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Here’s a couple of documents that make mention of it occurring whilst airborne / hovering / drifting - one is European and the other American:
https://www.easa.europa.eu/en/downloads/22663/en
https://core.ac.uk/download/pdf/36727638.pdf
https://www.easa.europa.eu/en/downloads/22663/en
https://core.ac.uk/download/pdf/36727638.pdf
Thread Starter
This generally occurs when a helicopter is taking off, landing or hovering with one skid/ wheel in contact with the surface. The helicopter may begin to roll about the point of contact with the surface (pivot point). The pivot point could be for example a skid/wheel, stuck or restrained to ground, ice, soft asphalt or mud. It could also be a skid/wheel contacting a fixed object/ground whilst hovering sideways or during slope operations.
The second very good article doesn't mention it at all, it is a perfect treatise on dynamic rollover and explains the difference between static and dynamic rollover far better than the EHEST document.
And bear in mind that the EHEST document isn't a training manual it is to help operators to implement their SMS.
The main difference is that in dynamic rollover, adding collective makes things worse (unless you are lucky enough to break ground contact) - but if you drift sideways into a fence or wall or similar obstacle, adding collective will put you above it and remove the problem.
I'm not saying you can't end up in a smoking heap by drifting into something - plenty have done it - but it isn't what is referred to as dynamic rollover as illustrated by the US article.
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Second article, Pg 1. of 3., Para 4 and 5:
“A potential problem develops, however, when the helicopter comes in contact with the ground (a lateral drift for example) and a new pivot point is established”
“Well, just imagine hovering in a brownout or whiteout situation and attempting to land. In the process, due to loss of visual cues, you establish a lateral drift and contact the ground with one wheel or skid.”
I concede the author uses the word “ground” whilst I previously suggested another type of inanimate object - but the principle is identical in that the aircraft is airborne / moving and contacts something that then sets up a pivoting moment.
Your assertion that using collective to rectify colliding sideways with an obstacle elegantly illustrates the point I was originally trying to make - if a rolling moment has been initiated, then adding pitch will likely tip you over due to main rotor thrust. If you chose to not call this dynamic rollover then you are obviously well within your rights; but the fact is that others take an opposing view as they have recognised that the aerodynamics, exacerbating factors and outcome are all identical.
As mentioned previously, this is not about winning an argument - rather it is to try and share some knowledge. It was imparted to me by some highly experienced Canadian instructors (some of who are sadly no longer with us) and I’m am merely passing it on.
“A potential problem develops, however, when the helicopter comes in contact with the ground (a lateral drift for example) and a new pivot point is established”
“Well, just imagine hovering in a brownout or whiteout situation and attempting to land. In the process, due to loss of visual cues, you establish a lateral drift and contact the ground with one wheel or skid.”
I concede the author uses the word “ground” whilst I previously suggested another type of inanimate object - but the principle is identical in that the aircraft is airborne / moving and contacts something that then sets up a pivoting moment.
Your assertion that using collective to rectify colliding sideways with an obstacle elegantly illustrates the point I was originally trying to make - if a rolling moment has been initiated, then adding pitch will likely tip you over due to main rotor thrust. If you chose to not call this dynamic rollover then you are obviously well within your rights; but the fact is that others take an opposing view as they have recognised that the aerodynamics, exacerbating factors and outcome are all identical.
As mentioned previously, this is not about winning an argument - rather it is to try and share some knowledge. It was imparted to me by some highly experienced Canadian instructors (some of who are sadly no longer with us) and I’m am merely passing it on.
Thread Starter
We will have to agree to disagree, the whole concept of dynamic rollover is that contact with the ground, whether or take off or landing with drift, where the aircraft is no longer free to move about its C of G but instead around the new pivot point created by the contact between wheel/skid and the ground.
The collision with an obstacle scenario is different, as well as being far less common than the landing/take off scenarios - you have created a temporary pivot point about which the aircraft could start to roll but because you are actually flying and have high collective position already, applying opposite cyclic will have a strong effect because you are modifying the direction of a lot of MR thrust. Additionally, and the reason I mentioned collective helping not hindering, is again because you are flying and a small collective input will gain height to clear the obstacle - that isn't the case with dynamic rollover where the further application of collective exacerbates the situation and accelerates you towards the stuck skid.
In the landing/take off scenarios, the collective is lower, the MR thrust is less and your lateral cyclic has less effect.
Remember also that the classic dynamic rollover happens when the wheel/skid on the advancing side of the disc is the one that sticks on the ground - mostly because the TR thrust is acting in the same direction as the aircraft is trying to drift in - further limiting the effectiveness of your lateral cyclic.
The idea of a 'limiting roll angle' when you are clear of the ground is an erroneous one, when you tilt the disc sideways you reduce the amount of vertical MR thrust but that is easily compensated for by application of more collective. Whereas dynamic rollover can occur with very low levels of roll angle - your 'collision' scenario implies much larger roll angles which, unless you are moving very fast sideways when you hit the object, are not going to be experienced.
In short, I, and most textbooks I can find, regard dynamic rollover as requiring ground contact which is made worse by application of collective - your 'collision' scenario doesn't meet either criteria. Yours is tripping over an obstacle - you would be better comparing a drifting helicopter attached to an underslung load that was too heavy to lift - that is closer to traditional DR but it can happen when moving in any direction, you just run out of cyclic authority.
We went into dynamic rollover in great depth in the Sea King world after two pilots on their Sea King course rolled one over carrying out an ASE out take off - it was unusual at the time because it was on a flat runway instead of a slope. Boscombe Down were tasked to reproduce the accident and successfully rolled theirs over too, leading to the understanding that the aircraft was far more prone to DR than previously thought and exacerbating factors like ASE out, wind from the left (lateral flapback reducing cyclic margins), nose down (increasing the height of the TR thrust) and high C of G (low fuel state) just brought you closer unless you used the correct technique for take off (I mentioned it in an earlier post). It explained a lot of wobbly take offs, especially on rolling decks aboard ship.
The collision with an obstacle scenario is different, as well as being far less common than the landing/take off scenarios - you have created a temporary pivot point about which the aircraft could start to roll but because you are actually flying and have high collective position already, applying opposite cyclic will have a strong effect because you are modifying the direction of a lot of MR thrust. Additionally, and the reason I mentioned collective helping not hindering, is again because you are flying and a small collective input will gain height to clear the obstacle - that isn't the case with dynamic rollover where the further application of collective exacerbates the situation and accelerates you towards the stuck skid.
In the landing/take off scenarios, the collective is lower, the MR thrust is less and your lateral cyclic has less effect.
Remember also that the classic dynamic rollover happens when the wheel/skid on the advancing side of the disc is the one that sticks on the ground - mostly because the TR thrust is acting in the same direction as the aircraft is trying to drift in - further limiting the effectiveness of your lateral cyclic.
The idea of a 'limiting roll angle' when you are clear of the ground is an erroneous one, when you tilt the disc sideways you reduce the amount of vertical MR thrust but that is easily compensated for by application of more collective. Whereas dynamic rollover can occur with very low levels of roll angle - your 'collision' scenario implies much larger roll angles which, unless you are moving very fast sideways when you hit the object, are not going to be experienced.
In short, I, and most textbooks I can find, regard dynamic rollover as requiring ground contact which is made worse by application of collective - your 'collision' scenario doesn't meet either criteria. Yours is tripping over an obstacle - you would be better comparing a drifting helicopter attached to an underslung load that was too heavy to lift - that is closer to traditional DR but it can happen when moving in any direction, you just run out of cyclic authority.
We went into dynamic rollover in great depth in the Sea King world after two pilots on their Sea King course rolled one over carrying out an ASE out take off - it was unusual at the time because it was on a flat runway instead of a slope. Boscombe Down were tasked to reproduce the accident and successfully rolled theirs over too, leading to the understanding that the aircraft was far more prone to DR than previously thought and exacerbating factors like ASE out, wind from the left (lateral flapback reducing cyclic margins), nose down (increasing the height of the TR thrust) and high C of G (low fuel state) just brought you closer unless you used the correct technique for take off (I mentioned it in an earlier post). It explained a lot of wobbly take offs, especially on rolling decks aboard ship.
sounds much more like ground resonance - that can easily lead to a rollover but it's not dynamic rollover in the normal sense
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Originally Posted by [email protected]
...Boscombe Down were tasked to reproduce the accident and successfully rolled theirs over too, leading to the understanding that the aircraft was far more prone to DR than previously thought...
Oh, and might be time to change the thread title to "Dynamic Rollover"!... But there probably already is such a thread.
Anyway crab, what ever you do, don't total that last flying Wessex, whether by dynamic rollover, collision with a post, ground resonance or any other way!
Thread Starter
Megan - sorry, I missed the smiley
Helispotter - yes, they did actually total a real Sea King, as I understand it, the US exchange officer who took their briefing for the sortie did a risk assessment and didn't like the outcome - they did it anyway!
I will be trying very hard not to damage the Wessex - it has no ASE due to lack of spares but it's still great fun to fly.
Helispotter - yes, they did actually total a real Sea King, as I understand it, the US exchange officer who took their briefing for the sortie did a risk assessment and didn't like the outcome - they did it anyway!
I will be trying very hard not to damage the Wessex - it has no ASE due to lack of spares but it's still great fun to fly.
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I guess if they "were tasked to reproduce the accident" they had remarkable success and should be commended for their diligence! 
The discussion also reminded me of a dynamic rollover case reported in Aviation Safety Digest 126 back in 1985, see page 18 of: https://www.atsb.gov.au/sites/defaul...126_spr_85.pdf
The unfortunate pilot of the media JetRanger (VH-CEC) got caught up on the slightly raised side of a concrete refuelling pad which is seen in a photo of the accident scene. Article says the pilot was bringing the 206B to the hover and attempted to correct with cyclic but the helicopter rolled over.
The discussion also reminded me of a dynamic rollover case reported in Aviation Safety Digest 126 back in 1985, see page 18 of: https://www.atsb.gov.au/sites/defaul...126_spr_85.pdf
The unfortunate pilot of the media JetRanger (VH-CEC) got caught up on the slightly raised side of a concrete refuelling pad which is seen in a photo of the accident scene. Article says the pilot was bringing the 206B to the hover and attempted to correct with cyclic but the helicopter rolled over.
Thread Starter
Helispotter - yes, it highlights the problems of aircraft with teetering (or near teetering) heads, they have very little control power (how much leverage the rotor head can exert on the fuselage) so any tendency to DR is even more difficult to fight with opposite lateral cyclic. 206 and R22 are classics in that sense.
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Avoid imitations
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Anyone remember the JetRanger that was filmed trying to tow a speedboat? It stayed airborne about four seconds before it rolled over and ditched with a flourish.
Link:
Here’s another one:
Link:
Here’s another one:
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Ive been to one of the hangar tours and met you and the team. Brew and pizza were yummy. The Wessex and collection there are so worthy of note. Not just because of the cabs, but all that is done to keep them airworthy. The tour is in my view, brilliant at getting up and close to machines that I watched as a boy sat on the stone wall by the threshold at HMS Osprey. That Wessex brings out the child in me every time. Bravo to all at HH.
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