Setting up the throttle curve
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 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.
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. 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. In some cases however, you will not be able to achieve the
above result and you will have to make adjustments to your curve to compensate.
This graph shows a typical throttle curve for the
'Normal' flight mode where you do most of your hovering.
The benefit of a curve like this for hovering is
that it is smooth. For example, moving the stick will give an even movement
on the throttle, i.e. it won't suddenly increase, or move more slowly.
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 my
Ergo 46, 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
at hover for launches or for when I'm doing maneuvers that require high
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.
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