Balance
Senior Heliman
Location: Rapid City, SD, USA
| "Left skid low"Or in the case of RC Helis:
"Right skid low"
Real full size American helicopters' mains rotate counter-clockwise, and the tail rotor thrust is to the left. The tail rotor in a helicopter serves one purpose only: to counteract torque created by the engine turning the main rotor. As torque increases (more throttle/collective), a greater tail rotor pitch is required to counteract and prevent the heli from yawing. This thrust to the left will cause a helicopter to "translate" to the right in relation to the ground. In order to counter this "translating tendancy," the cyclic must be rigged to lean the heli to the left in a hover. This will cause the machine to hover with the left skid lower than the right in calm conditions. Some helis are built with cyclic rigging (cyclic trimmed for correct hover), while some are built with the mainshaft actually leaning left physically, and still others simply need to be piloted to counter the translating tendency. Pilots flying real American helis refer to this hovering characteristic as "Left skid low."
All these things are opposite in machines from other countries, and in our RC machines, where the mains rotate clockwise, and tail thrust is to the right, but all the same principles apply. The machine needs to be trimmed with a little right cyclic input in hover to counter tail thrust. Some computer radios offer the added benefit of programming an offset to center this trim when the radio is switched to a different flight mode, but the small amount of right trim needed to hover easily is hardly noticed in forward flight. I cannot speak for the difference felt when flying aerobatics and 3D.
Now, let's make it more confusing: If you were to hover your machine in a steady 5-10 mph crosswind blowing from the left of your machine, then the heli would hover nearly level to the ground. Reverse the direction of the wind, by turning yourself and your machine around in the same wind, so it is blowing from the right, and the heli will lean twice as much. The question is, does any of this change the translating tendency or the aggregate amount of cyclic correction you need to make? NO! It only changes the attitude of the machine in relation to you and the ground. The machine knows no different. Think of it this way. If you are flying 0 mph (in relation to the ground) in a 10 mph headwind, how fast is the bird flying? Put an airespeed indicator on it, and it would read 10 mph. Groundspeed means nothing. If the wind increased to 20 mph, and you were to maintain the 10 mph airspeed, then the machine would actually be moving backwards in relation to the ground, and still flying FORWARD at 10 mph.
The point of all this is that you have to train your brain to think in terms of airspeed only. Flying is a different 3D world than we are accustomed to with our feet on the ground. When the helicopter is leaning to the right, it is simply hovering with a slight sidewind. That wind from the side is created by the pilot who wishes to keep the machine in one place in relation to the ground by countering tail thrust.
Enjoy. You are doing it correctly, RIGHT SKID LOW!!!
B
KIS, don't MIC |
