Another question about Dynamic R/o

[Vfrpilotpb]

Ages ago I asked if Big Helis were suseptable to this problem and had agood response, Last week I posted a picture of (I now know) its a Hillier fitted with floats,

My question is :- Can any sort of float equipped Heli suffer from Dynamic R/O whilst on water?

Peter R-B
Vfr

[IntheTin]

Would like to say yes, why not. You need all of these 3 things present to get into Dynamic rollover.
1- Pivot point. The A/C (skid) may be anchored to something.
2- Thrust. Taking off.
Which in turn
3- Exceeds the critical angle, thus getting dynamic rollover.

[MightyGem]

But, as you try to roll the aircraft it will tend to move across the water, possibly not.

[Matthew Parsons]

The water will create a drag force that could cause rollover with a lateral velocity and/or too much lateral cyclic. Consider moving sideways at 35 kts over water then quickly dumping one float into the water...could cause a rollover.

There is a new rollover to consider with floats. Assymetric inflation or deflation has and will continue to cause rollover.

Matthew.

[Vfrpilotpb]

Having thought about this before I posted the question, I too thought like Mighty Gem that the Heli could possibly skid across the water, due to the lack of grip compared with say soil.sand,grass or tarmac, unless the Heli was some how tethered,

My reasoning for this is the way that Helis start to spin on the water untill tail rotor authority is available on start up, that spinning shows lack of friction, to what less extent I don't know.

PeterR-b

[Johe02]

The theory is there but I would be very surprised if anyone could actually do it. . especially with the size (width) of the floats on that Hiller.

[Arm out the window]

The footprint would be wider, which would increase the static rollover angle (where a line straight down from the C of G points outside the outer edge of the landing gear), but we're not just talking about friction (ie one surface slipping over another), it's the buildup of water pressure on the 'leading' edge of the float that would provide a pretty big force as soon as you had a few knots sideways happening.
I've done a bit of float work, and letting sideward speed build up isn't good - can damage the floats, and I wouldn't want to push it too much anyway, because I think the risk of rolling it over would be quite real.

[breakscrew]

Given the right conditions, all helicopters are suceptable to dynamic roll-over.
There is a great article about it in the DASC Journal called AViate. The link is: http://www.mod.uk/dasc/journals/aviate.htm The editor is a Sqn Ldr Dick Oddie on 0208 8387618 - he will be please to forward you the article free of charge.