Falcon Eye: Building the System
By Larry N. Lydick
Engineering Project Manager
The security guard said good night and the hangar door clanged shut in front of the AFTI/F-16. The remaining dim ceiling lights set the mood for some serious thoughts about night attack. I slid into the cockpit and closed the canopy as my thoughts came together. There just has to be some way to let the pilot see the world around the airplane in a fashion more natural than forward looking infrared, or FLIR, imagery in a static display.
I moved a small piece of Plexiglas through various positions around the cockpit as if it were a mobile combiner while I tried to imagine how a gimbaled projector might always present to the combiner just the right FLIR image and regard needed by the pilot. In a flash I had it. The projector could be a miniature CRT buried in the pilot's helmet with a small attached combining glass just in front of the pilot's eye. The FLIR would need to be head-steered. I could hardly wait to disclose my idea to the world at large.
The year was 1982, and can you imagine the chuckles coming from my friends, Johnnie Stegemoller of GD's Pilot/Vehicle Interface Group and Dr. Tom Furness at the Armstrong Aerospace Medical Research Laboratory, as I described my invention. They had been working with the idea for fifteen years. Tom grinned mischievously as he described the history of visually coupled systems and revealed that the concept was entering flight test in the Army AH-64.
Well, the fact remained that a system that would allow a fighter pilot to look wherever he wants and examine targets with an easily controlled narrow field of view, or NFOV, was a great idea, so we all began advocating a head-steered FLIR program for the F-16. In late 1984, senior management at General Dynamics requested that I start a technology transition program as a next step beyond night vision goggles, or NVGs. Thus, the Falcon Eye Program was born. In just two and one-half years, John Fortune, John Curtis, and Mitch Snyder guided the program to first flight using F-16B No. 2.
Falcon Eye, a title applied to the avionics suite of head-steered FLIR, helmet-mounted sight and display, called HMS/D, and low-light-level TV, called L3TV, has evolved through a complete cycle of design and fabrication, ground and flight tests, and flight demonstration. First flight, a day shakedown flight, took place in August 1987 with Jon Beesley at the controls; the first night sortie occurred only days later.
The Falcon Eye concept is unique among fighter night nav and attack systems. It provides the pilot with one-to-one registered FLIR imagery in a thirty-degree-field-of-view helmet display. The pilot head-steers the FLIR and display through virtually the same unobstructed regard as normally available for daytime contact flying. The FLIR is equipped for 5.6X NFOV operation, and the visual coupling with the HMS/D ensures that the FLIR's line of sight is the same as the pilot's. This arrangement appears to be a uniquely satisfying answer to the old bugaboo of "how to steer the soda straw." To date, after twenty-five development flights, there have been no complaints of vertigo or disorientation from the pilots. Pilots can smoothly head-track targets in the NFOV after two or three flights. Thus, the Falcon Eye concept may meet critical requirements for orientation and safety during low-level night operation.
Also unique to the HMS/D concept is the availability of off-axis symbology. The helmet-mounted display, or HMD, is in reality a miniature head-up display, or HUD, with full stroke and raster capability. With much of the developmental testing behind us, the pilots fly the entire sortie with the fixed HUD turned off. F-16 bombing accuracy is undegraded when the HMD reticle is used to attack the HMD image of the target. During the attack phase of a mission, the system instrumentation shows the pilot to be looking from wingtip to wingtip and high up into the canopy during tight turns.
The head-steered FLIR was built by Texas Instruments. It is easily removed from the nose of the F-16 by first removing the streamline fairing, removing an extra line of bolts from the equipment access door and frame, and sliding the FLIR out sideways in the usual fashion. The turret LRU weighs only seventy pounds, so special handling equipment is not required.
Two helmet displays have been tested. One system built by GEC Avionics is biocular (one CRT servicing two eyes) and helmet-mounted. The other is monocular and mounted on the oxygen mask. The mask and display are supported by a thin nylon string connected between the mask nosepiece and a Velcro patch on the helmet brim. Both systems introduce much less head-supported pitching moment than do night vision goggles, and both have been ejection-windblast certified, including proof of nil effects on ACES II pitot pressures. The entire Falcon Eye system has been integrated with the other system in F-16B No. 2. Special techniques were used to reduce digital signal transport lags in the headsteering signals from the HMS.
Let's see what the pilots have to say about the visual experience, the development flight testing, and the philosophy of designing a system directly to the pilot vehicle interface requirements.
Falcon Eye: Developmental Flight Tests
By Jon Beesley
Test Pilot
Recently, I flew a series of close air support attack runs against tanks operating at Fort Wolters west of Fort Worth. The digital database and automatic target handoff systems, or ATHS, made navigation to the targets easy. The target location, elevation, and type were passed to the FCC without the need for voice communication. No pause was required on the way to my simulated war. I flew straight toward the tanks in the continuously computed release point, or CCRP, mode at 500 knots at low altitude.
Four nautical miles from the target, I actioned left to set up for a pop-up and right roll-in (yes, the airplane rolls right). At three and one-half miles and prior to beginning the pull-up, I was able to acquire the targets near the target designator box, or TD, approximately forty-five degrees right of the nose (obviously not a standard F-16). During the pull-up, I once again checked the target formation and pulled the nose toward them for a continuously computed impact point, or CCIP pass. On final, I selected the center tank for my simulated wrath and made a ten-degree CCIP pass. Weapons release was followed by a hard turn off and then back to low altitude for egress. Sound standard? Hardly. It all occurred on a moonless night.
I've had the good fortune to be involved with the Falcon Eye program from the first flight through the majority of its developmental flights and all of the demonstrations so far. I'll recount flight segments to provide a brief history of the twelve-month developmental flight test effort.
Nose-Mounted FLIR
First flight, first problem. I had hardly cleared the traffic pattern when it started: a low-frequency rumble when I turned my helmet left or upward. Obviously, the aerodynamics of the FLIR fairing needed some work. As it turned out, a small pocket between the FLIR and the fairing resonated like low C on an organ. Some judicious carving on the fairing left side after the flight cured the problem throughout a 550-knot- envelope. Subsequent flights cleared the system for operation to seven g's (design point is nine g's) and we were ready for night operations.
In the early night flights when I had manual forward-looking infrared, or FLIR, control available, I attempted to tune the FLIR better than the automatic schedules. No way. TI obviously brought a lot with them from their LANA programs.
A more difficult problem concerned the tremendous number of scenes that the FLIR must adjust to (for example, wherever you want to point your head). Optimizing this situation took about ten flights because the system has to adjust rapidly for varying proportions of hot F-16 nose and cold sky.
Helmet-Mounted Sight and Display
The head-mounted displays, or HMD, were relatively trouble-free from the beginning. Both displays were easily adjusted to give four g's without losing the raster image. Less satisfying was a bad habit of the helmet position tracker, which occasionally created a glitch in its line-of-sight commands. The most famous glitch caught Joe Bill while he was upside down in a high pop. The FLIR tumbled and Joe Bill reverted to the head-up display, or HUD, to recover. In those earlier flights, obviously, we were flying at conservative altitudes, between 500 and 1,000 feet. The head tracker software is now glitch-free and we are comfortable at low altitude.
Low-Light-Level Television (L3TV)
The Falcon Eye mechanization allows the pilot to select his forward scene between FLIR/HMD (the helmet-mounted display) and L3TV/HUD, thus providing extra capability on poor FLIR nights. However, an on-going effort to develop a L3TV to complement the Falcon Eye sensor has met with frustration. Thus far, we have not been able to obtain a camera and display with the sensitivity of the night vision goggles, or NVGs. An alternative would be a helmet that incorporates both NVGs and CRT functions.
System Operation
I can detect tank signature targets at the action point using the narrow field of view, or NFOV, and begin to maneuver accordingly. NFOV takes some training since we normally finetrack with our eyes rather than our heads, but most pilots have been pleased with their abilities after two or three flights. Maneuvering for the attack is almost like in the day. NFOV is used like a cross-check item. Wide field of view (one-to-one registered) is used for orientation and final pipper placement.
Having the stroke HUD symbols in the HMD helps retain orientation, particularly after rainstorms when the world goes to one temperature. The IR scene may not be the best under such conditions, but the targets still shine because their IR level remains high.
Now, when I fly other airplanes in the daytime, I reflexively look off-axis in the direction of the turn points or targets expecting to see their marking symbols. No such luck. I have found myself spoiled by Falcon Eye.
Falcon Eye: Design Philosophy Comparisons
By Joe Bill Dryden
Senior Experimental Test Pilot
Gear up ... turnout of traffic ... fence check. I fly at 100 to 200 feet at 480 ... then 540 ... and finally Vmil. I scan left and right as far as I like to survey the approaching and receding terrain. As I do so, I get symbology information in front of my eyes all the time. I zooOMM (the picture that is ... you have been watching too many Top Gun movies) to inspect closer various things that attract my attention.
I was a little skeptical the first time I flew the Falcon Eye system, but I am now convinced that this approach will surpass the use of the night attack systems I elaborated on in the last issue. As I pointed out, the best approach to flying in the dark is to have several systems on board to ensure that you have some capability to fly on any given night. You will recall that I tried to point out most emphatically that you need an accurate navigation system. This appears to fall in the general category of digital terrain system, or DTS, but more specifically a system called TERPROM for terrain profile matching. You need to modify the cockpit lighting system (not a major mod but rather a very simple one), and then you need something to see outside the cockpit. There are two technologies that enable you to do this, forward looking infrared, or FLIR, and night vision goggles, or NVGs. Since they operate in different parts of the frequency spectrum, you will have some capability to operate on any given night. In the past, we have displayed the FLIR information (from a fixed FLIR pod) on the head-up display, or HUD, field of view and used low-light-level goggles to fill in the total field of regard.
Now, with Falcon Eye, we have mechanized a head-steered FLIR system that is displayed on the helmet in much the same manner as the combining glass with the Cats Eyes NVGs. I think you'll see how this will be better when I point out that, because of the way this FLIR information is passed to the helmet, we can now superimpose symbology over the FLIR imagery. (In essence, you carry the HUD along with you everywhere you look. I love it.) The FLIR system is still susceptible to the present humidity and haze conditions. But with the addition of this symbology, the vastly increased situational awareness really goes a long way to improve the level of comfort in flying the airplane at high airspeed and low altitude.
The increased situational awareness, resulting from the ability to look around while keeping the information from the HUD visible at all times is really great. Of course, as you look off the bore line of the airplane, the symbology changes slightly as you are no longer looking along the flight path of the airplane. Therefore, you will not see the pitch ladder as soon as you turn your head enough to be out of the normal HUD field of view. You will still be able to see the horizon line regardless of where you look, which is nice. In addition, you still have the altitude and airspeed scales and a heading scale to show you where your head is pointed. (As you look where the airplane is going, the symbology changes just slightly to show you that where you are looking is now also the heading of the airplane.) You can see fairly comfortably looking left to the aft fins of a tip missile (station one), to the seeker head of the right tip missile (station nine), down to the top of the radome (just like in the daytime), and up just about as far as you can comfortably raise your head.
Of course, all the nav and weapons-delivery symbology is on the helmet display. With this step, the fun really begins. (All the caution, warning, fuel, and other displays are also incorporated in the helmet, so you safety guys can relax.)
You have seen how I feel about the importance of a system like TERPROM. (Check the last issue.) The system is seldom more than fifty meters off. I said that, if the nav or target symbol is in the center of the HUD field of view, the worst that the system gets would have the target or turn point in the field of view of the HUD. Well, with Falcon Eye, this incredible accuracy can now be used to an even greater advantage because the symbology set includes these same symbols when I am looking off the HUD field of view. As a result, I can now keep track of their location even when I don't have the airplane pointed at them. Further, if neither the airplane nor my head is pointed in the right direction, I still get an arrow in the field of view to show me which direction to look so I can see the point of interest. (Hang on - it gets even better.)
Now that I am looking at the point of interest, I can zoom the field of view to inspect it while I am still some distance away. This allows much more freedom of action, as I have advance knowledge of what I am looking at (which I didn't have with NVGs), nor do I have to overfly the turn point to know just exactly where I am. You still can't say the same in the daytime. Ha.
If you fly close air support, or battlefield interdiction missions for that matter, you can get updated target location information through the datalink system airborne target handoff system, or ATHS, that Jon mentioned and know the symbology will be overlaying the target even though you do not have the airplane pointed at it at the time. You can see the target better, much earlier than you would with a navigation FLIR, because you can take advantage of the zoom capability to see things at a greater range. You can do off-axis pops and still keep track of the target the whole time. If the moon is right, you can do this with the previously mentioned NVG/fixed FLIR combination. But it is much easier with the Falcon Eye and its accompanying symbology. As you get really proficient, you can zoom in the picture even during the pop.
It is a slick system. I like it.
So, building on the last Code One article, I've offered you a different and potentially much better approach to flying and fighting in the dark.
Check three and eight and eleven ... meanwhile keeping track of the HUD symbology and potentially doing some serious killing in the dark.
