If there really is a uber plane in AH, the Yak-9U is it. Almost as fast
as La-7, but slightly more maneuverable, it is among the fastest
planes at low altitudes, and does pretty well even up to about 15k.
The acceleration, like other soviet planes, is incredible, handling
is pretty easy. Not very good handling at extremely high speeds
though, and the roll rates are about average. Also climbs better
than 109s up to 5000 ft altitude. The Yak-9U in every way, is a
devoted 109 killer. (except weakness at over 15k)
But, it does not turn better than a Spit9. It is obviously an illusion
that this plane can turn as well as a Spitfire. It has a decent turn
rate at mid to high speeds, but low speed turn characteristics are
pretty bad(I once remember being out turned by a 109G-10 at near
150 mph).
Why it feels that way is because, as I said, the plane has smooth
handling and has very good temporary turn rate at mid-high speeds.
And if the pilot is good, he can play the 'Cat and Mouse' game with
the Spit. Chasing the Spit into a corner, letting him escape and blow
E, follow the Spit, drive him up to a corner again, wait till the Spit
makes a desperate move and blows E, let him go.. and on and on
until the Spit blows all the Energy he has so he can be out turned
even by P-47s. Then the Yak bites.
Don't play the game.
Against a Yak, the only advantage a Spit pilot has is guns and better
turn rate. You have to try everything so the fight ends up low and slow.
Trick the Yak into making hard moves to catch you. Tempt him to gain
gun solution on you, then keep escaping just out of the reach with your
superior turn rate. Drain the E on the Yak. That's your best shot.