Setting up the pitch curve

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

Setting up the pitch curve on your helicopter is one of the most crucial parts of setup. What is a pitch curve you ask? OK...

First up, I'm no aerospace engineer, so I'm not going to give you the physics behind everything. I'm gonna give you the story from my point of view.

First of all, lets define 'pitch'. Pitch describes the angular movement of the rotor blades in relation to the horizontal plane. For example, when the angle of the blades is upward, the blades are described as having 'positive pitch'. Likewise, when the angle of the blades is downward, the blades are described as having 'negative pitch'.

The amount of pitch is measured in degrees above or below the horizontal plane. A normal pitch range for many helicopters is about 22 degrees in total, that's positive and negative pitch combined.

When the rotor blades get more positive pitch, the helicopter will ascend (climb), likewise, the more negative pitch, the faster it will descend (fall). Unless ofcourse it's upside down, but we'll get to that later :).

Now, back to the pitch curve situation. The amount of pitch on the blades is dictated by the position of the collective stick on your transmitter. If your transmitter didn't have pitch curve point adjustment, you'd have a pitch curve that looks like this:

The graph on the left illustrates a 'linear' pitch curve. This means that moving the collective stick along will represent an equal change in the amount of pitch on the blades.

If it weren't for the provision of pitch curve point adjustment, the amount of change of pitch in the rotor blades would be linear. Meaning that movement of the collective stick would yield equal movement of the pitch on the rotor blades. In some cases, this is fine, but what about if you want to set up different modes of flying? A pitch curve that enables you to hover nicely is probably not going to let you do inverted flying very well. For this you need to be able to adjust your pitch curves.

Most good radios have points on their pitch curves that can be adjustable. The cheaper radios have about three points, good radios have five, while the top-of-the-line radios can have about thirteen. The more points that are adjustable on your radio, the more you will be able to tune your pitch curve.

Most radios also have multiple flight modes. This means, at the flick of a switch, you can change the flight characteristics (pitch curve, throttle curve etc) of your helicopter. So for each flight mode, you can set up different pitch curves that suit different types of flying, hovering, fast forward flight, inverted etc. Flight modes are often called 'Idle Ups'. Not sure why! Some radios have one idle up mode, others have two, some like the Futaba 9Z can many more than this.

You need to set your helicopter's pitch curves up as well. Some examples of different flight mode pitch curves are listed below. It should be noted that these are just the curves I fly with and are no means written in stone, but they're a good start from which you can tune to suit you and your heli.

Make sure you use a pitch gauge to set up your curves. Doing it by eye is just useless.

The graph on the left illustrates a 'normal' flight mode pitch curve. I use this mode for hovering only and therefore can set it up to give a nice 'soft' feel which yields good hovering performance. You'll notice that the curve flatten's off between points 2 and 4 in the same way that the associated normal mode throttle curve does. You'll also notice that with this curve, I'm hovering at mid-stick or just slightly above. This is just personal preference.

The graph on the left illustrates an 'Idle Up One' pitch curve. As you can see, this curve has a lot more negative pitch at the bottom. I use this curve for fast forward flight and basic aerobatics (loops, stall turns etc). You'll also notice that the Idle Up One and Two pitch curves are the same with 0 degrees at mid stick. You might wonder why even have two seperate Idle Ups? I do this so I can set the helicopter up for smooth fast flight in Idle Up One using controls such as Expo etc, and also have the machine snappy and quick for 3D in Idle Up Two. With this setup, I'm hovering between the 3rd and 4th points.

The graph on the left illustrates an 'Idle Up Two' pitch curve. You can see that this curve is linear. I use it for inverted flight and 3D etc. You can see that there is an equal amount of negative pitch as there is positive. This means that the helicopter will perform similarly upside down as it will right side up. With this curve, you hover at either position 2 (when upside down), or position 4 (right side up). Hovering with this curve is more sensitive because moving the collective yeilds an increased movement in pitch in comparison to the other two curves.