The Electras were destroyed by a single catastrophic coupling of two frequencies that converged, the propellor shaft wobble and turbulence flexing the wing. Even people who should know fail to see it has nothing to do with anything but converging frequencies. If there is a rotor bounce at a certain frequency and a wobble at the tail rotor gearbox nothing will happen if those frequencies remain discreet. Matched up, they destroy the helicopter simply because they are on the same frequency. Voodoo, witchcraft, whatever. It cannot possibly have anything to do with engineering.

How many of those you have knowledge of have thrown a blade inertia weight?

If talking about the lead weight bonded inside the blade spar, not aware of any 206 that had "thrown" an inertia weight. However, there were a couple 206 blade failures due to inertia weight bond voids that caused fatigue cracks in the spar and its subsequent failure in flight. These events were one of the examples I commented on earlier in the thread that the NYC 206 wasnt the 1st 206 to lose its MR drive and roof beam as a unit.

You're thinking what I'm thinking, just the weak link was not the gearbox case. That would explain the bend in the mast at the top of the case as the fulcrum and the folding of the tailboom.

A main rotor shaft under load has considerable amount of twist under normal conditions. It has been decades since I actually saw the twist when witnessing a calibration, but I think that it is in the 60-90 degree range. That is why a small amount of localized damage will lead to a total failure. Also, there is much discussion on the net about mast bumping which seems to focus on Robinson accidents, which does not apply to most Bell accidents. In a Bell product, the main rotor shaft contacts adjacent structure and causes the localized damage that cascades into total failure.

No, it has not.

His insinuation that the rotor head bumping the mast would cause the mast to deform 3 feet away from the fulcrum is a stretch of physics to say the least. I don’t know when the bend happened either but I’d be putting my money on impact with the ground/water if I was forced to place a bet.

ASN summarises the Kentucky accident with: "The wreckage distribution was consistent with an in-flight separation of the main rotor and tailboom... Both the main rotor assembly and tailboom separated in overload". It took something significant to cause that to happen.

There must be a point where mast deflection causes resultant off-centre rotor mass to cause even greater deflection of the mast and everything to spiral out of control until the whole system is torn from fuselage. With a detailed dynamic finite element model of rotor system, this could be simulated without killing anyone in the process.

The explanation proposed by The Sultan seems reasonable for New York accident. I wonder if the rotor tip that was missing as seen in the recovery footage has been located? I had read that the search for components had ended some days back.

FWIW: you'll find the Kentucky accident, along with a subsequent Canadian 206 accident, were both due to fatigue cracks in the blade spar. And both those accidents share distinct differences from the NYC accident even though it appears there is a similar failure mode. So it might be a bit premature to group them all together at this point.

Correction: I intermixed two separate Air Evac accidents in my recollection of events. The MR spar failure was in Indiana, not KY, and did not result in the loss of the roof beam, but did result in the mast shearing at the hub and the transmission departed at the lift links with the roof beam stayed with the aircraft. The Canadian 206 spar failure did lose the MR/roof beam. However, my comment there being distinct differences between the NYC 206 still stands.

Yeah, the significant thing that caused the Air Evac breakup was the guy probably ended up inverted or falling backwards. The thing broke up because the aircraft ended up way outside of its flight envelope.

The mast bending at the swashplate… do you really think you can drop a transmission and rotor system assembly from 500 feet and all of the damage to it must have happened before it slammed into the ground? The torque on the mast when the blades and transmission hit Mother Earth doing terminal velocity wouldn’t have an effect on any of the components that are designed for dynamic strength and not static strength? I think blades are gonna break, masts are gonna bend, pitch control rods are gonna snap, things in general are gonna get nasty. There was a chunk missing out of the Air Evac’s MRB but notice how it wasn’t attributed to being just a fact of life when your machine is breaking up.

I would suggest that the torque on hitting the water would be relatively low. As the rotor system descended there would be negligible torque with the forces being gravity and rotational speed from the blades rotating. On impact the only torque would be generated by water resistance.

and water is really quite hard when hit at speed.

What about looping back to the initial sequence with the sound that Blancolirio added to the video?

The ~ 1/rev noice must be a lead to something.

The videos of the rotor assy winding down show one blade shorter than the other.

If it did it start with a blade throwing the outer part it would explain most of the things, maybe even the bent rotor mast.

In the video there is another object visible for just a few frames as the tail departs, a little bit higher up. It's easy to miss without single stepping through the frames. It is there for only a few frames, then not seen again. I haven't noticed anyone commenting on it. I suppose it could be a puff of smoke, or perhaps it's the missing blade tip?

Could a sudden loss of anti-torque thrust caused by:

1. Tail rotor blade failure,
2. Tail rotor gearbox failure; or
3. Tail rotor drive shaft failure,

Have been the starting initiator for this whole failure sequence, as it appears on the videos?

Loss of anti torque would be from one of the above mentioned or similar.

But if the Blancolirio video is properly synced in audio, the initial happening is a 1/rev. sound.

The rotational speed of the yaw is very fast despite the forward airspeed. About the same as in hover in a sim when practicing the same thing.
I would expect the yaw to be much slower in Forward flight from a loss of anti torque thrust.

I would not expect the dynamic forces to rip the tail away in the yaw after having lost the tail rotor.
The tail rotor causes a opposite torque equal to the main rotor torque when working properly and that is caused by a single force in the dnd of the tail boom. For bending/breaking the tailboom, a aerodynamic widespread force probably causes less strain on the tail boom than a single force.


Back to the 1/rev. sound it might be related to:

- Throwing a part of the blade, causing a thremendous imbalance in the dynamic parts shaking the complete helicopter apart?

- Or, what? VH Blades shaking?

-Or, what?

SPLAT!
 

I was told that, because of surface tension, water is as hard as cement when impacted at speed.

Surface tension has nothing to do with it. It's just the incompressibility of the water, and its mass resisting any force trying to accelerate it to get it out of the way of the impacting object. The surface tension is a much weaker force by far.

I think the nodal beam system is quite robust, despite being tuned for the OEM blades. Assuming the maintenance schedules are adhered to, would VHA hopping ever be more than an uncomfortable experience?

But it's still very hard, regardless of the reason - ask SAR divers who try to jump as low and slow as possible.