Aviation Week & Space Technology
April 17, 1989
Falcon Eye Flir, GEC Helmet Aid F-16 Mission Flexibility
BYLINE: WILLIAM B. SCOTT
SECTION: INTEGRATED AVIONICS FOR CLOSE AIR SUPPORT; Vol. 130, No. 16; Pg. 35
LENGTH: 4597 words
DATELINE: FT. WORTH, TEX.
The Falcon Eye system was designed specifically for CAS/BAI and reconnaissance applications, while Lantirn is tailored for high-precision strikes and deep interdiction missions.
Having seen both systems demonstrated on low-altitude night flights, I believe Falcon Eye and Lantirn are not competitive, as some have suggested. Their capabilities differ significantly, and Lantirn costs about four times what Falcon Eye will.
The head-steered Flir of Falcon Eye adds an excellent degree of tactical flexibility and night situational awareness by allowing the pilot to look in any direction -- including directly above the aircraft. When augmented by digital terrain database and automatic target handoff systems, Falcon Eye greatly improves the chances of hitting a ground target on the first pass. It still requires a ground or airborne controller to identify the target location, however, and pilots run the relatively small risk of colliding with objects which may not be in the digital database during low-level terrain-following operations. The Falcon Eye system is expected to sell for about $ 1 million per aircraft.
Combining a navigation Flir, a dual field-of-view targeting Flir, terrain following radar, laser designator/rangefinder, and boresight correlator for automatic handoff of targets to Maverick missiles, the two-pod Lantirn system is designed for autonomous operations deep in enemy territory. It will be employed most effectively against high-value tactical targets rather than in support of Army ground units. Although the Falcon Eye Flir affords improved situational awareness, it lacks the degree of targeting sophistication and terrain following capability available with the Lantirn system.
The Air Force Tactical Air Command (TAC) and Systems Command currently are defining requirements and evaluating cost, schedule, performance and risk tradeoffs for a low-cost, head-steerable Flir that will meet CAS/BAI mission criteria in the mid-1990s. When released to industry, these requirements probably will differ substantially from the ones that launched the Lantirn program.
If a system like Falcon Eye eventually reaches the field, it probably will be installed in modified F-16s (or A-16s) and A-10s also configured with target handoff systems. These aircraft would be dedicated to CAS/BAI missions, and would not be assigned to Lantirn-equipped units, according to officers at TAC headquarters.
Contractor and Air Force officials also noted that pod-type Flir systems cannot be ruled out as cost-effective candidates for improving the night navigational and attack capabilities of tactical aircraft. Martin Marietta and Westinghouse both have assured TAC that head-steered Flir capabilities can be incorporated into their proposals, which probably will include pod-type systems.
Jon S. Beesley, a General Dynamics experimental test pilot, occupied the front seat for the Aviation Week demonstration flight. He was equipped with GEC Avionics Cat's Eyes night vision goggles, which ensured an independent non-Flir system was available to enhance the pilot's visibility during our low-level flight over west Texas. The Cat's Eyes advanced prism goggles are a key element of the Marine Corps' Harrier 2 night-attack system suite -- particularly for improved situational awareness during low-level flight -- and are being evaluated by the Falcon Eye team for similar applications (AW&ST Aug. 8, 1988, p. 34).
Normally, Beesley's out-of-cockpit view would have been augmented by a Flir image projected on the head-up display (HUD). The Flir information is provided by a Martin Marietta Pathfinder pod mounted on the F-16's engine inlet, and is routinely used as an added safety measure on these flights. An erroneous switch configuration in the F-16 testbed prevented the Pathfinder's operation on our flight, however. Both the Pathfinder and the GEC Avionics Atlantic Flir pods have been evaluated during the program and have been ''very reliable,'' General Dynamics officials said. Postflight maintenance checks of the Pathfinder confirmed it was operational.
With a full moon and clear skies for our flight, Beesley elected to continue with only the goggles, noting that the light intensifier devices presented an excellent view of the outside world. If it had been an overcast or moonless night, the Pathfinder Flir image -- projected on the HUD -- would have been essential for safe flight. General Dynamics has routinely flown with independent night vision systems in the front and rear cockpits during the Falcon Eye development effort.
In the back seat, I was fitted with the GEC Avionics helmet-mounted display (HMD), which projected biocular Flir imagery and HUD-type, stroke-written symbology on two small combiner glasses mounted directly in front of my eyes. Both displays present the same beamsplit image derived from a single, 1-in. cathode ray tube in the helmet's optics.
The display system adds 15 oz. of head-supported weight, but its center of gravity is far enough back that the helmet still feels well balanced. I found it quite comfortable up to the 4-5g maximum we pulled during the demonstration flight. In contrast, night vision goggles add about 1.5 lb. and are suspended from the front of the helmet, which tends to increase pilot fatigue.
LONG FITTING PROCESS It had taken Mitch L. Snyder, a General Dynamics avionics engineer, about 2 hr. to adjust the helmet and optics to fit me, ensuring the projected Flir images and symbology were clearly visible in the lower one-third of each display. Fitting the helmet system to a variety of people has presented a significant challenge to the development team, often taking up to 4 hr. of repeated modifications to get a proper fit. A full-scale development version will have more adjustments built in and will use form-fit helmets.
A Honeywell helmet-mounted sight (HMS) consisting of a magnetic sensor affixed to the helmet and another attached to the canopy's inner surface provided head position data to the Flir steering system. When I moved my head from left to right or up and down, a Texas Instruments Flir sensor mounted on the F-16 upper fuselage directly in front of the canopy followed my head movements. Output signals from the rotating sensor were processed and presented on the eyepieces as an infrared video image of the outside scene.
The Flir sensor is built into a 5-in. ball mounted on a three-axis, gimbaled turret on top of the aircraft nose just left of the centerline. This turret allows the sensor to slew in azimuth, elevation and tilt (roll) while maintaining a horizon-stabilized image. Two-axis helmet-mounted systems -- such as those used on some helicopters -- cause the Flir horizon to tilt when the pilot leans to one side or the other. This was deemed unacceptable for fighter-type aircraft, which dictated that the Falcon Eye Flir have three-axis stabilization.
The sensor ball extends in a fixed-periscope fashion a few inches above the aircraft skin, positioned on top of a Plessey-built optics assembly. It is controlled by two line replaceable units (LRUs) buried in the forward fuselage. A power supply in the ammunition bay completes the three-unit prototype Flir system. A full-scale development version would be repackaged into two LRUs that would occupy space made available by elimination of the F-16 electronic component assembly (ECA). This unit converts pneumatic pressures to electronic signals in F-16s having analog flight control systems, but is deleted in Block 40 and subsequent aircraft equipped with digital flight control computers. In pre-Block 40 aircraft, the ECA could be relocated to make room for a retrofitted Falcon Eye sensor assembly, according to General Dynamics officials.
The helmet-mounted sight and Flir sensor systems were coordinated very well, allowing rapid head movement without any discernible lag or image instability. Once the helmet was boresighted -- about a 30-sec. process performed before each flight -- the outside world registered on a one-to-one basis with the Flir image of that scene. The helmet-mounted Flir provided a field of regard close to what a pilot would experience during daytime flight. Rotating my head, I easily could see most of the left wingtip missile, the forward end of the right missile and as far up as I could comfortably tilt my head back. This covered an area +- 165 deg. in azimuth and an elevation range from 72 deg. up to 32 deg. down, and about +- 20 deg. in roll (head tilt to each side). Because the sensor is mounted to the left of centerline, downward vision is better to the left than the right.
FRONT SEAT VIEW The Flir sensor's position provided a unique perspective -- a clear view of the nose-mounted pitot boom and everything directly in front of the aircraft. Even though I was in the rear seat, I was afforded the same forward sight picture as the front seat pilot enjoyed.
Our F-16B was the second B-model built in the late 1970s and had been repeatedly modified for flight test work. As a result, its configuration was well-suited for development testing, but was not representative of today's operational F-16 fleet. It also had been modified further with systems tailored for CAS/BAI evaluations. These included:
-- A British Aerospace terrain profile matching (Terprom) navigation system. The digital terrain database for our flight contained all natural and man-made cultural features, including elevation information, for an 80 80-km. area of west Texas.
Linked with real-time radar altimeter data, this system is capable of providing covert terrain following guidance, predictive ground proximity information, and passive ranging to a known target location (AW&ST May 4, 1987, p. 85). By matching radar altimeter data of actual terrain features below the aircraft with profiles of the same terrain stored in the digital database, this system provides accurate navigation information, as well as target or waypoint location.
Terprom was integrated with the F-16's fire control computer to present a terrain-following box on the HUD and Falcon Eye displays. Manual terrain following proved to be a simple task of flying the aircraft to keep the flight path marker in the box -- exactly how Lantirn manual terrain following is flown.
-- A Rockwell-Collins automatic target handoff system (ATHS). Information about target location and type can be sent from a ground-based or airborne forward air controller, an airborne scout helicopter or Army ground forces over a data link to the F-16. Digital information is transmitted as a brief burst over standard military ultra or very high frequency radio channels, then is loaded automatically into the F-16's fire control computer. Target location is represented as a small square -- called the target designator or TD box -- in the HUD or helmet mounted display symbology. The type of target, such as ''armor,'' is displayed in the lower left area of the HUD. The Army is installing ATHS units in its McDonnell Douglas AH-64A Apache and Bell OH-58D helicopters, and the system is being evaluated now for CAS applications on the AFTI F-16 at Edwards AFB (AW&ST Nov. 7, 1988, p. 51).
-- Low-light-level television (L3TV). Although intended to be an integral part of the Falcon Eye concept, General Dynamics' development team has had disappointing results with three out of four low-light systems tested so far. In theory, a night-capable TV image displayed on the HUD would compensate for Flir degradation when athermal (uniform temperature) conditions and high atmospheric moisture content prevail. The fourth low-light TV system -- now under evaluation -- is offering ''encouraging results,'' Lydick said. For the Aviation Week demonstration flight, a low-light-level TV system was not installed.
-- Modification of the cockpit lighting controls for use with night vision goggles. General Dynamics adopted a simple approach to the NVG/cockpit night lighting compatibility problem -- turn the lights off when inside information is of secondary interest. Cockpit lighting levels are adjusted before flight, then a modified lighting control panel is set up to activate a push-button switch at the base of the pilot's sidestick control. Pressing this switch with the small finger of his right hand, the pilot toggles the cockpit lights on or off. This philosophy holds that most data required for night flight are on the HUD or helmet display, and in-cockpit fuel or system checks require only an occasional brief update. For these, the lights are momentarily turned on. Otherwise, the cockpit is kept essentially dark, which also reduces the chances of being detected by other aircraft or ground-based low-light systems, according to Joseph W. (Joe Bill) Dryden, Jr., senior experimental test pilot for General Dynamics.
The night Beesley and I flew, the air was clear and cold following an unusual six-day stretch of rain and fog in the Dallas/Ft. Worth area. As a result, the ground, trees and man-made objects were ''cold soaked,'' creating athermal conditions that are considered less than optimum for Flir operation.
While we waited for takeoff clearance at the Carswell AFB, Tex., runway adjoining General Dynamics' production facility, I tried to find and track aircraft in the area with the helmet-mounted Flir and display system. A Cessna Citation and a Navy F-4 were readily identified by the shape of their Flir images as they approached the field for landing. Switching to narrow field of view provided a 5.6 magnification that proved very effective in quickly checking an airborne ''hot spot'' first detected in wide field of view. This wide-to-narrow field of view switching technique -- accomplished by pressing the throttle-mounted UHF/VHF radio button inboard -- later proved quite effective at locating ground targets, as well.
DEVELOPING TRACKING TECHNIQUE On takeoff roll, I could see the runway -- marked with tire skid strips -- race toward us and disappear under the nose, giving the impression I was sitting in the front cockpit. The forward perspective of the Flir display is very close to what the pilot normally experiences visually and is more natural than that presented by the Lantirn navigation Flir. The Lantirn image, derived from a pod mounted under the engine inlet, presents an eye-position perspective about 4 ft. above the ground. Once airborne, Beesley set the Terprom's terrain following set clearance plane to 1,000 ft. and turned west. My Flir picture appeared too bright after takeoff, so Beesley selected a gray scale pattern for display along the bottom of the Flir sight picture, allowing me to adjust brightness and contrast for the best image. He also suggested deleting HUD-type symbology from the helmet display to assess the Flir image better.
After reinstating the symbology, my attempts to locate and track ground vehicles on Interstate 20 and other aircraft in the area with the helmet-mounted display produced mixed results. Tracking required controlled head movement to keep the vehicles under the display's crosshair symbol, Beesley said. This took some adaptation, since humans typically turn their heads to bring a target into view, then perform the fine tracking by moving only their eyes.
I found head-tracking easier if it could be done as a slow, steady movement, keeping a constant rate going. Holding the aiming cross stable enough to simulate designating a target was not a trivial task, especially in narrow field of view. The key, I found, was to concentrate on making corrections through slow head movements, preferably as a steady, continuous motion in one direction.
The Terprom system quickly self-adjusted its navigation confidence factor to level K1 (K0 being the best possible on a 0-9 scale) after having drifted to a K5 level while we had waited to take off. Its accuracy was confirmed at our first steerpoint, a dam on the Brazos River.
As Beesley descended to 500 ft. altitude, I located the dam in the Flir's wide-field-of-view image by looking for the target designator (TD) box symbol, turning my head to place the box near the center of my display, then going to narrow field of view. The Terprom-directed target box was just slightly above the right end of the dam. Beesley said the terrain matching system's accuracy was good enough to attack any desired corner of the dam, even if the target remained hidden until the last few seconds on run-in.
Turning toward our next steerpoint, the terrain-following box -- also driven by the Terprom system -- continued to provide smooth vertical guidance cues, even in a 70-deg. bank. Although holding bank or pitch angles above 30 deg. for an extended period of time will ''starve'' the terrain correlation process of radar altimeter data, the system will continue to provide reliable TF and navigation for about 5-6 min. before it starts to decrease its confidence factor.
At one point, Beesley demonstrated Terprom's ground proximity warning feature by pulling up, rolling inverted and pulling the nose gently toward the ground. The system continuously predicted our flight path, and displayed a ''LO TF'' warning when we descended below 75% of the set clearance plane altitude. An attention-getting large ''X'' flashed across my Flir display (and the HUD) when Terprom demanded a 2g pull-up to avoid dropping below 50% of the set clearance plane.
The only real anomaly I saw on the HMD during the entire flight occurred during this inverted maneuver. My Flir image slowly brightened for no apparent reason, then gradually returned to its previous balance of brightness/contrast after we completed the demonstration point. Neither the General Dynamics pilots nor engineers had seen this before, and no explanation for it was available in the post-flight review.
All terrain proximity warnings were based on knowing our position accurately, then comparing the flight path with terrain elevation information stored in the Terprom database, even when radar altimeter data was not available during inverted flight. Towers and other obstacles in our flight path would cause ''OBST'' and ''NO TURN'' alerts to flash on my display, whether I was looking to the side or directly ahead of the aircraft.
ACCURATE GUIDANCE The Terprom system proved to be quite reliable, although it is limited by the accuracy of information stored in its database. If a new tower or construction crane had been erected since the last database update, we would have received no indication of its presence. For the majority of tactical situations, however, Terprom -- or another digital terrain system -- would be an excellent mission aid for navigation, targeting and terrain avoidance, especially for aircraft not equipped with sophisticated Lantirn-like TF radars.
The locations of navigation turn points (stored in the flight control computer) were identified by the TD box on my HMD as soon as Beesley selected them. Finding these points was a matter of turning my head until the box appeared, then pulling the aircraft nose to the heading seen at the top of my display. One waypoint, a truck stop along Interstate 20, was depicted so accurately that the TD box overlayed the facility's large road sign visible in the Flir image. Being able to look in any direction and see terrain and man-made objects in the night provided a situational awareness that closely approximated that of daytime visual flight. This and other head-steered Flir advantages were most apparent when we started making simulated attacks on a bridge, dam and vehicle targets. The dam and bridge target locations were loaded into the F-16's computer before takeoff. Beesley selected them on the fire control/navigation panel (FCNP), offset about 60 deg. from a straight-in track to the target, and asked me to verbally guide him to the TD box. As we turned inbound, the box was positioned just below the top of a ridge until we got close enough to see the bridge, which had been hidden behind the hill. Beesley had selected a continuously computed impact point (CCIP) weapons delivery mode, enabling him to place the pipper over the bridge as soon as it came into view on the HUD. The simulated bomb delivery was made with ranging data computed by Terprom; the radar -- which normally, provides range information -- was in standby mode.
Slight turbulence at low altitudes made tracking the targets with the helmet-mounted display more difficult, but still well within a pilot's capability. The ability to keep the target in view, even off-axis, allowed day-type delivery tactics to be used without hesitation.
For example, our attack run on the Possum Kingdom dam involved an offset pop-up maneuver typical of daytime tactics. Beesley flew at a TF altitude of 200 ft. until we were 4 naut. mi. from the dam, then started a climb and turn to our offset heading, about 30 deg. from the run-in line. Looking to my left, I found the target in my display, switched to narrow field of view for a brief, closer look, and directed Beesley to turn toward the target. Once the TD box was visible in his HUD display, he completed the attack in CCIP.
While setting up for CAS-type attacks, Beesley spotted two transports flying in formation several miles away and directed me to them. I saw them as two ''hot spots'' in wide field of view, switched to the ''zoomed'' narrow view, and could identify them as C-130s by their Flir image against the cold sky. Finding other aircraft at night -- without their position lights on -- is another obvious advantage of a head-steered Flir.
Our CAS targets were three personal vehicle-sized vans General Dynamics had outfitted with propane-heated surfaces to simulate the thermal signature of an M-60 tank. We contacted the vans -- call sign ''Roadshow'' -- and told them we were making our first pass. Roadshow was in position and was ready to upload their coordinates through the automatic target handoff system.
ACQUIRING TARGET Beesley then ''digitally'' requested their position by activating a mode select button on the properly-configured FCNP, which commanded ATHS to transmit the digital message: ''F-16 ON STATION, SEND TARGET.'' About a 1-sec. ''squelch'' tone could be heard over the intercom when the message was trans- mitted. It was answered immediately by a second tone, alerting us that target coordinates had been transferred to the F-16's fire control computer. The word ''ARMOR'' appeared in the lower left corner of my Flir/symbology display, as did a distance of 15 naut. mi. in the right corner. Beesley said, ''That replaced a very long series of events that used to be done by voice. Now, we know the coordinates of our targets, what type they are, and how far away they are.'' Turning my head left and right, I found the TD box marking the vans' location, and Beesley switched my Flir polarity to ''white hot'' so the hottest objects appeared lighter than the background. Experience has shown that the human eye is most proficient at picking light objects out of a darker background. Three miles from the target, I switched to narrow field of view -- still in white hot polarity -- and immediately saw three equal-sized hot spots in a line-abreast pattern. Beesley flew to the TD box location but never saw the vans with his night vision goggles until we passed over them.
As the targets went under our wing, I realized I was trying to stretch and look over the canopy rail when the aircraft fuselage appeared in the bottom of my Flir image. The sense of realism offered by the Flir display, coupled with the freedom to look in any direction, spoke well for how the head-steered system had been mechanized. Normal flight tasks soon became almost as routine as they would be in the daylight as I became accustomed to the Flir display.
We made several more attacks on the simulated tanks, approaching from different directions, from behind masking terrain, offset left and right, and making arcing approaches. Offset maneuvers allow a pilot to place the target about 30-45 deg. to his right or left, pull up in a standard pop-up, then roll in to put the pipper on target. The off-axis helmet display allowed me to keep the targets in sight throughout the maneuver, tracking them by looking up through the top of the canopy during roll-in.
Pod-type Flir systems such as Lantirn require pilots to make straight-ahead pop-ups, roll inverted and pull the nose down until the target comes into view, then roll back to an upright, descending attitude for weapons delivery. This tactic works well, but requires flying directly at a target, losing sight of it during the pop-up, and rolling inverted while relatively close to the terrain. The offset maneuver with Falcon Eye allows a pilot to keep his target in sight throughout the pop-up and roll-in, and avoids inverted maneuvers at low altitude. It is typical of standard daytime conventional weapons delivery tactics.
On each attack, Roadshow would transmit target update information over the ATHS, refining TD box placement over the targets' location. I was able to detect the targets about 4 naut. mi. away, switching between wide and narrow field of view. With night vision goggles, Beesley could pick out the targets at about 1 naut. mi. if the moonlight was hitting the vans at the proper angle, but was hampered by the goggles only having a single field of view.
I typically located the TD box in wide field of view, centered it in my display, then switched briefly to narrow field of view to actually detect the individual targets and relay their position relative to the TD box to Beesley for the attack. He normally simulated deliveries in CCIP mode, using Terprom data for ranging. Our run-in angle to the target determined how effectively I could head-track the vans. If they were about 45-90 deg. to left or right, it was more difficult to track them until we turned inbound. Being able to designate their location and lock the TD box on specific targets should simplify head-steered tracking and deliveries.
Returning to Carswell AFB, Beesley suggested I look at downtown Ft. Worth to assess the Flir image of large, clustered buildings on an athermal night. I found that the city's bright lights overpowered the Flir image and were mildly disorienting, even when I adjusted the brightness and contrast or switched between black and white hot polarity. It seemed that my eyes could not decide which image to concentrate on -- the Flir picture or the actual light-illuminated scene.
My view of the approach and landing was not a lot different than it would have appeared in the daylight. The Flir sensor position is so close to the pilot's eye position that the runways, lights, flare height and attitudes looked very natural. This may be considered a minor difference when compared to the image presented by a pod-mounted Flir -- which causes pilots to start a flare too high at times -- but reinforces the desirability of having a Flir sensor near the pilot's eye level if night, blacked-out landings ever are required for tactical reasons.
The Falcon Eye system is a significant technological and systems integration step that could open the night to effective CAS/BAI missions. Since Army operational doctrines are dominated more and more by night maneuvers, the Air Force must adapt its capabilities to provide close air support around the clock. Systems like Falcon Eye can provide an extra measure of flexibility that should give new confidence to the Army commander in desperate need of timely, accurate firepower from the air.
