If you want precision bombing it's better to use and practice with one of the dive bombers. :)

There are ways to make planes stay at altitude etc using sensors and math brick etc but that's not somethign I'm interested in dealing with (especially on WW2 planes) but feel free to add such a mechanic if you find someone who can do it.
Also remeber that these planes were definitely NOT precision bombers back in the day but were lucky to get within half a mile of the target, albeit from a lot higher altitudes.
Again I say jsut practice a bit and you'll get a feel for when to drop the bombs if you use the same altitude and speed repeatedly. I have tested enough to pretty reliably drop the bomb load on the center of the city 9 times out of 10 from 300 meters, and if I miss it's not by much.

The issue is the plane behaves VERY differently with a full bombload (extra weight plus a lot of aerodynamic pieces on the fins) and without the bombs, so I've trimmed it as best I can with and without bombs on my PC which runs at 144 FPS. If you FPS is lower or higher than that or if you're in MP with some ping added all that goes out the window due to the fatc that the physics engine behaviour is tied to FPS.
I recommend you pick an altitude of 3-400 meters, stick to that and close to top speed and then just repeat bomb drops until you get the feel for it. Using the "bomb sight" is pointless, just gauge by eye and experience.

okay, well a little problem is there, because the planes wont stayon altitute wich makes it even harder to learn bombing yk? it just smth thati have noticed since i playbrickrigs, that a lot of bombers dont hold the altitude, i dont know how to build that so that they keep altitude at 0

I tested on the Grid Map and at max speed 340 kph and at 300 meters altitude the bombs travelled 600-650 meters before hitting the ground. That's about as precise as I can be.

I couldn't say TBH. THe lower you fly the easier it is of course, but if you're flying near full speed at 300 meter altitude it's pretty easy to learn to estimate the drop point. But it's something you have to practice and learn since at leat I am not able to build any useful bomb sight and I have no specific figures to give you.

Hey can you tell us wich is the optimal dropping height and speed for the plane to hit the target?

LETS GOOO B-24 REMAKE