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Vuichard again

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Vuichard again

Old 31st Mar 2022, 00:57
  #21 (permalink)  
 
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Originally Posted by ShyTorque View Post
As I wrote here before in previous discussions on the "Vuichard" recovery technique, the claim made is that it provides a full recovery with a height loss of 100 feet or less. How can it do that from a rate of descent of what is possibly 3,000 feet per minute or more? I've experienced VRS of around that rate of descent in a Puma and it took far, far more height to recover..
A key part of VRS recovery is recognition.
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Old 31st Mar 2022, 06:06
  #22 (permalink)  
 
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Originally Posted by helonorth View Post
A key part of VRS recovery is recognition.
Or better still, avoidance.

So hot and hi, you have recovered from fully developed VRS (several thousand fpm RoD, random pitching rolling and yawing) in less than 100' then?

if you are only in the very early stages then pretty much any technique works - including pulling in a handful of power.
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Old 31st Mar 2022, 08:00
  #23 (permalink)  
 
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Originally Posted by ShyTorque View Post
As I wrote here before in previous discussions on the "Vuichard" recovery technique, the claim made is that it provides a full recovery with a height loss of 100 feet or less. How can it do that from a rate of descent of what is possibly 3,000 feet per minute or more? I've experienced VRS of around that rate of descent in a Puma and it took far, far more height to recover. The aircraft randomly pitched, yawed and rolled until we gained some forward speed by holding full forward cyclic and even then the recovery from the descent couldn't be stopped within 100 feet! During RAF rotary wing training I was shown what was purported to be VRS in a Whirlwind 10 and it was nothing like fully the developed VR state; the aircraft almost recovered by itself with very small control movements.
Same here - Puma demonstration of Incipient VRS by the wonderful "Parts" (RIP). We entered at 6500' AGL backwards and down with 0 airspeed, got a bit mushy through 500' ROD but nothing outrageous however, as we hit 800' ROD it pitched what felt like 90 degrees nose down and rolled 180 degrees, We came out about 1800' AGL fully out of balance with about 30kts IAS and about 20 degrees ND. It were horrible. Oh it was night too. No idea how many times we rolled but it was completely out of control, no ifs or buts, we ended up pointing 180 degrees from our entry heading but I think we had gone around a few times. I'm not sure if Vuichard would have been any better or not.
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Old 31st Mar 2022, 08:43
  #24 (permalink)  
 
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An ETPS graduate demonstrated fully developed VRS to me in a Wasp in Singapore some 55 years ago. We started at 9000ft and recovered at 4000ft. The lack of control was scary. No way could that have been recovered with a height loss of only 100ft. As Crab says, in the early stages if you recognise it, then practically anything works - including Vuichard probably.
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Old 31st Mar 2022, 08:50
  #25 (permalink)  
 
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Very nice video from 2:10:



This maths might be useful to some on this thread:

Using Speed Difference and Distance

Convert the initial and final speeds to units that will be useful for calculating the acceleration (feet per second or meters per second). Also make sure the distance over which the speed change occurs is in a compatible unit (feet or meters).

Square the initial speed and the final speed.

Subtract the square of the final speed from the square of the initial speed.

Divide by two times the distance. This is the average deceleration rate.

Calculate, as an example, the deceleration required to stop a car in 140 feet if it is traveling 60 mph.

Convert 60 mph to 88 feet per second. Because the ending speed equals zero, the difference is this result squared: 7,744 feet squared per second squared. The deceleration rate is:

77442×140=27.66 feet per second per second 7744 / {2 x 140}=27.66 { feet per second per second} ​=27.66 feet per second per second

Deceleration in Gravity Units (G’s)

Calculate the deceleration rate using one of the two methods described above.

Divide the deceleration by the standard gravitational acceleration. In U.S. units, this is approximately 32 feet per second per second. For metric units the standard gravitational acceleration is 9.8 meters per second per second. The result gives the average number of G’s applied to achieve the deceleration.

Enhance understanding by considering an example: Find the G force required to stop the car in the previous example.

The calculated deceleration equaled 27.66 feet per second per second. The deceleration is equivalent to:

27.6632=0.86 G’s {27.66/32}
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Old 31st Mar 2022, 10:43
  #26 (permalink)  
 
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No idea why the maths examples given, but that’s a very convoluted way of saying Vsquared = Usquared + 2as.
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Old 31st Mar 2022, 11:37
  #27 (permalink)  
 
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The video is the same garbage that was promoted when we first started having the conversation on PPRuNe.

Note the first action is to apply full power with collective - if you are any deeper into VRS than the very early stage, that alone will make things much worse very quickly.

It works on the Vuichard video because he is never in anything but the very early stages ie he has low speed and a building rate of descent.

According to Nick Lappos, if you have enough power available, you can power out of full VRS - but that takes so much power (to overcome the drag from the vortices) that most helicopters cant do it.

Come on AnFI show the actual figures for a 2, 4 and 6 ton helicopter doing 500'/min, 1000'/min and 2000'/min since you like the maths so much.
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Old 31st Mar 2022, 11:38
  #28 (permalink)  
 
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Yes quite right 212 total agree tried it before with not traction

rearrange and forget about U^2 (zero)
s= v^2 / 2a
then for 4000fpm (roughly 20m/s) stopping at acceleration (a) of 1g ((10m.s^-20) additional to usual g) then the distance required is

v^2 / 2 a = 400/20 = 20m

20m is not that dramatic at 1 g

at ROD 3000fpm stopping in 20m gives

a=v^2/2d = 225/40 = 5.6m^s^-2 is about 1/2 'g' ... no big deal
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Old 31st Mar 2022, 11:50
  #29 (permalink)  
 
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So that was something of a red herring then....

You'd be better off calculating the downwash speed for a selection of helicopters - then apply the notion that your RoD has to be at least 0.6 and ideally 0.75 of your downwash speed to encounter actual VRS (according to wind tunnel tests and modelling).

Then see if the Vuichard technique works at those rates of descent with 50' to 100' recovery.
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Old 31st Mar 2022, 14:37
  #30 (permalink)  

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I think an analogy is the difference between recovering a fixed wing spin at the incipient stage, where centralising the controls will bring the aircraft back under control. Try that technique in a full spin and it can get very exciting shortly afterwards.
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Old 31st Mar 2022, 14:47
  #31 (permalink)  

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Originally Posted by SimonK View Post
Same here - Puma demonstration of Incipient VRS by the wonderful "Parts" (RIP). We entered at 6500' AGL backwards and down with 0 airspeed, got a bit mushy through 500' ROD but nothing outrageous however, as we hit 800' ROD it pitched what felt like 90 degrees nose down and rolled 180 degrees, We came out about 1800' AGL fully out of balance with about 30kts IAS and about 20 degrees ND. It were horrible. Oh it was night too. No idea how many times we rolled but it was completely out of control, no ifs or buts, we ended up pointing 180 degrees from our entry heading but I think we had gone around a few times. I'm not sure if Vuichard would have been any better or not.
“Parts” was actually a student of mine on the Puma OCU, in the mid 1980s but we didn’t deliberately demo VRS on the course back then! My encounter was on a night operation where we were required to hover on instruments at 10,000 feet or so (if you’re ex Pumas you probably know the role). The handling pilot (another previous student of mine) lost his concentration after a very long night in poor visibility and mishandled the attempt to get to the hover (I think we probably fell out backwards). Down we went, very quickly indeed and I prompted him to regain airspeed; I think I probably assisted him by pushing the cyclic to the forward stop… we lost a great deal of altitude, it was very sobering how quickly it happened.
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Old 31st Mar 2022, 15:28
  #32 (permalink)  
 
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Do we really want to go down that rabbit hole again?
I would like to know something else, because I tried to find it out and failed. Vuichard claims he saves thousands of people with his(!) "new" technique. Does anybody know, how many accidents are really caused by VRS? Not SWP, VRS, the real thing. Apart from a famous accident with a Puma and one with REGA, I can't find anything. No statistics show that a significant part of the helicopter accidents are caused by VRS. If there aren't many of them, our training up till now seems adequate.
That does not mean, we can't do better, but me thinks, VRS is not something that should get so much attention.

For those of you who are so into Vuichard, let me give you some food for thought. And think about flying in the mountains, where terrain will make the decisions to take sometimes quite different.
You will encounter VRS in real life when doing steep approaches. Most of the time, you will decide on an escape route, and that one will be more or less (debatable, but the smaller the angle the better) in the direction of your approach. In the moment you feel the incipient stage of VRS, do you really want to fly in a complete other direction than your escape route?
In training Vuichard's method might be a nice trick, but in the heat of the action and reduced mental capacity stage when your helicopter begins to feel mushy in the controls, do you really think, you are capable to do that whole thing with all controls moving in a non-intuitive way?
Next one, you come in high, with a long line and a load. On the ground are people waiting for you to precisely lower the load on the spot. Because this has always been done like this, if anything goes haywire, they expect you to stay on a straight flight path. Therefore, they do not stand in your flight path, they are off to the side. Now, because this day there is almost no wind or even a slight tailwind, you feel VRS coming. Now what? You do the sidestep, but your load does not know that and follows later and now you have a load swinging from side to side you have to catch and a helicopter on a different flight path endangering people on the ground. You can't pickle the load, because you can not judge, where it will land. What now?

Or you get close to the ground, but still OGE and you feel VRS coming, but you are not quite sure, if you have enough hight AND power to save you before hitting the ground. You rather crash in a straight line or going sideways?

Remember, this is all in the incipient stage of VRS, where with both methods, you have the same outcome, which means you essentially loose the same altitude while getting out of it. Because in all these scenarios, if you let get VRS out of hand to the even remotely developed stage, your dead anyway.

If you have some ideas how to get around this, please post, because the more I think about it, the less I think, that this technique is really made for real life.
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Old 31st Mar 2022, 16:49
  #33 (permalink)  
 
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Originally Posted by Rotorbee View Post
In training Vuichard's method might be a nice trick, but in the heat of the action and reduced mental capacity stage when your helicopter begins to feel mushy in the controls, do you really think, you are capable to do that whole thing with all controls moving in a non-intuitive way?
.
In my personal experience with the only time (in the real world) I've ever experienced vortex ring,...no. In fact my first thought was, "How does that new thing go again?" Then I lowerd the collective and pushed forward like I had done a bazillion times in training.

Of course I'm and old dog whose only done this new trick a handful of times. From what I've seen lately though, the training world seens totally ga ga over this new technique. On my BFR last month we did it a few times, yet not once did we do it the old way. I'm guessing that soon we'll have a whole generation of pilots/cfis who think of it as their go-to recovery method.

I'm not saying that not enough (or too much) pedal doing this new technique is what caused this most recent R44 accident, but it does make me wonder?
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Old 31st Mar 2022, 22:56
  #34 (permalink)  
 
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Originally Posted by ShyTorque View Post
“Parts” was actually a student of mine on the Puma OCU, in the mid 1980s but we didn’t deliberately demo VRS on the course back then! My encounter was on a night operation where we were required to hover on instruments at 10,000 feet or so (if you’re ex Pumas you probably know the role). The handling pilot (another previous student of mine) lost his concentration after a very long night in poor visibility and mishandled the attempt to get to the hover (I think we probably fell out backwards). Down we went, very quickly indeed and I prompted him to regain airspeed; I think I probably assisted him by pushing the cyclic to the forward stop… we lost a great deal of altitude, it was very sobering how quickly it happened.
Who or what would have you hovering at 10k on instruments. What a ridiculous thing to be doing.
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Old 31st Mar 2022, 23:07
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Originally Posted by helonorth View Post
Who or what would have you hovering at 10k on instruments.
The British military.

What a ridiculous thing to be doing.
Not if you knew the tasking requirements over a very specific area of the UK.

Last edited by Nescafe; 31st Mar 2022 at 23:25.
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Old 31st Mar 2022, 23:19
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Originally Posted by Nescafe View Post
The British military.



Not if you knew the tasking requirements over a very specific area of Great Britain.
Great Britain or United Kingdom?
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Old 31st Mar 2022, 23:20
  #37 (permalink)  
 
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Oh. Sounds very mysterious and important.
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Old 31st Mar 2022, 23:26
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Originally Posted by 212man View Post
Great Britain or United Kingdom?
My mistake, but at least the military were British👍
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Old 1st Apr 2022, 06:52
  #39 (permalink)  

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Originally Posted by helonorth View Post
Oh. Sounds very mysterious and important.
Let’s just say that a certain government department liked it that way.
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Old 1st Apr 2022, 09:17
  #40 (permalink)  
 
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Back in those day such sensor technology was very hush hush but nowadays every police and SAR aircraft has much the same capability (along with UAVs) so we shouldn't be too precious about the Puma role.

It was quite A-level at the time but it was more dangerous down in the weeds with SA and MANPADS threats really.
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