For all those who want to help people with theyr xml-problems or for those who need it for themselves. Here is my advanced xml-modding toutorial. Its about things you dont need usually, but they are quite usefull to know. with this Forum i try to offer scientific reasearch to you so may be a bit more easy to make advanced replicas

Make bomb-shooting guns with a specific ammount of ammo
First of all, making one takes time. In order to be faster, you should use this wich is the default version. You just have to replace the values like
"bomb-1" with "bomb-2"
activationGroup="0" with activationGroup="6"
MassScale, scale, power...
You can automatically replace scale="0.25,0.25,0.25" with scale="x,x,x".
You can automatically replace thing with ctrl+h.
if you want to define the Speed of the projectile, please read the cheatsheet.

Make cameras/scopes
It can be quite painfull to figure out where to put the camera. So here is what you do:
Use xml to put the camera at exactly the height of the reddot/camera/human head/whateveryouwant.
Use finetuner to put the camera 0.5 lower.
You can also use the orbit camera and set the type to FirstPerson

Makeing vehicles hovering
You can either test every value for the enginepower or you can calculate it.
Calculating is simple:
P=M/f
P is the power of the engine (the value we want to calculate)
M is the planes mass (e.g. 392718 lbs)
f is the power of the engine. You can find it out by clicking the engine in the partlist.
The power of the vtol engine is 13490 lbf
For this and for the next one, i recommend using wheigtless fuel

Scaling things to a specific size
The formula for this one is:
S=W/G
S is is the scale
W is the wanted size
G is the size of the unedited plane

Converting from metric to imperial or between
At this point I'd like to advertise duckduckgo
Duckduckgo is a searchengine (that doesnt track you), also it can convert measurements.
Simply type
100cm in ft
8.3mm in inch
2kilometers in miles
293lbs in kg
Or whatever you want.

If you need a good calculator, you should use this one. All formulas in this post can be pasted in there. (Of course you'll have to replace the variables with values)

Cheatsheet:

Gun damaged needed to cause an explosion and shots needed to destroy:
UssBeast:5000;18
Destroyer:5000;10
UssTiny:5000;12
AATank:3000;1
Truck:480;1

Inputs cheatsheet:
VTOL
Trim
Throttle
Pitch
Yaw
Roll
LandingGear
Activate1
FireGuns
FireWeapons
Brake

Others (i´ll try to add Things whenever something Comes to my mind):
-When a detacher has a power of 0.2235, it can accelerate 1lb to 1mph.
-A rotator needs 1 second for 360° when the speed is 1.15
-a block with the health of n needs on everage n×10 shots to be destroyed
-when a force of 2lbf is applied to a damper with the spring strenth of "1", it will be lowered by 0.18 increments
-a damper with a spring strenth of "1" is completly compressed, when a force of 5400 lbf is applied to it

if you have any other ideas on what i could add, make sure to add a comment!