Immediately after the completion of these test phases in September 2022, Coen says, NASA plans to conduct its first public-response test campaign over a community in the southwest U.S. that, unlike Edwards AFB, is not routinely exposed to sonic booms.
“We plan to conduct two community-response tests a year, for a total of 4-6,” says Coen. Flights to gather data from noise measurements and public surveys will be conducted over communities that range from large cities to small towns and rural areas. “The data will be representative of the diversity of communities exposed [to booms]” to meet the requirements of the regulators, says Waggoner.
Lockheed is confident of staying on schedule, in part because most of the X-plane’s systems and subsystems are off-the-shelf and taken from other aircraft. The engine is a General Electric F414-400 from a Boeing F/A-18E/F, the landing gear is from a Lockheed F-16, and the cockpit, ejection seat and canopy are from a Northrop T-38.
The X-plane is 94 ft. long and the nose, shaped to break up the bow shock, is essentially empty from the cockpit forward. Jim Less, a research pilot at NASA Armstrong and one of the LBFD project pilots, says the lack of forward visibility from the cockpit over the aircraft’s long nose presents several challenges.
These range from ground handling, particularly taxiing, to avoiding other aircraft in the air. “We can land without being able to see most of the way down—you can look out the side, and line yourself up—but the other part is being able to see other air traffic that is out there,” he says.
A forward view will be provided by the NASA-developed synthetic external vision system (XVS), which uses a high-definition camera located just forward of the cockpit, image processing and a 4K ultra-high-definition (UHD) display to enable the pilot to see other air traffic.
“We have been evaluating different systems and cameras in a Beechcraft UC-12 King Air at NASA Langley,” says Less. As flown in the King Air, the system has a camera with a 33-deg. horizontal by 19-deg. vertical field of view that provides 3,480 X 2,160-pixel UHD color imagery at 60 Hz, with only 25-millisec. latency.
The long nose will present ground-handling challenges. “We shall have to see what the turn radius is, but we won’t be able to operate out of little airfields,” says Less. For landing and ground maneuvering, the pilot will use a camera under the nose that looks downward when the gear is extended. The imagery is merged into the XVS display to provide a full picture.
To validate its models for sonic-boom signatures in the build-up to the LBFD project, NASA has been flying F-18s on a special dive trajectory that simulates a shaped boom. In August 2017, crews from Armstrong and Langley deployed to the Kennedy Space Center in Florida for a series of F-18 flights called Sonic Boom in Atmospheric Turbulence, or SonicBAT.
The tests were targeted at gathering data on the effect of humid-atmosphere turbulence on sonic booms, and illustrate the complexity of the problem. The impact of turbulence “turns out to be a little unpredictable,” says Less. “Most of the time it softens the edge of the boom, but amplifies it at other times. It is like the way light is reflected off the bottom of a pool; some of it is all broken up and mostly shadows, but every so often you will just see a flash which momentarily focuses the light.”
Coen says F-18 dive flights will be used again in the near future for risk-reduction tests of the noise measurements and community surveys to be used during the LBFD program. “As the aircraft is being built, we will plan the response testing in detail,” he says. “We are working with the international community to craft questions for the surveys that will get us the right answers.”
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