2 supersonic aircraft programs reach testing milestones

By Jonathan S. Litt, Tim Conners and Jeffrey D. Flamm |December 2019

The Inlets, Nozzles and Propulsion Systems Integration Technical Committee focuses on the application of mechanical design, fluid mechanics and thermodynamics to the science and technology of air vehicle propulsion and power systems integration.

Boom Supersonic made substantial progress in the design, assembly and testing of its XB-1 supersonic demonstrator aircraft. This work culminated in engine ground testing, which concluded in February at the U.S. Air Force Academy in Colorado. The test demonstrated that measured inlet distortion levels were acceptable for XB-1’s three GE J85-CAN-15 engines. This achievement followed wind tunnel testing of the inlet at the Boeing Polysonic Wind Tunnel in St. Louis in late 2018.

The XB-1’s 2D hybrid compression inlet model was designed for sustained Mach 2.2 operation and uses modular fore and aft ramps, spill door geometry and a wide-throat bleed slot that was based on Concorde’s. An aft-mounted auxiliary intake effectively reduces low-speed distortion, although it is not required to meet flow demand. Analysis of test data proved that high throat bleed gives the inlet a modest amount of efficient internal compression and produced test-based pressure recoveries across the operating range that met or exceeded Concorde’s published performance. The functional design and analysis of the inlet was completed in nine months, with the model fabrication taking an additional three months. A shortened development phase was made possible by baselining the design from a known successful example, Concorde’s wide-throat slot inlet; by judicious use of well-understood computational tools and methods along with the ability to upsurge CPU demand as needed using cloud computing; and by restrained parametric surveys that allowed rapid convergence toward a high-performance, though not necessarily optimized, design.

Another noteworthy XB-1 development at Boom this year is the design of the vehicle’s aerodynamically complex secondary flow path through the extensive use of computational tools. This involved modeling the throat bleed management, engine bay cooling flow, pressure relief systems, integrated ejector nozzle and J85 variable nozzle geometry. Ejector nozzle performance was characterized using high-fidelity computational fluid dynamic models of the fully coupled secondary flow path. This effort improved aero-model fidelity and reduced uncertainty of the overall vehicle mission performance. Along with axisymmetric inlet concepts, the test-verified 2D inlet geometry and architecture are supporting conceptual design studies for Overture, Boom’s commercial supersonic airliner.

In preparation for the X-59 Quiet Supersonic Technology critical design review, which occurred in September, engineers from Lockheed Martin, General Electric and NASA completed NASA’s low-boom flight demonstrator inlet dynamic distortion test entry at the 8-by-6-foot Supersonic Wind Tunnel at NASA’s Glenn Research Center in Cleveland in May. The test verified the acceptability of the unsteady inlet distortion characteristics. The 9.5% scale model was tested at Mach numbers from 0.3 to 1.55. A mass flow plug was used to vary inlet mass flow. Instrumentation included an 80-probe rake at the aerodynamic interface plane: 40 pitot pressure probes and 40 high-response Kulite probes in side-by-side arrangement.