RAH-66 Comanche avionics taps into commercial, mil-spec electronics components

The U.S. military's first "new" aircraft of the 21st Century, the Boeing-Sikorsky RAH-66 Comanche reconnaissance/attack helicopter, also will boast the most advanced avionics suite when the first unit reaches initial operational capability (IOC) in 2006.

Jun 1st, 2001
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By J.R. Wilson

PHILADELPHIA — The U.S. military's first "new" aircraft of the 21st Century, the Boeing-Sikorsky RAH-66 Comanche reconnaissance/attack helicopter, also will boast the most advanced avionics suite when the first unit reaches initial operational capability (IOC) in 2006.


Avionics for the Boeing-Sikorsky RAH-66 scout/attack helicopter, pictured above, uses a wide variety of COTS and mil-spec electronics, including the Digital Map Generator hardware from Harris Corp.
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The various systems and subsystems that constitute that suite also will have varying levels of commonality with other recent additions to the U.S. military aviation fleet, including the upgraded U.S. Navy F/A-18 E/F Hornet jet fighter and U.S. Army AH-64 Longbow Apache attack helicopter, the Marine Corps V-22 Osprey tiltrotor, and the still-in-development Joint Strike Fighter (JSF).

Oddly, the Comanche's avionics will least resemble that of the F-22 Raptor advanced tactical fighter, with which it originally was to have shared the greatest commonality under recommendations from the old Joint Avionics Working Group. JIAWG formed in 1987 to define military avionics standards across the three services, starting with developing common systems for what became the F-22, RAH-66, and the ultimately canceled A-12 Advanced Tactical Aircraft (ATA).

In approaching how to make avionics elements common to several different aircraft, "we take the worst of each environment and make a common design that will survive either platform's worst requirements," says Ken Nerius, advanced program engineer-avionics at Harris Government Communications Systems Division in Melbourne, Fla. "There are several things we are doing on the Comanche that will be useful on future programs." Harris provides the Comanche's fiber-optic high-speed databus, color multifunction display, and several other avionics subsystems.

Systems integrators are converting Comanche avionics to a Fibre Channel-based fiber optic network that uses a common design and components with the F/A-18 E/F, especially the active electronically scanned array (AESA) radar, Nerius explains.

"Our baseline has fiber bringing in the optical signals to the mission computer. We still have legacy [MIL-STD] 1553, but we'd like to replace the high-speed databus with Fibre Channel in production," Nerius says.

The Comanche's memory storage unit (MSU) is a common design that integrators will install on Longbow Apache Lot 7 and, he adds, and the flight controls share a common heritage and generic architecture with the V-22.

The Comanche display generator — a set of three line replaceable units (LRUs) with standard electronics module, type E (SEM-E) printed circuit cards — was part of the JIAWG effort. This approach was to lead toward two-level maintenance, which also reduces the supply chain requirement. Two-level maintenance means open the mission computer, pull and replace a module, and get the aircraft back in the air quickly rather than pulling the entire rack.

"While they never achieved module interoperability, we developed the fiber optic network components for both Comanche and F-22 and provided both programs with development savings on the high-speed databus," Nerius says. The video and sensor datalink optical point-to-point networks are common on the two aircraft, which resulted in cost savings for both programs, he says.

"There has been a real explosion in the telecom market that has allowed us to take advantage of components that have recently been developed for the fiber optics network," Nerius says. "Boeing allowed us to make changes in the aircraft specs because it resulted in an overall cost savings."

The Comanche will replace the current fleet of AH-1 Cobra light attack helicopters and the OH-6A Cayuse and OH-58A/OH-58C Kiowa light observation helicopters in all air cavalry and light division attack helicopter battalions. The Comanche also will supplement the AH-64 Apache in heavy division/corps attack helicopter battalions. Its primary role will be using its advanced infrared sensors to seek out and designate enemy targets for the Apache at night, in adverse weather and through battlefield obscurants. It also will perform the attack mission itself in support of the Army's light divisions.

The mission equipment package (MEP), built with SEM-E boards, comprises a night-vision pilotage system (NVPS), helmet-mounted display (HMD), electro-optical target acquisition and designation system, aided target recognition, integrated communication/navigation/identification avionics system, and turret-mounted cannon. Targeting includes a second-generation forward-looking infrared (FLIR) sensor, a low-light TV camera, a laser range finder and designator, and a small version of the Apache Longbow millimeter wave radar system.

Aided target detection and classification software will automatically scan the battlefield to identify and rank targets long before the targets are aware of Comanche's presence. The target-acquisition and communications system allows burst transmissions of data to other aircraft and command-and-control systems, while digital communications links provide situational awareness to the RAH-66 crew.

Flexible avionics architecture

The Comanche avionics program, which several major subcontractors support, has been more flexible than most military aviation programs as it has moved through a decade-long process of design, prototyping and now EMD. The avionics designers have had their share of challenges. They started a decade ago planning to use the Intel 80960 (i960) microprocessor as the primary avionics mission computer, yet had to change that in the middle of design because of software issues.

"We do have an open architecture and were able to demonstrate the usefulness of that just prior to first flight, when we had to change processors at almost the last minute to support flight because the software requirement had grown," explains Steve Glusman, chief engineer on Comanche at co-prime Boeing Rotorcraft in Philadelphia.

"We went from one i960 to another with additional memory. We made that transition relatively seamlessly," Glusman says. "We've retained that open architecture and have gone the next step for the EMD program to a Pentium P5 [the 133MHz industrial version of the Pentium 1, packaged two per card, compared to one i960 per card]. We did a [trade-off comparison] between the P5 and PowerPC at the beginning of the EMD program. At that time, the Pentium won out. Some of our subsystems do include the Motorola [PowerPC] chip, however, and we do like the PowerPC. The decision we made to go with the Pentium will get revisited in another two or three years and we'll recompete them. Hopefully, we will get to the point where we can support that with minimum effect because of the work we're doing up front."

The Comanche also boasts a unique level of reconfigurability, due in large part to its lack of a master/slave processor system. "The V-22 has two identical systems — one a master, one a slave — and if the master has a problem, they switch to the slave. We have eight processors and split up all the required programming among them. If we have a failure, we reorient the program to run on the remaining parallel processors," Glusman says.

"A third area that makes us unique is our fault detection/fault isolation. The MEP is really the brains of that. We get out of the 'swaptronics' that is today's methodology, where if you have a failure the technicians switch out boards because they can only isolate to a box, not a board. We can isolate to a board, if not to the component level, so our maintenance technicians can determine which board is the problem."

Commercial-off-the-shelf (COTS) has become increasingly prevalent in military programs through the life of the Comanche program, but the severe environmental stresses of military helicopter operations have made it difficult for Boeing, which has primary responsibility for avionics, and its subcontractors.

"We're going through a balancing act [on COTS]," Glusman says. "The only way you can do the fault detection/isolation is to design it into the boards, but we are trying to do at least MOTS [military-off-the-shelf] so we don't have to design everything from scratch. We do have some COTS in the system, but its use is minimized because of the fault detection/isolation requirement and the environment we have to deal with. That is a struggle for any military program, but especially for a helicopter, which has vibration and acoustic problems most COTS was not designed to deal with."

Comanche avionics designers are keeping their eyes on several different military platforms from which to draw technology. "That's more of an opportunity for us than commercial opportunities," Glusman admits.

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Another issue dogging every military program is rapid component obsolescence and diminishing manufacturing sources (DMS). Designers consider technology insertion within open architectures as the primary weapon in that battle, but Glusman says Boeing and its teammates are trying to create as many of their own solutions as possible. One example is displays, where Harris experts resolved a shrinking source problem by militarizing commercial glass.

"The whole military display market has kind of collapsed, but the commercial stuff has gotten so good we can now use it in the advanced avionics area where we have high brightness and high vibration concerns such that we could not have used commercial a few years ago, says Harris's Nerius.

Members of the Comanche avionics team are developing several major subsystems. First is the Integrated Crewstation Controller, otherwise known as the ICC, from Harris. "We're about halfway through development of the ICC, which is basically a Nintendo game controller with a full QWERTY keyboard used for all data entry," Nerius says. "It also is used for pointing and shooting weapons in a heads-down operation. That's never been done on an aircraft before.

"They literally came up with the idea by taking what today's kids know and are familiar with and put it into the aircraft, so essentially tomorrow's Comanche weapons officer is pre-trained," he continues. "Don't build a system for today's pilots, because they won't be flying it. The kids playing with Nintendo today are the ones who will be flying it."

Next comes the Memory Storage Unit (MSU), also from Harris. The MSU uses commercial PC memory cards (one gigabyte or more of solid-state flash memory) for data loader functions. It also operates as a solid-state video recorder. It can access up to 48 gigabytes of data using four PC cards. The MSU Video Record (MSUVR) option includes MPEG encoding of video and audio for record and playback on aircraft and Fibre Channel interfaces to the mission computers.

"The MSU actually was something the program didn't want initially," Nerius says. "We came up with the concept of using commercial PC cards, which were only about five megabytes, far less than the 600 megabytes they wanted, but we said they would grow. Before we could ship our first unit, we went from a unit that was significantly under what they wanted to one that was significantly higher — from 40 megabytes to 1.2 gigabytes."

Next comes the Harris Image Data Distribution Networks (IDDN). Ultra-high-speed laser fiber optic point-to-point 1 gigabyte-per-second Fibre Channel data links carry sensor data to signal processors, video data to the cockpit controls and displays and video data for record/playback between the mission computers and the MSUVR, using standard electronic modules to reduce life-cycle costs and eliminate intermediate shop level maintenance.

The Harris 80-megabyte-per-second Fiber-Optic High-Speed databus is the control link among major processing subsystems, It runs over one pair of small optical fibers, and is one of the key elements in the common avionics module approach that reduces the size, weight, and cost of avionics systems.

The Harris Digital Map Generator DMG on the Comanche uses stored terrain data to generate moving terrain map presentations. It eliminates paper maps in the cockpit while improving the pilot's situational awareness. The map presentations can be digitized representations of standard aeronautical charts or topographical displays created from digitized elevation and cultural feature data. Symbology overlays are added to show such mission features as waypoints, flight paths, threat and target positions, and to assist the pilot with terrain-aided navigation and ground collision avoidance.

The Comanche's Integrated Navigation Subsystem (LINS-2510) is from the Litton Guidance and Control Systems unit in Salt Lake City. It is composed of three Litton LN-251 embedded inertial navigation system/global positioning system (INS/GPS) units, a GPS antenna, and a high anti-jam antenna electronics unit. The LN-251 is an integrated navigation system with an embedded 12-channel, all in view, Selective Availability/Anti-Spoofing Module (SAASM) and P(Y) code GPS.

The Comanche's Mission Computer Cluster (MCC) comes from the Northrop Grumman Electronic Sensors & Systems Sector (ES&SS) in Baltimore. The multifunction core computer is built around a centralized architecture of lightweight modules. The MCC's data processor is Pentium-based, while the signal processor is a third-generation derivative of the array processor Northrop Grumman provides for the Longbow.

"The integrated processor approach results in a 50 percent reduction in hardware versus a distributed processor system," says Northrop Grumman program manager Barbara Mathews. "There are features that are quite modular so we can upgrade as needed. The MCC is COTS-based because we have COTS components in it, but certainly not COTS modules; it has only been fairly recently that COTS at the module level has come out onto the market. COTS — or more accurately MOTS — is being looked at for preplanned program improvement at the module level for future generations."

The helicopter's Target Acquisition Software System (TASS) also comes from Northrop Grumman ES&SS. TASS reduces aircraft exposure time and pilot workload by automating the FLIR search and performing automatic tracking and threat management functions.

The helicopter's fire-control radar (FCR) system comes from the Longbow Limited Liability Co. in Orlando, Fla., a joint venture of Northrop Grumman Corp. and Lockheed Martin Corp. It is a reduced-size version of the Longbow Apache system, incorporating recent advances in digital electronics to achieve a significant weight and volume reduction. "Aided target detection/classification is a new functionality on Comanche," Matthews says. "That enables us to automatically detect, classify and prioritize targets and threats and display them on the target map. That will reduce the time required to locate classified targets and threats by 90 percent. That's what gives Comanche its 'see first, shoot first' capability."

Comanche's Suite of Integrated Radio Frequency Countermeasures (SIRFC) comes from ITT Avionics in Clifton, N.J. The SIRFC (ALQ-211[V]3) is a stand-alone radar-warning receiver designed to provide radar warning, situational awareness, and electronic countermeasures to help the Comanche detect, evade, and defeat modern and emerging air defense threats.

As an overall electronic warfare suite manager, it fuses on- and off-board sensor threat data to give the pilot a real-time picture of the battlefield and support evasion of multi-spectral threats. SIRFC also coordinates appropriate RF or IR countermeasures and the dispensing of chaff or flares.

The aircraft's Electro-Optical Sensor System (EOSS) comes from the Lockheed Martin Missiles and Fire Control unit in Orlando, Fla. The EOSS uses advanced focal plane array and digital imaging technologies to provide targeting and navigation. It is composed of a solid-state TV camera, a two-color laser designator/rangefinder, and two second-generation FLIRs. The Electro-Optical Target Acquisition/Designation System (EOTADS) two-bar scan provides a high-speed, wide-area sector search with reduced aircraft exposure, while the Night Vision Pilotage System (NVPS) enables night and adverse weather operations.

The helicopter's Flight Control Computer (FCC) comes from BAE Systems in Santa Monica, Calif. Company engineers have been contracted to design and develop a new FCC for the RAH-66. The flight-control computer is fundamentally different from the Comanche's mission computer. While the mission computer, which is based on the Pentium P5 microprocessor, processes sensor, fire control, and display data, the flight-control computer manages mission-critical aircraft systems that keep the helicopter flying correctly and safely. Often the mission computer and flight-control computer architectures are kept separate to keep one from interfering with the other.

"We're going to use industrial-grade electronic components rather than full military," says Howard Sweeney, BAE Systems program manager. "One of the key elements of the new Comanche is all mil specs have been downgraded to just guidelines; they've opened the arena to use industrial parts as long as they meet requirements. We're using the PowerPC 603E microprocessor, four of them per FCC, which is pretty leading technology when it comes to military aircraft. Along with that we're going to use other industrial-type components where suitable, such as memory devices, programmable logic arrays, etc.

Project manager Mike Freeland says many commercial standards do not support Comanche's harsh operating environment, especially EMI and vibration.

"We typically provide a very robust printed circuit board, often using aluminum or some exotic material for our core between two surface-mounted printed circuit boards to provide a low thermal resistance path to the chassis walls, which is our primary cooling path," Freeland says. "Our major issue with industrial components has been getting them to operate in our temperature environment. However, the lower temperature range for this system has been raised from minus 55 Celsius to minus 40, which has been a key enabler for us to use industrial parts. They were changed to reflect more real operational needs in designing the aircraft to operate in colder regions or at higher altitudes."

Freeland says the PowerPC 603r microprocessor best meets the new temperature requirements.

The Comanche's Helmet Integrated Display System (HIDSS) comes from Kaiser Electronics in San Jose, Calif., a subsidiary of Rockwell Collins in Cedar Rapids, Iowa. Comanche boasts the only solid state, digital helmet-mounted display, forgoing the heavy cathode ray tubes (CRTs) employed by previous systems. By using liquid crystal displays instead, Kaiser Electronics engineers have been able to package the HMD with a standard aviator's helmet, which is relatively light and balanced.

The HIDSS is a third-generation binocular HMD that offers night-vision imagery combined with accurate weapon and flight symbology. This enables members of the Comanche flight crew to spend most of their time looking outside the aircraft, rather than inside at control displays. Driven by the fully digital, open architecture Expanded Display Electronics Unit, the HIDSS combines second-generation FLIR video, raster graphics symbology, and on-head Image Intensified CCD video for a day/night, all-weather HMD.

There are two HMDs per aircraft. If one develops problems with the video, it automatically reroutes to the other crewmember. An image intensifier TV camera also can attach to the left side of the helmet, giving the pilot an enhanced image of what he cannot see with the naked eye. This enables pilots to fly in poor visibility even if all other onboard sensors are dead. The binocular design also offers a 30-by-52-degree field of view, compared to a maximum of 40 degrees with other HMDs.

The Comanche's Communication, Navigation, and Identification (CNI) system comes from the TRW Space & Electronics Group in Rancho Carmel, Calif. The CNI combines previously discrete avionics and electronics — including COTS processors — into one lightweight rack roughly half the size and weight of previous onboard discrete systems, TRW officials say. It is to reduce the pilot's workload by communicating with ground controllers and with other aircraft, navigating to and from targets, and identifying friendly and enemy aircraft.

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