I'm just a Flight Simulator player with no real-life flying experience, so I apologize in advance if I'm asking a stupid question :)
I watched a TV show and saw that certain courier companies (DHL for example) tend to have multiple shorter flights with refueling instead of one long flight with larger initial amount of fuel, because in that way they burn less fuel.
Then I started thinking about the relation of fuel quantity and the range of an aircraft. On one side, the more fuel an airplane has, the longer range it will have. On the other side, more fuel means more weight, which will then increase the fuel consumption (but both the weight and the consumption rate will decrease gradually during the flight). Of course, let's observe a theoretical case, where the plane has constant speed and altitude, and there is no wind.
Is there any equation/graph for a certain aircraft type which shows how much fuel is "too much", i.e. if there is a "sweet spot" which will give the best ratio of fuel consumption and flight range?