Archer Aviation has dropped about 22% over the past year. Should you buy while it's trading in single-digit territory?Archer Aviation (ACHR +8.18%) is an aviation company selling a vision: A sky of air taxis ("Midnight" aircraft), carrying happy passengers above congested roads, on a 10-minute flight that would have taken an hour or more in the bumper-to-bumper traffic below.If you've ever sat in traffic like that (say, from New York City to Newark Liberty), you'd appreciate the electric vertical takeoff an ...