Here's some numbers from "The Great Book Of World War II Airplanes", written by 8 authors including legendary Jeffrey L. Ethell. I am sure some of you have this book. For those that don't, it is over 600 pages in length and covers 12 of the great combat aircraft of WW2, including every variant and prototype. I would assume the data is at least accurate enough to compare to performances in AH.
First a quote about the NiK2-J: "In combat 'George' was regarded as an ineffective interceptor due to it's relatively poor climbing capability. However, the Shiden Kai, as it was named, was considered an outstanding fighter in air engagements on equal terms with the best Allied fighter aircraft."
There are two interesting points here. First it had a poor climb rate for interepting allied bombers. Second, it was considered on equal terms with the best allied pacific aircraft. We all know it is a great turner and has good top speed, it is the climb rate that I argue. Someone stated that AH models the Niki as climing to 6000 meters in just over 5 minutes. That seems like a pretty good climb rate to me. Now for the official data from this same book.
Model 21 NiK2-J "George"
Max speed: 321 kts (369 mph) at 5600 m (18,370ft)
Time to climb to 6,000 meters (19,690ft): 7 min 22 sec.
Weights: Empty 5858 lbs, Loaded 8820 lbs.
Engine: Nakajima Homare 21 rated at 1825 hp at 5740ft.
Seems to me that if AH models the Niki at just over 5 min to 6000 meters, something is definately wrong.
fscott