Shoot ‘Em Up

Sometimes you have to destroy the aircraft in order to save it.

A live-fire test on a North American F-86. During the Vietnam War, engineers looked for ways to toughen aircraft against ground fire and surface-to-air missiles. (U.S. Navy)
Air & Space Magazine | Subscribe

(Continued from page 2)

Between the Super Hornet and a Vietnam-era F-4 Phantom, there is no comparison: A Super Hornet has self-sealing polyurethane fuel tanks located away from ignition sources; short, self-sealing feed lines; redundant fuel pumps; wing tanks lined with open-cell foam; fire extinguishing systems in its dry bays; fire walls between the engine and the auxiliary power unit; redundant flight control computers with four separated electrical signal lines to actuators; and redundant, independent, and separated hydraulic power systems. Despite being 25 percent larger than the earlier F/A-18 Hornet, the Super Hornet’s vulnerable area is the same. Says Tyson: “The F/A-18E/F is the most thoroughly tested and aggressively protected tactical aircraft in the U.S. inventory.”

Yet only 34 of the 622 shots in the Super Hornet survivability test program were shot at a genuine Super Hornet, and even then, the aircraft was never loaded with the munitions it would carry to battle. This testing history highlights an important part of the legislation requiring live-fire testing: The 1986 Live Fire Test Law allows a waiver from realistic, full-up, systems-level testing if it would be “unreasonably expensive and impractical.” Had E/F hardware been used exclusively, according to live-fire test engineers, the tests would have cost several millions more than the $60-million-plus  spent on the program, which, they say, met the ultimate goal—understanding the vulnerability of the aircraft’s various systems.

“In order to be granted a waiver,” notes Tim Horton, the head of the Survivability Division at China Lake, “the service, the defense department, and Congress must first approve a comprehensive alternative to a full-up test program that ensures the system will be tested adequately to meet both the spirit and intent of the law. In the case of the F/A-18E/F, a waiver was approved at all levels.”

But to Jim O’Bryon, the waiver process is a loophole, through which every aircraft program has been slipped since passage of the law. “What you want to learn in live fire is what you’d learn on the first day of combat,” says O’Bryon, “but the services hold that if they test all the pieces and use modeling and simulation, that means they’ve tested it all. But it’s not true. Not a single model based on physics exists today that can predict the effect of fire, the number-one killer. And you can’t do user casualty estimates from doing component testing. Can you predict how a car is going to react in a crash by testing the bumper alone? You have to test the whole thing.”

The day after my tour of the boneyard, I meet up with Manchor in the K-2 test pad control room. After the shot is fired, Manchor will try to run the helo at full power for 30 minutes—to simulate the time it would take for a pilot and crew to make it back to friendly territory.

“Okay, starting engine one,” says Chris Fisher, toggling a switch beneath a computer monitor displaying the helicopter engine’s vital signs. One of the five television screens shows the helo in full view, its rotors starting to spin. “Good start on one,” he says. “Moving to two.” The rotors spin faster, and Manchor watches oil pressure and engine temperature rise. Computers have already modeled the effects of this shot at the control link, and real shots have been fired at identical links under load in a static test stand, but those tests don’t show what this test will: what happens in response to a hit when all the forces are at work on the MH-60 in a hover. “We want to see if it fails, and if it fails gracefully or catastrophically,” says Manchor. A graceful failure means that even if it breaks, nothing else happens and the helicopter continues to fly.

The possibility of a catastrophic failure is the reason we’re hunkered down behind steel plates. The link could fail and start a cascade of other, far more deadly failures. Tests on the AH-1 Cobra are a classic example. Shots at the rotor blades and rotor drive controls under static load produced no surprises. But the results were very different when in 1996 the WSL conducted the first test of fast-moving rotor blades and rotor-drive train components while the Cobra was strapped under full power in a hover—a helicopter’s most stressful flight envelope. (The test was conducted not to teach the engineers how to improve the survivability of the helicopter but to develop methods for testing rotor components.) A video of the test shows shots at the end of the blades taking out chunks but affecting no other part of the helicopter; a shot near the rotor root, however, caused the rotor system to start vibrating, and in milliseconds the blades, traveling at 500 mph, sliced through the helo’s tail while the rotor mast transmission went flying 600 feet. One shot and the Cobra was dead.

In a few minutes Fisher pushes the helo to full power and lifts it off. Air bags atop and below four attach points deflate slightly, leaving the MH-60 in a hover. When Manchor sees the red dot of a gun-mounted laser reflecting off a piece of tape on the control link, which is spinning at some 250 revolutions per minute, he nods. “Start sequence,” says Tim Taylor, who is operating the firing system. “Five, four, three, two, one…”

Exactly what happened 0.0012 second later is classified, but Manchor will say that the tests showed “nothing unexpected,” and later, at the China Lake boneyard, I can see from a distance that the MH-60 is intact.

Over the next three years Manchor’s tests will grow potentially more destructive (when he starts shooting the rotors themselves, for example), and it seems hard to fault their realism. Then again, this is a helicopter, which is expected to fly into the kind of threats it’s being tested against. What worries people like Chuck Myers and Jim O’Bryon is that new stand-off precision weapons and low-observable technology may make people think they’ll never get hit, undermining the work at China Lake. “People on [the Joint Strike Fighter] say the plane will never have to fly lower than 15,000 feet,” says Myers. “But the day will come when it’s daylight and overcast, and you’ve got troops fighting other troops in jungles or forests or a city, and you’ll have to. In peace people think you’ll never get hit. But I flew B-25s in World War II and got hit. I flew F-9s off carriers in Korea and I got hit. If your testing causes improvements that extend the time you can stay with your aircraft for three to 10 minutes, man, that’s a big thing!”

Comment on this Story

comments powered by Disqus