[daltonlp]

If you like SR-71 nerdery, clear your calendar for a few hours to read these:

https://authors.library.caltech.edu/105515/

"As flight testing increased to the higher Mach numbers, new problems arose. One, which today may be considered simple with our modern computer techniques, concerned the remote gearbox. The gearbox mounts started to exhibit heavy wear and cracks, and the long drive shaft between the engine and the gearbox started to show twisting and heavy spline wear. After much slide-ruling, we finally decided that the location of the gearbox relative to the engine was unknown during high Mach number transients. We resorted to the simple test of putting styluses on the engine and mounting a scratch plate on the gearbox. We found, to our astonishment, that the gearbox moved about 4 inches relative to the engine. This was much more than the shaft between the engine and the gearbox could take. The problem was solved by providing a new shaft containing a double universal joint."