"Cam"
Veteran
Location: Asia
| My understanding is the feathering spindle teeters with respect to the rotor head (mast and heli).
IF the ball link on the blade grip was in-line with the mast, the ball itself will not move up or down when the disc and spindle teeter - this is zero delta.
I like this the most. To me, hard dampers, centered linkages and good geometry all make the heli always handle the same whatever you do- the heli never gets snatchy and the roll rate is always the same.
IF the ball link is off-centre, say on the grip side of the mast on a TE control setup, when the blade flaps up (disc and spindle teeter due to cyclic and setup) the linkage will 'hold' the ball back and the grip will feather to give more pitch - this is like positive gain on the cyclic. This will give a snappy and faster cyclic response, but only more cyclic rate if the dampers give a little.
There are 6 combinations for this setup. You can have The linkages on the grip sides, centered, or on the far side of the mast, and have TE and LE for each.
If you reverse either of the one parameters in the above setup you will invert the delta gain. For example if you have grip-side LE control, when that blade and grip flaps-up, again the linkage will 'hold' the ball back, but the change of angle of the grip is now the opposite to before. SO the effect is you get less cyclic than what you asked for. Likewise if you have a long arm on the blade grip and have the ball on the far side of the mast on a TE control, you get the same effect as having a grip-side LE control.
Delta can be neutral, convergent and divergent. In reality neutral is hard to get. As components flex the nature of the delta also changes.
So, "LE grip-side" and "TE far-side" are convergent, more stable
and "LE far side" and TE grip-side" are divergent, more snatchy -faster off the mark.
No-one does far-side linkages because they stress the hell out of the blade grip arms - but you do see them on multi-blade heads.
Short-arms are better for less flex- giving more consistent flying characteristics and a more pleasant heli to fly, but they introduce a lot of delta. This is why flipping you blade grips normally has a massive effect - because you are going from a lot of one delta to a lot of the other. A slicker way to change the cyclic feel is to adjust the length of the grip arms. (Across the mast, not away from it).
For me heli flying is about that 'locked-in', secure feel. So I always want the heli to behave in the same way, regardless of if I'm hovering of doing a tail slide.
I am almost sure this simple parameter is what makes it for some helis over others.
All the Align helis have TE grip-side - giving them '3D' cyclic. BUT I find the TRex will 'snatch' into high-speed turns. Making the flying not as smooth as a Raptor head with zero-delta. But then a raptor's cyclic is slower off the mark, but has more holding power through maneuvers. |
