Frame - Propeller Size
Tarot X4, which measures 960mm from motor to motor spacing, is 24 inches as the appropriate propeller size for the frame. However, I want to make the propeller size 28 inches to increase the flight time of my drone, is the 960 mm Tarot X4 suitable for a 28 inch propeller, or is it necessary to extend the size from motor to motor spacing?
If you increase the size of the propeller, the drag will increase and the energy required to overcome the drag will also increase, so it sounds like either you have to simulate this in some physics modeling tool (e.g. ANSYS) or just make one and see how long that it can last.
At the very minimum you will need to see how much current @ a specific motor voltage is to determine the electrical energy consumed for sustained flight. And this is also heavily dependent on the amount of weight that you need to lift.