No way around it.
It's made that way and if you want fighters that can stay in the air for longet than 20 seconds then you have to use T1 or T2.

really??? that's disappointing men........ i thought there is other way to improve shinden flight time........ shinden is like a lightning when it flies out to my ship........ oh well.... i guess im going to use the other fighter plane....... :(

That tier of fighters is called "locals". They are designed to provide close air support for your BB lines. They don't have the fuel to help with sight, but have much higher speed and attack. I suggest you use tier 2 fighters and scout for your team, and find incoming waves of bombers for easy kills.

A technique for low tier fighters is dragging. Select your fighter group and rapidfire click away once engaged. This will make the enemy planes chase yours. Search dragging for more info.