Originally Posted by
A0283
Remember at least one all fatal crash with early Electra's where the complete engine plus nacelle and mounts vibration that you seem to describe took the wing off. It appeared that the wing was too stiff. Redesign changed the natural frequency.
Do not remember reading in that report about such earlier events. Which is rather amazing.
Too lazy to look it up. I remember the problem was the length of the shaft and the novel gyration (at certain rpm and Thrust) of the system that caused the shaft to spiral out of its axis, asymmetrically. The resulting vibration was too much for the wing box, and a wing was shed.
This is what I saw on the day.... I was literally within two feet of the Propellor's arc
https://m.youtube.com/watch?v=j6Q5ggtV-y8
By the way, I was aboard well after 1960. They did not fix it, they "mitigated" whirl mode.