Second X-51 hypersonic flight ends prematurely, brings new flight test data

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The X-51 Waverider’s second hypersonic test flight on June 13 did not go according to plan as the aircraft failed to achieve full power, but officials say the Mach 5 flight generated significant amounts of research data.

The hypersonic aircraft was successfully boosted to just over Mach 5 during its flight over the Point Mugu Naval Air Test Range, and the scramjet engine lit but failed to transition to full power. The aircraft was expected to reach a speed of Mach 6.

US Air Force Flight Test Centre officials said after a flawless flight from Edwards Air Force Base, a US Air Force B-52H Stratofortress released the experimental vehicle from an altitude of approximately 50 000 feet. After release the X-51A was initially accelerated by a solid rocket booster to a speed just over Mach 5.

The experimental aircraft’s air breathing scramjet engine lit on ethylene and attempted to transition to JP7 fuel operation when the vehicle experienced an inlet un-start.

The hypersonic vehicle attempted to restart and oriented itself to optimise engine start conditions but was unsuccessful. The vehicle continued in a controlled flight orientation until it flew into the ocean within the test range.

According to Charlie Brink, the Air Force Research Laboratory’s X-51A program manager, AFRL, Boeing and Pratt-Whitney Rocketdyne engineers are reviewing the large amount of telemetry data collected during the test flight to identify the cause of the anomaly.
“Obviously we’re disappointed and expected better results,” said Brink, “but we are very pleased with the data collected on this flight. I am extremely pleased with the AFFTC and Point Mugu’s support and execution of this complex flight test mission, as they provided us every opportunity for success in this endeavour. We have attempted two scramjet experiments now where one successfully lit, and one did not.
“We will continue to examine the data to learn even more about this new technology,” he said. “Every time we test this new and exciting technology, we get that much closer to success.”



Boeing and Pratt-Whitney Rocketdyne built four X-51A flight test vehicles with the program goal of reaching Mach 6 in hypersonic flight. The next flight is tentatively schedule for the third quarter of this year.

In May last year the X-51 broke the world record for the longest ever scramjet flight, flying under scamjet power for three and a half minutes at a speed of Mach 5.

The second flight was originally scheduled for March but cancelled because “all required test conditions could not be met”.