Setting up the throttle curve

Once you have read this article, read the tutorial on Helicopter Setup then the tutorial on Radio Setup.

Just as crucial as setting up the pitch curves correctly is setting up the throttle curves. Throttle curves work in similar fashion to pitch curves.

In the same fashion as pitch curves, a throttle curve determines how far the throttle body of the carburetor opens based upon the position of the collective/throttle stick.

You can set up different throttle curves for different flight modes. For example in Normal flight mode, where you do most of your hovering, you'd probably want to set your throttle curve up so that the helicopter isn't screaming when it's hovering. Correspondingly, when doing aerobatics and such in Idle Up One or Two, you want all the power and headspeed you can, so you set your throttle curves accordingly.

A good 'Normal' throttle curve is very nearly linear. This means for each movement of the throttle/collective stick, there's an equal movement of the throttle servo no matter where on the curve the stick is. This means that there is a consistent movement in engine revolutions. An Idle Up One curve can be whatever you feel you like with the style of flying you like, and a usual Idle Up Two curve very much resembles a 'V' because it has 100% power at both ends (for flying upside down etc.).

Governors
Governors are cool little boxes of electronic wizardry that monitor the helicopter's headspeed and manage the throttle servo to keep the headspeed within predefined parameters. You set them to keep the headspeed at a certain level and it increases or decreases throttle to keep the headspeed at your defined level. This means that instead of your throttle curves managing the engine speed, the governor is. However, it is still important to have good curves because when governors fail, they revert back to the curves you set up.

Throttle Linkage
As with all linkages on a helicopter, it is important that you set up the linkage between the throttle servo and carburetor arm correctly. Ideally, for every degree the throttle arm travels, you want the carburetor arm to travel the same distance. This means that both the servo arm and the carburetor arm should be the same length.
If you're planning on using a governor, a good throttle linkage is essential to get proper operation out of the governer.

The illustration below outlines an ideal setup...

Notice the throttle and carburetor arms are the same diameter and that the throttle are is of such a size that for every degree the throttle servo travels, the carburetor arm moves an equal amount. Having your linkage setup in this way will allow you to set your throttle curves more precisely.

Setting up your throttle linkage in this manner will allow you to accurately program all your throttle curves. It is highly important that you set your throttle servo travel limits (ATV's in Futaba speak) are symmetrical (ie both the top and bottom values are equal or very close to being equal. For instance 57% and 80% is not ok. When setting up for a governor, it is recommended your ATV's are set up around 100% both ways. You may have to experiment with different length throttle arms and servo arms to achieve this.

This graph shows a typical throttle curve for the 'Normal' flight mode where you do most of your hovering. This curve is an example of what you might find on a 50 or a 90 size machine. You'll see that the throttle ramps up quite early on then flattens out between 2nd and 4th points. This is so that the headspeed doesn't change. You want the headspeed to stay constant. You'll also notice that this curve doesn't go all the way to 100%. That's cause all this mode is used for is hovering and it is very rare that you would ever feel the need for 100% power during any hovering you'd be doing. If you were to make this curve go to 100%, then you would find that the headspeed would rise and fall quite dramatically between points 4 and 5 which is not what you want.

There are many differing opinions as to what your Idle Up One curve should look like, some have theirs looking like a 'tick', while others just program theirs to their own taste. The curve illustrated here is what I use to fly the Raptor 90 SE, the heli flies how I like it with this curve so that's why I use it. I have it setup like this cause I like the headspeed to be high during Fast Forward Flight and for stall turns and loops.

Here you see why it's called the 'V' curve. With this curve, the machine hovers at around 70% power both inverted and right side up. Also, 100% power is present at both top stick and bottom stick for climbouts and inverted climbouts respectively. You can also see that the throttle is more sensitive with this curve as the throttle servo moves more with each movement of the collective/throttle stick than any of the other curves. If you find that the helicopter flies well with this setup, but seems to need more power when doing flips and such, you can always add a little Elevator to Throttle and Aileron to Throttle mixing. This will increase the throttle when the various cyclic inputs. If however, you're running a governor, this will be done for you.