A T-38C from the Air Force Test Pilot School served as a target for NASA’s schlieren imaging system.
Credits: U.S. Air Force Photo
The next step was to advance the technology, optimize it wherever possible, and determine the feasibility of using AirBOS to obtain imagery beyond the top-down view. The second AirBOS campaign conducted flights in September and October 2014 at Armstrong, and involved both NASA F-18 and F-15 aircraft as targets. For this series, Heineck designed an imaging system with higher resolution and faster frame rate cameras in order to acquire more images per pass and then average the results from each image.
NASA technicians installed the two state-of-the-art high-definition, high-speed cameras in the King Air in addition to the original AirBOS equipment. Images from the new cameras represented a dramatic improvement over those produced by the original system. The use of different lens and altitude combinations and knife-edge aircraft maneuvers by the pilot of the target aircraft provided the opportunity to obtain side-on images.
Researchers continued to refine and improve techniques during the AirBOS 3 series in February 2015. Supersonic target aircraft included a NASA F-15 anda T-38C from the Air Force Test Pilot School (TPS) at Edwards. Air Force test pilots Maj. Jonathan Orso and Maj. Jeremy Vanderhal spent several weeks working with NASA to plan the T-38 flights and determine how to precisely align the jet’s flight path beneath that of the B200 to capture the schlieren images.
Synchronizing the flight paths of the supersonic T-38 and subsonic King Air required complex integration of the airplanes’ navigation systems to ensure that both would be properly positioned over the background target area.
“Safely coordinating two very dissimilar aircraft, operating in close proximity and with a rapid closure rate required a total team effort between NASA, the 412th Test Wing, and TPS,” Orso said.
To obtain detailed images, Orso and Vanderhal had to fly the T-38 directly underneath the King Air. According to Vanderhal, “These passes posed a unique safety and technical challenge due to the small window of time during which the camera could view the target aircraft.”
Following each flight the AirBOS team used NASA-developed image processing software to remove the desert background and reveal rough shock wave images. Next, researchers combined and averaged multiple frames to produce clean and clear images of the shock waves.
The AirBOS effort was funded by NASA's Aeronautics Research Mission Directorate and managed by the Commercial Supersonic Technology (CST) project in the directorate's Advanced Air Vehicle Program. CST Project goals include providing research and leadership to enable the development of a new generation of supersonic civil transport aircraft. The project’s near term objective is to develop the tools and integrated concepts that will enable demonstration of overland supersonic flight with acceptable sonic boom impacts. The current regulatory prohibition against flight that produces a sonic boom over populated areas is viewed as the principal barrier to future supersonic civil aviation.
“It is hoped that the AirBOS images can be used to validate or improve current design techniques,” said Brett Pauer, CST project support manager at Armstrong, “In addition, this research technique may be used to validate design models of future prototype and demonstrator low-boom aircraft.”
According to Tom Jones, CST Project’s associate project manager for flight, “The end goal is to facilitate the ability for a new speed regime and open a new commercial market for civil transportation.”
NASA is using a 21st century version of schlieren imagery, invented by a German physicist in 1864, to visualize supersonic flow phenomena with full-scale aircraft in flight.
Credits: NASA Photo