SR-71의 RCS는 아음속에서 20제곱인치였지만, 마하 3.2에서는 10제곱마일까지 늘어났다.

[위종민]

A-12/SR-71은 저RCS 설계가 반영돼 RCS가 20제곱인치였지만, 마하 3.2에선 고열로 기체 주변 공기들이 이온화되면서 이 공기들이 레이다 전파를 반사해 길이 10마일 가량의 눈물방울 모양의 형태를 레이다 스크린에 만들었다고 합니다. 미사일 유도에 쓸 정도로 선명하지 않지만 무언가가 오고 있다는 걸 아는 데에는 충분했다고 하네요.

중국은 A-12와 SR-71의 RCS는 알고 있었지만 무인 드론인 D-21의 RCS는 끝까지 몰랐다고 합니다. 

SR-71의 레이더 반사면적(RCS)은 아음속에서는 20제곱인치였지만, 마하 3.2에서는 10제곱마일까지 증가했다. 그 이유는 무엇일까?

린다 셰필드 밀러

2026년 7월 12일

이 기사의 내용

* Oxcart
* 레이더 반사면적(RCS)
* 아음속과 마하 3 이상에서의 SR-71 RCS
* Oxcart
* 블랙버드 조종사가 밝힌 SR-71이 427℃를 넘지 않는 한 마하 3.55로 비행할 수 있었던 이유

CIA는 U-2의 후속기로 극비리에 A-12 Oxcart를 개발했다. 이 항공기는 소련의 방공망을 회피할 수 있을 정도로 매우 빠르고 매우 높은 고도로 비행하는 정찰기에 대한 미국의 요구를 충족시키기 위해 설계되었다.

A-12는 스텔스 기술의 출발점이었다.

록히드의 수석 엔지니어 클라렌스 "켈리" 존슨은 거의 불가능에 가까운 과제를 맡았다.

서류상 요구사항은 마치 공상과학 소설 같았다. 7만 피트 상공에서 매우 선명한 사진을 촬영할 수 있는 정찰기. 수 시간 동안 마하 3으로 지속 비행하며 실제로 미사일보다 빠르게 날아갈 수 있는 항공기. 적 레이더에 보이지 않는 공격기였다.

레이더 반사면적(RCS)

A-12는 적의 탐지와 대공화력을 회피할 수 있는 정찰기를 개발하기 위한 록히드의 첫 번째 시도였다. 외형 설계를 통해 레이더 반사면적(RCS)을 최소화한 최초의 "스텔스" 항공기였다. 검은색 도료는 기체 내부의 열 방출을 증가시키는 역할을 했으며, 여기에 작은 철 구슬이 포함된 도료를 사용해 초기 형태의 스텔스 성능을 더욱 향상시켰다.

탄소섬유 기반 구조재가 개발되기 전까지는 티타늄이 A-12 개발에 사용할 수 있는 최선의 재료였다. 제작된 A-12의 약 85%는 티타늄으로 만들어졌으며, 티타늄은 주로 가장 높은 열에 노출되는 부위에 사용되었다. 나머지 약 15%는 고분자 복합재료로 제작되었다. 새로운 레이더 흡수재(RAM)는 RCS를 더욱 개선하는 또 하나의 요소였다. 기존의 필렛(fillet)을 대체했으며, 철 페라이트와 실리콘 적층재를 석면과 결합해 레이더 반사파를 흡수함으로써 항공기의 스텔스 성능을 높였다.

SR-71 블랙버드 모형

이 모형은 AirModels에서 다양한 크기로 판매되고 있다.

1968년부터 A-12를 대체하기 시작한 SR-71에도 RAM이 적용되었다. 레이더 흡수재는 블랙버드의 RCS를 줄이는 데에도 도움이 되었다.

아음속과 마하 3 이상에서의 SR-71 RCS

미 공군 전 원사이자 『Lockheed SR-71 Blackbird: The Illustrated History of America’s Legendary Mach 3 Spy Plane』의 저자인 짐 구달(Jim Goodall)은 다음과 같이 설명했다.

“수십 년 전 SR-71의 첫 시험비행 조종사였던 밥 길릴랜드(Bob Gilliland)와 이야기를 나누던 자리에서 나는 SR-71의 레이더 반사면적이 어느 정도인지 물었다. 그는 아음속에서는 약 20제곱인치였고, 마하 3.2에서는 약 10제곱마일에 달한다고 말했다.

‘어떻게 그게 가능하냐고? 블랙버드가 초당 3,200피트 이상의 속도로 공기를 가르며 비행하면 기체 주변의 공기가 이온화된다. 이 이온화된 공기가 레이더를 반사하기 때문에 눈물방울 모양의 흐릿한 RCS가 형성되며, 길이는 약 10마일에 이른다.

‘이 신호는 지대공미사일(SAM)이 정확히 조준하기에는 선명하지 않지만, 적이 경계 태세를 강화하기에는 충분히 크다.

‘또 베트남전 당시 중국은 A-12와 SR-71의 RCS는 알고 있었지만 D-21의 RCS가 무엇인지는 알아내지 못했고, 결국 끝내 밝혀내지 못했다. 내가 그 사실을 어떻게 알았느냐고 묻자 밥은 그저 미소를 지으며 이렇게 말했다. “우리에게는 우리만의 방법이 있지.”’

블랙버드의 멋진 사진과 이야기를 보고 싶다면 린다 셰필드 밀러(콜 리처드 '버치' 셰필드의 딸이며, 셰필드는 SR-71 정찰체계장교였다)의 X 계정 **Habubrats SR-71**, 인스타그램 **SR71Habubrats**, 페이스북 **Born into the Wilde Blue Yonder Habubrats**를 확인해 보기 바란다.

시뮬레이터 훈련 없이 9만 피트 이상까지 SR-71 블랙버드를 비행한 조종사

『Ohio to Supersonic: Flying the SR-71 Blackbird to the Secret World of the Skunk Works』(리처드 "E." 버치 셰필드 대령, 린다 마리 셰필드 공저)는 주문할 수 있다.

사진 제공: 록히드 마틴

린다 셰필드 밀러

린다 셰필드는 헬리온 출판사의 신간 『Ohio to Supersonic: Flying the SR-71 to the Secret World of the Skunk Works』의 공동 저자이다. 그녀는 아버지인 SR-71 정찰체계장교 리처드 "버치" 셰필드 대령의 책을 완성하는 데 중요한 역할을 했다. 린다는 주로 캘리포니아 빌 공군기지에서 성장했으며, 이곳은 SR-71의 본거지였다. 그녀는 노스다코타주립대학교를 졸업했으며, 10년 넘게 공립학교에서 대체교사로 근무했다. 현재 다양한 소셜미디어를 통해 SR-71, A-12, U-2에 관한 글을 매일 작성하고 있다. 린다는 남편 로드니 밀러와 함께 워싱턴 D.C. 교외에 거주하고 있으며, 세 딸과 네 명의 손자를 두고 있다. 그녀는 SR-71 모임인 Habubrats의 공동 창립자이기도 하다. 또한 Distinguished Flying Cross 매거진과 Evergreen Museum 뉴스레터에 기고를 요청받았으며, 현재 The Aviation Geek Club에 매주 기사를 기고하고 있다.

린다 셰필드 밀러: 전체 기사

SR-71 RCS was 20 square in. at subsonic speeds, at Mach 3.2 the RCS was 10 square miles. Here’s why.

SR-71 RCS was 20 square in. at subsonic speeds, at Mach 3.2 the RCS was 10 square miles. Here’s why.

SR-71 RCS was 20 square in. at subsonic speeds, at Mach 3.2 the RCS was 10 square miles. Here’s why.

By Linda Sheffield Miller

Jul 12 2026

In this article:

• Oxcart
• RCS
• SR-71 RCS at subsonic speeds and at Mach 3+

Oxcart

CIA developed the highly secret A-12 Oxcart as the U-2’s successor, intended to meet the nation’s need for a very fast, very high-flying reconnaissance aircraft that could avoid Soviet air defenses.

The A-12 represented the Genesis of Stealth.

Lockheed’s chief engineer, Clarence “Kelly” Johnson, had almost an impossible task.

On paper, the specifications read like works of pure fantasy: a spy plane capable of taking crystal-clear photographs from 70,000 feet. A Mach-3 aircraft that could fly continuously for hours on end and literally outrun missiles. An attack aircraft that rendered itself invisible to enemy radar.

RCS

The A-12 represented Lockheed’s initial efforts at developing a spy plane capable of evading enemy detection and anti-aircraft fire. It was the first attempt at a “stealth” aircraft through the exterior design, minimizing its radar cross-section (RCS). The black paint helped increase the emission of internal heat and paint was used with little balls of iron to further escalate the very beginning of stealth.

Before the discovery of carbon-fiber-based building materials, titanium was the best choice available for the A-12 while it was being developed. Only about 85% of the manufactured A-12 was made from titanium, and the titanium was used mostly on components that were exposed to the highest temperatures. The other 15% of the aircraft was made from polymer composite materials. The new radar-absorbing materials (RAM) were in fact another improvement in RCS. They replaced the fillets and the were made from iron ferrite and silicon laminate, both combined with asbestos to absorb radar returns and make the aircraft more stealthy.

This model is available in multiple sizes from AirModels – CLICK HERE TO GET YOURS.

The SR-71 that started to replace the A-12 in 1968 featured RAM too. Radar-absorbing materials helped reducing the Blackbird RCS too.

SR-71 RCS at subsonic speeds and at Mach 3+

Jim Goodall, former Master Sergeant at US Air Force and author of the book Lockheed SR-71 Blackbird: The Illustrated History of America’s Legendary Mach 3 Spy Plane, explained to me;

‘In a sit down with Bob Gilliland [the first man to fly the SR-71] many decades ago, I asked him what the Radar Cross Section was for the SR-71. He said that at subsonic speeds, the RCS was about 20 square inches. At Mach 3.2, the RCS was about ten square miles.

‘How’s that possible you ask? As the Blackbird moves through the air at over 3200 feet per second, the air around the Blackbird is ionized, and the ionized air is reflective causing a fuzzy ball RCS that looks like a teardrop, and is about ten miles long.

‘It’s not sharp enough for targeting a SAM, but big enough for the enemy to heighten security.

‘And during the Vietnam War, the Chinese knew the RCS of the A-12 and the SR-71, but couldn’t figure out what the RCS of the D-21 was and they really never found out. I asked how he knew that Bob just smiled and said…”We have our ways.”’

Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Twitter X Page Habubrats SR-71, Instagram Page SR71Habubrats and Facebook Page Born into the Wilde Blue Yonder Habubrats for awesome Blackbird’s photos and stories.

The book Ohio to Supersonic: Flying the SR-71 Blackbird to the secret world of the Skunk Works by Colonel Richard “E.” Butch Sheffield and Linda Marie Sheffield is available to order here.

Photo credit: Lockheed Martin

Linda Sheffield MillerLinda Sheffield co-author of Helion’s new book “Ohio to Supersonic: Flying the SR-71 to the Secret World of the Skunk Works,” Linda helped bring her father, SR-71 RSO, Col. Richard “Butch” Sheffield's book to life. Linda grew up on Air Force bases primarily at Beale Air Force Base California. The home of the SR -71. Linda is a graduate of North Dakota State University and taught public school for over a decade as a substitute teacher. Linda writes daily about the SR -71 the A-12 and the U-2 on her various social media accounts. Linda lives in the suburbs of Washington DC with her husband Rodney Miller, they are the parents of three daughters and four grandsons. She is the co-founder of the SR-71 group, Habubrats. Linda has been asked to write articles for the Distinguished Flying Cross magazine, and the Evergreen Museum newsletter. Linda enthusiastically enjoys contributing articles weekly to The Aviation Geek Club.

Linda Sheffield Miller: All articles

[백선호]

빨리 달리면 흔적을 남기게 되는데 그 흔적이 레이다 전파를 잘 반사하는 것이군요. 구름의 물방울이 전파를 잘 반사해서 레이다로 일기 예보를 하듯이요.

[위종민]

마하 3에 가깝게 날아다니면 저런 현상도 일어나네요 ㅋㅋ

[김유철]

조금 이야기가 새지만...아직 SU57이 베일에 쌓여있을 때 플라즈마 스텔스에 대해 회의적으로 봤던 것이 저런 이유죠.

[위종민]

기사에 있는 것처럼 기체를 락온하거나 ARH 미사일이 호밍을 하지 못하게 하는 거라면 모르겠는데 레이다에 정체는 다 드러나겠습니다.