Downwind Quickstops
Is there really a need for quickstops to be taught as part of the PPL syllabus
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VR, Has it happened to you?
I am curious to know how many pilots have experienced some form UNINTENTIONAL incipient vortex ring close to the ground at some point in their careers. What I mean by that is that when you pulled in some power at 300 feet or less your sink rate increased, not to be confused with the helicopter not having enough power to do what you have asked of it and it continues to mush towards the ground so to speak.
VR seems to get covered in basic flight training, and for many it gets reviewed in recurrent company training, so most pilots are exposed to the theory and possibly practice at high altitude, but what percentage have actually unintentionally experienced it close to the ground?
This seems like a good opportunity to share so that others may learn!
VR seems to get covered in basic flight training, and for many it gets reviewed in recurrent company training, so most pilots are exposed to the theory and possibly practice at high altitude, but what percentage have actually unintentionally experienced it close to the ground?
This seems like a good opportunity to share so that others may learn!
Okay, I'll bite. I used to fly a "field ship" in the GOM. Ten platforms total. I was bouncing around the field one day, headed for "Charlie" platform but there was another ship already there, picking up or dropping off someone. He wasn't going to be there long, so I pulled into a 700' hover just downwind of the platform.
Taking a rare opportunity to "play" a little, I started sliding left and right, fore and aft. On one of my slides to the rear, I must have let a little RoD build up (not paying attention?). Next thing I know, the ship is shuddering and sinking...fast backward. Oops. Okay, correct it. Pulling collective did nothing but increase the RoD. Yikes! Water coming up fast...like an idiot I dropped the nose. Wrong corrective action, RoD increased more, dropping vertically now. Heart firmly in throat, I'm waiting, waiting, waiting for ETL. Finally got it and was able to fly away, arresting the RoD at 100' *indicated* (we know how altimeters lag). Got a rate of climb established and started breathing again. It was close.
Glad I hadn't decided to hover around at 500 feet or I would have pranged a perfectly good 206B into the water with no good explanation why. At the time I had about 7 or 8,000 hours. And we wonder sometimes how so-called "experienced" pilots can crash doing extremely dumb things? I do not even question it anymore - I'm living proof that it can happen (the dumb mistake part).
Taking a rare opportunity to "play" a little, I started sliding left and right, fore and aft. On one of my slides to the rear, I must have let a little RoD build up (not paying attention?). Next thing I know, the ship is shuddering and sinking...fast backward. Oops. Okay, correct it. Pulling collective did nothing but increase the RoD. Yikes! Water coming up fast...like an idiot I dropped the nose. Wrong corrective action, RoD increased more, dropping vertically now. Heart firmly in throat, I'm waiting, waiting, waiting for ETL. Finally got it and was able to fly away, arresting the RoD at 100' *indicated* (we know how altimeters lag). Got a rate of climb established and started breathing again. It was close.
Glad I hadn't decided to hover around at 500 feet or I would have pranged a perfectly good 206B into the water with no good explanation why. At the time I had about 7 or 8,000 hours. And we wonder sometimes how so-called "experienced" pilots can crash doing extremely dumb things? I do not even question it anymore - I'm living proof that it can happen (the dumb mistake part).
Avoid imitations
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Here's a link to an earlier discussion on vortex ring, which might be of interest.
http://www.pprune.org/forums/showthr...ht=vortex+ring
http://www.pprune.org/forums/showthr...ht=vortex+ring
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FH1100 pilot, thanks for sharing. Certainly a lesson that VRS is not just an exercise and really can catch the unwary. Would any instrumentation help to alert incipient VRS? Maybe something linked to collective and VSI - i'm thinking something along the lines of a fixed wing AOA stall alarm...
Mart
Mart
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Avoidance of the conditions for possible vortex ring is a very basic concept. The best piece of safety equipment in a helicopter is a well trained pilot 
I concur with FH100 that "backwards and down" is a good way to find oneself losing control, but normally speaking, this is not a usual configuration to be in!
Once seen, never forgotten, especially when the aircraft tends to weathercock into the rearwards airflow and pitch nose down due to "upwards" airflow over the horizontal stabiliser. These factors tend to remove the VR conditions but do nothing to help the piot's adrenaline level.
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I concur with FH100 that "backwards and down" is a good way to find oneself losing control, but normally speaking, this is not a usual configuration to be in!
Once seen, never forgotten, especially when the aircraft tends to weathercock into the rearwards airflow and pitch nose down due to "upwards" airflow over the horizontal stabiliser. These factors tend to remove the VR conditions but do nothing to help the piot's adrenaline level.
.
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Can't think of any instrumentation that could easily be made to work cheaply. Presumably something that integrated rate of descent/TAS/engine power information electronically could be made to work but would have to be individually calibrated to a particular type and I'm not sure whether weight might have to be considered as well.
I do remember a presentation a long while ago on a pitot system where the intake aligned itself with the relative airflow and presumably could indicate when the inflow was reaching a critical angle.
Personal experience: Helicopter camourflage trials in the desert, landing with different backgrounds and on specified headings unrelated to wind direction while the fighter recce guy rushed past taking photos. Got bored after about the 10th and didn't pay attention to the downwind component. Classic VR, R of D increasing, raise lever, ground coming up, oh s..t, no airspeed. Fortunately ground fell away to the right into a wadi, so was able to stuff the nose down, roll right, gain some airspeed and just graze the brown bits. Comment from the jet jock, "can we do that one again, it looked interesting". Get stuffed!
I do remember a presentation a long while ago on a pitot system where the intake aligned itself with the relative airflow and presumably could indicate when the inflow was reaching a critical angle.
Personal experience: Helicopter camourflage trials in the desert, landing with different backgrounds and on specified headings unrelated to wind direction while the fighter recce guy rushed past taking photos. Got bored after about the 10th and didn't pay attention to the downwind component. Classic VR, R of D increasing, raise lever, ground coming up, oh s..t, no airspeed. Fortunately ground fell away to the right into a wadi, so was able to stuff the nose down, roll right, gain some airspeed and just graze the brown bits. Comment from the jet jock, "can we do that one again, it looked interesting". Get stuffed!
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Believe it or not, downwind is a good way to AVOID VRS because the rotor must have a slight FORWARD velocity to develop true VRS (between 7 and 12 knots forward, and ROD of about 800 to 1500 fpm, depending on the helo's disk loading). However, downwind quickstops make power margin problems even more severe because when downwind, the aircraft must be taken to zero velocity while nearer OGE, thus requiring more power at that zero knot point than will be needed later when the aircraft is in an IGE hover.
When I get some time, I will build a web site that discusses this in detail and lets the pprune crowd tear it apart.
When I get some time, I will build a web site that discusses this in detail and lets the pprune crowd tear it apart.
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FH1100,
Sounds like a real eye opener, thanks for sharing.
There must be a few other guys that have experienced some form of unintentional incipient VR ...with all the very vocal people that have posted about it over the years...anyone?
Many seem to have extensive knowledge in the area, are we all just quoting theories and high altitude practice senarios, or are there people that have actually experienced it?
Sounds like a real eye opener, thanks for sharing.
There must be a few other guys that have experienced some form of unintentional incipient VR ...with all the very vocal people that have posted about it over the years...anyone?
Many seem to have extensive knowledge in the area, are we all just quoting theories and high altitude practice senarios, or are there people that have actually experienced it?
Avoid imitations
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dammyneckhurts,
The link I posted half a dozen or so before yours will lead you to previous discussions on the subject.
The link I posted half a dozen or so before yours will lead you to previous discussions on the subject.
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"Believe it or not, downwind is a good way to AVOID VRS because the rotor must have a slight FORWARD velocity to develop true VRS (between 7 and 12 knots forward, and ROD of about 800 to 1500 fpm,"
Before everyone gets too complicated with something simple, it may be best to repair to the whiteboard before the flight, which is what i do when FIRST discussing DOWNWIND THEORY with so called qualified pilots.
As Nick says 7 to 12 knots.
Same as the books say at or below ETL
Same as it happens, see below,
Helicopter is proceeding in the same direction as the wind.
Say the wind is 20 knots.
Say the helicopter has entered the procedure at 15 knots IAS.
it now slows to zero knots Groundspeed.
After it has gone past the zero knots IAS it then proceeds to a positve disk airspeed of twenty knots (from behind
).
Big mobs of room in that equation to find VRS at +7 to +12 knots. All is needed is to add descent at the appropriate rate.
In essence that is downwind theory.
Before everyone gets too complicated with something simple, it may be best to repair to the whiteboard before the flight, which is what i do when FIRST discussing DOWNWIND THEORY with so called qualified pilots.
As Nick says 7 to 12 knots.
Same as the books say at or below ETL
Same as it happens, see below,
Helicopter is proceeding in the same direction as the wind.
Say the wind is 20 knots.
Say the helicopter has entered the procedure at 15 knots IAS.
it now slows to zero knots Groundspeed.
After it has gone past the zero knots IAS it then proceeds to a positve disk airspeed of twenty knots (from behind
). Big mobs of room in that equation to find VRS at +7 to +12 knots. All is needed is to add descent at the appropriate rate.
In essence that is downwind theory.
