If the advantages to the fins at the end of stabilizer is so great why don't all helicopters have them? And it seems like most attack helicopters, ah 1, ah 64, mi 24 hind have conventional stabilizers.
horizontal stabilizer design differences1.jpg
Eric Hunts post above stated the main reasons for these endplates.
Rather than being directly behind the fuselage and rotor hub, some engineers found that placing vertical endplates on the end of the horizontal stabilizer made for a more effective horizontal stabilizer and vertical endplate, since the endplate is out in relatively cleaner air. The vertical endplates being displaced from the tail rotor, also minimized their effect on tail rotor flow patterns.
These vertical endplates aid in unloading the tail rotor thereby further reducing tail rotor flapping in forward flight. Furthermore, endplates are often incorporated to address directional stability issues. Engineers have difficulty predicting analytically whether a design will be stable or unstable. The aerodynamic environment at the tail rotor and empennage are influenced by the disturbances produced by the main rotor and fuselage.
As an example, this helicopter with SAS off, Dutch roll was unstable without endplates on the horizontal stabilizer but stable when small canted endplates were installed. The dramatic change in stability was much more than could be predicted by any known analytical method and must be attributed to some peculiar flow conditions in the main-rotor wake. In the final design, they went from the T-Tail to a conventional horizontal stabilizer and found endplates were not necessary. Overall design considerations, trade-offs, advantages, and disadvantages along with flight test, weigh-in to determine whether endplates are necessary.
Edited by iChris, 09 April 2017 - 02:49.