Concerning the N1K1-J Shiden:
" It [the undercarriage] was very poor - much worse than on the average
Japanese aircraft. When dive-bombing or strafing, if the aircraft reached
420 mph, the gear was apt to fall apart in the air. About a quarter of the
pilots we lost in combat fell for this reason. The Shiden-Kai got to be a
better airplane toward the end, however."
I have read this passage several times and I believe they are referring to the Shiden-Kai, not the N1K1-J Shiden.
The full quote, translated by an American who was fluent in Japanese, appears in "Genda's Blade" (pg 48). Sakaida's version contains more information and makes it clear that he's referring to the Shiden-Kai. There's potentially some bad translation. Genda said that the landing gear was not falling apart, it was deploying and causing aerodynamic drag. "apt to fall apart in the air" may be a mistranslation. The quote makes it seems like this issue was corrected in the N1K2-J Shiden-Kai rather than something that was introduced in the redesign.
Also, the previous paragraph mentions that a Shiden-kai pilot almost died when his landing gear came down during a fight.
I think this error appears in a lot of books because the N1K1-J had defective landing gear.
However, Genda stated that about 25% of their combat losses related to the faulty landing gear. That quote is important because the 343rd was mostly equipped with Shiden-Kai. If 25% of their losses were N1K1-J with defective gear, then that would mean they had a lot of N1K1-J in service. But you can see from Genda's Blade that the N1K1-J was a reserve aircraft and never made up more than a small percentage of most sorties.
From Aircraft of the Aces No.129:
" The performance of the Homare engine continued to be lower than
expected. Fuel quality was down to 85 octane because it was mixed with an
oil extract from pine tree roots - this proved to be very volatile. Pilots in the
front line still claimed that the Shiden-Kai's performance was good up to
30,000 ft."
This is another problematic quote probably based on a poor translation, but fortunately you also linked to an unimpeachable source as well which mentioned that the pine root oil was 95 octane iirc. However, it was extremely high in aromatics, which made using it as a single-source of fuel impossible. The imperial japanese military decided to dilute their lower octane fuels with pine root oil to bump up octane. This is similar to using MMT to boost octane ratings.
RE: US Aircraft VS the Shiden-Kai and Shiden
I wanted to add a little more to this discussion about what made the Hellcat worse on paper, but a superior aircraft compared to the N1K2-J:
The Shiden's fuseless 20mm cannon ammunition may have technically had more destructive power and similar velocity compared to the M2 0.50 caliber machine gun, but it also contributed to the Shiden's poorer survivability.
The ball armor piercing ammo would have been less prone to exploding when hit by enemy fire. In fact, one of the 343rd's officers Naoshi Kanno, died as the result of a cannon malfunction from a defective batch of 20mm shells. On top of that, the ammo belts on the Shiden Kai's cannon were staggered between high-explosive, armor piercing, and tracer. Except that the fuseless were significantly faster than the AP rounds, which would lead to velocity mismatch and reduced accuracy.
Also, as mentioned on this forum, the
Hellcat also had automatic flaps. It's strange that no other publication has this information in it.
All books that I've consulted on the Hellcat completely ignore what made the Hellcat the best US dogfighter of the war (if it's true). Going off the description provided by
N4521U , the flaps are hydraulically activated and a compression spring controls the extension of the flap.