Code One Magazine: F-22 Perspectives

Bret Luedke, lead avionics contractor test pilot, flew the first avionics Raptor, 4004, on its first flight in November 2000. Luedke is actively involved in all phases of the flight test program but has concentrated on the avionics development. Before joining Lockheed Martin, he served twelve years as an F-16 pilot in the US Air Force. He is a graduate of USAF Test Pilot School where he later taught high angle-of-attack testing as an instructor pilot. He has over 4,000 hours of flight time in more than fifty aircraft types, including the F-4, F-16, and F-22.

A key phrase used in discussing F-22 avionics is sensor fusion. As the name implies, the F-22 derives target information from multiple sensors. The avionics then sort, filter, evaluate, and ultimately fuse this information to provide the pilot a single, highly defined target. Of the 3,800 total hours planned for F-22 flight testing, approximately 2,000 hours will involve avionics testing with almost two-thirds of this focused on the integration of multiple sensors or sensor fusion. Compared to previous US fighter programs, this portion of flight testing represents a significant increase in the amount of avionics testing conducted during an initial development. The Development Test and Evaluation phase of the F-15, for example, consisted of twenty-five percent avionics testing. The F-16 consisted of twenty-eight percent. By comparison, the B-2 bomber DT&E consisted of fifty-two percent avionics testing.

Tools And Parts Of Avionics Testing
Six of the first nine F-22s are dedicated to avionics flight testing. The avionics test program relies heavily on simulation, modeling, development laboratories, and a flying testbed. These tools allow a thorough evaluation of the F-22 avionics before they fly on the real aircraft. Due to the highly integrated nature of the F-22’s avionics, testing each individual component does not guarantee that all the pieces will work together as expected. However, some limited testing is conducted to look at individual sensor operation as a buildup to the integrated testing and as a means to validate and update models of those sensors.

The key components of the F-22 integrated avionics suite are the radar; communication, navigation, and identification system, or CNI; electronic warfare system; common integrated processors, or CIPs; and cockpit controls and displays. The major sensors, which consist of the radar, CNI, and electronic warfare, have antennas and electronics distributed throughout the aircraft. The information from these sensors is processed, digitized, and sent via fiber-optic lines to the CIPs, which function as the brains for controlling and processing sensor information.

Development Process
The F-22 avionics development process begins at the individual software component level. Each software component is programmed and tested with other software components in several software development labs where models of sensors and threats are heavily used. The avionics software, commonly referred to as mission software, is loaded in the CIPs, and inputs from the sensor software models are fed into the CIPs for processing. For example, the radar and electronic warfare simulation act as if they have detected various targets. They then provide the appropriate digitized data to the CIPs for fusing.

These simulations are, in effect, complex software models of the sensor built to perform the signal analysis and processing as the real sensor would. The test facility also provides a target environment for these sensors. This environment contains multiple air and ground targets distributed at various locations relative to the simulated position of the F-22. The individual targets are themselves software models programmed with proper radio frequency signals and radar cross sections. This method can produce very dense simulated threat environments to stress the sensors and processors.

After software is developed and tested in the individual software labs, the entire suite of mission software is taken to the Avionics Integration Lab. This lab allows the mission software to be integrated with real sensor hardware and software, as opposed to hardware and software models used in the software labs. The lab, located in Seattle, Washington, contains a special tower that houses an F-22 radar array and a partial F-22 wing. The partial wing contains the embedded apertures and electronics for the electronic warfare and CNI systems. The sensors are arranged to enable them to detect and track real-world targets in an open-air environment. Mostly targets of opportunity are used, but dedicated targets, such as F-16s, F-15s, and T-33s configured with radar simulator pods, are used for specific profiles. All sensor information is sent to the laboratory where actual CIPs process the information and display it in a control room and in a simulated F-22 cockpit for real-time monitoring and control.

Flying Test Bed
After testing in this laboratory, the mission software is moved to the F-22 Flying Test Bed for the next step of the development process. The test bed is a Boeing 757 configured with an F-22 radar in its nose and a sensor wing above the cockpit. This sensor wing allows for realistic angular placement of electronic warfare and CNI apertures, enabling multiple sensor fusion. The aircraft also carries actual CIPs and a simulated F-22 cockpit with real controls and displays. The aircraft contains multiple engineering test stations that allow sensor and software engineers to control and monitor the performance of the system. Targets are again F-15s, F-16s, or T-33s that have been accurately measured for radar cross section. These aircraft also carry pods to simulate various radars and stimulate the F-22 sensors in the Flying Test Bed. Unlike the land-based laboratories, the Flying Test Bed allows for airborne integrated avionics testing with real mission software and hardware in a dynamic, real-world environment with multiple maneuvering targets.

Testing On The Raptor
The final step in avionics testing is aboard the F-22 itself. The fourth flying F-22, which completed its first flight last November, is the first F-22 configured with an avionics suite. Upon arrival at Edwards AFB, initial radar cross-section measurements of this F-22 will provide a baseline RCS for evaluation. Initial avionics testing focuses on those capabilities in the first software release — Block 1, which contains basic radar and CNI functions. While Block 1 mission software looks at individual sensors, Block 3 mission software to be flown for the first time on 4005 builds to more complex scenarios in which all sensor inputs are integrated. Additionally, this initial testing helps refine the software sensor models used in the initial mission software development. Later blocks of mission software build upon previous blocks to quickly increase the capability and integration of the F-22 avionics system.

The process of developing mission software for the F-22 is very lengthy and rigorous. However, it has proven its worth time and time again on the Flying Test Bed and, most recently, in the successful first flight of the fourth F-22.

Randy Neville and Al Norman contributed to this article.