It’s Gravity Defying
A funnel is a maneuver where the helicopter is flying sideways in a horizontal circle in the air. When done at high speed, the angle of the rotor disk relative to the ground will approach 90 degrees. To those not familiar with the capabilities of modern RC helicopters, it will appear that the helicopter is defying gravity because it will look as though the rotor is not creating any downward thrust. In actuality, the amount of downward thrust has to equal the weight of the helicopter or it will descend during the stunt. The angle of the disk relative to the ground will approach 90 degrees as the funnel is flown faster and tighter.
As far as 3D stunts go, the funnel is one of the easier ones to learn. If you think about it, a funnel is simply a normal turn that just happens to be done sideways. When flying sideways, the cyclic pitch and cyclic roll functions become reversed, where fore-aft cyclic controls the angle of bank and the side-side cyclic can control the rate of ascent or descent.
There are four basic variations of the funnel. It can be performed with the nose of the helicopter either nose pointed up or down, and with the skids pointed in towards the center of the circle or out of the circle. The skids-out variations start with the helicopter upright, whereas the skids-in variants start with the helicopter inverted.
For the first few attempts, let’s start with the nose up, skids-out variation. Begin with the helicopter in a stable hover about 50 feet up, 100 feet out, and to the right of center field. With the helicopter tail in, start flight sideways to the left at slow to moderate speed. As the heli flies past center field, pull back slightly on the elevator to create a bank angle. Once a bank is established, use right cyclic to maintain altitude and use left rudder to keep the tail pointed towards the center of the circle. It will probably take you a few tries to get everything just right. When everything comes together, the heli will almost lock into a funnel, and it will take only slight corrections to maintain the maneuver. To exit the funnel, simply release roll cyclic and rudder, then push the nose back to level to return to sideways flight.
Once you’ve mastered the basics, you can start mixing things up by entering at higher speeds. For the same diameter circle, the higher entry speed will make the funnel steeper. Once the funnel is established, you can also play with collective. Increasing the collective during the funnel and changing nothing else will cause the helicopter to spiral upwards in a corkscrew flight path, while reducing collective will result in a descending corkscrew. You can also play with the bank angle and vary the diameter of the circle to maintain altitude during the funnel, by adjusting the amount of left or right cyclic you apply during the maneuver.
Once you’ve figured out all the ways you can modify the basic funnel, you can practice the other three variants by either pushing the nose down, to create a nose down funnel, or start off the funnel in an inverted orientation to create a skids-in funnel, or both, to do a nose down, skids-in funnel. There are also many different ways to build it into your flight routine. One of my favorite ways of entering is to start with an inverted backwards flyby. Then, as the helicopter passes in front of me, I give it a left rudder and forward cyclic to get the nose pointed skywards. Then I feed in left roll cyclic to enter a nose up, skids-in funnel.
Keep practicing all the variations and don’t forget to try both clockwise and counterclockwise circles and in time, you too, can be a funnel expert!