infrared, visual, contrails, engine smoke, acoustics, and electromagnetic emissions. Clearly, radar signature, infrared signature, and electromagnetic emissions have the greatest potential for exploitation by threat systems. Have Blue employed a variety of design features to reduce these aircraft signatures including highly swept, faceted surfaces; radarabsorbing edges; radar-absorbing coat'dded inlets; unique nozzle designs; and special antennas. All of these developments came together in the Have Blue demonstrator.

HAVE BLUE - Low observables
demonstrated in flyable test aircraft

Under the Have Blue program, Lockheed designed and tested largescale radar-signature models and then designed, built, and flight tested two demonstrator aircraft. An 18-month flight test program validated Have Blue's low-observable characteristics while proving the aircraft's flight characteristics. The highly swept Have Blue design was unstable in all axes and relied on a fly-by-wire flight control system for aircraft control.

The success of Have Blue led to development of the F- 117 -an operational aircraft with full avionics, weapons, and systems that meets USAF fighter-attack mission requirements.

ECHO - A new signature prediction computer program

Lockheed's Skunk Works met the challenge of developing a weapon system that incorporated the breakthrough stealth features, yet was readily producible and affordable, highly reliable, and easily maintained by the Air Force.

In spite of the technical challenges, the F-117 was developed and fielded in significantly less time than other modern tactical aircraft. First flight was in June 1981, only 3I months after the November 1978 go-ahead. The accelerated full-scale development effort was accomplished by a relatively small Air 20 Force, Lockheed, and subcontractor team working closely together in a non-adversarial, problem-solving environment.

Lockheed signed the first of a series of fixed-price production contracts in December 1979 - 18 months prior to first flight. With production concurrence, initial operational capability (ioc) was achieved only five years after development go-ahead. Fifty-nine production aircraft were built for the Air Force's 37th Tactical Fighter Wing over an eight-year period. We guaranteed the aircraft's range, weapondelivery accuracy, and radar cross section.

The production F-117 is a single-seat, subsonic aircraft powered by twin, non-afterburning, General Electric F404 engines. The core engine is the same as used in the U. S. Navy F/A-18. Maximum weight is 52,500 Ib with an internal weapons load up to 5,000 lb.

ECHO - A new radar signature prediction computer program.

The F-117's primary mission is to penetrate high-threat areas at night, using its stealth technology and intelligent mission planning, and attack high-value, heavily defended targets.

Targeting and weapon delivery is accomplished using an infrared acquisition and designation system that enables the delivery of laser-guided weapons with extreme accuracy as we observed many times in the memorable images televised during Desert Storm. In addition to laser-guided weapons, the F-117 can also deliver generalpurpose, cluster, and practice bombs.

Airfields, aircraft shelters, command and control centers, early warning radars, and surface-to-air missile sites are just a few examples of targets the F-117 is designed to attack

By successfully attacking critical targets, the F-117 greatly increases the survivability and effectiveness of conventional aircraft forces in a complex battle environment. This was clearly demonstrated in Operation Desert Storm where a small force of F-117 fighters had a major impact on the air and ground war.

Although we incorporated breakthrough stealth technology, we utilized proven systems from existing aircraft to reduce the overall system development risk. Examples of off-theshelf items incorporated into the F-117 include:

  • F404 engines from the F/A-18
  • Cockpit components from the F-16 and F/A-18
  • Navigation system from the B-52
  • Environmental control system from the c- 130
  • Fly-by-wlre flight control computers from the F-16.

Low-observable design features of the F- 117 build on the capabilities demonstrated by the Have Blue aircraft. The highly swept facets, radarabsorbing structure and materials, and inlet and exhaust-nozzle concepts are similar to Have Blue, yet many new design challenges had to be mer, such as:

  • Integration of multiple communications and navigation systems with unique antennas and sensors.
  • Integration of the infrared/laser weapons delivery system with its unique apertures that readily pass IR and laser energy yet appear as metalized surfaces to radar.

These and other applications of stealth technology dramatically reduce the ability of threat systems to detect, acquire, and track the F- 117.

As illustrated, in general terms, major reductions in radar cross section are required to achieve significant reductions in detection, acquisition, or tracking range by threat surface-to-alr missiles or threat aircraft. We designed the SR-71 25 years ago to have a radar cross section well below those of conventional tactical fighters. Low signature, high altitude, and Mach 3 speed ensured its survivability against all air and ground threats. We then designed the F- 117 to meet a radar cross section goal significantly below that of the SR-71. The result is an attack aircraft capable of penetrating the most hostile threat defenses and delivering weapons with extreme accuracy.

F-117 mission performance compares favorably with current fighter/ attack aircraft. While the F-117 pays aerodynamic penalties for shaping, inlets, and nozzles, these performance degradations are offset by the performance penalties incurred by conventional aircraft when operating at high speeds and low altitudes to avoid threat defenses.

Unrefueled mission radius is 6oo nautical miles with a 5,ooo-lb payload. Operating from central Saudi Arabia, the F- 117 could cover a significant portion of the Iraqi theater with refueling inbound and outbound over friendly airspace.

A key contribution to the F- 117's survivability and effectiveness is the fully automated mission-planning system designed and built by the Skunk Works. Automation has eliminated manual methods. Housed in two airtransportable vans, the system uses threat laydown, detailed aircraft signatures, and performance characteristics to compute the optimum route to and from the target.

This system computes time, fuel, and distance for all route segments including takeoff and landing data. It also generates pilot cards and loads all mission data onto a data-transfer module that programs the aircraft's flight- managernent system.

Following takeoff, the mission can be flown hands-off. The system will navigate through hostile airspace and put the aircraft at the weapon-release point at a precise time. After the mission, data is downloaded onto the transfer module for post-mission analysis.

The F- 117 mission-planning system was operational many years before other comprehensive systems. The F- 117 system has evolved into the Sanders STAMPS system, and lessons learned from the F- 117 will be incorporated into the Sanders missionsupport system of the future.

Lockheed's unique test range to develop
aitcraft with low radar signatures

Lockheed'S F- 117 has proven that stealthy aircraft can be both reliable and maintainable. As the system matured, reliability and maintainability goals have been met. Mission reliability is defined on this aircraft as the probability of completing a successful mission from engine start through shutdown. The specific values Of F- 117 mission reliability are classified; however, I can say that they are very high.

Excellent performance has also been achieved in aircraft maintenance. Total aircraft maintenance manhours per flight hour are roughly equivalent to other twin-engine, front-line fighters. The portion of maintenance devoted to low observables is but a small fraction of the total.

Maintenance and support of a lowobservable aircraft were major concerns from the start of the program, and the Skunk Works developed many innovative solutions. For example, locating the accesses for servicing of aircraft subsystems within landing gear and weapons bays, and utilizing a single avionics bay minimizes the need to remove and replace RAM coatings around access areas.

Low-observable maintenance methods were developed and validated. Visual inspection, and straight-forward tech-order procedures and groundsupport equipment are used to meet the 49th Fighter Wing's requirement that all F- 117s be maintained in full stealth condition.

Use of proven systems also provides support benefits. A large percentage of the F- 117's systems is common to other Air Force aircraft and the aircraft meets NATO interoperability standards.

The F- 117 system was designed to deploy to forward operating locations. We developed modular, airtransportable vans for support of avionics, subsystems, and the missionplanning system. Today, we operate out of five maintenance vans and two mission-data-planning-system vans that can be airlifted in C-5, C-141, or, C-130 transport aircraft. These vans are fully weatherized with self-contained heating and air conditioning to support long-term deployment operations at bases with minimum facilities. The day-to-day peacetime operations at Holloman AFB, New Mexico are supported out of these vans in concert with the wing's philosophy of training exactly the way they plan to fight.

Air Force and Lockheed efforts have resulted in a weapon system that provides a unique combat capability-one that has now been conclusively demonstrated. Its record in Desert Storm speaks for itself.

  • Only aircraft to attack heavilydefended Baghdad
  • Suffered no hits and no losses
  • Attacked 31 percent of the dayone targets with two-and-one-half percent of allied tactical assets
  • Attacked 40 percent of the strategic targets overall, with only two percent of the allied tactical assets a
  • Precision bombing minimized civilian casualties and collateral damage.

Low observables dramatically reduce
threat capabilities

Although operational since 1983, the F-117 has not been allowed to gradually grow obsolete. It is being kept at the technology forefront through a planned weapon-system improvement program that upgrades the F- 117's avionics, airframe, and support equipment. With aircraft continually cycling through, by year-end the F-117 depot facility in Palmdale, California will have redelivered 73 upgraded aircraft.

Key avionic enhancements include an improved cockpit with new color multi-purpose displays, a new digitaltactical situation display, and a revised flight management system that automatically controls time at a point in space, as well as the normal latitude, longitude, and altitude parameters. Also incorporated during these upgrades is an automatic pilot-recovery system. These new systems enhance both pilot situation awareness and flight safety.

In addition, the F- 117 program has recently developed and flown a major primary structural component made entirely of graphite-thermoplasticcomposite material. New F- 117 vertical fins are being made of this exceptionally strong, damage-tolerant material. This program has prepared u.-, well for the introduction of advanced materials into the F-22.

The F- 117 has just begun to reach its full potential. Future enhancements in sensors, weapons, low observables, and system support, which both increase performance and reduce ownership costs, are being considered. In summary, the F- 117 is a unique national asset. It is:

  • Survivable
  • Lethal
  • Reliable and maintainable
  • A force multiplier
  • Combat proven and operational today!

PAUL W. MARTIN is F- 117 Program Manager in the Lockheed Advanced Development Company. Responsible for all of Lockbeed'S F- 117 related activities, his duties cover manufacturing, support, and maintenance programs as well as continuing development and improvement to keep the aircraft at the forefront of technology.

Martin came to Lockheed in 1981 after I3 years offlight test activities witb the U.S. Air Force and the Federal Aviation Administration. His experience during that period included primary project-engineering responsibility for sucb aircraft as the F-15 air-superiority fighter and the L- 1011 TriStar commercial jetliner, and two years at FAA headquarters in Washington, D. C.

While progressing to division engineer level in Lockbeed's Engineering Flight Test Division, Martin directed a variety of L-1011 TriStar, P-3 Orion, and S-3 Viking flight test activities. In January 1985 Martin joinedLockheed's YF-22 Advanced Tactical Fighter team as deputy chiefengineer, participating in thepreliminary design andproposal activities that helped the company win a demonstrationl validation contract in November 1986. Appointed chief engineer for technology and design in 1987, Martin's responsibilities included maturing the YF-22 design to the prototype design-freeze configuration. After becoming cbiefengineerfor YF-22 system integration in i988, Martin left the program to take over as deputy program manager, SR-7I strategic- reconnaissance programs.

Martin holds a bacbelor's degree in aeronautical engineeringfrom Cal Poly and a master's degreefrom ucLA. He is also a graduate ofthe Industrial College oftbe Armed Forces and of the U. S. Air Force Test Pilot School-flight test engineers' curriculum. Active in many professional and community organizations, including SAE, AIAA, and the Aero Club ofsouthern California, Martin is a charter member and past director of the Society of Flight Test Engineers.

© copyrights 1992 by Lockheed Corporation, 4500 Park Granada Boulevard, Calabasas, CA 91399-0610
published by plweb publications - Gregor Mima, Technical University Vienna.