美 Boeing X-51A Waverider, 시험비행 결과 분석 소식...

 

지난 5월 26일 美 공군과 Boeing 社 그리고 Pratt & Whitney 社가 개발하고 있는 X-51A Waverider 의 시험비행 소식을 전한 바

있습니다.  --->

 

X-51A Waverider Test Flight

 

당시 계획 되었던 약 300초 내외의 시험비행을 지상 관제소와의 Telemetry Data 전송 실패로 인해 발사 후 약 140초 부근에서

자동 폭파시켰으며, 전체 총 비행시간은 약 200초, 최대속도는 M5.0 으로 발표한 바 있습니다.

 

그 동안 시험비행 결과를 분석하고 조사한 결과를 마침 AW&ST 최근호에서 다룬 기사가 있어 아래 소개합니다. 시험비행 당일

발표된 자료와는 달리 최대속도와 총 비행시간에 있어서 수정된 내용과 함께, Scramjet 엔진과 Waverider 비행 본체와의 연결

문제에서 발견된 문제를 남아 있는 3대의 시제기를 통해 보완한 후 금년 말 다시 시험비행을 진행할 것이라는 내용입니다.

 

이번 시험비행에서 해상에 추락한 Waverider 시제기를 회수하지 못함으로써 좀더 정확한 원인을 규명하는데 어려움이 있지만,

과거 wind tunnel 시험과정에서 이미 확인되었던 내용이므로, 향후 보완이 가능하다는 내용의 기사입니다.

 

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Dissecting Scramjet

Initial X-51A test data reveal promising performance despite suspected seal failure

Aviation Week &Space Technology, 08/02/2010

Author: Guy Norris

 

Overall performance of the X-51A experimental hypersonic vehicle and its scramjet engine was robust and “better than expected” despite the early termination of the May 25 flight due to an as-yet-undetermined cause, say program officials.

 

Revealing previously unseen data at the American Institute of Aeronautics and Astronautics Joint Propulsion Conference here, the U.S. Air Force Research Laboratory (AFRL) says the Boeing-built X-51A WaveRider suffered an initial anomaly around 65 sec. into the flight. “For the first 15 sec. it was doing really well, and performance from the engine was slightly better than expected,” says Richard Mutzman, AFRL X-51A program chief engineer. The anomaly was indicated by elevated temperatures “at certain locations in the rear of the vehicle,” and at 120 sec. the X-51A began developing a pronounced bank angle along with a slight sideslip.

 

Following the anomaly, Mutzman says the rate of positive acceleration began slowing, even though the vehicle continued to climb to more than 62,300 ft. after the start of scramjet operation at 61,300 ft. Overall, the measured acceleration totaled about 0.15g. At 160 sec., the inlet to the Pratt & Whitney Rocketdyne engine suffered an “unstart” in which the flow choked at the inlet throat. “But the vehicle recovered itself, and whatever was causing the anomaly throughout the flight went away,” says Mutzman. The acceleration resumed strongly, only to suddenly drop off a few seconds later.

 

The dropoff was associated with loss of telemetry data, and 5 sec. later the vehicle was terminated by range safety officials. Engine cutoff followed and the vehicle splashed down into the Pacific. The recovery from the inlet unstart — a number of which had also been experienced during wind tunnel tests of the SJX61-2 — proves the overall robustness of the engine and its control system, says AFRL X-51 Program Manager Charles Brink. “It wasn’t perfect, but we did pretty good.”

 

The loss of the vehicle into the ocean makes exact identification of the failure challenging, says AFRL. “It’s difficult to do an autopsy without a body,” adds Brink, who points to leakage of hot gases through malfunctioning seals as a prime suspect for the early termination. The focus is on thermal and pressure seals between the scramjet and airframe-mounted nozzle; the seals accommodate expansion of the engine as it heats up. Based on analysis of the sensor data, heat buildup and failure modes, investigators say it is possible the aft seal may have become displaced, partially blocking the scramjet’s exhaust stream.

 

The timing of the vehicle’s subsequent self-correction could also fit with this scenario, says Brink, as the seal would have been burned through, allowing the flowpath to reestablish itself. However, with the seal damaged or displaced, the hot gas ingestion into unprotected areas would soon have caused the vehicle’s final demise, he adds. There is also speculation the inlet unstart could have been triggered by a fault in the forward seal, although whether this could be connected to the flowpath shocks caused by the aft seal problem remains unclear.

 

The X-51A team is inspecting seals on the three remaining vehicles, as well as looking at sealing concepts, temperatures, installation issues and ways to strengthen the seals. AFRL hopes to resume flights by early December, although January 2011 is considered more realistic.

 

In terms of overall performance, the X-51A reached a maximum speed of Mach 4.88, against a target speed of around Mach 5.9. However despite its failure to reach beyond Mach 5, 143 sec. of the vehicle’s 210 sec. of total powered flight time was under scramjet power, making the flight 11 times longer than any previous air-breathing hypersonic flight. The time, though less than hoped for, is also four times greater than the total flight time cumulatively amassed by all previous air-breathing hypersonic vehicles during the past 50 years.

 

 

  ⓒ USAF

 

  ⓒ USAF