The minimum speed of a helicopter, also known as the hover speed, can vary depending on the type of helicopter and its design characteristics. In general, helicopters can achieve a stable hover at speeds as low as 0 to 15 knots (0 to 17 miles per hour or 0 to 28 kilometers per hour).
The hover speed is the speed at which the helicopter can maintain a steady hover without descending or ascending. It is determined by several factors, including the rotor design, power output of the engine, and the helicopter's weight.
Helicopters generate lift through their main rotor blades, which create a downward flow of air to counteract the weight of the aircraft. To hover, the helicopter must maintain a balance between the lift generated by the rotor and the weight of the helicopter. As the helicopter slows down, the pilot needs to increase the rotor's pitch (angle of attack) and engine power to maintain lift and overcome the increased drag.
Different helicopter models have different hover speeds, and some specialized helicopters designed for specific purposes, such as reconnaissance or close air support, may have lower minimum speeds. Additionally, external factors such as altitude, temperature, and wind conditions can also affect the helicopter's minimum speed.
It's important to note that while helicopters can hover at low speeds, their normal cruising speeds are typically higher, ranging from around 80 knots (92 miles per hour or 148 kilometers per hour) to several hundred knots, depending on the helicopter's design and purpose.