Ground effect

Flying any kind of helicopter type aircraft, the pilot has to be aware of the ground effect. This will affect hovering characteristics in close proximity of the ground, however once you gained some altitude the ground effect disappears.

The below tables will explain how the ground effect works. For a beginner pilot is always a challenge to gain some altitude because they are usually afraid of crashing the aircraft from a higher position. However an effort has to be made to leave the ground proximity as soon as possible to achieve stable hovering.

The easiest way to see the ground effect is to hover a mini quad in a closed space with the 4 walls not further than 3-4 meters away from your quad.  You will find that if you only try to hover the quad at 20-30cm (about one ft.) above the ground, the quad will wonder a lot and it will be harder and harder to keep it in position. As soon as you leave this close proximity of the ground and lift it to at least 50-60cm, the quad will start to hover more stable. The pushed down air has more space to dissipate and will create less turbulences. As you go higher, you will find that you need less and less stick input to keep a stable flight (assuming your quad is trimmed properly).

Ground effect 1In close proximity above the ground the air pushed down by the propellers will return and will be sucked into the same propeller again and again. This will cause additional vibration, less lift and less stable flight. The quad will wonder around a lot and it seem to a beginner pilot that it is almost impossible to keep the aircraft in one position.
Ground effect 2When your craft gained some more altitude, the air pushed down has enough space to spread evenly without being sucked back into the rotors again. This way there is a better lift produced and the flying and hovering will be much smoother. Your aircraft - if properly trimmed - will be able to hover almost steady without the need of much stick input from the pilot.

So the lesson learned from the above is, to leave the ground as soon as possible and lift your aircraft to about waist – eye level to achieve stable hovering position.

Of course, the ground effect will be different for every single aircraft. Standard helicopters are affected much more by the ground effect because these usually have a single large rotor on the top. Larger multi-rotor helicopters like Okto and Hexacopters from Mikrokopter due to their size and weight will be less affected by ground effect. Racing quads like the Vortex, the QAV250, Pats Minion, Pats hybrid spyder hexa or the NGH 250 Diablo when flown in a larger empty space are less affected by ground effect, however if you try to fly them in your living room be aware of the ground effect and be ready to stay on top of it.