How Smooth Is It?

AN AIRPLANE AND A HELICOPTER are flying in formation in gusty air. In which aircraft would you rather be a passenger? If you said the helicopter, you would agree with most people who have had the chance to make the comparison.

One reason why helicopters are smoother is due to the fact that the rotor blades are attached to the helicopter airframe through flapping hinges-or flexible blade roots. When they are suddenly subjected to additional lift, the blades respond by coning (the blades ‘bend’ upwards towards the tips causing a ‘coning’ effect). This means that there is an “inertial relief” as some of the force is expended in accelerating the blades upward before they can exert a force on the airframe. Most airplanes get no such relief.

The only exceptions are large jet airplanes, whose wings do have some flexibility. Nervous passengers readily notice this during a takeoff roll or in flight, in turbulent air.

For a single sharp-edged gust, the relief is short lived, since the coning will be complete in a fraction of a second. However, it might be significant in “choppy” air, where the gusts are coming up and down rapidly. In this case, the rotor actually will act as a vibration absorber.

In other words, a helicopter will provide a much smoother ride than an airplane under the same flying conditions.