Scary situation on rooftop-helipad
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If it was GR? (impossible to tell from a video; as it only shows up clearly on video when it's pretty much passed the recovery stage) quick action on the part of the pilot prevented this becoming far more dramatic... My own choice on an elevated helipad would also be to take it airborne rather than try to shut it down quickly (being shaken off the roof with engines spooling down and rotor brake coming on doesn't appeal much 
I can easily imagine him looking back to check how the unloading is going and experiencing a skid settling,incipient GR event, and struggling to get into a normal seating position and fly the machine off at the same time...Just supposition on my part...
Looks like He did an good job to me...
I can easily imagine him looking back to check how the unloading is going and experiencing a skid settling,incipient GR event, and struggling to get into a normal seating position and fly the machine off at the same time...Just supposition on my part...
Looks like He did an good job to me...
I bet this was a surprising not controlled take-off and the pilot was at least not standing in the pedals. The ships turns like a humming top.
That uncontrolled a/c is not initiated by ground resonance and this was not a pilot controlled take-off. The a/c was short before to kill the guy standing on the left skid and stuffing things into the cabin. Not the most stupid pilot would eject his ship in such manner into the air knowing his mate is unsecured on the skid, head inside the cabin on a more than 50m high rooftop.
May be there was something wrong with the pilot seat, bringing the pilot out of rudder control.
The austro control (CAA) examination found yesterday no mechanical faults on the ship.
That uncontrolled a/c is not initiated by ground resonance and this was not a pilot controlled take-off. The a/c was short before to kill the guy standing on the left skid and stuffing things into the cabin. Not the most stupid pilot would eject his ship in such manner into the air knowing his mate is unsecured on the skid, head inside the cabin on a more than 50m high rooftop.
May be there was something wrong with the pilot seat, bringing the pilot out of rudder control.
The austro control (CAA) examination found yesterday no mechanical faults on the ship.
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Avoid imitations
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I think some folk don't understand what ground resonance is. There was a similar discussion some time ago about another supposed "ground resonance" incident when an Agusta 109 chopped off its own tail after "*landing*". I said immediately that it wasn't ground resonance but others insisted it must have been. Read *very heavy landing* causing structural failure...
Ground resonance cannot, by definition, continue once the wheels / skids are off the ground. This aircraft wasn't in contact with the helipad during its gyrations. Things got very much worse once lift off took place.
The video quality is quite poor. However, it does look like something got drawn up into the main rotors. This might just be a function of video "colour bleeding".
Ground resonance cannot, by definition, continue once the wheels / skids are off the ground. This aircraft wasn't in contact with the helipad during its gyrations. Things got very much worse once lift off took place.
The video quality is quite poor. However, it does look like something got drawn up into the main rotors. This might just be a function of video "colour bleeding".
Agree on your stand that after aircraft left ground "Ground Resonance"
can not be considered but please advise us what force
can push pilot to take of like that, all after that - we can fully agree
Lucky chain was initiated with GR, after "escape" from GR was partial
lost of control aka "rodeo drive"....
can not be considered but please advise us what force
can push pilot to take of like that, all after that - we can fully agree
Lucky chain was initiated with GR, after "escape" from GR was partial
lost of control aka "rodeo drive"....
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bell 412
ok try this link
Video: So trudelte der Heli am Klinikdach - oesterreich.ORF.at
Video: So trudelte der Heli am Klinikdach - oesterreich.ORF.at
Video: So trudelte der Heli am Klinikdach - oesterreich.ORF.at
Video: So trudelte der Heli am Klinikdach - oesterreich.ORF.at
Last edited by SLINGKING; 11th Mar 2011 at 17:45.
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I think some folk don't understand what ground resonance is. There was a similar discussion some time ago about another supposed "ground resonance" incident when an Agusta 109 chopped off its own tail after "*landing*". I said immediately that it wasn't ground resonance but others insisted it must have been. Read *very heavy landing* causing structural failure...
Ground resonance cannot, by definition, continue once the wheels / skids are off the ground. This aircraft wasn't in contact with the helipad during its gyrations. Things got very much worse once lift off took place.
The video quality is quite poor. However, it does look like something got drawn up into the main rotors. This might just be a function of video "colour bleeding".
Ground resonance cannot, by definition, continue once the wheels / skids are off the ground. This aircraft wasn't in contact with the helipad during its gyrations. Things got very much worse once lift off took place.
The video quality is quite poor. However, it does look like something got drawn up into the main rotors. This might just be a function of video "colour bleeding".
You must be in contact with the ground (or any other surface) to experience ground resonance. Once contact with the ground is severed the resonance ceases, and the rotor system will return to a balanced state.
I would have doubted that the 412 with its unique rotor head could experience significant ground resonance, given the elastomeric dampers only allow limited movement in lead and lag, however it is technically possible.
I would have doubted that the 412 with its unique rotor head could experience significant ground resonance, given the elastomeric dampers only allow limited movement in lead and lag, however it is technically possible.
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K9
"If the aircraft is not on the ground then it can't be ground resonance!")
It is an inter-reaction between the undercarriage and the main rotor that can sometimes occur to a helicopter with an articulating main rotor. It only happens on the ground, not in flight.
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Okay, I had the terminology wrong. What I was thinking of was more of a ground interference aerodynamic resonance situation, where a wave of air being directed downward by each blade pass can reflect back up from the ground and, in the resonance case, meet up with the next blade. This obviously requires being close to the ground (a rotor diameter or so), but does not require being on the ground. Only occurs in a hover or in certain cases of slow translational flight with a following wind to match. Much less common than ground resonance (dynamic instability of the rotating structure).
.
To add further clarity ..
This is what it looks like (even on a roof pad) and how to get out of it. Like mast bumping in the 'teetering' Bell's - you've got milliseconds to respond to this phenomenon.
And this is what it looks like when you don't take corrective action.
S.
To add further clarity ..
This is what it looks like (even on a roof pad) and how to get out of it. Like mast bumping in the 'teetering' Bell's - you've got milliseconds to respond to this phenomenon.
And this is what it looks like when you don't take corrective action.
S.
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K9
.... ground interference aerodynamic resonance situation, where a wave of air being directed downward by each blade pass can reflect back up from the ground and, in the resonance case, meet up with the next blade
Re-circulation from nearby walls isn't going to manifest itself as a condition like G.R., and I can't see how a downbeat of air from a blade of a hovering helicopter could 'bounce' back up and interfere with the following blade - have a look at a diagram of rotor downwash in the hover and you'll see why.
If you theory is correct, how would any helicopter manage to land or take-off without looking like the one in the video?
Last edited by TRC; 11th Mar 2011 at 19:53. Reason: Add an after thought.....
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Ground resonance occurs when an out of balance main rotor interacts with the helicopter undercarriage. This can occur due to poor design or a temporary issue, or a combination of issues, such as a failed main blade lead/lag damper, and/or a wrongly pressurised tyre or oleo leg.
The centre of gravity of the rotating mass becomes divergently displaced until the helicopter either shakes itself to pieces, or rocks from side to side over its undercarriage, so far that it rolls over.
In this situation, as soon as the helicopter leaves the ground, the rolling moment is removed because the undercarriage is no longer in the equation.
In an instance where something big and draggy (like a blanket) flies into the main rotor, the affected blades may well lag back against their damper back stop, causing an out of balance rotor with no damping to help recover the situation. This could set off ground resonance. If the pilot now lifts off, the drag from the blanket will continue to cause aerodynamic issues. It's easy to imagine why the helicopter will "rock and roll" in the air (once experienced, never forgotten, believe me, I've had this happen).
But how it might also cause yawing as it did in this case, is less easy to explain. Unless it caused so much blade drag that Nr was lost and a subsequent loss of tail rotor effectiveness was also experienced. OR the pilot lifted to the hover before rotor rpm was was up to normal.
Air resonance can occur when carrying a large underslung load, btw. The weight/inertia of the load has the effect of "tethering" the helicopter, in a similar way to the undercarriage when the helicopter is on the ground. Again it would need a "trigger" such as a failed blade damper.
Here's a useful link: http://www.asl.ethz.ch/education/mas...-Rotorhead.pdf
The centre of gravity of the rotating mass becomes divergently displaced until the helicopter either shakes itself to pieces, or rocks from side to side over its undercarriage, so far that it rolls over.
In this situation, as soon as the helicopter leaves the ground, the rolling moment is removed because the undercarriage is no longer in the equation.
In an instance where something big and draggy (like a blanket) flies into the main rotor, the affected blades may well lag back against their damper back stop, causing an out of balance rotor with no damping to help recover the situation. This could set off ground resonance. If the pilot now lifts off, the drag from the blanket will continue to cause aerodynamic issues. It's easy to imagine why the helicopter will "rock and roll" in the air (once experienced, never forgotten, believe me, I've had this happen).
But how it might also cause yawing as it did in this case, is less easy to explain. Unless it caused so much blade drag that Nr was lost and a subsequent loss of tail rotor effectiveness was also experienced. OR the pilot lifted to the hover before rotor rpm was was up to normal.
Air resonance can occur when carrying a large underslung load, btw. The weight/inertia of the load has the effect of "tethering" the helicopter, in a similar way to the undercarriage when the helicopter is on the ground. Again it would need a "trigger" such as a failed blade damper.
Here's a useful link: http://www.asl.ethz.ch/education/mas...-Rotorhead.pdf
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I understand how vibrations and resonance occurs in structures and I'm familiar with how the added mass of a payload or the interference of the ground with the helicopter structure can change the characteristics to allow ground resonance to occur.
The other case I mentioned (aerodynamic resonance) is something we briefly discussed in a lower-level class I took several years ago, but I'm not knowledgeable enough on the subject to offer any more of an explanation than I already have. My academic areas of expertise are design, aerodynamics, and propulsion of airplanes; I work in flight controls and hydraulic systems design and certification.
The other case I mentioned (aerodynamic resonance) is something we briefly discussed in a lower-level class I took several years ago, but I'm not knowledgeable enough on the subject to offer any more of an explanation than I already have. My academic areas of expertise are design, aerodynamics, and propulsion of airplanes; I work in flight controls and hydraulic systems design and certification.
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re resonance
i actually was flying with a other pilot this machine in aerial work and we grounded this machine due to the bad maintenance, this WAS a part of the whole situation the resonance, but further more the incompetence due to lack of training.
the company has a reputation u even wont have as crash test dummy
the company has a reputation u even wont have as crash test dummy