SR-71 Blackbird...from a pilot

[VarkWors]

And (as with the B 747) most calculations and designs were done with only a pen and paper.

[Rocket36]

If I remember correctly, the skin of the SR-71 leaked fuel during flight, as the fuel was used to keep it cool...

It leaked fuel whilst on the runway. Gaps closed once it was up in the air.

At the speeds it flew at, the SR-71 generated ENORMOUS amounts of heat caused by friction. Under such conditions, the surface areas would all expand quite a lot. For this reason it was designed with gaps everywhere and as a result it took off leaking fuel. It would do a supersonic run to heat up and close all the gaps, then slowing back down would refuel mid air from one of the support tankers before everything contracted and the gaps opened up, then continued with full tanks and no leaks for its mission.

Talk about an engineering masterpiece!!!