Collaboration, Coordination Key to Successful Supersonic Flight Testing Program Written 17 June 2016
Panelists: Moderator Sandra Magnus, executive director, AIAA; Doug Cooke, principal aerospace consultant, Cooke Concepts and Solutions; retired U.S. Air Force Col. Lee Archambault, chief systems engineer and test pilot, Sierra Nevada Corp., and former astronaut, NASA; retired U.S. Air Force Maj. Gen. Joe H. Engle, former astronaut, NASA; John Olson, vice president, Space Exploration Systems, Sierra Nevada Corp.
by Lawrence Garrett, AIAA web editor
Communication and collaboration between flight test engineers and test pilots was significant in developing hypersonic flight — from the early X-1 and X-15 rocket planes to the progression of the now retired shuttle program — and will remain so into the future, aerospace industry experts agreed June 17 at the final session of AIAA AVIATION 2016 in Washington, D.C.
Just as important is the collaboration between overlapping generations, panelists in “Hypersonic Flight Testing: X-15 to Space Shuttle and Beyond” said, citing how the X-15 program helped the shuttle program and how the shuttle program is helping with Sierra Nevada’s Dream Chaser spacecraft.
Retired U.S. Air Force Maj. Gen. Joe H. Engle, test pilot for the X-15 in the 1960s and early space shuttle missions in the 1970s, touched upon a number of challenges in the X-15 program, including the difficulty in landing a hypersonic aircraft that touched down at over 200 mph.
Because the drag was at the back of the X-15 and experiments often onboard increased the aircraft’s touchdown weight, Engle explained, pilots found it challenging to touch the nose down gently, the signature of a good landing.
With most aircraft, pilots pull back on the stick to lift the nose, but this did not work on the X-15, Engle noted, adding that the first several landings of the X-15 were a little rough with the nose dropping hard following touchdown of the main landing gear — like someone had “cut the rope.” But, he said, through frequent collaboration with flight test engineers, pilots discovered that they had to push forward on the stick when landing the X-15.
“Pilots are trainable,” Engle joked.
Doug Cooke, principal of Cooke Concepts and Solutions and a former NASA associate administrator, called the X-1 and X-15 aircraft the prime predecessors to the space shuttle program. In 1975, Cooke was tasked with defining and implementing an entry aerodynamic flight test program for the space shuttle.
The “shuttle’s terminal part of its flight was based on basically the flight profiles from these programs,” he said.
The shuttle program was significant in human spaceflight and aviation history and offered many technological advances, Cooke said, highlighting its main engines, which are “still to this day on the edge of theoretical efficiency for a hydrogen-oxygen engine.”
Participants in the panel discussion, "Hypersonic Flight Testing: X-15 to Space Shuttle and Beyond,” on the morning of 17 June, at AVIATION 2016, in Washington, DC.
Collaboration and coordination were essential, he continued, adding that the success of the shuttle flight test program "took a lot of coordination" between a team of engineers from Dryden Flight Research Center, the Air Force Flight Test Center at Edwards, McDonnell Douglas, and Rockwell International, who built the orbiter. Cooke said members of the team possessed "knowledge on past programs."
Cooke said the main challenges with the program were the shuttle's stability and control, due to early testing of a scaled-down model in a wind-tunnel at speeds of about Mach 20. The first shuttle orbital flight flew from Mach 25 to touchdown. The X-15 held the previous winged-vehicle flight testing record at Mach 6.7.
Cooke said they were able to overcome the testing concerns through calculations and testing via motion-based simulators, noting that what they accomplished was state-of-the-art at the time but is probably “old school” today.
Retired U.S. Air Force Col. Lee Archambault, chief systems engineer and test pilot for Sierra Nevada Corp., called both Engle and Cooke “legendary” in the aerospace industry. Archambault, who served as a shuttle crew member on STS-117 and STS-119 with AIAA Executive Director Sandy Magnus, who moderated the panel, credited the work from 1963-1975 as being beneficial to current-day aerospace engineers.
“We’re the new kids on the block with the next lifting body,” Archambault said of the Sierra Nevada team working on the Dream Chaser spacecraft. “Hopefully we’ll be there in about four years.”
Sierra Nevada was selected to participate in NASA’s Commercial Resupply Services 2 program. The Dream Chaser, which at 30 feet nose to tail is only a quarter the size of the space shuttle. Despite the size difference, Archambault noted, their designs are similar, and the Dream Chaser flies with a similar approach angle as the space shuttle and has similar lift to drag, profile and airspeeds.
The Dream Chaser’s next scheduled test flight is in December, and Sierra Nevada will continue its work on future plans for manned vehicles, he said.
John Olsen, Sierra Nevada’s vice president of Space Exploration Systems, echoed the sentiments expressed by his colleagues on the panel.
“I think this is still very much a growth industry in flight test,” he said. “I think it’s an extraordinarily fun and challenging domain that’s never really done.”
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