## 3 Results
### Results per EIS
This is because some UAVs with greater service ceilings (HALE) may not necessarily be heavier than their MALE counterparts. The reader is advised to take this into account when analyzing the data. Figure 24 presents the ratio of the payload weight to GTOW per NATO classification, in 10-year intervals. It is observed that the micro-mini categories have an almost constant  
Figure 27: Cruise speed progression. Figure 28: Maximum speed progression. mean of 0.2. However, the dispersion has increased dramatically from 2005 onwards, indicating that more models of this category are being introduced within a greater design space. The small category fluctuates between 0.2 and 0.25 as the corresponding ratio slightly increases (24%), and their box dispersion decreases. For the tactical category, the mean appears in the same range, although with an exact opposite trend, i.e., the mean decreases (28%), and the box dispersion increases. Lastly, the MALE and HALE categories are below 0.2. Their mean values remain practically constant, and their box dispersion decreases. Figure 25 presents the evolution of the \(W_{e}/W_{0}\) ratio for all NATO categories, where no specific tendency can be observed for the mean and median values of the distribution. The results indicate that the empty weight fraction of the MALE and HALE categories appears to be decreasing, suggesting a market trend towards higher payload and fuel weight fractions. The decrease in empty weight fraction can be attributed to the improvements in material sciences and UAV manufacturing techniques [19; 20]. However, it is important to note that the dispersion of the sample has increased in recent years; therefore, researchers and design engineers are advised to proceed with caution when using a general trendline for future UAV designs. Figure 26 presents the evolution of the \(W_{\text{P}}\cdot\text{E}\) product, per NATO category, as a function of EIS. A logarithmic scale is employed so that a better visualization of the results is possible. The results of this chart can be used complementarily to the ones of Figure 25, indicating that UAV operational capabilities expand over the years, as the \(W_{\text{P}}\cdot\text{E}\) product increases for most categories. Combining this observation with the fact that the ratios of \(W_{\text{P}}\) over \(W_{0}\) remain more or less constant (Figure 24), it can be suggested that the UAV market is prioritizing increasing flight times (endurance). Figures 27 and 28 show the progression of cruise and maximum speed, respectively, as a function of EIS, per NATO classification. One interesting finding is that in the first two decades, the cruise speed parameter for all categories is similar, with only HALE platforms deviating. However, in the 21 st century, an increasing deviation is observed. Similarly, for the maximum speed, the small, tactical, and MALE categories are grouped together before 1995, while in the 2005-2015 decade, a clearer trend emerges, indicating that larger UAVs have a higher maximum speed. The last chart of this section (Figure 29) shows the number of UAV platforms that have been introduced in the past three periods per region. The regions of America and Europe present a steady advancement. Africa and Oceania have fewer entries in this chart, while in Asia it appears that UAV development has boomed since the beginning of the century. Note that the entries from USA and Israel do not appear to increase at the same pace, although both are amongst the pioneering nations in UAV development (first period). However, this chart only shows the number of new entries (i.e., new fixed-wing UAV models) per EIS period and does not show the number of units produced, as the latter is not a publicly available value. Therefore, this lack of new entries for the USA and Israel may be attributed to the high maturity of UAV technology in these regions. That is, a few well-designed fixed-wing UAV models may be enough to carry out the required missions, if produced in large numbers.