Aerion to begin some SSBJ tests

 - November 29, 2006, 6:53 AM

Supersonic business jet hopeful Aerion is still building a consortium to develop its airplane. In March the board of the Reno, Nevada-based company approved continued funding of the project through to program launch.

Brian Barents, Aerion vice chairman, told EBACE Convention News on Monday that discussions continue with OEMs who, thanks to the newly energized market for conventional business jets, already have their resources well occupied. “The good news is that there’s plenty of interest,” said Barents, who added that about 30 percent of the entities expressing interest in participating in the project are based outside the U.S. “Not everyone has money lying around to devote to a $1.5 billion program,” he noted with a chuckle.

Barents and his partners–including company chairman Robert Bass, who is funding these formative technical and financial stages–expect that between $1.2 and $1.5 billion will be required to carry the program through the third year of production. Aerion estimates there will be a market for 280 to 320 aircraft in this class over 10 years.

High-speed Validation

On the technical front, Aerion plans to conduct a sled test within the next couple of months to validate the high-speed performance projections. Wind-tunnel tests have already validated Aerion’s low-speed expectations for its design, but at this stage the company hopes to get proof of its high-speed numbers through tests on a rocket sled rather than in a supersonic wind tunnel. Interference in a supersonic wind tunnel, said Barents, can introduce the risk of corrupting the validation process.

This summer at Sandia National Laboratories near Albuquerque, New Mexico, engineers will attach a half-wing model to a sled that a cluster of five-inch-diameter rocket motors will accelerate at 30gs to a speed of Mach 1.5. The wing will maintain that speed for a fleeting 1.7 seconds before the sled hits a water brake at the far end of the 10,000-foot-long track.

Although brief, the test will give the engineers the chance to record several types of data. They will film the test wing with infrared cameras to see the different heating rates of the laminar and turbulent boundary layers. Boundary-layer total pressure probes mounted at the trailing edge of the wing will measure the thickness of the boundary layer, and accelerometers on the non-imaged side of the wing will characterize the vibration of the wing.

Although potentially more revealing than a supersonic wind tunnel, the sled method is not without its risks of corruption. The high unit Reynolds number makes airflow much more sensitive to surface roughness than it would be at full scale, says Aerion, and the vibration of the sled on the track could cause transition (the point at which the boundary-layer state transitions from laminar to turbulent) sooner than would occur in flight.

Also, reflections of the sled’s trailing-edge shock off the ground and track could alter the airflow and cause transition sooner than would occur in flight. The rapid changes in speed and the short duration of the test, too, might not heat the surface enough for the IR thermography to be effective.

Too swift for wheels or bearings, the sled runs on a pair of precisely aligned I-beams and its metal shoes wrap around the top flange so it cannot lift off the track.

In the event the sled run fails to deliver the expected results, Aerion is evaluating two backups.

One is the NASA Dryden F-15, but with a new pylon that will allow a larger test model than Aerion used in its F-15 tests six years ago. “NASA’s proven on-board infrared video data system provides high-fidelity transition location over the entire test wing surface at near-steady-state conditions,” Dr. Richard Tracy, Aerion chief technology officer, told EBACE Convention News. Downsides: schedule and cost can be issues; airflow in the vicinity of the test article can be disturbed; and the maximum Reynolds number attainable is somewhat less than that of full-scale cruise.

The second backup possibility is a modern, low-disturbance, high-Reynolds-number wind tunnel. “We have identified a candidate facility,” said Dr. Tracy, “and they are planning tests to establish the feasibility of creating full-scale conditions with acceptable disturbance levels.”

Dr. Tracy said, “There is a considerable body of flight data that validates the theory of supersonic laminar boundary layer stability and the computational methods for predicting the transition to turbulence, which form the basis of Aerion’s suite of laminar design tools. The primary reason for the Aerion tests is to closely simulate flight conditions for the specific wing shapes generated by those tools to enable further refinement of our methods.”

In the meantime, business aviation continues to plod along at Mach 0.9-something, but at least Aerion (and a few other contenders) is working to resume the quest for speed that has been driving aviation history since 1903.