NTB: What are the vehicles you test?
Dr. Jackson: All sorts, but flight craft, mostly. We are affiliated with space exploration, so right now, we are testing a boilerplate, which looks like the bottom of a flying saucer. It has some weights attached to it and some instrumentation. Underneath of it, where the surface is curved, we have all the energy attenuating devices that we are considering. Right now, we’re testing airbags. That’s one test article.
We’ve tested all the general aviation aircraft. We’ve done a number of crash qualification tests for helicopters. The Bell and Sikorski Advanced Composite Airframe program helicopters that were tested back in 1987. We’ve tested both the Blackhawk and Huey helicopters to qualify external fuel tanks to increase the payload or range of those models.
We even tested a car from NASCAR. This was after the Dale Earnhardt accident in the 2001 Daytona 500. NASCAR was seriously looking at what kind of barriers they could place around the racetrack to absorb some of the energy of these crashes. We had been developing some energy-absorbing subfloors, and one of the coworkers of mine that was working on that program said we could apply this to a soft-wall design. So we approached it, NASCAR said they wanted to look at it, and we said we could do a crash test here. We placed the barrier design on the ground, and used a NASCAR racecar donated by Richard Petty. We hooked a cable that was attached to a 10,000-pound weight to the car and ran the cable up to the top of the gantry. At the time of the test, we released the weight, accelerating the car into the barrier. We didn’t do the test like an airplane crash test, where we swing the article into the impact surface. But it was a successful test. It was a different kind of test we’ve never done before.
NTB: How is a crash test conducted?
Dr. Jackson: First, there are several weeks to a month of preparation before the actual test. We have to know what the instrumentation plan is. The center of gravity, or CG, of the aircraft must be determined, because you want to lift the aircraft through the CG. This prevents rotations or any kind of rocking motion when the aircraft is lifted and so that it hits at the impact attitude we want it to hit. There is a lot of preparation with finding the CG and attaching the lifting devices.
We also have to manufacture the cable, and there are two sets that get attached to the aircraft, the swing cable and the pullback cable. The pullback cable is used to pull the aircraft back to the drop-at position. During the test, when they say “t-0,” the winch releases and the aircraft swings to the ground. There is a lot of work in instrumentation; sometimes we have as many as 200 channels of data. We typically have anthropomorphic test dummies, and these are instrumented with lumbar load cells, head accelerometers, and chest and pelvic accelerometers. We have a completely on-board data collection system, and it has to be set up and checked out. The technician has to go out with a hammer and beat on the dummy’s chest to see if we are reading accelerations. We used to use an umbilical system, where all the data cables came to a single point, a long, large cable we called an umbilical, and it ran up and then back into our building. It wasn’t the best method, because we often had a lot of chatter and noise in the data. It even lost channels.
On the day of the test, the aircraft is brought out, put in the actual impact position, and then all the external and on-board cameras are set up — we use high-speed film cameras and video systems — and these cameras focus on a specific thing, like an airbag. We may want to see how the dummy with the airbag reacts. We may put the camera in the nose of the aircraft and focus it on the dummy occupant just to see how he responds to the airbag.
When in comes time to do the test, there is a long checklist. All the cables have been attached at this point, the swing cables are generally placed on the western end of the gantry, and the pullback cable has been installed with the winch. All these cables that are attached have “pyro-cutters” in them, pyrotechnic cutters, because when we conduct a test, you want the craft to be in a free-flight condition. We don’t want to constrain it by having cables attached. So right before impact, about three or four feet off the ground, all the cables are pyrotechnically separated from the aircraft. All that has to be set up.
During the countdown, we do a t-5 and the cameras are turned on. At t-3, the data acquisition system, or DAS, is triggered so you capture the full event — the aircraft swinging down, impact, and slide-out. At t-0, the pullback cable is released from the winch and the aircraft swings, pendulum-style, to the ground. Of course, the height of the aircraft and the length of the swing cable determine what the impact velocity is going to be. Occasionally, we will have a harness system that is attached to the cables that will allow us to get pretty much any roll, pitch, or yaw attitude at impact that we want.
After the test, there is a lot of post-test work that goes on. We have pre-test pictures, post-test pictures, and all of the data that has been collected on board has to be saved to the disk. It’s quite a lot of work. There are a lot of people around here on the day of a test.