Hauksbee 103 Posted February 25, 2012 (edited) Ran into this while perusing headlines this morning. Not sure what "Ground Resonance" is, but sure trashed this chopper. http://news.yahoo.co...-224458312.html The article had this to say: "It was the most stunning helicopter accident Para, Brazil has ever seen. And it all happened without the helicopter even leaving the ground. The shocking destruction of the plane was caused by a phenomenon called ground resonance. Like an out-of-balance washing machine, the plane starts shaking more and more violently until the force tears it in half. Though the destruction was pretty epic, no one was hurt in the accident. They're probably going to need to buy a new helicopter, though." Turns out there was a link describing Ground Resonance: Ground resonance is a hazardous condition that can occur any time the rotor of a helicopter or gyroplane is turning while the aircraft is on the ground. Similar in concept to the behavior of a washing machine when the clothes are concentrated at one point during the spin cycle, ground resonance can occur with a rotorcraft when the spacing between blades becomes irregular or the damping system, including drag hinge dampers, landing gear oleo struts, or wheel tire pressure, is operating out of limits. Ground resonance occurs at three rotor rpm bands, the first at about one-third of normal rotor speed, the second at a range including normal rotor speed, and the last in a range above normal rotor speed. Ground resonance is precipitated by a shock to the aircraft arising from excessive motion of a rotor blade in its plane of rotation thereby moving the rotor center of gravity from the axis of rotation. Inadequate damping allows the rotor center of gravity to spiral away from the rotor axis of rotation, causing the rotor to generate unbalanced rotating moments beyond the compensating ability of the damping system. In addition to damping system malfunctions mentioned above, such blade movement can occur as a result of taxiing over rough ground with the rotor turning at a speed within a susceptible range, or takeoff/landing in which a shock occurs to one side of the landing gear. Under extreme conditions, the initial shock can cause violent oscillations that quickly build and result in catastrophic damage of the entire airframe. In some cases, complete destruction occurs, e.g. body panels, fuel tanks, and engines are torn away, even at normal rotor speed. Recovery is possible in some cases. If sufficient rotor RPM exists, immediate takeoff can restore rotor balance. If rotor RPM is low, complete shutdown may be sufficient Edited February 25, 2012 by Hauksbee Share this post Link to post Share on other sites
tranquillo 10 Posted February 25, 2012 (edited) Saw that on the news last night - luckily no-one was hurt. Not sure what "ground resonance" is - not a new Brazilian coffee is it? Should have read your complete post. Ground resonance explained Edited February 25, 2012 by tranquillo Share this post Link to post Share on other sites
carrick58 23 Posted February 25, 2012 i I have been to a" Resonance Fair " but it didnt have that kind of ride. Share this post Link to post Share on other sites
nbryant 8 Posted February 25, 2012 During one of my Hawaii tours a sister squadron had a CH-46 that entered ground resonance when they taxied into a closed "hot" pit and lifted the nose and attempted to back taxi out. The entire event lasted less than what you see in the video. No one was hurt but by the time they realized what they were experiencing the aft pylon of the aircraft had completely detached. If I recall properly the crechiwef never flew again. Share this post Link to post Share on other sites
Olham 164 Posted February 26, 2012 Would you really want to trust an aircraft, that is doing THIS during the whole flight??? Share this post Link to post Share on other sites
turkeydriver 4 Posted February 26, 2012 Ground Resonance is a phenomenon inherant in all helos but mostly twin rotors like the H-46/47. It's instantly cured once you get airborne. Basically a Resonant vibration is induced that the helos vibration absorbers cannot affect and the helo begins to shake itself apart. Once the you leave the deck, the landing gear/skids can move and assist in vibration damping. Share this post Link to post Share on other sites
MikeDixonUK 5 Posted February 26, 2012 Would you really want to trust an aircraft, that is doing THIS during the whole flight??? Olham! Everyone knows that if you think about it too hard then helicopters will actually stop working - don't risk it! Share this post Link to post Share on other sites
CaptSopwith 26 Posted February 26, 2012 I'll take my aircraft with wings, thank you very much! Share this post Link to post Share on other sites
Olham 164 Posted February 26, 2012 Olham! Everyone knows that if you think about it too hard then helicopters will actually stop working - don't risk it! Or, as some American "Air Cavallery" officer said: "Helicopters cannot fly. Helicopters beat the air, until it will carry them." Share this post Link to post Share on other sites
MikeDixonUK 5 Posted February 26, 2012 Or, as some American "Air Cavallery" officer said: "Helicopters cannot fly. Helicopters beat the air, until it will carry them." I thought it was that Helicopters are so ugly that the ground repels them? Share this post Link to post Share on other sites
Olham 164 Posted February 26, 2012 That must have been another officer - probably one who had problems with landing. Share this post Link to post Share on other sites
Hauksbee 103 Posted February 26, 2012 Everyone knows that if you think about it too hard then helicopters will actually stop working - don't risk it! ...and let us not even start to discuss the aerodynamics of bumblebees, or pollination as we know it will end. Share this post Link to post Share on other sites
carrick58 23 Posted February 26, 2012 Would you really want to trust an aircraft, that is doing THIS during the whole flight??? I always wondered why Airplanes Wave at people. I had thought that they were a friendly airline ? Share this post Link to post Share on other sites
UK_Widowmaker 571 Posted February 26, 2012 I was convinced that was an RC heli...until the people got out! Share this post Link to post Share on other sites
Olham 164 Posted February 26, 2012 My same thought, Widow! Share this post Link to post Share on other sites
gaw 5 Posted February 27, 2012 amazing vid nevertheless.....and a reminder of the hidden dynamics behind the machine.......makes me wonder what writing an FM must be like....not only the demands of realism but the quirks of a computer sim as well....wonder if the Sikorsky guys ever modeled that destructive cycle? Share this post Link to post Share on other sites
Bullethead 12 Posted February 29, 2012 Helicopters are necessary evils, because sometimes you just need the things they can do. But I try hard to avoid ever needing those things. Helicopter accidents killed more of my friends in the service than enemy fire. Share this post Link to post Share on other sites
UK_Widowmaker 571 Posted February 29, 2012 Never been in a Helo...and don't ever want to!....I would never sit in one voluntarily, which means..if I was in one..it would be an Air Ambulance, or Air/Sea Rescue jobby! (neither of which appeal) Share this post Link to post Share on other sites
RAF_Louvert 101 Posted February 29, 2012 . hel·i·cop·ter /ˈheliˌkäptər/ - 10,000 moving parts surrounding a hydraulic leak, all trying to get away from each other. . Share this post Link to post Share on other sites
Herr Prop-Wasche 7 Posted February 29, 2012 I don't think I've seen a better definition than that! Share this post Link to post Share on other sites
UK_Widowmaker 571 Posted February 29, 2012 This was my favourite (wrong wording, but you know what I mean) http://www.bbc.co.uk/news/world-asia-pacific-15848886 Share this post Link to post Share on other sites
Flyby PC 23 Posted March 3, 2012 Helicopter = Apache. I want one. Share this post Link to post Share on other sites
Flyby PC 23 Posted March 3, 2012 Hey!!! The new OFF P4 preview has carriers? http://www.bbc.co.uk/news/uk-17238393 How did the Fleet Air Arm get a beta copy of P4? Share this post Link to post Share on other sites
