The Mighty J58 - The SR-71's Secret Powerhouse
Why Aviation Stack Exchange recommends it
Aviation Stack Exchange answerers point people to it when explaining how the SR-71's variable inlet spike and engine airflow work.
Recommended by 2 people across 2 different months, 2015 to 2019.
What it is
A short animated explainer from the TechLaboratories channel on how the Pratt & Whitney J58 engine powered the SR-71 Blackbird to Mach 3.2. It uses archive footage and animation to show the airflow through the engine, including the moving inlet spike that slows supersonic air.
Cited in 1 Wikipedia article, including Pratt & Whitney J58.
What people said
Recommends Steve · 2015-11 · Aviation Stack Exchange · on “Why is the nose of the Mig-21 shaped so differently compared to other fighter aircraft?”
This video on YouTube shows how the SR-71 engine worked [this video] . In particular, it has an animation and explanation of the reason for the inlet cone, which is to reduce the supersonic airflow so that the engine can use it. I was surprised that the inlet cone actually moves forward/backward within the intake, dynamically changing the geometry to match conditions.
Recommends user33651 · 2019-05 · Aviation Stack Exchange · on “Why do the inlet cones on an SR-71 retract at higher speeds while the one on a MiG-21 extends at higher speeds?”
This is only a guess, so please take this with a grain of salt. An important characteristic of supersonic engine inlets is the total pressure loss (or also sometimes pressure recovery). The total pressure loss over a normal shockwave is a lot higher than if you would slow down the air to the same speed through several oblique shock waves. If you want to understand why the sr-71 spike retracts I recommend you watch this video. The sr-71 had a quite complex inlet geometry to ensure that the air was slowed down over many oblique shocks. sr-71 engine inlet [this video] On jet engines that don’t have such a complex inlet geometry as the sr-71, the best pressure recovery is mostly achieved by getting t
Cites Peter Kämpf · 2015-05 · Aviation Stack Exchange · on “What is a ramjet?”
A jet engine compresses air, heats it by mixing it with fuel and burns it, and lets the heated air escape at the end, where it accelerates to more than its initial speed in a convergent-divergent [LINK] nozzle [LINK] because the density of the heated gas is lower, thus needing a higher volume at the same pressure. By converting the kinetic energy of the flow into pressure (potential energy), the intake creates high-pressure air to feed the engine. This is called pressure recovery and increases with the square of flow speed. Please see below for a plot: This puts a pressure of 1 at Mach 0.5, which is on the high side for flow speed near the compressor face in a jet engine intake. Note that in