3D Helicopter Basics; Idle-Up Flight Modes
Posted on December 4, 2009 by aaronredbaron
Many people see 3D helicopters doing their thing the first time and ask the same question; How does it fly upside down?Although the answer could be made overly technical, the usual response is; It has negative pitch and fully symmetrical blades. To a burgeoning heli pilot, however, that answer just leads to more questions such as; How do you operate the throttle and pitch together so you don’t kill the power with negative pitch? And do you have to flip a switch to fly upside down?
Idle-Ups
Idle-Up flight modes offer an RC heli pilot a separate mode specific for aerobatics. Some references to the old method of using a switch for inverted still linger, but invert switches have gone the way of the Dodo bird. In the old days, when a pilot hit the invert switch the model would reverse pitch and elevator control making the helicopter fly similar upside down as it did right side up. The problem with this is your orientation to the helicopter is constantly changing with an invert switch, and you have to flip the switch any time you go from upright to inverted or vise versa. Timing of when to hit the switch and where your throttle stick is when you flip it would have also been critical to make the flying look smooth.
Since the 1990’s Idle-Up flight modes have become the dominant method of flying a model helicopter upside down. With Idle-Up modes, a pilot uses a normal mode to start the helicopter’s engine at idle, accelerate the rotor head and get the model off the ground. In normal mode the throttle and pitch operate together on the same stick, the throttle ramps up from an idle to full as one would expect. Flipping a switch puts the model in an Idle-Up flight mode for aerobatics. With the Idle- Up activated, the model is set up to maintain a consistent RPM (with a V-shaped throttle curve and/or an electronic governor) on the main rotor for maximum power the entire time. In Idle-Up a pilot is able manipulate the pitch using the full pitch range while having full power available the entire time. You only need to flip a switch to get into Idle-Up mode for aerobatics, and then back to normal for when you want to land.
Throttle and Pitch Curves
Each flight mode has its own throttle and pitch curve. Each one of these curves allows you to set where the throttle or pitch is at several points along the stick’s range. The pitch range is usually close for all flight modes. Low stick should give you full negative, half stick should be zero pitch, and high stick should be full positive. You don’t need much negative for normal, but the point on the curve where you get zero pitch (should be exactly half stick) and the hover point should be the same across all modes to prevent the model from jumping when you change between modes. In Normal mode, the throttle curve starts with the stick all the way down resulting in low throttle, and ramps up to full throttle at high stick. Putting it in an Idle-Up mode makes it so low stick will result in full throttle for power while inverted, half stick brings the throttle down to prevent over-speeding the rotor head while the rotor head has minimal load at zero pitch, and full stick gives you full throttle again for positive pitch. The throttle curve and any governor used work hand in hand to maintain rotor speed when the model is in an Idle-Up mode.
Idle-Up flight modes are difficult to comprehend at first, but they simplify the world of helicopter aerobatics once you begin to wrap your head around them. If you want to be able to fly your model helicopter upside down, you need to get acquainted with your radio’s pitch and throttle curves, and learn how to adjust them to fine tune your helicopter’s aerobatic prowess.
