This is a wonderful story - and one that I managed to miss until reading it in EETimes. Such public displays open up conversations that otherwise would not occur. I'm also impressed by the advances in skywriting freom what I'd previously known. The ability to make a message quickly is essential to achieve legibility.
Apart from smoke generator, airplane need fuel to drive thier engine. 100LL aviation gasoline (AVGAS) still contains lead (LL is short for "Low Lead") - not exactly eco-friendly :-( It has been long argument when / how do we transision from AVGAS to something else, and what is that "something else". Automobile gasoline, methanol, diesel has been proposed but not widely adopted yet (FAA certification is costly and time-consuming).
It is interesting to hear other "Integer substitution of Pi", 22/7 and 201/64. I will put them in my toolbox. Slide rule and 8-bit CPU days are fading, but I may need them someday, just in case :-)