I've seen some evidence that the HY400 class Windmax units tend to hunt around a bit for the wind if mounted rather low to the ground or just above a pitched roof (turbulent wind). People have modified the tail to reduce this problem and it appears to help. I understand that the general design guidelines include: The surface area of the tail vane should be between 5 and 10 percent of the swept area. Shape is not critical; however, taller is better than wider. The tail boom length should be about the same as the length of one blade. Can someone compare this to what the HY400 has to see if size/shape falls short of the guidelines? Also, I suspect the reason some of the car pma w/sword blade turbines tend to appear to track better in the same situation could be due to the higher gyroscopic influence from these turbine's higher RPMs vs. a HY400. Anyone have a view on that?