And then I find this....

"None of the AirXs tested met or even approached the power curves in Southwest Windpower's owner's manual."
"At rated wind speed the AirX delivers only 103 W 99 W, and 51 W respectively, not the 400-525 W advertised."
http://www.wind-works.org/articles/sm_AirXtest.html

And more complaints here
http://www.greenerbuilding.org/product_detail.php?cid=39&pid=96

I noticed it doesn't seem to be anywhere near the output advertised, these posts may be confirming that.

This Air-X has too short of a tail. It isn't tracking the wind like it should.

It rotates out of the wind slightly which causes it to make more noise than it should, and it will sort of kick itself out of the way completely when a wind gust stops.

What it needs is a longer tail. If you have one of these you might want to look at this picture of an extended tail to get an idea of how to do it.