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HeliTorque :: View topic - Vortex Ring sting
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HeliTorque Forum Index » Flight Dynamics

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Heli-Ops
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PostPosted: Fri Jun 24, 2005 2:43 am    Post subject: Reply with quote

SS - I agree with you 100% about who the majority of members here are and my comment was probably too much of a generalisation, and for that I apologise. I was merely trying to point out that the school room approach doesnt necessarily work for the real world working environment, and by that I mean in the utility side of the industry.

For most of the low timers and private pilots your advice would be spot on as thats the everyday type of location they are going to encounter.

Didnt mean to offend.

Regards

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Dammyneckhurts
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PostPosted: Fri Jun 24, 2005 3:39 am    Post subject: Worlds apart is true.... Reply with quote

SilsoeSid.....trying to figure out how I should respond to this......

Well, since as SilsoeSid pointed out, this may not be the right forum to get into these techniques, what does everyone think...Want to hear more?
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PostPosted: Fri Jun 24, 2005 4:24 am    Post subject: Reply with quote

Maybe it needs to be moved into the Professional Rotorheads section.

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PostPosted: Fri Jun 24, 2005 6:18 pm    Post subject: Reply with quote

DMNH,

Yes please - I'd like to hear more having found your post both interesting and informative (and no - I don't plan to try it popping me mum into Eastwell Manor for afternoon tea...). And no, I don't think it makes any difference what forum it is in - it makes damned interesting reading wherever it is!

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PostPosted: Fri Jun 24, 2005 6:52 pm    Post subject: Reply with quote

Over to you Dammyneckhurts, the thread is all yours!

SS
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PostPosted: Fri Jun 24, 2005 8:36 pm    Post subject: Reply with quote

...

Last edited by Rdriver on Wed Nov 07, 2007 4:09 pm; edited 1 time in total
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Dammyneckhurts
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PostPosted: Sat Jun 25, 2005 4:59 am    Post subject: To continue..... Reply with quote

Perhaps I can temper my contribution and offer some food for thought for the average new/hobby pilot.

The reality is that Vortex Ring is most likely to happen close to the ground. As a few posters have mentioned, some of the flight regimes conducive to the onset of VRS are being in a high hover and not maintaining altitude.

For example your heading for a fly-in lunch and your passenger wants to stop and take pictures of something, your paying more attention to getting the right camera angle than you are to flying the aircraft and all of a sudden the bottom drops out.

An even more likely twist to the same scenario is that you are not hovering, but in slow forward flight (10 kt ground speed)..... passenger is taking pictures....asks you to turn for a better angle and you unknowingly turn downwind, you sense that you are slowly losing altitude, and as soon as you pull collective it feels like someone pulled a chair out from under you. This exact scenario has happened to me in an R44.

A more likely situation where you are going to accidentally stumble into VRS completely unaware, is landing area that requires a steeper approach. You have several hundred hours now....your are at a point where flying the helicopter doesn???t require the co-operation of every available brain cell, maybe you have been into this spot several times before and you are chatting away with your passenger. While on short final a glimmer of thought flashes through your head that your approach is a bit fast for some reason. Shouldn???t be....closure rate seemed ok a few seconds ago....You apply aft cyclic and the nose is quite high, another fleeting though of maybe aborting flashes by, but no, your have brought it back together from this approach profile before...collective sure is low too...hmmmm. Ok, seem to have it together now, almost at the spot and it finally seems like the right time to bring in some power ( much later that you normally would) and as soon as you pull you are dropping like a stone.

There is nothing wrong with a steep approach as long as you don???t allow the three ingredients of VRS to mix in the same pot. In this case the pilot is unintentionally downwind and doesn???t realize it at all.

If the pilot had the skills to recognize some of the screaming protests that the helicopter was offering, ample time to abort would have been available wayyyyy before the onset of vortex ring. We talk of the benefits of early recognition of vortex ring, but not much gets said about recognizing on unintentional downwind approach. This is a major contributor to the onset of VRS

So lets break it down.....

-First thing the pilot noticed was that ground speed seemed a bit fast (due to tail wind....airspeed low...ground speed high) RED FLAG!

-Nose seems high in attempt to reduce the high closure rate ANOTHER RED FLAG!

-Collective is low because of flare attempting to reduce ground speed RED FLAG!

-Another thing that will be amiss is that you will loose the string much sooner that normal (by loose I mean it wont be blowing straight back, Robinson and Astar)

-Coupled with this will be the shudder as the helicopter slows through translation (much further back from the landing spot than you would expect) RED FLAG!!

If a pilots notices any of these things, an abort should be seriously considered, I am sure many will say its a given.

Note: for the pundits out there, if your were doing a constant angle steep approach, you would not likely get some of these symptoms, but you would in a normal initial approach, terminating on a short steep final.

I really think that we should practice downwind approaches at flight school. Not because we should go out and do them all the time (although is necessary in some situations), but having the ability to recognize the signs that the helicopter is giving us is a valuable skill. It may well save you from all the nasties of unintentionally being downwind.....mushing into the ground due to lack of power....or maybe even vortex ring.

With that I pass the floor to Paco!! Anything to add?
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Bierbuikje
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PostPosted: Sat Jun 25, 2005 6:52 pm    Post subject: Reply with quote

Hi Dammyneckhurts

An R22 on a photo flight crashed a few month's ago here in Belgium sadly killing both people on board the cause was incipient vortex ring by the look of things.

I agree we should teach more down wind approach's so pilots can recognise the symptoms of a downwind approach easily (For all the reason's you stated)

I learned to fly in the UK and the method there for a confined area landing is similar to where I am now but here in Belgium they fly a wind circle to help find the direction of the wind (The Belgium military use it and it seem's to have filtered its way into the civil flying) This works realy well if there is no other visual referance for the wind.

Line up on two ground features in a straight line in staight & level flight at 500ft AGL and 60 knots. Commence a turn at constant speed & constant bank, After a 360?? turn if you are right of your original two points the wind is from the left and visa versa. You may have to make a few turns on differant headings if you want to know preciesly where the wind is from.

I believe we should set each approach up to avoid vortex ring in the first place (Airspeed VS Sink Rate) but we should know the symptoms of the down wind approach and early onset of incipient vortex ring, Just in case weve made a mistake and ended up on a down wind approach. The only way pilots will recognise these syptoms is if we teach it.

The segment of the market that I'm talking about is normal A - B flying, Not specalized work such as external load which I know nothing about. I am interested in hearing more on these tecniques.

All the best Bierbuikje.
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Dammyneckhurts
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PostPosted: Mon Jun 27, 2005 4:28 pm    Post subject: Reply with quote

Bierbuikje, a bit of an overview of the Canadian helicopter scene??

In Western Canada we do a lot of long line work, it???s more the norm than the exception, and it???s not really thought of as being specialized as pretty much all the pilots are proficient to some degree. The skill level varies of course, some pilots do nothing but long line work, some will only use it on occasion. The pilot flying the other 205 on the job I am currently on has about 9000 hours heli logging in an S-61, that???s just 61 time??not including the other types he is rated on. That???s a lot of long line experience!! The length of line is generally around 130 feet, with some operation using as much as 250 feet (logging)

I suppose the reason we do so much of it is because of geography and vegetation. There is a lot of work to be done in areas where there are no roads, and lots of big trees. Examples are heli logging, oil and gas exploration, and mineral exploration. For the most part, we also use a long line when water bucketing on forest fires.

The logging and oil exploration segments require a pilot to carry perhaps a few hundred loads per day. If a pilot carries 200 loads??.that means he delivers an empty hook 200 times, and delivers a load to the destination 200 times, that???s 400 approaches in a day??.very high repetition indeed.

Often the loads are only carried a short distance, anywhere from a few hundred meters to a few kilometers. If you are doing 400 approaches in a day, taking the time to do a circle so that each approach is into wind takes a lot of time. In a back and forth scenario, sometimes you will be nose into wind for the delivery, and have a tail wind when you go back for the pick up on the next load. Sometimes you will have a cross wind on both ends.

So the challenge for the production long line pilot is to learn ways to move quickly in a non favorable wind condition. The degree of accuracy required, and also the power available determines if the nose of the aircraft will be brought into wind on very short final, or if you will stay out of wind the entire time.

On some jobs we just release the load close to the target (within a 30 foot circle) and some precision work (Drills) require precise hovering with the load almost touching the ground so that crews can rotate it by hand and land it in a precise spot (within 30 cm)

Not allowing the 3 factors of vortex ring to meet are the key to working downwind. If I know I am down wind, then I have to keep the approach very flat with the load just barely above the trees and the descent rate at zero while I reduce speed
Once ground speed is near zero then the load is lowered through the trees and the nose is allowed turn into wind if required for the final placement.
If a direct on the tail downwind condition is stronger than you can handle due to power limitations (heavy load) then most guys will deviate a few hundred meters to one side or the other so that the you can turn somewhat cross wind on very short final??

We use all the visual indicators available to find the wind?? leaves, water, dust, smoke etc??.if none are available then its all in the feel of the aircraft. In a stronger wind, vortex ring is less likely because you always know the wind direction, and you can plan accordingly. It???s the light and variable conditions that are the trickiest. Add in mountainous terrain and the affect it has on wind and reading the local wind is an art form. By local wind I mean the wind in that exact spot , not 100 meters away, and not at ground level but at helicopter level as the wind can easily be quite different 200 feet off the ground as it is on the surface.

The biggest thing though regarding vortex ring is awareness and knowledge . Awareness of wind??and knowledge of just exactly how much you can push each ingredient, and how you can vary the ratio of those ingredients without getting into trouble.

After awareness comes the ability to recognize the early symptoms of vortex ring , followed of course by swift corrective action.


The fog just lifted to I am off to work wahoo!!

More later if anyone has any specfic questions...
DMNH


Last edited by Dammyneckhurts on Tue Jun 28, 2005 1:45 am; edited 1 time in total
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PostPosted: Mon Jun 27, 2005 5:37 pm    Post subject: Reply with quote

...

Last edited by Rdriver on Wed Nov 07, 2007 4:07 pm; edited 1 time in total
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PostPosted: Mon Jun 27, 2005 9:40 pm    Post subject: Reply with quote

Hi DMNH

Thanks, I do find it interesting its a world apart from what I do.

How do people start off doing that external load work? I know pilots can follow a basic course but gaining experiance is something else. Do they start off with an experianced pilot or just do a course and gain more experiance on the job?

All the best Bierbuikje.
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PostPosted: Tue Jun 28, 2005 2:45 am    Post subject: Reply with quote

Bierbuikje...

Some people get an intro to the basics at flight school, in Canada a commercial license is 100 hours of training. From there they will get some training by their employer, usually after they have maybe 500 ish hours of time....
Once they have the basics, they will use the line whenever they have a chance for easy non precision jobs, usually tasks that just require a few lifts. After a few years...the company they work for will give them some more training time in preparation of going on a job where they will be long lining all day.

The first few jobs will still be considered relatively easy, and most companies will have an experienced pilot on the job at the same time as the trainee until they are comfortable on their own.

In Canada, long lining is not a specific rating, and there is no official course required.

It's very stimulating to say the least, a great tool and is invaluable given the geography in Canada. The down side is that same geography means a lot of time spent away from home. For example I am currently in a camp in the middle of nowhere, it's a 2 hour drive to the nearest town!. Thank-fully we have satellite telephone and satellite internet so we can stay in touch and check weather forecasts etc.

All the best!

DMNH
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PostPosted: Fri Jul 01, 2005 4:26 pm    Post subject: Reply with quote

Please don't forget SS that there are PPL's out there with more hours than you might think Wink

Experience can't be taught or bought! Just because someone has a licence saying CPL doesn't mean a) "he's not in our club" or b) he/she's inexperienced - a lowly PPL. Wink
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PostPosted: Fri Jul 01, 2005 5:37 pm    Post subject: Reply with quote

Hi DNMH - hope Ontario's warming up for you! Miss those fires.......

You pretty much said it all, a lot more politely than me! My concern is that people are *aware* of what *could* happen, which is one reason why I take people up in bad weather - it's not to say that you should do it, but as you know over those trees where you are, the fog can roll in right behind you, as anyone who lives in Dartmoor knows. Knowing what to watch for and how not to get into it, or get out of it if sh*t happens, is an essential part of the safe pilot's armoury. I have always wondered whether the hours spent giving "instrument appreciation" are better spent being trained how not to get into trouble. That is what I mean by saying that flying is more of a mental occupation. Half the problems people have are in their head.

With reference to VR, or the incipience thereof, a typical scenario for most readers of this forum is coming into an hotel, nicely set up and suddenly a host of people come out and occupy your landing site, so you steepen up the approach to land in front of them. Be careful! What you should do is go araound, but it's difficult for many pilots to accept that they are not going to make their chosen landing spot. Get that fixation out of your head, and a lot more will go right for you, especially when the engine quits.

As an aside, I think it's patronising to say that, just because someone "only" has a PPL, that they are not worthy of being spoken to or given knowledge. I've flown with plenty of bozos who have a CPL/ATPL, and I expect to meet many more. A "professional" attitude is different from a "professional" attitude. Think about it.

Phil
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Last edited by paco on Fri Jul 01, 2005 9:31 pm; edited 1 time in total
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PostPosted: Fri Jul 01, 2005 6:02 pm    Post subject: Reply with quote

Thank you TC, I am well aware of that point. Especially when I read through the AAIB reports!

I think I said, "I would like to point out that IMHO my posts reflect what I believe the viewers/contributers to be.

If I was to think that most here were bush pilots, I wouldn't feel the need to point out that you can set yourself up nicely for landing, minimising the risk of VR.

Similarly, if I believed most here were low houred PPLs....."

I still believe most here are of the latter.

As it would seem that only 22 of the 247 registered users on helitorque are professional pilots (based on the response to the thread), and their hours are available at http://www.helitorque.com/portal/modules.php?name=Forums&file=viewtopic&t=246&postdays=0&postorder=asc&vote=viewresult perhaps a similar poll for the majority would be interesting.

Hi paco, I don't believe anyone here has referred to someone else as, "only a PPL". The only problem that has been highlighted here is that some of the advice given is dangerous and there are low houred PPLs looking at that advice with open mouths taking it all in because it sounds impressive.

What you don't want to hear is me saying, hold on chum, watch youself. If it feels wrong, go round. That's boring and doesn't make such a good story as dmnhs'.

You get KNOWLEDGE by listening to others and reading , not EXPERIENCE.
The problem is, that a little or even wrong knowledge is dangerous.

Have a safe weekend,

SS
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