Helicopters do not take off immediately when the blades start spinning because several factors come into play during the process of helicopter lift and flight. Here are a few key reasons:
Weight and lift: Helicopters, like any other aircraft, need to generate enough lift to overcome the force of gravity and become airborne. Lift is generated by the rotation of the helicopter's main rotor blades. However, in the initial stages of rotation, there is not enough lift being produced to overcome the weight of the helicopter and its occupants.
Rotor inertia: Helicopter rotor systems have significant inertia due to the mass and size of the blades. Inertia is the resistance to changes in motion. When the helicopter starts, it takes some time for the rotor blades to accelerate and overcome their inertia before generating sufficient lift.
Torque effect: As the rotor blades spin, they create torque or a twisting force that tries to rotate the helicopter in the opposite direction. To counteract this torque effect, helicopters use a tail rotor or other anti-torque mechanisms to provide a balancing force. Initially, before the anti-torque system is fully effective, the torque effect can make it difficult to maintain balance and control.
Collective and cyclic controls: Pilots use collective and cyclic controls to manipulate the pitch and angle of the rotor blades during takeoff. These controls allow the pilot to gradually increase the lift and adjust the helicopter's orientation and position. The pilot needs to coordinate these inputs while managing other factors such as wind conditions and the helicopter's weight.
Overall, helicopters require a controlled and gradual buildup of lift, proper balance, and coordinated control inputs to safely take off. The process involves overcoming inertia, managing torque effects, and providing sufficient lift to counteract the helicopter's weight.