TimW68 Posted March 12, 2009 Report Posted March 12, 2009 PPL with about 95 hrs. and not allot of "real" experience with turbulence. I have felt some minimal turbulence but nothing to speak of. Was hoping a few of you would describe some of your experiences with it and things you have learned through the encounters. Also was wondering about the effects of low-g with mod-strong turbulence, and even degree of roll from rogue wind or wind shear. I appreciate the input as it always nice to have a good general idea of what to expect if/when it happens. Quote
Goldy Posted March 12, 2009 Report Posted March 12, 2009 PPL with about 95 hrs. and not allot of "real" experience with turbulence. I have felt some minimal turbulence but nothing to speak of. Was hoping a few of you would describe some of your experiences with it and things you have learned through the encounters. Also was wondering about the effects of low-g with mod-strong turbulence, and even degree of roll from rogue wind or wind shear. I appreciate the input as it always nice to have a good general idea of what to expect if/when it happens. What do you fly? The same level of turbulent air will be felt a lot more in an R22 than a 300 or B47....or an R44 for that matter. When you cannot fully control your airspeed or altitude, your in it. Slow down to better handle it, 65 knots in the R22 and about 75-80 in the 44. Dont fight it, let the ship move around, but I am always ready for a low rpm or low G condition. I've had times I wanted to just land, but you have to fly thru it. I learned a lot by putting in some glider time. What you look for in a glider....I now avoid in a chopper! Knowing wind direction and how wind interacts with mountains and buildings can really help you avoid surprises. If you have never really experienced it, I would pick a nice gusty day and take a CFI for a ride. What I have been thru, I know others that have been thru twice as bad conditions. Fly safe, Goldy Quote
TimW68 Posted March 12, 2009 Author Report Posted March 12, 2009 I fly the R-22 and was fortunate enough to have a very good CFI do some extensive hovering/field practice w/me in high winds, 25 gusting to 33 and that was a great experience. My question was more related to mast bumping, over stressing rotor system, or even possibly rolling the ship from a sudden side wind. I have a good idea of POH and Jeppersen suggestions but rely heavily on what I read here from these forums. Quote
West Coaster Posted March 12, 2009 Report Posted March 12, 2009 I don't think mast bumping should be an issue. You'll of course get that sinking feeling of negative G's, but the disk will still be loaded. As far as the machine is concerned it's still flying straight thru a mass of air. The fact that air mass is falling or rising makes no difference to the helicopter, it doesn't care so long as you don't over controll the thing. Wind shear though is another animal. That can cause any number of ugly reactions from the machine. You could expect uncommanded roll, overspeeding the rotor, blade tip stall, loss of all effective lift, and possible mast bumping depending on the machine type. Flew thru a wicked squall line at night once just after departure, very nearly went swimming! Quote
jfcorey Posted March 12, 2009 Report Posted March 12, 2009 I don't think mast bumping should be an issue. You'll of course get that sinking feeling of negative G's, but the disk will still be loaded. How is the disc loaded if you've got the sinking feeling in your seat? I though the sinking feeling is what indicated a low-g/ unloaded-disc condition. Quote
West Coaster Posted March 13, 2009 Report Posted March 13, 2009 How is the disc loaded if you've got the sinking feeling in your seat? I though the sinking feeling is what indicated a low-g/ unloaded-disc condition. You'd be in a mass of subsiding air for a moment, the helicopter would descend to an extent along with it. The feeling is the same but the mechanism is totally different. A low-G pushover or something that could unload a disk is a result of control inputs by the pilot. Flying thru a mass of falling air will create the same feeling in the seat of your pants as you experience negative G forces from the air pushing you down, but nothing has changed as far as the helicopter is concerned. In relation to the ground yes you are descending, but all the helicopter thinks is it's just flying thru a mass of air. The only thing that's changed is the direction the air mass is moving. Quote
jfcorey Posted March 13, 2009 Report Posted March 13, 2009 thank you that helps quite a bit when you explain it that way. Quote
TimW68 Posted March 13, 2009 Author Report Posted March 13, 2009 West, Any change in the relative wind or angle of attack on the advancing blade? If so what is the effect. Quote
Gomer Pylot Posted March 14, 2009 Report Posted March 14, 2009 Helicopters handle turbulence much better than fixed-wing aircraft, because of the higher disk (wing) loading. As long as you keep positive G forces on the rotor, there is no problem. Just keep your airspeed at or below the max turbulence penetration airspeed (and this is pretty high for a helicopter) and you'll be fine. The aircraft will bounce around a little, but less than an airplane would, and while it's not dangerous, it can be uncomfortable for some. Quote
choppedair Posted March 14, 2009 Report Posted March 14, 2009 Just slow down and ride it out without over-controlling. Imagine being in a boat in choppy water. The only concern I ever have in heavy turbulence is rotor and engine limitations in the r22 and r44, mostly in 'rugged' terrain. It's not particularly fun having to do over-speed prevention in normal flight with huge updrafts and downdrafts. However that is generally only in extreme conditions with very strong winds and rugged terrain.Strong winds are over more flat terrain is usually much less of an issue. If you are concerned about it you should take some time to fly somewhere mountainous with an experienced CFI. Learn how wind moves through the mountains and what places you should avoid. Quote
Wally Posted March 14, 2009 Report Posted March 14, 2009 I'm going to have to disagree with a view previously advanced, that the aerodynamic loads on the blades are not changed in turbulence. When you encounter a "down draft", the disk isn't loaded exactly the same or identically with a pitchdown control input. But, if they're producing less lift, even short term, then there's a change, however transient, and you need to consider that.Helicopters generally handle turbulence better than airplanes. I've never had stuff fly around in the cockpit, but I have had various fluids move (Low XMSN pressure caution panel, for instance), fuselage swing, and I've observed the tip path plane changing. Those all support less load on the disc.I can't pretend knowledge of the Robinson head, but I'd certainly be cautious in strong turbulence in a 2-bladed Bell. Quote
West Coaster Posted March 14, 2009 Report Posted March 14, 2009 Good point Wally, there would be a minor change in the disk loading. Not sure it would be anything to worry about. But something I was pondering yesterday, could a violent updraft unload a disk and lead to disaster? West,Any change in the relative wind or angle of attack on the advancing blade? If so what is the effect. Too early in the morning.... haven't had any coffee and can't wrap my brain around that one yet lol. Quote
gizmo Posted March 14, 2009 Report Posted March 14, 2009 I believe a major updraft thru the rotor system would not change the disc loading. But consider Settling With Power practice maneuvers. You're adding a major updraft thru the rotor system by dropping at least 300 FPM. Sometimes during practice, the R22 can easily increase to 1200-1500 FPM (depending on winds, density altitude, blah, blah, blah). I've yet to feel any indications of an unloaded rotor system (weightlessness, right roll). I could be wrong about this one so I'm looking forward to any additional input Quote
TimW68 Posted March 15, 2009 Author Report Posted March 15, 2009 This is what I was hoping for, keep it going !!! Quote
choppedair Posted March 15, 2009 Report Posted March 15, 2009 I believe a major updraft thru the rotor system would not change the disc loading. But consider Settling With Power practice maneuvers. You're adding a major updraft thru the rotor system by dropping at least 300 FPM. Sometimes during practice, the R22 can easily increase to 1200-1500 FPM (depending on winds, density altitude, blah, blah, blah). I've yet to feel any indications of an unloaded rotor system (weightlessness, right roll). I could be wrong about this one so I'm looking forward to any additional input So if you encountered a strong sudden updraft, that made you feel heavy(ier) in your seat, you wouldn't see that as in increase in disc loading? Is that not what is causing the increase in rotor rpm during a strong updraft...? Or conversely, causing a decrease in rotor rpm with a strong sudden downdraft? Ever noticed changes in manifold pressure (and subsequent yawing) during large updrafts and downdrafts, even though the collective has stayed put?Still I wouldn't be worried about low g mast bumping due to turbulence. I believe low g is much more attributed to pilot inputs. Think of entering an auto and being "light" in your seat. No crazy roll going on there and no need to be concerned as long as you aren't throwing the cyclic around. Quote
gizmo Posted March 15, 2009 Report Posted March 15, 2009 I stand corrected with my previous post. Choppedair is absolutely correct. There is a change in disc loading with an updraft. I guess my memory is going with age But I still can't see how a major updraft (or any updraft) can lead to a Low-G situation. As you said, a Low-G is mainly attributed to pilot inputs. Pilot moves cyclic forward abruptly which unloads the main rotor blades. The forward momentum increases the induced flow which results in a decreased AOA. Low-G is due to the increasing amount of air moving DOWN thru the rotor system, not up Quote
MN Heli Flyer Posted March 15, 2009 Report Posted March 15, 2009 I thought I would add my 2 cents. When you do a push over it changes the component of lift from vertical to horizontal abruptly. Also keep in mind that the rotor blades are changing momentum because they are now trying to change direction. When the momentum and the low G ( 0 gravity) occur at the same time the blades loose control and flail about until mast bumping occurs and worse, separation. In turbulence you are generally flying with very little cyclic movement maintaining control. When you encounter turbulence it is usually momentary and it could be an updraft or a downdraft. In either case it is usually short term. I was told by a CFI that if you feel light in the seat use a little aft cyclic to be sure you keep the rotor loaded. In thermals updrafts are stronger than downdrafts. If I am wrong on this someone please let me know. Quote
West Coaster Posted March 15, 2009 Report Posted March 15, 2009 Thought I'd add more food for thought and share an experience with squall lines. Three years ago flying an S76 at night on one of the worst wind storms Vancouver has seen in 50 years. Winds on the pad were showing about 35 kts or so and had been that way or worse all day. With a ful load of passengers and tanking fuel for the IFR we were pretty much gross weight. We lift from the pad into the blackness of the Victoria harbour, I'm the NFP. Going thru 100' I start the post takeoff checks and just as I finish all hell broke loose. In an instant the wind swung 90 degrees and increased to about 80 kts off our side. Our ASI went from showing 80 kts or so to zero in a flash, we had an huge uncommanded yaw to the right and left roll and the torque started to fly off the dial. The scream from the transmission was awefull. The FP nosed over hard to try and regain some airspeed and dropped the torque to save the transmission from itself, and to give him room to fight the yaw with pedal. He regained directional control and a little airspeed and had control of the torque again... for a moment. Then we came out the other side of the squall line and everything went bonkers again. The wind went back to about 35 kts off the nose in a snap. There was again a massive yaw but this time the torque dropped off and we started to sink again. The FP was able to recover about 100' above the waters surface. Just relating the story so that if you ever see a report of a squall along your route, do not take it lightly. Sometimes the tower's radar can spot them but often they don't as was the case with us. Quote
IFLY Posted March 16, 2009 Report Posted March 16, 2009 In thermals updrafts are stronger than downdrafts. If I am wrong on this someone please let me know.Most of the time downdrafts are about equal or stronger than updrafts. Friday I flew a 100K triangle in a glider and I had the vario pegged at 1000 fpm down more often than up. At the end of the day there was more area moving up than down so updrafts were light at around 5-600 fpm and the downdrafts were still 800+. You find most of the updrafts on the leading edges the clouds with windshear from the downdrafts just before the updrafts. Jerry Quote
Whistlerpilot Posted March 16, 2009 Report Posted March 16, 2009 Hi All, Copied this from another forum because it's really good relevant info on flying in winds in the mountains. Rating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Mar 14 2009, 07:59 PMPost #2 Member** Group: MemberPosts: 37Joined: 28-December 08Member No.: 5,265 QUOTE (mixmaster @ Mar 14 2009, 07:14 PM) *Hi to all. Been floating around here for a couple of years and not really posted that much, but I do find this forum to be a great resource. I am from down south and really the the mountains around here are more hills (less that 3000 ft) but i have been following a couple of the threads (the heli logging one, also watching on TV and the heli skiing one). Anyway a quick question for the more experienced among us. At what point does wind go from being helpful to dangerous to deadly in the high mountains (think above tree line, heli skiing, Canadian Rockies, Colorado Rockies, Sierras, Utah, etc). What about the type of rotor system (Bell 206B/L, 205/212 vs Astar, 407, 412) and how does that change the equation. I know every situation is different, but around here hills are 500 to 1000 ft above surrounding area and not really craggy, just rolling hills, so up to 30-40mph is good to go as not too much turbulence. How does the really high stuff, or mountainous terrain (cliffs, cirques, pinnacles, knife edge ridges, etc) change things and when do you shut it all down. Attending a mountain course (the best ones are in Canada from what I hear) is the best way to find out, but that is out of the question for now. Thanks in advance for any informative reply's. Mixmaster Mixmaster, Once you get winds above 20 knots or so, every cirque, ridge, or mountain top will have a surprise for you. Also depends on your load. I won't get into the technique that I use here as you are better off to seek advise from a school for the technical explanation. We have been heliskiing here with a B2 and L-4, same landings, similar loads and as I hate to say it, the Astar works better in gusty conditions, 30-40 knot with gusts to 60 or so, 6000-9000feet, leeward side of the range (Coast Mountains, Central B.C.). After 2 attempts- my limit, I would pick a lower landing and the B2 ran the guests to the top. (2 runs later he quit as well) Main thing to remember- don't get on the leeward side of the ridge in down flowing or circulating air. Always have an escape route when the bottom drops out, because it will.Strong steady wind, the sideways approach works good for me and you always have an escape route in front of you, straight ahead. Fly Smart, Fly Bell(unless it is too windy) B.M.Go to the top of the pageReport Post +Quote PostmtnhopperRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Yesterday, 01:00 AMPost #3 Advanced Member*** Group: Advanced MemberPosts: 218Joined: 5-January 05Member No.: 976 laugh.gif laugh.gif punk.gif --------------------Twins are the most fun!!!!!!!Go to the top of the pageReport Post +Quote PostT tailRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Yesterday, 03:27 AMPost #4 Advanced Member*** Group: Advanced MemberPosts: 236Joined: 7-June 05Member No.: 1,309 QUOTEAt what point does wind go from being helpful to dangerous to deadly When it stops doing what it was doing half a second before i.e change direction/strengthGo to the top of the pageReport Post +Quote PostmixmasterRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 11:01 AMPost #5 Newbie* Group: MemberPosts: 3Joined: 7-March 07Member No.: 3,005 Black. Mike.Thanks for your reply, it answers some questions. I guess by the number of views (500+) in a day and a half this is a subject that quite a few people are interested in. Anyone else care to share any information or experiences.Thanks MixmasterGo to the top of the pageReport Post +Quote PostOver-TalkRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 12:57 PMPost #6 Senior Member**** Group: Advanced MemberPosts: 363Joined: 3-July 03Member No.: 422 Hi, Mixmaster,The speed of the wind is not so much of a factor as how turbulent it is.The turbulence can be caused by the shape of the mountain it is flowing past, or by the nature of that particular weather system.Some pilots describe some weather systems as being very "mechanical". This is represented in the aircraft by a short, sharp chop and a 'banging' flight.Some days the wind has a huge amount of 'downflow' to it. Though this doesn't always make a landing more difficult, it will slow your ascent, it will need to be allowed for on the approach path you choose, and shows that each day brings its own challenges.Because of the vagaries of the weather on any particular day, there are not too many fixed rules that you can use on such days. You will have to assess the conditions at that time. What is more predictable is the effect of the shape of the peak you are working with. This will have a huge influence on whether you can land there or not. It makes sense that round, smooth knobs are much easier to work with.Some peaks feature a cliff on one side. If the cliff is on the downwind side, the peak will be easier to work with, but don't get into the diving curl behind the peak. Landing on a shoulder behind a peak will also be difficult, and worsened by a windy day as even a smooth wind will now be disturbed by the peak.Cirque landings are to be avoided on windy days if possible. The wind swirls inside them, and is very unpredictable. If you 'have to' land in a cirque, make sure you have a large power-margin, have an abort route, and do a few recces to see if the wind is acting the same each time.(and remember, there is only one "have to" in our industry.......you 'have to' make it back to the hangar, whether you landed in the cirque, or called it off!!) Always consider the altitude you are at. The aircraft will not be as responsive in thin air, so it may not be as safe to land at a higher peak on the same day. Before landing somewhere, consider the take-off.For example, the bottom of glaciers are usually troughs of downflowing air between two moraine walls. They often feature a lot of descending air which you won't be able to climb into, because of the rising terrain ahead. Therefore you will have to depart downwind. If it is snowy, the snowball will be charging down the icefield with you, so your visibility will be hampered. If the departure path is a flat, white surface.......be very careful!! Types of aircraft.........hmm, this should start a debate.Bell mediums have been popular for years but their problem can be in the engines.....i.e they must speed-up and slow down a lot as you work in turbulent air. Because of the big, fat blades these aircraft have, it is sometimes hard for the governors to keep the rotor RPM at 100%.Some of the multi-blade systems will have a lower inertia to them, and be easier for the engines to compensate for rapid power changes......especially if the helicopter is fitted with a good FADEC control system.Please remember....if you are requiring a lot of big power changes to land somewhere.....maybe you should go somewhere else. And just because your passenger "landed there last week in a 407 on a windier day", it doesn't mean you can land a 212 there today. Tail rotors.........A mountain approach will require a crisp tail rotor that responds well to pedal inputs. I like the basic design of two or three tail rotor blades back there.I have not liked the "mushy" effect that a fenestron or NOTAR system give the aircraft. Eventually you will learn how to fly on windy days, and be able to handle more wind/turbulence as your experience and skill level increases. You will also be more comfortable about saying "sorry, not that peak today".The approach is vital. If you can't get the aircraft to set-up 'smoothly' on the approach... the landing will be a disaster. "Smoothly" is a relative term depending on all the factors mentioned above. Even if a wind is strong and/or rough, you may still be able to land if it is predictable.A recce flight on your approach path (which always features an abort route) will tell you so much. And a second recce will tell you MORE than twice as much !! If you can't figure-out what the wind is doing after a few recces......go somewhere else.WC Fields said, "If at first you don't succeed, try again. If that doesn't work...give up, 'cos there's no point in making a fool of yourself." Be careful out there. --------------------oops, I over-talked again !!Go to the top of the pageReport Post +Quote PostslingRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 02:24 PMPost #7 Senior Member**** Group: Advanced MemberPosts: 400Joined: 10-July 08Member No.: 4,710 QUOTE (Over-Talk @ Mar 16 2009, 12:57 PM) *Hi, Mixmaster,The speed of the wind is not so much of a factor as how turbulent it is.The turbulence can be caused by the shape of the mountain it is flowing past, or by the nature of that particular weather system.Some pilots describe some weather systems as being very "mechanical". This is represented in the aircraft by a short, sharp chop and a 'banging' flight.Some days the wind has a huge amount of 'downflow' to it. Though this doesn't always make a landing more difficult, it will slow your ascent, it will need to be allowed for on the approach path you choose, and shows that each day brings its own challenges.Because of the vagaries of the weather on any particular day, there are not too many fixed rules that you can use on such days. You will have to assess the conditions at that time. What is more predictable is the effect of the shape of the peak you are working with. This will have a huge influence on whether you can land there or not. It makes sense that round, smooth knobs are much easier to work with.Some peaks feature a cliff on one side. If the cliff is on the downwind side, the peak will be easier to work with, but don't get into the diving curl behind the peak. Landing on a shoulder behind a peak will also be difficult, and worsened by a windy day as even a smooth wind will now be disturbed by the peak.Cirque landings are to be avoided on windy days if possible. The wind swirls inside them, and is very unpredictable. If you 'have to' land in a cirque, make sure you have a large power-margin, have an abort route, and do a few recces to see if the wind is acting the same each time.(and remember, there is only one "have to" in our industry.......you 'have to' make it back to the hangar, whether you landed in the cirque, or called it off!!) Always consider the altitude you are at. The aircraft will not be as responsive in thin air, so it may not be as safe to land at a higher peak on the same day. Before landing somewhere, consider the take-off.For example, the bottom of glaciers are usually troughs of downflowing air between two moraine walls. They often feature a lot of descending air which you won't be able to climb into, because of the rising terrain ahead. Therefore you will have to depart downwind. If it is snowy, the snowball will be charging down the icefield with you, so your visibility will be hampered. If the departure path is a flat, white surface.......be very careful!! Types of aircraft.........hmm, this should start a debate.Bell mediums have been popular for years but their problem can be in the engines.....i.e they must speed-up and slow down a lot as you work in turbulent air. Because of the big, fat blades these aircraft have, it is sometimes hard for the governors to keep the rotor RPM at 100%.Some of the multi-blade systems will have a lower inertia to them, and be easier for the engines to compensate for rapid power changes......especially if the helicopter is fitted with a good FADEC control system.Please remember....if you are requiring a lot of big power changes to land somewhere.....maybe you should go somewhere else. And just because your passenger "landed there last week in a 407 on a windier day", it doesn't mean you can land a 212 there today. Tail rotors.........A mountain approach will require a crisp tail rotor that responds well to pedal inputs. I like the basic design of two or three tail rotor blades back there.I have not liked the "mushy" effect that a fenestron or NOTAR system give the aircraft. Eventually you will learn how to fly on windy days, and be able to handle more wind/turbulence as your experience and skill level increases. You will also be more comfortable about saying "sorry, not that peak today".The approach is vital. If you can't get the aircraft to set-up 'smoothly' on the approach... the landing will be a disaster. "Smoothly" is a relative term depending on all the factors mentioned above. Even if a wind is strong and/or rough, you may still be able to land if it is predictable.A recce flight on your approach path (which always features an abort route) will tell you so much. And a second recce will tell you MORE than twice as much !! If you can't figure-out what the wind is doing after a few recces......go somewhere else.WC Fields said, "If at first you don't succeed, try again. If that doesn't work...give up, 'cos there's no point in making a fool of yourself." Be careful out there. Wow !!! very usefull info there OT....thank you! --------------------Quebec tower.....we got no problemGo to the top of the pageReport Post +Quote PostCJM91Rating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 02:52 PMPost #8 Member** Group: MemberPosts: 15Joined: 11-June 08From: Vancouver IslandMember No.: 4,623 QUOTE (Over-Talk @ Mar 16 2009, 09:57 AM) *If you can't figure-out what the wind is doing after a few recces......go somewhere else.WC Fields said, "If at first you don't succeed, try again. If that doesn't work...give up, 'cos there's no point in making a fool of yourself."Be careful out there. Excellent, can't add much. My instructors used to say that the wind was more often your friend than not. * get close to the terrain. Contour fly tight to the hill to feel the wind there but always leave an exit path. * no steep approaches. Makes for less downward momentum to overcome on late final and less power changes, easier to sense the power required for the landing as you're gradually adding it on the way in. * be aware of the "demarkation line". This is the "line" separating the smooth, upflowing air on the upwind side of a ridge or cliff from the roiling air back from the lip. Stay out of the later. This may require a steeper approach in the smooth air or another spot! The demarkation line varies in steepness with wind speed and tends to lie down at higher speeds but at much higher speeds could be steeper with a strong flow up the cliff. I'm open to correction on this one from other moss backs! * explain a bit of this to your customers so they understand why you're rejecting one spot for another. I don't think we've been good as an industry with educating our customers about the limitations we face (weights, winds, experience, etc.). These vary daily, too. Does anyone have a "manual" or graphics on this? Great topic. Cheers . . . .Go to the top of the pageReport Post +Quote PostSkids UpRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 03:22 PMPost #9 Veteran Member***** Group: Veteran MemberPosts: 1,232Joined: 20-March 03From: OkanaganMember No.: 163 I was told once a hundred years ago, that if you thought about water flowing over and around the mountains, you would have a good idea of what to expect from the wind. It tends to give you a "good visual" of what you might encounter... Watch a creek full of rocks and boulders and you will see all the things that the wind does, from swirling, turbulence, eddies, and whatnot. --------------------Skids Up; The only way to FLY through life... Funny, I don't remember being absent minded....Go to the top of the pageReport Post +Quote PostsherpaRating: 0View Member ProfileAdd as FriendSend MessageFind Member's TopicsFind Member's Posts post Today, 04:46 PMPost #10 Newbie* Group: MemberPosts: 8Joined: 18-December 08From: all over the placeMember No.: 5,252 Good posts.On a turbulent day in the mountains, my favorite is the AS350B3. Hands down. Quote
Gomer Pylot Posted March 17, 2009 Report Posted March 17, 2009 (edited) In vortex ring state (incorrectly called settling with power) there is not a "major updraft through the rotor system", nor is there at 300fpm descent. The air is still being accelerated through the rotor downward, at a much higher rate than that. At a hover, the downwash may reach 1000fpm, depending on the model and the weight, mostly on the weight. Go down 300fpm, and the air is still being blown down, but you're starting to catch up with it, to some extent. In full vortex ring state, the air is still going down, but the rotor is descending into the downwash so that the vortices from the end of the rotor go up and come back onto the top of the rotor, and are accelerated downward through it again, at a much higher rate. The air is always going down, but it starts to go down at a very high rate. The only time you have airflow upward through the rotor system is in full autorotation. When you enter autorotation, the airflow changes from down to up. There is no updraft at any other time, assuming little or no airspeed. Above transitional lift, the airflow changes, and the downflow is on the downwind side of the disk. Under almost all conditions, the chance of the rotor being completely unloaded is nil. Reduced, yes, but I don't think it can be completely unloaded for long enough to cause damage unless the gusts are really extreme. The situation described by West Coaster is usually caused by the loss of translational lift. Going into a strong headwind, and then encountering a strong tailwind, or quartering wind, it's possible that you can wind up at an OGE hover for awhile, and there may not be enough power available for that. That's one of the dangers of a downwind takeoff - the rotor may be in translational lift at a hover, with a tailwind (the main rotor doesn't care which direction the wind is blowing at a hover), and when you accelerate forward, you lose translational lift, maybe without sufficient power to continue acceleration or to stop. It's similar for a downwind landing - you can end up at an OGE hover at altitude, without enough power to maintain it. Crashes have happened because of this. Edited March 17, 2009 by Gomer Pylot Quote
Whistlerpilot Posted March 17, 2009 Report Posted March 17, 2009 Thanks for your story WC. Sounded harrowing. GP that was a great succinct (sp?) explanation. I was talking to a really experienced heliski pilot about flying the 22 in gusty winds and updrafts and downdrafts just yesterday. He advised me that at some point flying in the mountains in a 22 I will get in a big updraft and that I should not dump collective and push forward which might be a panicky reaction. Instead keep pitch on the blades, and accept the climb to avoid getting into any disc unloaded situation. My understanding is that the updraft is not the problem so much as the pilots reaction to it. A few days ago we were heliskiing in clean air (not gusty) 40 kts outflow conditions. It was interesting to land generally flying sideways and backwards with really steep (almost vertical) approaches to avoid the wicked demarcation lines. Quote
West Coaster Posted March 17, 2009 Report Posted March 17, 2009 Thanks for your story WC. Sounded harrowing. Nothing a liberal application of toilet paper can't fix. Quote
choppedair Posted March 18, 2009 Report Posted March 18, 2009 A few days ago we were heliskiing in clean air (not gusty) 40 kts outflow conditions. It was interesting to land generally flying sideways and backwards with really steep (almost vertical) approaches to avoid the wicked demarcation lines. This is pretty similar to how I like to land on ridge lines or pinnacles on a very windy day. A lot of people seem to get into this state of thinking that they have to make their whole approach and landing into the wind, and it gets people into trouble when they're flying in the mountains with strong wind. Either they don't understand how the wind flows or they just get into a habit. I often prefer a "sideways" approach on to the ridgeline with the nose in the direction of the wind, relatively slow and steep. On the other hand I have a couple of LZ's in areas with steep terrain everywhere, and the LZ is in the middle of a hole almost completely surrounded by steep ridges. They can be pretty tricky on a very windy day. The R44 will float in the updrafts on days like that, you could easily split the needles trying to descend if you're not careful. Some times I will actually intentionally get in the down drafts to lose some altitude. With all of the heavy equipment operating (surface mines) it is really neat to see how the wind circulates on very windy days.With strong wind and a big ridge line, you can actually see a full circular rotation on the downwind side. The wind on the surface on the downwind side is often completely opposite of what it is on top of the ridge line.Anyway I guess we're straying well of topic now... hah! Quote
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