How does ground resonance happen?

Ground resonance is usually precipitated by a hard landing or an asymmetrical ground contact, and is more likely to occur when components of the landing gear or damping system are improperly maintained, such as the drag hinge dampers, oleo struts, or wheel tire pressure.

Do helicopters have ground effect?

Since the ground interrupts the airflow under the helicopter, the entire flow is altered. This reduces downward velocity of the induced flow. The result is less induced drag and a more vertical lift vector. Rotor efficiency is increased by ground effect up to a height of about one rotor diameter for most helicopters.

Is an aerodynamic force that acts on a helicopter when it is off the ground?

Drag is the portion of aerodynamic force that is measured as the resistance created by an object passing through the air (or having the air passed over it). Drag acts in a streamwise direction with the wind passing over the airfoil and retards forward movement. Figure 2-4.

What is ground resonance in helicopter?

ground resonance. A resonance that manifests itself as a violent rocking of the helicopter when it is on the ground. This phenomenon is most evident when the helicopter is on hard surfaces that do not absorb vibration. It is caused by the resonance between the skid and the rotor system.

When can resonance occur?

Resonance only occurs when the first object is vibrating at the natural frequency of the second object.

How does a helicopter get lifted from the ground during take off?

For a helicopter, a lift is generated by the way the main rotor blades are formed so the air is pushed in a downward movement when the blades spin. As the air pressure changes, the helicopter lifts up.

What is helicopter ground resonance?

How are helicopters moved on the ground?

Helicopters without wheels can only move on the ground by use of a dolly, tow-cart, or ground-handling wheels. Helicopters with wheels can be towed using a tow vehicle and towbar and can move by using the thrust produced by its main rotor when running. Helicopters without wheels need to hover taxi.

How forces act on the helicopter during?

There are four forces acting on a helicopter in flight. They are lift, weight, thrust, and drag. Thrust is the force that propels the helicopter through the air. Opposing lift and thrust is drag, the retarding force created by development of lift and the movement of an object through the air.

Why do helicopters fly low to the ground?

While airplanes need to maintain an altitude of 500 feet over land and 1,000 feet over congested areas, helicopters can fly much lower. The reason for this exemption is that helicopters can execute pinpoint emergency landings and are much more flexible compared to airplanes.

What is ground resonance in a helicopter?

Ground resonance is a vibration that can be destructive to a helicopter. Ground resonance is primarily a problem in a fully-articulated rotor system. In these systems, ground contact can jolt the aircraft and produce a shock wave that can resonate in the aircraft.

Do helicopters have damping?

Many helicopters also have damping features within the rotor system as well, such as the 300CB. Should ground resonance be suspected and rotor RPM allows, the pilot should immediately lift the helicopter off the ground, stopping the resonance.

What causes a helicopter to shake after landing?

It basically is an out-of-balance condition in the rotor system of a helicopter on the ground that rapidly increases in frequency until the helicopter shakes itself apart. It is usually caused by a hard ground contact, and is much more likely in aircraft with improperly maintained landing gear (deflated oleo struts, for example).

What is the Emergency Action of a helicopter?

The emergency action is to lift the aircraft to a hover. Ground resonance has not been “solved”, and is still a big concern for anyone who flies a helicopter with a fully-articulated rotor system.