NASA YF-12C

Taken in 1975, the interesting photos in this post show NASA Blackbirds carrying the so called “coldwall” heat transfer pod on a pylon beneath the forward fuselage.

The Blackbirds portrayed in these photos are usually referred to as YF-12s, but actually one of them was an SR-71: the one on the top is a YF-12 but the one on the bottom is an SR-71.

B-58 navigator recalls dropping Mark-53 nuclear bomb (without plutonium pit) while flying at 500 feet and at 628 knots, low level recce missions, dinner with Doolittle Raiders and Jimmy Stewart
CLICK HERE to see The Aviation Geek Club contributor Linda Sheffield’s T-shirt designs! Linda has a personal relationship with the SR-71 because her father Butch Sheffield flew the Blackbird from test flight in 1965 until 1973. Butch’s Granddaughter’s Lisa Burroughs and Susan Miller are graphic designers. They designed most of the merchandise that is for sale on Threadless. A percentage of the profits go to Flight Test Museum at Edwards Air Force Base. This nonprofit charity is personal to the Sheffield family because they are raising money to house SR-71, #955. This was the first Blackbird that Butch Sheffield flew on Oct. 4, 1965.

Another interesting thing about those pictures is that NASA was not allowed to have an SR-71 but they did and they passed it off as a YF-12!

In fact, the “YF-12C” was a then-secret SR-71A (serial no. 64-17951, the second production SR-71A) given the NASA tail no. 60-6937. The reason for this bit of subterfuge lay in the fact that NASA, while flying the YF-12A interceptor version of the aircraft, was not allowed to possess the strategic reconnaissance version for some time.

In 1970s NASA was not allowed to have any SR-71s, yet they received one and they passed it off as YF-12C (with a bogus A-12 tail number)
Two NASA Blackbirds: the one on the top is a YF-12, the one on the bottom is the YF-12C/SR-71.

The coldwall project

The bogus tail number actually belonged to a Lockheed A-12 (serial no. 60-6937), but the existence of the A-12 remained classified until 1982. The tail number 06937 was selected because it followed in the sequence of tail numbers assigned to the three existing YF-12A aircraft: 06934, 06935, and 06936. Isn’t that amazing?

The coldwall project, supported by Langley Research Center, consisted of a stainless steel tube equipped with thermocouples and pressure-sensors. A special insulating coating covered the tube, which was chilled with liquid nitrogen. At Mach 3, the insulation could be pyrotechnically blown away from the tube, instantly exposing it to the thermal environment. The experiment caused many inflight difficulties, such as engine unstarts, but eventually researchers got a successful flight.

Noteworthy the Flight Research Center’s involvement with the YF-12A, an interceptor version of the Lockheed A-12, began in 1967. Ames Research Center was interested in using wind tunnel data that had been generated at Ames under extreme secrecy. Also, the Office of Advanced Research and Technology (OART) saw the YF-12A as a means to advance high-speed technology, which would help in designing the Supersonic Transport (SST).

Given that the US Air Force (USAF) needed technical assistance to get the latest reconnaissance version of the A-12 family, the SR-71A, fully operational, the service offered NASA the use of two YF-12A aircraft, 60-6935 and 60-6936.

Eventually, with 146 flights between Dec. 11 1969 and Nov. 7 1979, 935 became the workhorse of the program while the second YF-12A, 936, made 62 flights. Given that this aircraft was lost in a non-fatal crash on Jun. 24 1971, it was replaced by the so-called YF-12C SR-71A 61-7951, modified with YF-12A inlets and engines and a bogus tail number 06937.

The YF-12A

Cool Video Explains how SR-71 Blackbird’s J58 Turbo-Ramjet Engine Works
This print is available in multiple sizes from AircraftProfilePrints.com – CLICK HERE TO GET YOURS. SR-71A Blackbird 61-7972 “Skunkworks”

The SR-71 differed from the YF-12A in that the YF-12A had a round nose while the SR-71 had its chine carried forward to the nose of the airplane. There were other differences in internal and external configuration, but the two aircraft shared common inlet designs, structural concepts, and subsystems.

The YF-12 was developed in the 1960s as a high-altitude, Mach 3 interceptor to defend against supersonic bombers. Based on the A-12 reconnaissance aircraft, the YF-12A became the forerunner of the highly-sophisticated SR-71 strategic reconnaissance aircraft.

The first of three YF-12s flew in August 1963. In May 1965, the first and third YF-12s set several records, including a speed record of 2,070.101 mph and an altitude record of 80,257.65 feet. For their speed record flight, Col. Robert L. “Fox” Stephens (pilot) and Lt. Col. Daniel Andre (fire control officer) received the 1965 Thompson Trophy.

Though the aircraft performed well, the F-12 interceptor program ended in early 1968. High costs, the ongoing war in Southeast Asia, and a lower priority on air defense of the US all contributed to the cancellation.

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 and Facebook Page Born into the Wilde Blue Yonder Habubrats for awesome Blackbird’s photos and stories.

Cool Video Explains how SR-71 Blackbird’s J58 Turbo-Ramjet Engine Works
This model is available in multiple sizes from AirModels – CLICK HERE TO GET YOURS.

Photo credit: NASA