I thought it had some connection to oil and cooling.
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Good point, Jim.I thought it had some connection to oil and cooling.
I have heard such a shaft vibration occured on the J2M, which was caused by the lack of propeller rigidity, but not about the J7W1. I will check.Shinpachi-san, I have read that the J7W experienced severe shaft vibration during it's testing.
With your exceptionally detailed renderings, where could this vibration source have come from?
Thanks for sharing the interesting and historically precious story, fannum. It is my honor to listen to you, sir.I was a docent with NASM from '70s through the '90s, head docent for one term, set up the public tours at the Garber facility, and as one with aircraft building and maintenance background, was involved with a lot of the restoration. Also served on the acquisition and restoration advisory boards.
Bob Mikesh was the curator most associated with Japanese aircraft, and I'm sure many have read his well researched and accurate books. There were always curious issues with restorations, dealing with various country's demands, different design teams, and especially in WWII, changes in emerging technology and material availability. The latter especially influenced German and Japanese designs as the Allies did a great job of denying their foes critical elements and materials.
Here lies a tale, but I fear my memory is a bit sketchy. This involves either the J7W1 Shinden, but is more likely the Nakajima J9N1 Kikka, and deals with the late war metallurgy involved. Since they were both being developed in the same period, it may apply to both designs. Because of their technical design and rarity, both aircraft were high on the priority for restoration and conservation, however some surprises altered those plans.
The problem was that while the Japanese engineers sought the best alloys, they were denied crucial elements and had to make compromises. The aluminum alloy used for the wing spar was strong, but it turned out to be unstable. That was not an issue as it would not have a lengthy service life ... either combat loss or obsolescence would end their life before the deterioration was a factor. No one expected them to be around 50+ years later.
When the examined closely the wing skins were visibly bulging around the main spar. You could look at the machined spar surfaces and see it coming apart internally ... almost like dissimilar metal corrosion, but within the atomic structure. Mikesh submitted samples to metallurgists, and they said it couldn't be arrested, and that a complete new spar would have to be fabricated from modern alloys. The time, effort and cost pushed the restoration back where it remains to this day.
I believe Senior Curator Russ Lee now handles Japanese aircraft, and perhaps could clarify my aging memory and provide an update.