I've flown the Yak-9U as my main ride for probably 2 years now, excepting the times when I was learning an aircraft for scenarios. That said, I'm a pretty untrained pilot, barely spent any time with trainers, so my stats aren't that good. I don't measure my fun by my kill stats, so it doesn't really bother me.
The guns are the biggest weakness. They might be ok if they had a larger ammo load, but they don't. They shoot straight and for sure can be deadly, but you can't just hit the enemy aircraft, you have to put the rounds into a specific vulnerable place, destroy something important on the enemy aircraft, and then let it drop out of the sky, hoping the two-weekers don't steal your kill on its way down. Good opposing pilots know this and willingly give you deflection shots while setting up a reversal, knowing you probably can't do enough damage until they are behind you.
I have a lot of problems with late war Spits because their acceleration is so great and the Yak's only advantage is higher top speed. It takes long enough to get to top speed that a Spit safely behind will catch up before the Yak pulls away. Diving for speed doesn't help because the Yak is lighter than the Spit, and at equal speeds has less E to gain. Climbing doesn't help because Spits climb faster. Turning doesn't help because Spits turn better, at least once below the G limit. There are two solutions I use: 1) Look at the acceleration and speed charts and climb/dive to an altitude that puts the Yak in the best possible altitude to extend. 2) Dive to the deck and hide in the trees. This last one is a lot of fun even if I get shot down. I fly around between the gaps in the trees at max speed, under the treetops, knowing that the Yak has one of the smallest wingspans in the game and can fit through spaces other aircraft cannot.
Also the 109-G4s are the super-ride of the day and if flown right you will never get more than one quick shot at them, and never be able to escape them either. The Yak is also out-performed by many other aircraft commonly found in the LWMA, but you don't fly a 23 ENY aircraft without accepting that fact when you take it out of the hanger.
The Yak is fun to get kills in knowing you are slightly outmatched flying it. Steve (who I don't see around any more) used to say that Yaks were a P-51 killer. I like fighting P-51s, the good pilots still beat me but I usually learn something when they do.
I typically don't even bother shooting until I see 400 on the distance counter. I like 200 a lot better. The Yak has great upwards views but a very poor over the nose view, which makes deflection shooting while turning even harder. As for fuel, if I have to fly a sector or more I usually take 100%. If the field is about to get vulched I take 50%. In between 75%. There is definitely a difference in taking less gas, performance-wise, but its not huge. It also glides very well, especially with the props feathered, but I have a really hard time seeing anything with an oil leak.
One more thing, the Yak is a bullet sponge, especially for non-cannon rounds from long distance. I've felt like that History Channel P-47 at times. You don't want to be taking cannon rounds though, you'll survive a couple spread out but not many or any to the same place as a previous one. Oil leaks are fairly common, radiator hits are less common but you don't have much time left if it happens. Fuel leaks are uncommon but they do happen, the usually don't get lit but sometimes do. If you're not on fire they aren't a big deal, they just cut your fuel in half, which makes your aircraft lighter and more deadly. Expend your ammo and go back home.
