It is very important to have minimum weight of aircraft equipment. It allows to increase the payload or #ight range or to improve some other aircraft characteristics. For the systems that are consuming energy during the #ight it is not less important to save the power spent on their functioning. &&Starting mass'' gives the opportunity to combine these two heterogeneous sides of the equipment properties into one complex characteristic, which depends on the #ight duration and on the aircraft engine parameters. The main idea in solving the problem of combining mass and energy in one complex parameter arises from the fact that practically the only on-board source of energy is the fuel stored in the aircraft tanks. Therefore, the energy consumed by the system may be substituted by the equivalent mass of fuel. Another component of the &&starting mass'' is the fuel spent on the transportation of the "rst two parts. The necessity of this third part arises from the di!erences in fuel expenditure on transportation of unchangeable and changeable loads during the #ight. The summation of these weight components is called &&starting mass'' because all of them should be present in the aircraft before take-o!.
The core of the method was developed by Bulaevsky and myself. It is re"ned and partially corrected in this paper.