폭격기 B-21 시험비행 사진 공개

[위종민]

B-2에 비해 더 납작해진 배기구가 보이고, 배기열 온도를 낮추기 위한 기술 (열흡수 타일) 등이 사용됐을 수 있다고 합니다. 배기구가 더 납작해지면 배기가스 온도가 높아질 텐데 그에 대한 대처도 하긴 했어야 겠네요. 

https://www.airandspaceforces.com/what-new-b-21-photos-show/

A B-21 Raider conducts flight tests, which includes ground testing, taxiing, and flying operations, at Edwards Air Force Base, California, where it continues to make progress toward becoming the backbone of the U.S. Air Force bomber fleet. The B-21 will possess the range, access, and payload to penetrate the most highly-contested threat environments and hold any target around the globe at risk. The B-21 program is on track to deliver aircraft in the mid-2020s to Ellsworth Air Force Base, South Dakota, which will be the first B-21 main operating base and location for the B-21 formal training unit. (Courtesy photo)

Expand Photo

SHARE ARTICLE

What the Air Force’s New B-21 Photos Show About the Raider

May 22, 2024 | By John A. Tirpak

Editor’s Note: This story was updated May 23 with an additional photo.

Just over six months after the B-21 Raider made its first flight in November 2023, the Air Force has released three images of the bomber going through testing at Edwards Air Force Base, Calif. A day later, manufacturer Northrop Grumman released another in-flight image. They are the only images of flight testing released so far.

The two Air Force in-flight images are in left profile; one showing the bomber taking off and one in flight at altitude, with the landing gear retracted. The third is a head-on shot of the bomber inside a hangar at Edwards. The Northrop photo shows the aircraft in the air in right profile.

Metadata from the photos indicates they were taken Jan. 17, May 22, and April 4, respectively, confirm‎ing that the B-21 has made at least two flights since its first on Nov. 10, 2023.

The Air Force declined to say how many total flights the aircraft has made, nor will it provide any kind of timetable of the anticipated test flight program.

Together, the three images offer only slightly more information about the aircraft than could be gleaned from unofficial photos taken of the first flight and circulated on the internet.

The takeoff image shows a very narrow, 2-D exhaust embedded in the jet’s tail. The broad, narrow exhaust is distinct from that on the B-2, the B-21’s elder stablemate, which had a more boxy, sugar-scoop exhaust. The B-21 exhaust suggests more attention to fanning out the aircraft’s heat to reduce its infrared signature, as well as keep its profile slim to defeat radar.

A lack of blackening around the exhaust could simply be an indication that the aircraft hasn’t flown very often, but it could also indicate that exhaust heat is somehow cooled inside the aircraft before being discharged as thrust. On the F-117 and B-2, this was accomplished with the use of panels very like Space Shuttle thermal tiles, which capture heat and only slowly release it.

An auxiliary air inlet can be seen, opened above the engines to provide them with more air as the jet rotates its nose up. This is necessary because of the top-mounted main air intakes, which would receive reduced air at high angle of attack. A similar, but more scalloped feature is present on the B-2.

Behind the cockpit is the heraldry of Air Force Materiel Command, the 412th Test Wing, and Global Strike Command. The “fuselage” serial number of the aircraft (0001) is visible, but it lacks the typical year of acquisition.

A long patch, in a different, darker color than the rest of the aircraft, is visible on the upper surface, roughly where the engine hot section should be. It’s adorned with a forward-pointing arrow and two apparent diamond-shaped vents are next to it. The forward part of the patch is sawtooth-shaped, a common practice in stealth aircraft where there is a surface discontinuity.

Pop-up navigation lights are visible on the outer wing, likely only used for operations in ATC-controlled airspace and clearly retractable to make the aircraft more stealthy.

Along with the images, an accompanying release from 412th Test Wing at Edwards reiterated comments made by Air Force acquisition executive Andrew Hunter earlier this month that the B-21’s test flight program “is proceeding well.” 

“It is doing what flight test programs are designed to do, which is helping us learn about the unique characteristics of this platform, but in a very, very effective way,” Hunter told lawmakers on the Senate Armed Services Committee on May 8.

Hunter also said the B-21’s design is “more digital than not.”

The release also stated that the B-21 will “incrementally replace the B-1 and B-2 bombers” now operated by the Air Force. The service recently told Air and Space Forces Magazine the B-21 will not necessarily replace the B-1 and B-2 on a one-for-one basis as the new bombers become available, but Global Strike Command has said it does not expect to have the money and manpower to field four different types of bombers at the same time. The plan is to neck down to a fleet of just B-21s and B-52Js after the B-1s and B-2s retire.

The Raider was described by the Air Force as a “long-range, highly-survivable, penetrating strike stealth bomber” which will “play a major role supporting national security objectives and assuring U.S. allies and partners across the globe.” It is “expected to enter service in the mid-2020s with a production goal of a minimum of 100 aircraft.”

Air Force Chief of Staff Gen. David Allvin said recently that the pace at which new technology is becoming available could mean the service moves on to a more advanced design, and that 100 aircraft may be the final fleet size for the B-21.

Northrop received a low-rate initial production contract for the B-21 in December, following first flight. The company has said it will not make any money on the first five lots of the B-21, mainly because of inflation and escalated labor costs.

The Air Force noted in its release that the initial flight test aircraft are being manufactured on the same tooling and with the same personnel as will be used for production of operationally-configured Raiders. The test aircraft are also intended to have test apparatus removed and be configured as operational aircraft after the flight test effort concludes.

[백선호]

보잉 777-9처럼 바이패스 비가 아주 큰 엔진에서 나오는 (대부분은 연소 가스가 아니라 팬을 통과한 공기) 공기의 온도와 B-21이 뿜어내는 공기의 온도는 얼마나 차이가 날 것인지 궁금하네요.

[위종민]

고바이패스 터보팬 엔진의 배기온도는 500~600도 정도라고 하네요. ( https://aviation.stackexchange.com/questions/20739/what-is-a-normal-egt-range-of-a-jet-engine) 저바이패스 엔진의 경우 밀파워 상태에서 600~650도 정도라고 합니다. 배기구에 온도저감조치가 안 돼 있는 상태에서의 온도는 아무래도 여객기용 고바이패스 엔진보다 높을 수밖에 없을 텐데 저런 조치로 열을 얼마나 내릴 수 있을지도 궁금해지네요.