Amy Butler Washington

Developers of the multinational F-35 are finally embarking on a multi-year campaign to demonstrate the single-engine stealthy fighter's ability to dispatch weapons. But uncertainties loom about the impact of internal-carriage requirements on those weapons' effectiveness.

The Lockheed Martin F-35, and the F-22 before it, have introduced a new level of complexity into the air-launched-weapons world by demanding that munitions long anchored on external wing and belly pylons of legacy fighters be carried in small, stealthy internal bays. The Air Force decided decades ago to forgo large payloads—epitomized by the F-15 Strike Eagle—in pursuit of a significantly reduced radar cross section, allowing for fighters to evade air defenses and penetrate into enemy air space.

While the F-22 was a step in this direction, the F-35 is expected to carry far more weapon types in its bay, which has a challenging thermal and acoustic environment. Although the bay has not presented developers with conditions beyond the specifications of weapons slated for use in the F-35, engineers acknowledge there is little margin. “We are within about 10-12 degrees in most cases. But it is close” to the design specifications of some weapons, says Charlie Wagner, weapons integrated project team lead for the F-35 Joint Program Office. “It is not that simple, though. Maybe I can get [a weapon] that hot. But can I get it hot for an hour? Or can it be that hot for two days?”

Wagner says experts in the military are studying the potential prolonged and cumulative effects of operating so close to margin for weapons such as the 1,000-lb. GBU-32 Joint Direct Attack Munition (JDAM) and GBU-31 2,000-lb. version. Both ground-attack weapons are slated for early use on the aircraft. A thornier issue, perhaps, will be the environmental impact of the bay on weapons employing more sophisticated electronics, sensors and motors, such as the Raytheon AIM-120C7/D Advanced Medium-Range Air-to-Air Missile (Amraam) or British AIM-132 Advanced Short-Range Air-to-Air Missile (Asraam). “I don't know if the weapons people know that for sure,” says Wagner. “We are pushing what they designed to. . . . If I'm going to the extreme of what they tested [a weapon] to, they may not have a real good understanding of how that is going to affect the weapon over the next 20 years.”

Operating near or at the margins is not new for the F-35 program, which has suffered problems keeping the F-35B to the required weight. Though the weight issues have been resolved—with roughly 300 lb. of margin now on the aircraft, according to Marine Corps Commandant Gen. James Amos—developers are loath to run into similar problems with the operating margins of weapons in the F-35 bay. This is especially true as the Pentagon faces major funding cuts in the coming years; shortcomings in programs could make them vulnerable for reductions or terminations by Congress.

As scientists and engineers continue to study these issues, the flight-testing program is moving forward. The first jettison test took place Aug. 8, when a GBU-32 was dropped from BF-03, a short-takeoff-and-vertical-landing F-35B at NAS Patuxent River, Md. The trial was designed only to ensure safe separation, and the weapon was inert. This is the first in a short series of such jettison tests. At least two are slated for next month, including the first drop of a GBU-31 from a conventional-takeoff-and-landing F-35A.

The F-35 maintained a speed of roughly Mach 0.65 at level flight for the first drop; higher speeds are slated for future demonstrations. However, Wagner notes that it is not urgent to test high bank angles for JDAM drops because, in the field, the F-35 will likely be employed primarily in level flying conditions to maintain the lowest radar cross section possible for ground-attack missions.