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 You will soon realize that airspeed varies with the attitude of the helicopter, and since the movement of the cyclic controls the attitude, we can say that the cyclic controls airspeed. Moving the cyclic aft will raise the nose of the helicopter and decrease the airspeed. Moving it forward lowers the nose and increases the airspeed. To maintain forward flight, the disc must be tilted forward to obtain the necessary horizontal thrust component; a nose-low attitude will result as the fuselage aligns itself with the drive axis and the airspeed increases. The lower the nose, the greater the power required maintaining level flight, and the greater the resulting airspeed. Conversely, the greater the power setting the lower the nose must be to maintain level flight.
In straight and level flight, increasing the collective while maintaining a constant airspeed with cyclic will cause the helicopter to climb. The opposite is also true. Decreasing the collective while maintaining airspeed with cyclic will result in a descent. Remember that these collective changes will require you to make pedal adjustments to maintain the helicopter in co-ordinated flight. To increase the airspeed in forward flight, you must apply forward cyclic, and raise the collective to prevent the helicopter from descending. To decrease the airspeed, apply aft cyclic, and decrease the collective to prevent the helicopter from climbing. We can examine  a reduction in airspeed step by step:
1. select a slightly nose-high attitude by moving the cyclic aft;
2. reduce power to prevent the helicopter from climbing by lowering collective, and correlating throttle if appropriate to the helicopter type;
3. prevent yaw through use of the tail rotor pedals;
4. pause, allowing the airspeed to stabilize; and
5. adjust collective and cyclic as necessary to maintain the new desired speed.
Increasing the airspeed can be analyzed in the same way:
1. select a slightly nose-low attitude by applying forward cyclic;
2. increase power to prevent the helicopter from sinking by raising collective, correlating throttle if appropriate to the helicopter type;
3. prevent yaw through use of the tail rotor pedals;
4. pause, allowing the airspeed to stabilize; and
5. adjust collective and cyclic as necessary to maintain the new desired airspeed.
You may find that the cyclic is quite sensitive, but there will in fact be a slight delay between your input and the main rotor disc reaction, and thereafter the movement of the fuselage. You will learn to anticipate the required control movements to achieve certain desired airspeeds so as to avoid over-controlling. Making all your control inputs as smooth and precise as possible will assist in avoiding this pitfall.
NOTE:  In certain types of piston helicopter whenever the collective is raised or lowered the pilot must correlate the rpm with throttle. From Exercise 4 onward, although it still applies, the above statement has been omitted to save repetition. 
EXERCISE 5 - CLIMBS AND DESCENTS
Entering a climb or a descent will involve changes in attitude, airspeed, altitude, forward visibility and power settings. Your instructor will review with you the recommended climb and descent airspeeds and power settings for your helicopter type. In the case of most helicopters the recommended speeds are specified in the flight manual. Your instructor will emphasize  accurate control of the helicopter, as this is vital to success in future air exercises.
CLIMBS
The best rate of climb speed is the airspeed that will afford the greatest gain in height in a given time. If it is important to reach a given altitude in the shortest possible time, this is the airspeed to use. The helicopter can be climbed at any airspeed within its operating limits, but the best rate of climb is obtained at the airspeed where power required for flight is at a minimum, and power available is near the maximum. Refer to the accompanying chart (Fig 5-1).
　
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