Crab

You hit the nail there
All loads have a Vne, normally most flight manuals have a Vne of 80 kts with something on the hook. Have flown a bambi happily at 70 kts and it has got no where near the tail rotor. The same with it on a 50 ft line. Although I can't quite follow why the line has to be more than 50ft, but if that was the manual says then that is what you do ?
The pilot must have been going at some speed to get the bucket into his tail !

Would it be more the latter than the former, Crab? The faster you go the more the load will fly up but also the tail will be higher?

But it would be interested to know ... when steaming along at speed, is there an area of circulating rotor wash updraft behind the aircraft and how far back is it at what speeds?

There seems to be a lot of input from Rotorheads with little or no experience of bucket work. A 50' or 100' line with a Bambi is a necessity for many fire ops when the water source is surrounded by trees or other obstructions, and the ability to fly such underslung loads is part of being checked to the line for fire work. As with most loads it will fly in a predictable fashion, full or empty, and a competent pilot will manoeuvre the machine to put the load where it is needed.

The real issue here would seem to be using a 10 metre (33 foot) line, with resultant flight characteristics which allowed it to put the bucket up into the TR. I'll find some photos later which show the way that an empty Bambi flies at the end of a medium length line.

Everyone is pointing out that anything less than a 50' line is an issue. Direct belly hook or 50' or longer is fine for Bambi bucket work, but in between is the danger area. I'm not sure how you have interpreted anyone's previous comments otherwise?

John

Done quite a lot of lifting and Bambi work, no one has ever really been able to say why a line shorter than 50 ft is so dangerous. Might be being really stupid here but I am sure I don't have a monopoly on stupidity !

I am thinking back to basic schoolboy physics. Feel free to shoot me down in flames if I am talking B******ks, but I reckon its like this:
The load is effectively a pendulum. To become a danger to the tail rotor, the amplitude of the swing has to be a large angle (close to 90 deg). To initiate a swing, when you resolve the geometry, involves raising the height/ altitude of the load from its rest position = work/force required. The longer the line, the greater the distance you need to lift the load to get the same angle. So, the greater the force required.
So, when you have a shorter line, its more sensitive to sudden acceleration. A longer line will take much more acceleration to achieve the same angle of dangle.

In short: Physics....
''Sporty'' handling which a short load facilitates, drop-speed, big change to the buckets weight vs volume (increased drag and decreased weight of the load) and turbulence....

This does not count for bucket work only, but any lightweight loads with a big surface area... Try a lined empty cargo-net as an example...

Surely the big issue with the length of the strop/rope/line is that if the bucket flies into the TR it is pretty much game over (as demonstrated here) but with a longer line, the bucket has to be higher in order to put the line into the TR and the damage possibly less (though not ensured) from a strop instead of metal fixings on the bucket.

KJ - I don't think that modern helos fly significantly nose down because the horizontal stabiliser keeps the fuselage more level. The difference between 60 kts and 100 kts is unlikely to be that great but the amount of drag affecting the bucket would be much more significant.

So you have a perfect storm if you have exactly the wrong length line, fly too fast and then handle the aircraft enthusiastically.

Makes perfect sense to me, especially given that the 10m reference began with the initial report....

I don't get it how you guys don't get it, except @Freewheel who does understand. The cargo hook is usually close to the aircraft CofG, which is a lot closer to the nose than the tail rotor. If the helicopter is 10m long, a 10m empty lifting rig on the hook if it goes aerodynamic is going to put it in range of the tail rotor. If you don't believe me, and heck, I've been slinging loads around the boonies for 20 years, read and comply with any warnings published for your role equipment. Or just look at the photo of what was left of that AS350 on the side of the hill. That's what can happen if you fly a 10m line on a piece of equipment that says don't fly me on a 10m line. Seriously guys, I don't understand what it is you don't understand.

FFS buddy!
With your explanation could a new pilot think it is ok to fly with a 7 meter long load as it is not as long as the 350....

I've had to teach some mentally challenged helicopter pilots in recent years, but I've found there is always a way to explain something to someone who doesn't understand your first explanation, or second. So here goes...
Hang that 10m long line on the nose of your 10m long helicopter. The way it might flail around in flight if it goes aerodynamic it would probably fly pretty close to the tail rotor, but not actually hit it. Now go and hang that same line on the hook of the same helicopter. Bingo, now that rig is potentially flying within range of the tail rotor.
I've dinged the underside of the tail boom a few times after loads hanging off 20' or 30' lines have fallen out of nets rigged by qualified load masters, but lucky they were all in B212 or S76 and the tail rotor, being bolted on top of a pylon, was out of range. Had I been in a B206 or AS350 it may well have been a different outcome.
As for said new pilot by way of example I would say, refer to the external load section of the operator procedures manual, the RFM, and the role equipment OM, and take heed of what they say.

Gullibal

The length of the helicopter has got nothing to do with it. the distance between the hook and the tip of the tail rotor is the critical dimension.

Seriously, I give up trying to explain it...I'm not going to repeat myself.

Gullibell

In your 10m example your 10 m line will still hit the tail rotor ! Unless I am mistaken the length of a helicopter would be nose to the last point of airframe. Now forgive me but in all the types I fly ( with the exception of those with either a Notar or Fenestron )the tail rotor blades have at least 50% of the turning circle within the total length of the helicopter.
It is much more critical to measure the distance between hook and tip path plane of the tail rotor

I agree !! I may be even thicker than Hughes but I don't understand the relevance of the length of the aircraft either 😳

I think we are lost in translation here and possibly saying the same thing in a different way. I'm saying don't fly with a short line, either belly hook it directly to the hook (assuming the wires on the bucket are the correct length for the aircraft) or use a 50' line or longer but nothing in between.

I think you confused everyone talking about the overall length which isn't really relevant. It's the distance from the cargo hook to the the extremities that that matters as that's where it's swinging from. Once again we are in agreement in not using a short line, and to follow the RFM and the bucket manual. It's just your original post didn't read like that is what you were trying to say.

Back when we were on a steep learning curve, the BK was tried out with shorter strops than we now know to be ideal. This was either a 20' or 30' from memory, but indicates well how the Bambi flies when empty; quite stable and predictable.

http://www.eacott.com.au/gallery/d/8...h+bucket+1.jpg

As a comparison, this is the Bambi directly onto the hook with the correct distance to the TR tips:

http://www.eacott.com.au/gallery/d/8111-1/BK117_3_.jpg

http://www.eacott.com.au/gallery/d/8...ondilli+01.jpg

John, what does the Bambi manual say?

I imagine it says what you posted in post #9?

If you're implying the photo of VH-BKK was me or my company with a 20-30' strop then you're sadly mistaken. I took that photo while flying in company; my ops we either had the Bambi on the hook or on a 100' kevlar line. My reference to 'we' was that in the 90's we were all on a learning curve and shared experiences, pilots do that. Or used to.