stupidest question ever

[Anaxogoras]

Thrust:drag also plays a part in sustained turn-rate.

[SectorNine50]

I've got another question:

Why would aircraft designers put a smaller wing on an aircraft if they knew it helped turn performance?

[Motherland]

I've got another question:

Why would aircraft designers put a smaller wing on an aircraft if they knew it helped turn performance?

Because a larger wing also produces more drag. Notice that most of the aircraft that turn poorly are also fast.

[BnZs]

I've got another question:

Why would aircraft designers put a smaller wing on an aircraft if they knew it helped turn performance?

In WWII, they weren't so much putting smaller wings on aircraft as they were putting progressively more powerful but heavier engines in aircraft. This is most evident with the 109 series over the years. This will tend to improve aircraft performance in every area *except* turning circle, which in turn leads to changes in tactics.

Even the seeming exception to the rule, the very fast, very good turning F4U-4 must be considered carefully. Its wing-loading is not so very low relative other craft, it gets its turn from a massive boost in lift created by very large flaps.

[bozon]

What makes one plane turn better than another? 

For instance, why does the 190A8 roll so well but turn like crap? Why does the zero turn so well but not roll that great?

Though it initially sounds like one, this is NOT a stupid question at all.  As some people above said, it is actually very complicated and even the meaning of "turn better" is very poorly defined. In certain conditions, 190A8 turns better than many other planes. This is what makes dog fighting so interesting and makes the pilot a much more important part of the equation.