Acropad, you seal a hinge line by installing covering between the control surface and the fixed surface. I use clear Ultracoat so I don't have to worry about matching the colors on the plane. I cut the Ultracoat into a strip about 12mm wide, then fold it length wise. While holding the control surface to its maximum deflection iron it in the hinge line. This prevents any air from leaking through the hinge gap and greatly improves response, reduces the chance of flutter, and keeps the control working an lower airspeed. I do not own the Kangke Cap 120, but there are two in my club and I have lots of stick time with them. I do own the Kangke Laser 2000 and the Texas Hurricane.