It is not as simple as you say. Just by reducing the processor size, you won't be reducing the weight drastically. How much of a difference do you think a pentium 4 (180nm) was from intel i3(22nm)? The few kgs of added weight means nothing. We can't just make the weight 0. It would be better to use composite than use such cheap products. High performance devices require not just high processing but also reliability. You are mistaking architecture for technology. Transistor architecture is what determines performance. Transistor technology like 22nm,180nm is what determines power size and weight. It is not necessary that 180nm processor is worse than 22nm ones. The architecture can be same for both and hence give same performance but with 180nm ones consuming higher power. Moreover, there is a massive difference between processors of PCs and dedicated processors. PC processors require processing of almost any data while the dedicated ones only need to process specific data and have specific usage. For example, UAV processor need not process graphics, movies etc and definitely do not need to use heavy use softwares like Matlab. They have limited processing needs and only those logics need to be written on them. The display or output is also limited. The heat release during flight from engines air drag or even high temperatures of the sun's heat will be more than enough to glitch 22nm or less processors. The whole point of making smaller transistor is to reduce power consumption to be used in battery powered devices. As the size decreases, accuracy of transistor making reduces and the chip gets higher number of faulty transistors. The limited weight savings will not be worth it. The whole problem of thin wafer processors is exactly that - they are too thin and made of fragile technology. The more robust technology needs thicker wafers. The transistor gets weakened with thickness reduction and becomes more susceptible to errors and glitches when subjected to hostile environments. Moreover, testing over a decade for reliability is also needed. The slight increase in power consumption is not a problem at all, especially considering that turbofan produces several KW of power in a jet. If you are comparing vacuum tubes with transistor, then you have to look at power, size etc.