Edson AB crash, VRS?
If you try and hold a stationary hover with a 30 knot tailwind, your collective will be up in your armpit as that little tail rotor tries to keep you straight. To stop a violent weather vane once you run out of tail rotor authority, you may try and reduce the pitch to stop the spin. Maybe he just realized he had no foot left, was close to the ground and let nature take over.
If you try and hold a stationary hover with a 30 knot tailwind, your collective will be up in your armpit as that little tail rotor tries to keep you straight.
with downwind, you might be on the back end of the power curve, with no induced flow and a very inefficient rotor system. as you slow down to a hover you will eventually have tail wind (beneficial to the induced flow and the rotor system effectiveness).
In this case he did not make it to having downwind on the aircraft.
A good pilot will realize the mistake by the level of vibration and the power setting being above usual, at that point in the approach but when you are tired and just want to wrap up your job things like that happen.
having a powerfull airframe will aslo mask out the early sign, Do that in an R22 with an overweight instructor and there is not much to save you, but the early signs will be comparatively amplified.
If you try and hold a stationary hover with a 30 knot tailwind, your collective will be up in your armpit as that little tail rotor tries to keep you straight. To stop a violent weather vane once you run out of tail rotor authority, you may try and reduce the pitch to stop the spin. Maybe he just realized he had no foot left, was close to the ground and let nature take over.
The tail will be more twitchy and you may need more yaw inputs to maintain the heading, especially in a gusty wind.
Being weathercocked back into wind is a real danger, but that’s not at all what it looks like happened in this case.
Downwind approaches - get the ground speed off early, keep the RoD under control and go around early if you are struggling to maintain your desired flight path or keep within power limits. It’s not rocket science.
Originally Posted by [email protected]
Being weathercocked back into wind is a real danger, but that’s not at all what it looks like happened in this case.
As long as the dumb meat-servo at the controls keeps these things in mind, he'll be okay and won't be surprised when the inevitable happens. Hovering with a strong tailwind is do-able, but you must, must, MUST be ready for the ship to want to swap ends. And, if you're even slightly late on the pedal application, you might not be able to prevent it. Crab is right that making an approach with a strong tailwind is do-able - with the proper technique - a technique that was, evidently and sadly, not imparted to our hapless Astar pilot. "Wait, what? You mean I was supposed to slow down and get through translation again FROM THE REAR?? That's insane!" Again, these are facts of life that all helicopter pilots should understand but many, obviously, do not.
Last edited by Chock Puller; 17th May 2023 at 18:21. Reason: Stick to the topic of the Thread.
..Crab is right that making an approach with a strong tailwind is do-able - with the proper technique - a technique that was, evidently and sadly, not imparted to our hapless Astar pilot. "Wait, what? You mean I was supposed to slow down and get through translation again FROM THE REAR?? That's insane!" Again, these are facts of life that all helicopter pilots should understand but many, obviously, do not.
You can get a vortex around your tail rotor in a tail wind, that swaps you around. Even in a Robinson. Frank was a master of the tail rotor, and Robinson helicopters have very good tail rotor authority. Even so, you can get in trouble in a tail wind, but with a slight wiggle on the cyclic, you can fix that (my own experience). Everything with a normal tail rotor from Airbus, has reportedly very good tail rotor authority. The rumor is, that only Bell pilots experience LTE and Bell invented the term.
That said, at the tail the situation will be vastly different. If not super quick on the pedals you will quickly have to test the stops in order to avoid playing sun and have the Earth rotate around you.
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That is, because LTE is mostly a Bell problem, it seams. Apparently, I could be wrong here, the first 206' had a very weak tail rotor. Later models hat less problems.
You can get a vortex around your tail rotor in a tail wind, that swaps you around. Even in a Robinson. Frank was a master of the tail rotor, and Robinson helicopters have very good tail rotor authority. Even so, you can get in trouble in a tail wind, but with a slight wiggle on the cyclic, you can fix that (my own experience). Everything with a normal tail rotor from Airbus, has reportedly very good tail rotor authority. The rumor is, that only Bell pilots experience LTE and Bell invented the term.
You can get a vortex around your tail rotor in a tail wind, that swaps you around. Even in a Robinson. Frank was a master of the tail rotor, and Robinson helicopters have very good tail rotor authority. Even so, you can get in trouble in a tail wind, but with a slight wiggle on the cyclic, you can fix that (my own experience). Everything with a normal tail rotor from Airbus, has reportedly very good tail rotor authority. The rumor is, that only Bell pilots experience LTE and Bell invented the term.
@helispotter: I very much doubt, that a model helicopter would be appropriate for this kind of test... Building a scaled down model of the rotor with all the correct flexing and flapping isn't as easy as it sounds... And then there is the Reynolds number... The budget isn't very high. I think for that money it is cheaper to use a real helicopter.
The rotor head on this model seems relatively scaled to me? Yes, perhaps the rotors themselves are stiffer (in relative terms) than a full scale Lama as they don't droop/sag much when rotor is stationary but it would seem fairly trivial to adjust stiffness of model blades using a different material. In any case, I wonder how much the stiffness of blades comes into influencing the dynamics of a VRS and getting out of it? While it might be more complex to accurately model 3+ blade rotorheads on scale models, it seems relatively trivial on 2 blade helicopters, of which there are of course many! I accept the Reynolds Number will be less than full scale, but no longer substantially so once you have a decent size model. Just as with blade stiffness, I wonder how much the Rn is actually influencing dynamics of a VRS? I appreciate Rn influences profile drag and lift coefficient at larger AoA. I accept it might actually be more straightforward to instrument a full scale helicopter for such a research project than to do so on a model. I was mainly thinking about reducing the risk of an accident involving aircrew if they deliberately seek out VRS conditions. I guess if you have altitude on your side to conduct experiments, the risk is managed...
Last edited by helispotter; 18th May 2023 at 03:36.
@Robbie: I only gave you the history of LTE, not an argument against or for anything. If you have lazy feet in almost anything that flies, except probably for the original Ercoupe, you will get in trouble. Even with a headwind.
Can I refer you to Nick Lappos amazing thread about Helicopter Urban Myth? A very interesting read. There are quite a few threads about LTE in Pprune.
@helispotter: Have it your way, but I am pretty sure, that those scale heads do not have lead/lag- or flapping hinges. Anyway, building an accurate model with all the instrumentation necessary fitted, would probably eat up the whole budget and take ages. The contract is for only two years. I am pretty sure Onera is up to the task doing it safely. They have already done some work on VRS a few years ago and can build on that.
Can I refer you to Nick Lappos amazing thread about Helicopter Urban Myth? A very interesting read. There are quite a few threads about LTE in Pprune.
@helispotter: Have it your way, but I am pretty sure, that those scale heads do not have lead/lag- or flapping hinges. Anyway, building an accurate model with all the instrumentation necessary fitted, would probably eat up the whole budget and take ages. The contract is for only two years. I am pretty sure Onera is up to the task doing it safely. They have already done some work on VRS a few years ago and can build on that.
Last edited by Rotorbee; 18th May 2023 at 06:16.
I'm not sure what further modelling of VRS will achieve - its existence is well documented and we know that avoiding flight regimes where low IAS is coupled with allowing a significant RoD and application of power will keep us clear of it.
Maybe pilot training isn't what it was or newer pilots have been spoiled with such powerful and capable helicopters compared to 50 years ago but of all the very many helicopter pilots I know or have flown with, few have experienced LTE and even fewer (probably 2 or 3) have experienced VRS.
Maybe it is a function of the modern generation that they can't accept what they have been told by the old guys, they have to find out for themselves and won't be happy until there is a VRS or LTE App for their I-phones to keep them out of trouble.
Maybe pilot training isn't what it was or newer pilots have been spoiled with such powerful and capable helicopters compared to 50 years ago but of all the very many helicopter pilots I know or have flown with, few have experienced LTE and even fewer (probably 2 or 3) have experienced VRS.
Maybe it is a function of the modern generation that they can't accept what they have been told by the old guys, they have to find out for themselves and won't be happy until there is a VRS or LTE App for their I-phones to keep them out of trouble.
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After this I stay quiet about RC helicopters for research, but earlier I did to a bit of basic searching on the internet and found out that drone / quadcopter manufacturers such as DJI apparently limit the rate of decent in their newer drone models in an effort to prevent occurrence of VRS. I also came across this video (and others) which suggest drone is caught in VRS condition in the footage shown:
Perhaps more interesting, in a discussion about drones and VRS, there was a link to this full scale AS350 accident footage from inside the helicopter. Title on YouTube attributes accident to VRS but description and comments provide few other details:
I tried to work out which helicopter it was. While N4075S is shown earlier in the footage, this doesn't seem to be the one involved in the accident which instead may have registration N?094S which is partly visible on cowling towards the end of the video. These helicopters appear to be operated by Sunshine Helicopters in Hawaii. ASN reports on the accident of N6094H in Hawaii on 17 June 2014 which sort of fits the description in this video, but the "H" in rego doesn't match rego seen in footage and the video was apparently posted 1 June 2012 so accident must pre-date it. Anybody know this case? Perhaps it has been discussed to death on PPRuNe already, but I couldn't find a thread after some key word searching.
Perhaps more interesting, in a discussion about drones and VRS, there was a link to this full scale AS350 accident footage from inside the helicopter. Title on YouTube attributes accident to VRS but description and comments provide few other details:
I tried to work out which helicopter it was. While N4075S is shown earlier in the footage, this doesn't seem to be the one involved in the accident which instead may have registration N?094S which is partly visible on cowling towards the end of the video. These helicopters appear to be operated by Sunshine Helicopters in Hawaii. ASN reports on the accident of N6094H in Hawaii on 17 June 2014 which sort of fits the description in this video, but the "H" in rego doesn't match rego seen in footage and the video was apparently posted 1 June 2012 so accident must pre-date it. Anybody know this case? Perhaps it has been discussed to death on PPRuNe already, but I couldn't find a thread after some key word searching.
Perhaps more interesting, in a discussion about drones and VRS, there was a link to this full scale AS350 accident footage from inside the helicopter. Title on YouTube attributes accident to VRS but description and comments provide few other details:
https://youtu.be/mP72wdgq5PU
I tried to work out which helicopter it was. While N4075S is shown earlier in the footage, this doesn't seem to be the one involved in the accident which instead may have registration N?094S which is partly visible on cowling towards the end of the video. These helicopters appear to be operated by Sunshine Helicopters in Hawaii. ASN reports on the accident of N6094H in Hawaii on 17 June 2014 which sort of fits the description in this video, but the "H" in rego doesn't match rego seen in footage and the video was apparently posted 1 June 2012 so accident must pre-date it. Anybody know this case? Perhaps it has been discussed to death on PPRuNe already, but I couldn't find a thread after some key word searching.
Maybe this one and the earlier portions of the event are missing in the video. Picture quality looks like 2000! It was also a definite loss of power event and nothing to do with VRS, I'd say. https://aviation-safety.net/wikibase/30181
But this, N6094S
Same company though
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