What causes helicopter ground resonance?
What causes helicopter ground resonance?
Ground resonance happens in helicopters with lead-lag hinges. It occurs only on the ground. It starts when the blades “bunch up” on one side of the rotor disc where they generate an unbalanced centrifical force that gets in phase with the natural frequency of the aircraft rocking on it’s landing gear.
What is ground effect helicopter?
In Ground Effect (IGE) is a condition where the downwash of air from the main rotor is able to react with a hard surface (the ground), and give a useful reaction to the helicopter in the form of more lift force available with less engine power required.
What is mast bumping?
Mast bumping is contact between an inner part of a main rotor blade or a rotor hub and the main rotor drive shaft (or ‘mast’). Serious mast bumping in flight usually results in the helicopter breaking up in flight, which is fatal for those on board.
How do you recover ground resonance?
When it does occur, recovery is often possible if action is taken quickly. If sufficient rotor RPM exists, immediate takeoff can restore rotor balance by allowing the airframe to freely move and help damp the oscillation. If rotor RPM is very low during a ground resonance incident, complete shutdown may be sufficient.
What is ground resonance test?
The current trend in ground resonance testing is aimed at providing aircraft modes of vibration appropriate to the free‐free condition. To achieve this objective the rigid body frequencies of the aircraft on its supports must be low by comparison with the frequency of any mode of distortion.
Does ground effect increase lift?
Since bringing a wing into ground effect increases lift, it follows that a given angle of attack will reach maximum lift at a lower angle of attack than it would in free air – but also that maximum lift will be less than in free air because of the reduced drag.
What Happens When a helicopter goes too high?
What Happens If a Helicopter Flies Too High? As the helicopter ascends, the air begins to thin. With thinner air, the main rotor becomes less efficient. When the blades can no longer generate enough lift to keep ascending, the helicopter reaches its maximum operating envelope (the coffin corner).
How safe are Robinson helicopters?
Between 2006 and 2016, Robinson R44s alone were involved in 42 deadly helicopter crashes. That is an average of 1.6 deadly crashes per 100,000 hours flown, a rate nearly 50% higher than that of the other dozen most common civilian models.
