Which is why it was given the code name "Tony." Heck, everyone knew the Japanese could only copy other people's planes.
- oldman
Interestingly the Japanese ignored proven designs - in tank building they ignored the Christie suspension, they were unimpressed with the American designs. The Japanese were interestingly the forefront of tank design in the mid 1930s - using Diesel tanks for example. By 1940 the Japanese had the 5th largest tank army in the world, if It wasn't for the shifting of industrial resources to aircrafts and ship building later in the war that slowed down tank building. Some people would argue; that Japanese "tank design sucked" and indeed it did; when you compare it to the 1940 designs. The reason is the Japanese had no need for "tanks" or as we call "Tank on tank" designs, rather they needed cruisers as the British developed in the early 1940s. The Chinese had no anti-tank guns, so tank design for the Japanese pretty much went towards what they assumed tanks were needed for; bunker busting and infantry support. If you look at the Russian Army in 1945, they basically adapted to what the Japanese were trying to produce in 1934.
That brings me to the Ki-61, the Japanese had no way to really copy the Bf-109's engine, instead they basically backwards engineered the engine and design to adapt to their own. The engine required precision machines to make it; something the Japanese industry lacked. In another words they were trying to produce something that was way out of their league to produce. It might of worked if the war progressed differently, but even simple Japanese maintenance was a little backwards; if one Ki-61 was damaged and two planes could be flyable with the spare parts from the one aircraft; the Mechanic was not allowed to salvage the parts off the damaged plane. That plane was from the Emperor - it was forbidden to use ingenuity, something most nations adapted during the war.
If you really want to know how bad japanese tank design became due to the shifting of industry in 1940; in 1945 the Japanese produced a "M4a2" killer; a prototype that never seen action with 3 inches of Armor and a 75mm main cannon. The prototype never went into action and actually was turned over to the united states because it had a 37mm cannon installed in the Hull; which any "armed" vehicle was taken after the war. It took the Japanese over 3 years to come up with a design to beat a simple Sherman tank.