CHAPTER 9—Float and Ski Equipped Helicopters


Helicopter floats have only a mild effect on aircraft performance, with just a slight weight penalty and reduction in cruise speed. However, the large surface area of the floats makes the helicopter very sensitive to any departure from coordinated flight. For example, in cruise flight, any yawing causes the helicopter to roll in the opposite direction, as shown in figure 9-4. A failure of the engine requires immediate pedal application to prevent an uncontrollable yaw, with a resulting roll.

Similarly, a tail rotor failure in cruise flight requires immediate entry into autorotation to prevent a yaw and the subsequent roll. Corrections to this rolling moment can exceed rotor limits and cause mast bumping or droop stop pounding.

Helicopters equipped with skids-on-floats are limited in ground operations. Minimize horizontal movement during takeoffs and landings from hard surfaces to avoid scuffing or causing other damage to the floats. Perform approaches, in which hover power may not be available, by flaring through hovering altitude in a slightly nose-high attitude to reduce forward motion. Just prior to the aft portion of the floats touching down, add sufficient collective pitch to slow the descent and stop forward motion. Rotate the cyclic forward to level the helicopter, and allow the helicopter to settle to the ground, then reduce collective pitch to the full down position. In helicopters with low inertia rotor systems, an autorotation to a hard surface requires a more aggressive flare to a near-zero groundspeed to ensure minimal movement upon landing. A running takeoff or landing on a hard surface is not recommended in helicopters equipped with skids-on-floats.

Helicopters equipped with floats-on-skids are capable of performing running takeoffs and landings, and autorotations to hard surfaces require the same procedures as non-float equipped helicopters. The surfaces should be flat and clear of objects that may puncture, rip, or cause other damage to the floats. Do not attempt to land on the heels of floats-on-skids as they may cause the tail boom to kick up and be struck by the rotor.

Helicopters equipped with stored emergency pop-out floats are operated with the same procedures as a helicopter without floats. When emergency floats are deployed, the helicopter may have similar characteristics to a helicopter with fixed floats and should be flown accordingly. If emergency floats are deployed during autorotation, the increased surface increases parasite drag with a resulting reduction in airspeed. To regain the recommended autorotation airspeed, the nose must be lowered.

Effects on aircraft performance must also be considered during water operations. Air is often cooler near bodies of water, thus decreasing the density altitude but also increasing humidity. Although the higher humidity of the air has little effect on aerodynamic performance, it can reduce piston engine output by more then 10 percent. Properly leaning the mixture might possibly return some of this lost power.

Turbine engines experience only a small, often negligible, power loss in high humidity conditions.

Warning: During water operation, if there is any possibility that the tail rotor struck the water, do not attempt a takeoff. Although a tail rotor water strike may not show any visible evidence of damage, a tail rotor failure is likely to occur.

 ©AvStop Online Magazine                                                                                                                                                      Contact Us              Return To Books

AvStop Aviation News and Resource Online Magazine

Grab this Headline Animator