Don‘t waste your time searching for a rental before you arrive - it won‘t work!
Also, loosen your requirements (e.g. from „at Flugfeld Böblingen or around that area“ to „anywhere between Stuttgart and Herrenberg“ to have a chance.
Also, although you did not mention it, many foreigners plan on (or rather dream of) furnished apartments, which are almost absent in the German market. There is an Ikea at Sindelfingen and a few thousand Euros will give you what you need without the headache of searching for a needle in a haystack (and then paying an arm and a leg for it).
Good luck and patience are your most needed virtues now!