It’s the higher flier, the fastest and most slippery, it’s the Blackbird. But have you ever wondered what’s behind its records? Have you ever thought about the insane engineering behind one of those engines?
The Sr-71 Blackbird, known between its pilots as Habu, is the conventional plane with higher flight roof, higher top speed and first stealth jet ever made. Designed by the Skunk Works team from Lookheed-Martin during the 60s, the Blackbird obeyed to a simple premise: spying the Soviet Union with impunity and it was worth it.
First, what do you need to reach such records? Easy to solve, just have some BFE (Big-Freaking-Engines), and so were the General Electric J59 engines. When you hear about aerospace engines, you are usually told about turbojets, turbofans, propfans, turboprops, ramjet, propfans… but have your heard about a turbo-ramjet? As the same name says, a turbo-ramjet is a mixture between a turbojet and a ramjet, but how do they work separately?
By one hand, the turbofan is composed by 3 main elements: a compressor, a combustion chamber and a turbine, sometimes followed by an afterburner. The science behind it is to accelerate a fluid so we get propelled forward due to the conservation of momentum, first the air gets compressed in the compressor, then it burns down in the combustion chamber to finally let it expand back in the nozzle, producing the thrust. The turbine produces the energy to feed the plane’s systems and avionics. You can also use an afterburner to re-expand the fluid inside the nozzle, increasing the thrust in almost a 25%.
On the other hand, the ramjet has a main handicap, it only works in M>1.5, because it doesn’t have a compressor to compress the air as it uses the shockwaves produced by the high speeds and the engine inlets, then the fluid goes straight into a combustion chamber and that’s all folks. As it doesn’t need compressor and other secondary elements its extremely efficient and worth it in high speeds (Mach>2).
So, what the famous turboramjet is? The J59 engine was both types in one, on the first stages of flight, when the speed is between 0 and Mach 1.5 the turbojet is in charge of producing the thrust, then, when the appropriate speed is reached, the inlets of the inside engine are closed, and the fluid goes straight into the gigantic afterburners the Blackbird has, just as the ramjet, all this while the correctly entrance of the shockwave-compressed is controlled by the movement of those funny pointed cones, that going inside and out the shockwave is directed right in the inlet.
Now, next time you see one of those on Insta’s reels you will have some interesting facts to tell your partner.