A-12 Blackbird Question!

If you look at early picture of the A-12 Blackbird, you will see that they are only partially painted. I know the A-12/YF-12/SR-71 series of aircraft were painted black to protect them from the intense heat of Mach 3 flight. What good is partial protection?

Here's a picture of the partial paint scheme I'm talking about:




Why did they Paint these A-12, but not Completely? What was the point of only painting them 1/2 way?

Tim

Take a good look at the photo and see just what they painted.

Leading edges - the places most likely to get hotter over other areas of the airframe.

The paint used for the A-12 was heavier than the paint developed for the SR-71, resulting in limited usage on the A-12. Also the A-12 didn't use the fuel as a heat sink to the extent that the SR-71 did, so there was no real need for the paint in most areas as it was mostly used to assist the radiation of heat from the fuel on the SR-71 rather than direct heat from friction.

In 1962, the first A-12 flew unpainted. Eventually, as the test program moved into performance envelope expansion, there was a need to paint the leading edges black to better radiate heat on the hottest parts of the aircraft. The partial-black paint scheme was introduced in 1963.The YF-12A initially shared this paint scheme.

In 1964, the A-12 fleet was painted overall black, along with the YF-12A and SR-71. As mentioned earlier, this provided better radiative heat characteristics. The only exeption was the TA-12 trainer. It was powered by J75 engines and never flew in the Mach 3 cruise regime, so it didn't experience the same heating profiles as the other Blackbirds. It retained its black and silver appearance.

For some reason, the first M-21 (Article 134) also remained black and silver, while its stablemate (Article 135) was painted overall black.