The astonishing way the Air Force tests ejection seats
Dr. John Paul Stapp earned the title "the fastest man on Earth" when he rode the Sonic Wind I rocket-propelled sled at the Holloman High Speed Test Track at Holloman Air Force Base, New Mexico, on December 10, 1954, to a land speed record of 632 mph in five seconds.
He sustained the greatest recorded G-forces endured by man, decelerating in 1.4 seconds, which equaled 46.2 Gs, more than anyone had previously undergone.
When he was pulled from the sled, Stapp's eyes flooded with blood from bursting almost all their capillaries. Stapp was rushed to the hospital, worried that one or both of his retinas had detached and would leave him blind. By the next day, he had regained enough of his normal vision to be released, though his eyesight would never be the same.
More than 50 years later, the Holloman High Speed Test Track at Holloman still exists, but its riders have changed. Stapp was the last human to ride the track and now egress missions use highly instrumented mannequins to look at what loads are and then determine whether or not aircrew survivability was achieved.
"With a human you're going to have to conduct a post-testing examination and then look at variables from human to human, where if you can put all the instrumentation on board a mannequin you can get all that data," said. Lt. Col. Jason Vap, commander of the 846th Test Squadron at Holloman AFB. "You can take that one step further and figure out what you need to do to your seat design, or perhaps a helmet design, or your flight gear to mitigate problems. Those are things that you are only going to get from a highly instrumented mannequin. Not from post-test examination of an individual or examining what kind of pains that they suffered from that."
The data is collected with a variety of onboard data acquisition systems or telemetered for post-test analysis. Additionally, technical imagery, including high-speed digital images, is available for scientists to examine the status of their payloads. Track personnel use the same imagery to determine the status of the sled vehicle during tests. All data can be post-processed and merged using a common time reference to verify the accuracy of the data, and to produce a unified data product.
"We're always pushing to open up new capability fronts. Thinking differently," he said. "It's built into our culture to think about those next steps. What do we need to do? How do we refine things? How do we look at problems differently based upon what we learn out of a mission outcome? So it's a constant learning process here."
At 10 miles, the track is also now the world's longest and it is used to test high-speed vehicles such as aircraft ejection seats.
"The Holloman High Speed Test Track hearkens back to the 1950's," Vap said. "The mission has changed over time and the track has grown over time, from 3,500 feet to now 50,000 feet of rail."
With the current track, the 846th TS has reached velocities in excess of 9,000 feet per second. That is around Mach 8.6 when calculating for altitude. However, the goal speed of Mach 10 has yet to be reached.
"We're going for success, but there's still a lot of territory to be explored and to learn from," Vap said.
Test missions on the track last a few seconds; however, there are weeks, if not months, put into the design effort, fabrication and getting prepped for a test. There are a litany of cameras along the track to make sure that everything is captured in a six-, 10- or 30-second test mission.
"We design the sleds, we fabricate them and we load them on the rail," Vap said. "Prior to that work, we look at the velocity profiles … We look at our rocket motor inventory and we put together the payload necessary to reach the velocities that are needed to carry out the test mission."
"But don't kid yourself. It's not a small measure," he added. "It takes a great deal of engineering staff and a lot of hard work to carry out these missions, on the order of weeks to months to prep for a 10 second shot."
The goal of these tests is to wring out some of the potential problems that could exist in an airborne environment.
"We don't just slap something on a jet and hope it works," Vap said. "Those are things that just aren't done from an operational standpoint. You have to verify that it's going work."
This means failure is inevitable. Not everything is going to be a success and what Vap tells everyone is that you learn more out of your failures than your successes.
"We're in the business of saving lives," said Staff Sgt. Brian Holmes, Egress Craftsman, 846th TS. "Our system isn't used as frequently as most, which is a very positive thing. Being able to come out in this environment and actually test [an ejection seat] and see it operate is pretty exciting."
Vap said there is no bigger "cool factor" in the Air Force than what the HHSTT does on a day-to-day basis. There is no other place in the Air Force that is essentially strapping rocket motors to a sled, pushing payloads down the track at flight relevant velocities and excess.
While the track's passengers are no longer flesh and blood, they are still pioneers – of speed, science and safety. And their contributions to the high speed test track are making the goal of Mach 10 more and more a reality.