Code One Magazine: Weapon Wizardry, 39th Flight Test Sq.,Eglin AFB, FL

Anything that falls from or shoots off an F-16 probably encountered its maiden flight over sunny Florida from the 39th Flight Test Squadron at Eglin AFB. The squadron is test central for certifying weapons for the F-6 and for expanding the F-16's flight envelope for existing weapons. The 39th FTS also plays a key role in developing the latest generations of a wide range of air-to-target weaponry to be used on a variety of aircraft, from F-15E strike fighters to B-2 bombers. Everything from the latest precision-guided munitions and off-boresight heat-seeking missiles to improved bomb racks, radar pods, and cluster bombs loaded with heat-seeking submunitions are accumulating flight time under the wings of F-16s from the 39th FTS.

"This has become the place to test weapons," says Capt. Gregg Carswell, the squadron's engineering flight commander. "Cost is the main reason so many of these weapons are developed here. The F-16 is such an inexpensive aircraft to operate. Another reason is capability. The F-16's avionics can talk to the bombs. We can use the aircraft's global positioning system, or GPS, to guide them. We can transmit weapon-critical navigation data to the aircraft with the airplane's internal data modem. The F-15E can do all this, too, but we can do it at a much lower cost. Weight may be our only limitation with the F-16."

One look at a list of upcoming tests posted on the wall of Carswell's office, however, indicates that weight does not present much of a limitation. The list includes a load of four GBU-24 bombs scheduled for certification tests this summer. A GBU-24 is a laser-guided bomb in the 2,000-pound class. The massive Norden radar pod-a 600-gallon fuel tank filled with an AN/APG-74 radar-recently took its first flight under the wing of one of the F-16s from the 39th. The Norden pod is being used to demonstrate sensor technologies for detecting, tracking, and identifying mobile missile launchers. Interestingly, a much larger Lockheed aircraft, a modified Navy S-3 Viking, was the first to carry the system.

This wide variety of testing, though, boils down to one purpose-to increase the combat capability of the F-16. A large part of that job involves determining whether existing or new weapons, racks, tanks, and pods are compatible with the F-16. These compatibility tests take many forms. They may involve launching a new missile (or a missile new to the F-16) from different positions on the wing. They may involve dropping newly developed bombs. The squadron also tests new combinations of existing loadings on the F-16 to see if the airflow generated around one loading interferes with the safe release of another at prescribed speed and altitude points.

"A weapon is useless if it limits the aircraft to 300 knots," explains Maj. Gary Plumb, an F-16 test pilot and the unit's assistant operations officer. "Ideally, we want a weapon that will allow us to go as fast as we can and to pull maximum g's. But there are always limits. Part of our job is to determine those limits and to make the jet as safe as we can."

Before any new loading leaves the ground, the aircraft with accompanying loadings goes through a series of ground tests. Detailed computer simulations and wind tunnel tests are conducted first to develop a basis of information. The loading is then put through fit checks. In these checks, the aircraft is placed on jacks and the gear doors and flaps are actuated to make sure these systems are not constricted. Mounting lugs on the loading are matched with those on the associated hardpoints or rails. Technicians check basic geometries to make sure nothing scrapes the ground when the aircraft rotates for takeoff and lands. After these initial ground tests, the airplane is powered up with the test item attached to see if the avionic system recognizes it and, in some cases, can communicate with it.

"Most of the engineering is done before any hardware gets here," explains Plumb. "Normally, our first flight with a test item, a new munition for example, is what's called a compatibility flight profile. Our engineers clear the munition to certain points in the aircraft's envelope. We start at a slow speed in a safe regime to see if the airplane handles normally. We may configure the aircraft asymmetrically with the weapon to see if the airplane is controllable at slower speeds and on landings. We fly a series of maneuvers and make sure that the weapon doesn't affect handling. We stress the munition with positive and negative g forces. We execute maximum performance rolls under increasing g's up to some limit set by the engineers. All the while, we look for handling performance problems and weapon structural failure."

In the last part of a compatibility flight profile, test items are flown at high Q-low and fast. "We call it a speed soak," says Plumb. "We go down to 1,000 feet and fly at 0.9 Mach or at some other prescribed maximum speed for half an hour. We are assuming that, in a high-threat war, pilots may need that high-speed, low-altitude capability to get to and get away from a target."

According to Plumb, speed soaks can push a piece of hardware beyond its limits of durability. "At high Q, I've seen doors come off," Plumb says. "Strange things can happen at the edges of the envelope. Bombs have come back with cracked or missing fins and nose fuzes have unthreaded themselves. A chase plane follows us to make sure we're not losing parts of the jet or parts of the weapon. We make sure it can function and talk to the jet at these speeds. This work establishes an envelope."

After the compatibility flight profile, test items designed to fall from the aircraft are put through a series of drop tests. "We may be able to carry a weapon at high speeds and under high g forces, but the flight envelope in which it can be released may be smaller," Plumb explains. "To establish this envelope, we drop a weapon at its negative and positive g limits and at its fastest and slowest airspeeds. We concentrate on the areas we think represent the worst conditions. Turbulence can alter the ballistics of a weapon. Some have come off the airplane and knocked off ventral fins. A weapon may also affect the airflow around adjacent wing tanks, so we test drop tanks as well. Just going out to a certain point in the envelope with weapons may cause the wings to flutter. Engineers can predict these characteristics with computer models, and they can fly shapes in a wind tunnel. But the results are never quite the same as what we actually see on the airplane in flight."

High-speed separation cameras mounted in orange blisters on the aircraft record the immediate separation of a weapon from its carrier. It is up to a unique group of aerial photographers, however, to document what follows. "Those onboard separation cameras are important," explains TSgt. Ralph Hallmon. "But things usually don't get interesting until a bomb falls out of its frame. I've filmed bombs that separate cleanly and then come back and almost hit the aircraft."

Hallmon heads up a four-person aerial photographic group within the 39th FTS. The photographers also support other flight test functions at the base. "Our primary duty is data collection," says Hallmon, who has been an aerial photographer at Eglin for eight years. "Regular aerial photographers tend to fly straight and level to get public relations photos. They usually put the camera down when the flying gets tough. Here, we often have to capture coverage while maneuvering. We chase bombs 200 feet above the ground and in dives up to sixty degrees. We often shoot while our aircraft is inverted. Our most difficult task is recording a high-g launch. These high-speed cameras weigh sixteen pounds. I have filmed missile launches at up to 8.5 g's. What's really tough, though, is holding these cameras while going from eight g's to zero g in one second."

The high-speed cameras run at rates up to 500 frames per second. Engineers review the films frame by frame to make sure that a bomb is doing what it is designed to do. "We also fly loads and flutter tests," says Hallmon. "Engineers have all the strain gauges and other sensors that quantify flutter characteristics. We show them exactly what the movements look like."

Test flights are scrutinized simultaneously on the ground by groups of engineers in sophisticated monitoring facilities. Depending on the test, these engineers may monitor hundreds of aircraft and weapon parameters during one flight. The aircraft flight path and the local weather patterns are shown on large screens above colorful consoles of computer monitors and strip charts that display and record signals transmitted from both the sensors in the test aircraft and the hardware being tested. Meanwhile, engineers wear headsets with microphones tied to everyone else in the room and to the test pilot.

"The people running around the flight operations building in a blur are probably test engineers," says Carswell, a test engineer himself. "The success of a test program lies squarely on the shoulder of the test engineer. He or she, simply by omission, can do a lot of harm by not collecting the right data, failing to collect it, or failing to say 'skip it' for a test point if something looks wrong. That doesn't happen here because we have a rigorous certification process for engineers. We try to have all the right people in the ground control facility for these tests."

A significant portion of the weapon development work being carried out by these engineers and test pilots involves increasing the lethality of existing bombs by improving their accuracy. "The United States has thousands of Mk 82 and Mk 84 bombs," says Plumb. "These bombs have about a five milliradian dispersion, which means if you drop two bombs from 10,000 feet under the exact same conditions, they may land fifty feet from each other because of tolerances allowed in the manufacturing process. If a bomb doesn't hit a tank right on, it will probably not destroy it. So we're taking those dumb bombs and making them smart."

These educated bombs are generally referred to as guided bomb units, or GBUs. The existing USAF arsenal contains about a dozen types of these weapons. The GBU-15, as one example, is a 2,000-pound Mk 84 bomb with a seeker head from a Maverick missile attached to the front end and large steerable fins affixed to the back. These bombs are released and guided for relatively long distances by laser or electro-optical (television) systems. The guidance systems themselves leave room for improvement-and testing.

"Laser systems require an airplane to stay around long enough to lase the target until impact, or they need someone on the ground and close enough to the target to lase it," explains Plumb. "And both laser and electro-optical systems are limited by weather. Many of these drawbacks can be overcome with guidance based on a global positioning system. The bomb, essentially, steers itself with position updates transmitted from a network of GPS satellites."

The 39th FTS has been demonstrating weapon guidance systems based on GPS. The program is called EDGE, which stands for exploitation of differential GPS for guidance enhancement. The EDGE guidance system, in simple terms, improves upon the accuracy of satellite-based guidance systems by supplementing them with information from receivers at precisely surveyed locations on the ground. This ground-based refinement of space-based GPS information is called differential GPS. Lessons from the program will feed into the next generation of precision guided munitions.

Gregg Costabile has been with the program for combining GPS with dumb bombs since its unheralded origins in 1991. "No one had done it before," says Costabile. "Our first drop, launched from over sixteen miles away, missed by six meters. That was with GPS only. EDGE, with differential GPS, improves upon that accuracy. Our first drop in May impacted within four meters of the target. The weapon was released at 30,000 feet at 0.9 Mach and over twelve miles and about 100 seconds from the target."

In the last drop test scheduled for late June, F-16s will drop two of these weapons ten seconds apart against one target. "We would like to see the second bomb fly through the hole made by the first," says Costabile.

Pinpoint accuracy at such long standoff ranges amounts to revolutionary destructiveness. Airplanes, it seems, are becoming platforms for unmanned airplanes.

"That's right," agrees Col. Harry Walker, the operations group commander for the 46th Test Wing at Eglin. "The smarter the bomb, the more it is like an airplane. We're producing bombs with sensors in a variety of spectrums-infrared, millimeter wave, electro-optical. We have bombs with guidance control systems that are basically offshoots of digital flight control systems."

Walker is one of a handful of "double patch wearers"-pilots who have graduated from both the Air Force Fighter Weapons School and Test Pilot School. He was one of the USAF test pilots for the joint DARPA/NASA/Air Force forward-swept-wing X-29 aircraft. His background and position as operations group commander at Eglin give him a broad perspective on the direction of weapon development.

"In general, we are trying to make weapons smarter, smaller, and more powerful," he says. "GPS and other sensor technologies make us smarter. We must have eyes to get to the target. GPS may be the right solution, but we need accurate coordinates for a target to begin with. That's another challenge. Long-range glide bombs, like today's AGM-130, will have to become more stealthy in themselves. Some day we will be building weapons with self-protection systems and bombs with their own active or passive countermeasures. Aircraft designed for low observability and internal carriage force us to think about making these weapons smaller-to use combinations of new chemical explosives and redesigned penetrators to produce bombs as or more powerful than current larger bombs. We are developing a new bomb, basically a GBU-28, that senses how many floors it has gone through as it goes through a building. The back part of the bomb can take out a given floor and the front part keeps going to the basement before blowing up. We have some very devious people putting this one together."

Permutations of the GBU-28 "bunker buster" bomb (a 5,000-pound bomb designed to penetrate twenty feet of concrete and originally dropped by an F-111) may fall just outside the F-16's payload capacity. The F-16, however, is the primary platform for developing a slew of new weapons. One of the more successful and evolutionary intriguing programs recently completed at the 39th FTS is an infrared air-to-air missile built by Raytheon.

The missile originated as a short-finned AIM-9 variant called the Stork, or Boxoffice I. It was designed to be carried in the F-22's internal weapon bay. Its significantly smaller tail fins (and lack of canards) produced several benefits. The compact control surfaces created a smaller radar signature and a greater range-almost double as a matter of fact. The aircraft could also carry more missiles in a given space. But these benefits came at a price-reduced control.

This drawback was addressed by a simple but highly effective thrust-vectoring system in a second design, called Boxoffice II. The thrust-vectoring system produced turn radii of less than 1,000 feet, which created another problem, or, more accurately, another opportunity. Essentially, the missile could out turn its own sensor angle. So the engineers attached a bulbous wide-angle seeker head to the front end of the missile, which gave it a sensor angle of plus or minus ninety degrees from its nose. The aircraft's radar sweep, though, is limited to about sixty degrees. So the engineers incorporated a helmet-mounted display designed by Honeywell for cueing the missile. It worked.

"We performed two guided shots with the missiles at QF-106 drones," recounts Capt. Brian Simpson, one of two 39th FTS test pilots for the program. "I shot the first one in May 1994. We used a standard AIM-9M seeker head. The drone was 1,000 feet in front of me and twenty-five degrees to the left, flying in the same direction. I launched the missile as the drone began a four-g break away from my aircraft. The missile, without a warhead, impacted two seconds later and knocked the drone out of the sky.

"For the second launch last July," Simpson continues, "we used the helmet-mounted display and the wide-angle seeker head. The drone and the F-16 approached head-on at 0.9 Mach each. They were separated by 2,000 feet vertically and 7,500 feet horizontally. The drone began a five-g maneuver into the F-16 when the test pilot fired the missile at a gimbal angle of fifty-six degrees. Six seconds later, the missile passed within fifteen inches of the drone."

Requirements for highly maneuverable missiles and precision-guided bombs come from real-world threats and experience. Boxoffice II, for example, addresses known USAF deficiencies as compared with threat missiles, namely the Russian-built AA-11 Archer. Requirements for highly accurate GPS-based guidance systems can be traced to experiences in the Gulf War. Whatever the source of requirements, however, the advance of technology behind these weapons seems unrelenting.

"After I graduated from the Fighter Weapons School and went on to become a test pilot," says Col. Walker, "one of the test engineers asked me, Why is it that whenever engineers develop something new, you operators always want us to do more?' I replied that the engineers have yet to satisfy our requirements. Every fighter pilot wants four things: invulnerability, invisibility, omniscience, and home-on protoplasm weapons. Until the engineers can give us those four things, we'll always want more."

Weapons In Work at the 39th FTS
DWS-24, an air-to-ground munitions dispenser, is made by a subdivision of Deutsche Aerospace. The unpowered dispenser is released during high-speed, low-level flight and flies autonomously to a target where it releases submunitions over an area up to 350 meters wide and 1,000 meters long. Several European countries are interested in the program. The 39th is currently evaluating a GPS guidance system and high-altitude launches for the weapon.

ASRAAM, the advanced short-range air-to-air missile, is being developed by British Aerospace. The infrared-guided off-boresight missile is a candidate for the next generation AIM-9.

JDAM, the joint direct attack munition, is being developed for the US Air Force and Navy. It will be a highly accurate, all-weather conventional bomb with its own inertial guidance system. The weapon will likely use technology demonstrated in the EDGE program, which is featured in the main article. JDAM is scheduled to be fielded in the 1997-1998 timeframe.

CBU-97, also called the sensor-fuzed weapon, is a cluster munition that releases ten submunitions on parachutes at about 150 feet above the ground. Each submunition dispenses forty target-sensing projectiles over a large number of ground targets, like tanks and armored personnel carriers. The 39th FTS is performing lot acceptance tests on the initial production run.

Wind-Corrected Munitions Dispenser, a kit with an inertial guidance system and steerable fins, will be attached to current cluster munitions. The kit improves the standoff performance of the CBUs by correcting for wind drift after drops from high altitudes. The kit is still in the early development stages.

JSOW, joint standoff weapon, is a modular, low-cost glide weapon developed for the US Air Force and Navy. The weapon can carry several different submunitions, warheads, nonlethal payloads, and terminal sensors. It also allows for different modes of propulsion.

HTS, a targeting system for the high-speed antiradiation missile, is currently fielded by several units flying the Block 50 F-16. The system is a super-sensitive receiver that detects, classifies, and ranges threats and passes the information to the HARM missile and to displays in the cockpit. The 39th FTS is working on software updates for the system as well as on a modem for transferring information from HTS-equipped aircraft to non-HTS aircraft.

PIDS 3, the pylon integrated dispenser system, is a Danish weapons pylon similar to a MAU-12. The pylon has a blister in the back that contains compartments for chaff or flare dispensers. It is being tested for the Air National Guard.

British Bomb Rack, a dispenser for dropping BDU-33 practice bombs, is a replacement for the SUU-20. The new rack uses a compressed gas instead of pyrotechnic charges to eject bombs. The rack is finishing operational tests on the F-16 and has flown in compatibility tests on the F-15E and F-111.

DSU-33, an inexpensive radar-based bomb fuze, is designed to replace more expensive radar fuzes in the curent inventory.

ALR-56M, a radar-warning receiver, evaluates threat radar and sends information to the ALE-47, which automatically dispenses flare and chaff accordingly.