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Vuichard again

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Vuichard again

Old 7th Apr 2022, 08:55
  #101 (permalink)  
 
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I wonder, if Vuichard's method has ever saved anyone?
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Old 7th Apr 2022, 09:01
  #102 (permalink)  
 
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You are correct Crab re the title but surely this one is early stages of VRS? Downwind approach with flare sounds like the set up to me.
It is one of the classic configurations used to showcase entry to VRS but I have done this myself (early days as a junior Sqn pilot into a field in NI full of troops) - my ambition exceeded my talent and I overtorqued the aircraft arresting the RoD before we hit the ground, coming to a low hover with a high heartrate!

The 412 is probably into IVRS - as was I - but I pulled enough power to muscle out of it, either he didn't pull hard enough or he did run out of engine muscle.
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Old 7th Apr 2022, 09:28
  #103 (permalink)  
 
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Rotorbee
why dont you ask Mr Vuichard ?
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Old 7th Apr 2022, 15:13
  #104 (permalink)  
 
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Originally Posted by [email protected] View Post
That is confusing SWP as per the video title, with VRS.

Whilst at that low level the symptoms are the same - you get the shudder and a rate of descent - a recovery with power isn't possible because there isn't enough available (hence the term settling with power).
How do you know there isn't enough power available here? Isn't it possible that the power he had couldn't stop his decent because he was in the vortex ring state?
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Old 7th Apr 2022, 16:56
  #105 (permalink)  
 
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Originally Posted by Robbiee View Post
How do you know there isn't enough power available here?
because he crashes with a manageable RoD and the RRPM droops as he pulls pitch.

If he had another 100' feet or so to get to the ground it could well have developed into full VRS and been a much harder landing.

As I said, I have done this myself but without hitting the ground thanks to a surplus of power in the Wessex.

There are many words that don't survive the crossing of the Atlantic but descent isn't one of them usually.
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Old 7th Apr 2022, 18:05
  #106 (permalink)  
 
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Originally Posted by [email protected] View Post
because he crashes with a manageable RoD and the RRPM droops as he pulls pitch.

If he had another 100' feet or so to get to the ground it could well have developed into full VRS and been a much harder landing.

As I said, I have done this myself but without hitting the ground thanks to a surplus of power in the Wessex.

There are many words that don't survive the crossing of the Atlantic but descent isn't one of them usually.
If the rpm droops as he pulls pitch, then doesn't that just mean he was too heavy to hover?
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Old 7th Apr 2022, 21:18
  #107 (permalink)  
 
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If the rpm droops as he pulls pitch, then doesn't that just mean he was too heavy to hover?
No. he might have had enough power to come gently to an OGE hover. However, he went for the very punchy quickstop arrival (which may well have been downwind) - that needs a shedload more power to stop and is why he then fell out of the sky.

Look at the disc tilt and think about the Total Reaction arrow of thrust the rotor can produce - then tilt it and see how much the vertical component - which is required to oppose weight - reduces.
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Old 7th Apr 2022, 21:39
  #108 (permalink)  
 
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Originally Posted by [email protected] View Post
No. he might have had enough power to come gently to an OGE hover. However, he went for the very punchy quickstop arrival (which may well have been downwind) - that needs a shedload more power to stop and is why he then fell out of the sky.

Look at the disc tilt and think about the Total Reaction arrow of thrust the rotor can produce - then tilt it and see how much the vertical component - which is required to oppose weight - reduces.
Is this a problem only common to large helicopters, because the situation seems strange to me?

​​​​​
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Old 8th Apr 2022, 04:20
  #109 (permalink)  
 
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Robbiee, when you were at the Robinson Safety course, didn't they show you the video what happened during certification? The one were an FAA pilot did very low level autorotations?
That ended it the same way, upright, bent blades and the prototype was toast. It ends with the pilot jumping out and throwing his helmet down. He seemed to be slightly upset.
I asked Nick Lappos, if that was VRS, he said, no that was HTG - Hit The Ground, as you can not have VRS with the lever down. Doing it right, you can even have that in a R22. Inertia can be such a b*****.
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Old 8th Apr 2022, 07:36
  #110 (permalink)  
 
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Is this a problem only common to large helicopters, because the situation seems strange to me?
No. The situation is not strange, just the severity of the manoeuvre.

Plenty of light singles run out of power trying to come to an OGE hover - the accident stats are there for SWP and it is often because they are overloaded, haven't done any pre-flight performance calculations or have been caught out by wind (or lack of it).
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Old 8th Apr 2022, 12:48
  #111 (permalink)  
 
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Plenty of light singles run out of power trying to come to an OGE hover.....
Sudden onset of excess gravity affects all sizes of helicopters.

Explaining the various causes of such sudden onsets is where it gets complicated.

SWP, IVRS,VRS, Excess Weight, Density Altitiude, Wind Direction and Velocity, Turbine Lag, Mechanical Failure, Pilot Technique.....and combinations of several factors will find you making an interesting arrival at your final landing spot.

Prevention is the key....perferably learned in a classroom or training environment and not by Trial and Error.

Some video can begin to show what the most likely cause of such landings might be....but a full analysis should be the basis for accurate assessment.

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Old 8th Apr 2022, 13:39
  #112 (permalink)  
 
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Originally Posted by Robbiee View Post
Is this a problem only common to large helicopters, because the situation seems strange to me?​​​​​
transient droop recovery
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Old 8th Apr 2022, 14:33
  #113 (permalink)  
 
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The only way I can wrap my head around this concept of running out of power even though I'm not too heavy to hover is that I must be coming in like a screaming banchi and just wait too long to put on the brakes.

Is this it?
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Old 8th Apr 2022, 14:46
  #114 (permalink)  
 
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The only way I can wrap my head around this concept of running out of power even though I'm not too heavy to hover is that I must be coming in like a screaming banchi and just wait too long to put on the brakes.

Is this it?
Pretty much Robbiee - when you are pushed for power, you need to make a gentle, level decel to an OGE hover so you are using power to balance weight/mass and a little to slow you down. gentle application of aft cyclic will tilt the disc a little and not reduce the vertical component of that rotor thrust and you will have a small benefit from flare effect.

With a screaming Jesus quickstop, you are initially holding the aicraft up with lots of flare effect which generates enough rotor thrust to balance the weight/mass and slow you down.

As the flare effect reduces with speed in the decel, you need to replace it with collective pitch to keep balancing the weight/mass and increase the rotor thrust.

In an ideal world, you gradually feed in the power and reduce the flare until you get to your OGE hover with no problem.

If you are late with the lever, the aircraft is starting to sink and now you need a big, rapid application of power to stop you AND control the height - it can require more power than you have available and that's when settling with power kicks in, the Nr starts to decay, more lift is lost and down you go as per the 412 video.

It is really about controlling inertia - if you ease off the gas in your car a long way ahead of a stop light you can brake gently all the way to the stop. If you keep the gas pedal down until the last moment, you'd better have really good brakes.

The analogy with the 412 video is that drove like he had carbon ceramic brakes when he really had sh8tty drum brakes that needed new shoes.
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Old 8th Apr 2022, 22:44
  #115 (permalink)  
 
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FWIW, as one who has made countless FR approaches, the 412 could hover OGE under the conditions of the video.

This is not VRS. It doesn’t even appear to be settling with power, unless one considers the reduced Nr.

This is primarily a demonstration of transient rotor droop.

Anyone care to count the duration of the 0 to max-up collective pull?

Never discount the V-squared term in the equation of lift.
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Old 9th Apr 2022, 05:08
  #116 (permalink)  
 
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The 412 has a bit of inertia built up as it falls into hover attitude and needs arresting.

An over-torque may have saved the bacon but a PT6T probably won't let you.

NO IVRS, NO VRS, NO SWP. I am sure there is more than enough power to hover.

Just a massive "handling error".

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Old 9th Apr 2022, 08:18
  #117 (permalink)  
 
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This is primarily a demonstration of transient rotor droop.
I'd have to disagree Jim - I've flown plenty of manoeuvres like that in a 412 and airtested a few of them as well - the Nr doesn't droop more than a % or two when you haul in collective.

Just a massive "handling error".
that's for sure.
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Old 9th Apr 2022, 11:59
  #118 (permalink)  
 
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Originally Posted by [email protected] View Post
I'd have to disagree Jim - I've flown plenty of manoeuvres like that in a 412 and airtested a few of them as well - the Nr doesn't droop more than a % or two when you haul in collective.

that's for sure.

These were my thoughts too Crab. I canít say Iíve been in the position that aircraft was in but I have never really experienced significant NR droop in a 412. Almost all my time is in EPís so Iím not sure if itís more of an issue in the earlier models. Quick stops isnít something we get to play with often but Iíve always found the EP rock solid on power changes.
I canít pick up any change of rotor speed in the video, well not until heís just about to hit the ground.
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Old 9th Apr 2022, 14:33
  #119 (permalink)  
 
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Originally Posted by SLFMS View Post
These were my thoughts too Crab. I canít say Iíve been in the position that aircraft was in but I have never really experienced significant NR droop in a 412. Almost all my time is in EPís so Iím not sure if itís more of an issue in the earlier models. Quick stops isnít something we get to play with often but Iíve always found the EP rock solid on power changes.
I canít pick up any change of rotor speed in the video, well not until heís just about to hit the ground.
my thoughts too - Nr in the video looks stable

PS can the thread title be edited to add an Ď!íat the end?
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Old 10th Apr 2022, 13:21
  #120 (permalink)  
 
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I will probably get a lot of flak for this but:
I was doing a job which entailed a lot of climbing, descending and hovering at high altitudes AGL.
I discovered that it is possible to enter VRS from a steady hover.
It was a great surprise the first time.
Due to the job it happened a lot. So I got the chance to try various things out.
Maintaining a vertical descent pulling power just increased the rate of descent.
Controls got sloppy but the aircraft did not enter any unusual attitudes.
There were no torque or RPM fluctuations.
Recovery was simple, Initiate forward or sideways movement and exit the column of descending air.
The aircraft was very light during these operations just myself and sometimes 1 passenger and around half fuel.
It warned you it was going to enter VRS. You would be happily sitting there at about 80%Q. The VSI would flicker (not even to 100FPM down) Altimeter would hardly move. If you did nothing it would enter VRS shortly thereafter. Pull a bit of collective and it usually entered VRS immediately and fully.
It only happened in calm wind conditions.
As we were hovering, climbing or descending on a ‘Laser’ beam you were never moving more than 2 feet in the horizontal from ground level to as much as 7000 AGL. Usually we only climbed 2000-4000 ft.
If you lost the ‘Laser’ beam you had to descend to ground level in order to reacquire it so sometimes I remained in VRS to descend.
The aircraft was being observed using a 50x theodolite so the surveyors could see the aircraft depart downwards. They would have me in the crosshairs as I hovered and suddenly I would depart downwards. They thought it was very funny to watch.
Just for info the aircraft had a cowling just abut under the fwd seats. The cowling had a screen on the bottom. Inside the cowilng was a video camera focused on the screen and a small 3 inch square monitor was installed on the instrument panel. A 10 amp gyro stabilized ‘Laser’ was placed on the ground pointed vertically upwards. You hovered low over the ‘Laser’ and placed the aircraft over it until you saw the ‘laser’ dot on the screen. You then initiated a climb at about 6-800 FPM keeping the dot as close to the center of the screen as possible. If you rapid control movements failed in this and you lost the dot you had to return to ground level and start over again. It took a lot of practice to learn the technique usually about 5 -10 hours. Some guys caught on quickly, some never could. The customer paid fro the training. They also allowed you to go out and practice if you didn’t do a shot for a day or two as it was a skill that required constant practice. Totally an eye, hands, feet coordination thing…if you had to think about it the dot was gone.

Last edited by albatross; 10th Apr 2022 at 13:56.
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