Why do I have to go to Russia...

...to make one of those zero-G flights? Surely the laws of physics
that make such a flight possible work just as well many thousands of
feet over North America as they do a few thousand metres over
Eurasia. It would be a lot cheaper to have this weightless
experience if the cost of an overseas trip were not automatically
included. Heck, in the time it takes to fly to Russia, I could have
more 20-second spells of weightlessness than is probably offered by
any company today, and then land right back at D/FW (or Love Field).

Also, does a faster plane offer longer spells of zero-G? Would the
Concorde give you 40-second spells, or something like that?

Finally, imagine a craft that can just barely win the X-Prize. It
gives you five continuous minutes of weightlessness, and reaches 101
Km altitude. Could the same vessel (we'll assume SSTsubO) extend
the period of weightlessness by using a shallower trajectory (yes, I
know that means it'll fall short of X-Prize altitude, but by then it
will either have won the Prize or been beaten to it)?

Xenophile the Not-Weightless