This question relates to one of the longest and hardest skills to master. Unfortunately, as you may have discovered, it is also the first thing you have to learn. You will have to change your mindset, which is probably still thinking of the helicopter in terms of a fixed pitch craft. With a fixed pitch rotor blade setup (all 4 ch helis and 3.5 ch helis), as you increase the throttle, the helicopter increase the main rotor speed in a linear fashion. For example, at 25% throttle you generate 1 pound of lift and at 35% throttle you generate 1 pound 2 oz of lift and so on until you overcome the weight of the helicopter and achieve lift off.
Collective pitch (variable pitch) helicopters provide thrust using another method which is night and day different. KDS blades have near zero pitch; they are flat and have a linear throttle curve, I.E. 0-25-50-75-100 as you increase the throttle. Additionally, there is a pitch curve which can be custom set (leave it in the default per the KDS default setting guide in our FAQ section) To keep the helicopter stable on the ground, at 10% throttle you actually have a negative pitch, so its pushing the helicopter down onto the ground, -10% lift. As you increase your throttle to 40% there is really not much blade pitch and the rotor head is just spinning at high rpm and ready for your commands. Then at 55%-65% throttle the blades change pitch very quickly and you start to get substantial lift as the blades change begin to force air downward. When you move the throttle position from 65% through 100%, you are in the air and at full power. This is the reason why you have to take off very quickly. Move the throttle to around 40%, get ready, then up to 60% and lift off. The main reason most crash down after liftoff is due to reducing the throttle too far when you want to descend. Remember, at 50% throttle there is almost no lift and if you push the throttle down to 25%, the helicopter will drop like a rock. If the throttle stick goes to zero while in the air the helicopter will drop down under tremendous force because of the negative blade pitch.
Flight simulators are not perfect but remove all risk factors. If you crash in a simulator, you can just hit restart. However when you're flying an expensive helicopter which you put all your work and money into, there is a real risk and pilots often become nervous. Even the best simulator is no comparison to real flight. A simulator is good to learn muscle memory and hand eye coordination. It teaches how to respond automatically to various scenarios. Most importantly, when the helicopter nose is facing towards you, the controls on the remote are reversed relative to normal. This is a difficult variable to learn, especially during high stress moments when you are flying. It is a skill that cannot be learned through reading and must be practiced by repeated flying. Suddenly, one day your hands will just know what to do. In the meantime, it is best to keep the nose of the heli always facing away from you.
One last thing to remember, when the helicopter is below 4 feet high, the prop wash from the rotors is so great that it will bounce off the ground and actually push your heli over or out of position. That is what actually causes most first crashes. Personally, I like to take off on cement that is directly adjacent to grass (taller grass is better for a soft landing) and once airborne I will try to fly over the grass at about 6-8 feet high to minimize damage on impact if an accident was to occur. Keep in mind that when your 6 channel helicopter crashes it is seldom the weight hitting the ground that causes the damage, it's the incredible kinetic energy created by the rotor blades turning at high speeds. Similar to a bullet hitting an object and releasing energy, inertia is the major factor. The faster an object is moving the more kinetic energy it releases on impact. Sometimes a higher flight path could give you more time to recover from the crash before hitting the ground. The final tip to keep in mind is in the event of a potential impact, always kill the throttle. This will reduce the damage by 50% or more.