For the present, the empty fraction is estimated, utilizing more straightforward methods. For the most part, it is estimated statistically from historical trends, as appeared in Figure-1, created from data identified with the sort of airplane we are designing. Empty-weight fractions vary from about 0.3 to 0.7 and diminish with an increasing total weight of the aircraft.
A & C are the constants obtained from the trendline using power fit.
While Figure 1 and Table 1 can be used for the initial estimation of the empty weight fraction, it is always better to develop a trendline. Obtain empty weight and total weight data for an airplane like the task, plot the information onto Figure 1, and draw a sensible trendline with a slope like those appeared. If using curve-fit software, be cautious; It might return a positive exponent depending upon the exact data fed it. Instead, force the software to use a negative number ‘C’ term like those in Table 1 and find the constant term with the lowest square error. This was the case for several of the classes of aircraft in Table 1.