Special note on deciding to install an SD or not...
Although you may not be doing autos now or just getting into them, it is well worth your while to install an SD -- At first thought, you might think the slipper is only useful to you if you want to control the tail on the decent.... Dave Storey (Team JR heli flier) recently highlighted that the heli's nose will tend to rotate right when you come back on positive pitch at the bottom of the auto if your tail is undriven (torque is working the other way in this scenario). This unexpected event is eliminated w. the SD and might make the difference between a crash or not.... Why take the chance!
In the beginning...
Recall that the main hub has a one-way bearing inside for autorotations - this allows the main rotor to rotate while main gear remains stationary. Without the SD, the tail rotor (driven by the main gear directly) is driven only by the friction in the one-way bearing (i.e. not very much). Virtually all tail (rudder) inputs will create enough drag to stop the tail from spinning.
Essentially, all SD's involve 'increasing' the mechanical connection (i.e. friction) between the main shaft and the main gear hub (... the main gear and consequently the tail rotor pulley). The slippers I've seen involve sandwiching a rubber O-ring between the main gear hub and another metal ring which is tightenned to the main rotor shaft or mast. The Vigor unit sits on-top of the main gear, while the KSJ unit is pressed on from below. Two factors control the amount of 'drive' provided by these SDs:
- The amount of lubrication used on the rubber o-ring (use Ceramic grease too!), and
- the pressure with which the SD (metal ring and o-ring) is pressed against the hub.
You have to experiment to get the proper amount of SD pressure. While you'll end up with at least enough tail authority to do a 180 deg rotation at the end of an auto with 15 kph (10mph), you will still only have a limited tail drive -- Hard tail inputs WILL still stall the tail drive.