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#1
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Turbulence
One of the things that TERRIFIED me for the longest time was turbulence.
In fact, the very reason why my wife bought me a "Discovery Flight" at the very beginning (and got me hooked to flying) was to get me to see that there was nothing to fear from planes, after me and her had a really bad (for me) flight back from Italy. Ok ... after a little less than 100 hours of flight I have had my dose of turbulence in flight ... while at the controls of a plane. It is reccommended that if you encounter turbulence you slow down below Va (manouvering speed), so if you encounter an especially stiff gust the plane will stall before pulling enough Gs to snap a wing. That's what the book says ... and I used to follow it to the letter, to the point that even the minimum turbulence would make me slow down to below Va. I remember once, during a mock checkride with a senior instructor we encountered some turbulence and I instinctively pulled the power to slow the plane below Va. The intructor's reaction was instantaneous and unyelding: "The hell are you doin'?" (Heavy Staten Island accent). "Slowing the plane below manouvering speed" I say, my tone of voice like that of a guy that has just been asked why the sun comes up in the morning. "Why?" "Ah .. " I stammer surprised by the question ... isn't it obvious why? "Because we are in turbulence?" it was supposed to be a statement but it came out as a question ... a sheepish question at that. The Instructor roars in laughter, for an instant louder than the engine. "Dude, this is not turbulence. Put that power back in. I want to see that needle at 2400 RPMs, in the RPM green arc." End of the argument. It was light turbulence with occasional moderate. It was one of those cold late winter days when winter is about to give up to spring but doesn't quite like the idea ... To me it felt like we were getting slammed. To him this wasn't even a tickle. Obviously our concepts of turbulence differed dramatically. So, question to the more seasoned and weathered pilots out the If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? I am just about done reading Rod Machado's IFR book and the bottom line is that you need to be inside a thunderstorm in order to start worrying about turbulence. In most conditions, just flying around VFR in your everyday CAT (Clear Air Turbulence) doesn't warrant fussing about it, and all you really have to do is just stay in the green arc. That's all. According to what the book is saying, only older planes really need to worry about Va in moderate turbulence. Modern planes (certified after 69) can fly right through it, as long as you stay in the green arc. I don't plan to fly into thunderstorms any time soon ... so, do I even need to worry about manouvering speed if I am just flying in one of those gusty fall or spring Northeast VFR days? Is staying below the green arc good enough? -- Marco Rispoli - NJ, USA / PP-ASEL My on-line aviation community - http://www.thepilotlounge.com |
#2
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Marco Rispoli wrote:
To me it felt like we were getting slammed. To him this wasn't even a tickle. Obviously our concepts of turbulence differed dramatically. To folks that haven't experienced a lot of turbulence, a little can seem like a lot. I gave a ride to a COZY builder who had never been in a small plane - he asked whether we were in moderate to severe turbulence when I hadn't really even noticed that we had hit a tiny burble. If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? Not really. I fly in the NE, like you do, and while I've experienced mild to moderate turbulence down low on VFR days, I've never really gotten hammered. Even when it __feels__ like I'm getting hammered, it's still considered moderate - go look up the definition of severe turbulence - basically, you can't control the plane. I don't plan to fly into thunderstorms any time soon ... so, do I even need to worry about manouvering speed if I am just flying in one of those gusty fall or spring Northeast VFR days? Nope. If you can keep the plane upright, there's no issue. Is staying below the green arc good enough? You mean red? Below the green arc, I don't think the plane will stay in the air :-). On my COZY (admittedly a homebuilt, but the concept is the same) the red arc begins at 220 mph IAS and the yellow arc begins at 140 mph IAS. Va is 140 mph, but I NEVER fly that slow - usually I'm cruising at about 175 - 180 mph IAS, no matter what the turbulence level (I'm VFR only). The only thing I slow down for in cruise is if the visibility sucks. -- Marc J. Zeitlin http://marc.zeitlin.home.comcast.net/ http://www.cozybuilders.org/ Copyright (c) 2004 |
#3
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You mean red? Below the green arc, I don't think the plane will stay in the air :-). Yea sorry. I meant below the yellow arc. Not below the green arc, but IN the green arc. Typo. Thanks for the info! -- Marco Rispoli - NJ, USA / PP-ASEL My on-line aviation community - http://www.thepilotlounge.com |
#4
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If I am in an area where moderate or greater turbulence can be expected (or
is possible) like desending to an airport in mountainous terrain with the wind howling, I slow down whether I am currently experiencing any turbulence or not. If I am flying along below small cumulus and experiencing some bumps, I don't slow down. There is nothing wrong with slowing down if you are uncomfortable. I would try to keep everything in the green arcs as much as possible though. Mike MU-2 "Marco Rispoli" wrote in message et... One of the things that TERRIFIED me for the longest time was turbulence. In fact, the very reason why my wife bought me a "Discovery Flight" at the very beginning (and got me hooked to flying) was to get me to see that there was nothing to fear from planes, after me and her had a really bad (for me) flight back from Italy. Ok ... after a little less than 100 hours of flight I have had my dose of turbulence in flight ... while at the controls of a plane. It is reccommended that if you encounter turbulence you slow down below Va (manouvering speed), so if you encounter an especially stiff gust the plane will stall before pulling enough Gs to snap a wing. That's what the book says ... and I used to follow it to the letter, to the point that even the minimum turbulence would make me slow down to below Va. I remember once, during a mock checkride with a senior instructor we encountered some turbulence and I instinctively pulled the power to slow the plane below Va. The intructor's reaction was instantaneous and unyelding: "The hell are you doin'?" (Heavy Staten Island accent). "Slowing the plane below manouvering speed" I say, my tone of voice like that of a guy that has just been asked why the sun comes up in the morning. "Why?" "Ah .. " I stammer surprised by the question ... isn't it obvious why? "Because we are in turbulence?" it was supposed to be a statement but it came out as a question ... a sheepish question at that. The Instructor roars in laughter, for an instant louder than the engine. "Dude, this is not turbulence. Put that power back in. I want to see that needle at 2400 RPMs, in the RPM green arc." End of the argument. It was light turbulence with occasional moderate. It was one of those cold late winter days when winter is about to give up to spring but doesn't quite like the idea ... To me it felt like we were getting slammed. To him this wasn't even a tickle. Obviously our concepts of turbulence differed dramatically. So, question to the more seasoned and weathered pilots out the If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? I am just about done reading Rod Machado's IFR book and the bottom line is that you need to be inside a thunderstorm in order to start worrying about turbulence. In most conditions, just flying around VFR in your everyday CAT (Clear Air Turbulence) doesn't warrant fussing about it, and all you really have to do is just stay in the green arc. That's all. According to what the book is saying, only older planes really need to worry about Va in moderate turbulence. Modern planes (certified after 69) can fly right through it, as long as you stay in the green arc. I don't plan to fly into thunderstorms any time soon ... so, do I even need to worry about manouvering speed if I am just flying in one of those gusty fall or spring Northeast VFR days? Is staying below the green arc good enough? -- Marco Rispoli - NJ, USA / PP-ASEL My on-line aviation community - http://www.thepilotlounge.com |
#5
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"Marco Rispoli" wrote in message
et... It is reccommended that if you encounter turbulence you slow down below Va (manouvering speed), so if you encounter an especially stiff gust the plane will stall before pulling enough Gs to snap a wing. Minor correction: the wings snap due to excessive lift (force), not due to excessive Gs (acceleration). Staying below Vne keeps the force from being excessive; staying below Va keeps the acceleration from being excessive. Vne does not vary with weight; Va varies in proportion to the square root of gross weight, becoming a stricter limit when weight is lower. That's because the less mass you have, the more acceleration is produced by a given force. If you don't feel more than 2G upward acceleration (or 1G downward) in turbulence, you're well within the acceleration design limits for a normal-category airplane. --Gary |
#6
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"Marco Rispoli" wrote in message et... One of the things that TERRIFIED me for the longest time was turbulence. In fact, the very reason why my wife bought me a "Discovery Flight" at the very beginning (and got me hooked to flying) was to get me to see that there was nothing to fear from planes, after me and her had a really bad (for me) flight back from Italy. Ok ... after a little less than 100 hours of flight I have had my dose of turbulence in flight ... while at the controls of a plane. It is reccommended that if you encounter turbulence you slow down below Va (manouvering speed), so if you encounter an especially stiff gust the plane will stall before pulling enough Gs to snap a wing. That's what the book says ... and I used to follow it to the letter, to the point that even the minimum turbulence would make me slow down to below Va. I remember once, during a mock checkride with a senior instructor we encountered some turbulence and I instinctively pulled the power to slow the plane below Va. The intructor's reaction was instantaneous and unyelding: "The hell are you doin'?" (Heavy Staten Island accent). "Slowing the plane below manouvering speed" I say, my tone of voice like that of a guy that has just been asked why the sun comes up in the morning. "Why?" "Ah .. " I stammer surprised by the question ... isn't it obvious why? "Because we are in turbulence?" it was supposed to be a statement but it came out as a question ... a sheepish question at that. The Instructor roars in laughter, for an instant louder than the engine. "Dude, this is not turbulence. Put that power back in. I want to see that needle at 2400 RPMs, in the RPM green arc." End of the argument. It was light turbulence with occasional moderate. It was one of those cold late winter days when winter is about to give up to spring but doesn't quite like the idea ... To me it felt like we were getting slammed. To him this wasn't even a tickle. Obviously our concepts of turbulence differed dramatically. So, question to the more seasoned and weathered pilots out the If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? I am just about done reading Rod Machado's IFR book and the bottom line is that you need to be inside a thunderstorm in order to start worrying about turbulence. In most conditions, just flying around VFR in your everyday CAT (Clear Air Turbulence) doesn't warrant fussing about it, and all you really have to do is just stay in the green arc. That's all. According to what the book is saying, only older planes really need to worry about Va in moderate turbulence. Modern planes (certified after 69) can fly right through it, as long as you stay in the green arc. I don't plan to fly into thunderstorms any time soon ... so, do I even need to worry about manouvering speed if I am just flying in one of those gusty fall or spring Northeast VFR days? Is staying below the green arc good enough? -- Marco Rispoli - NJ, USA / PP-ASEL My on-line aviation community - http://www.thepilotlounge.com I wonder what setting them pilots use when flying in to hurricane's now that has to be unsane and very turbulent. |
#7
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"Marco Rispoli" wrote in message
et... [...] If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? I guess you have to define "worry". If the air is bumpy, it always potentially could exceed the design limits of the airplane. For that matter, you could be flying along in completely smooth air and experience sudden and severe turbulence. In that respect, you should *always* worry about turbulence. It's always potentially there, and always potentially greater than the limits of the airplane. However, as others have mentioned, pilots, especially relatively inexperienced ones, typically overestimate the strength of turbulence. It's probably true that general bumpiness out in the open, away from severe weather (includes strong winds) and terrain is probably going to be safe at any normal cruise airspeed. That said, "away from" is an ambiguous term. Terrain can still be quite far away and still cause strong turbulence (50-100 miles or more in some cases). Similarly, strong winds can seem trouble-free for long distances, but due to wind shear result in very significant, isolated clear-air turbulence as you fly through an area where there's another fast-moving air mass going a different direction. I am just about done reading Rod Machado's IFR book and the bottom line is that you need to be inside a thunderstorm in order to start worrying about turbulence. In most conditions, just flying around VFR in your everyday CAT (Clear Air Turbulence) doesn't warrant fussing about it, and all you really have to do is just stay in the green arc. That's all. According to what the book is saying, only older planes really need to worry about Va in moderate turbulence. Modern planes (certified after 69) can fly right through it, as long as you stay in the green arc. I haven't read Machado's book, so I don't know what he says and what he doesn't. I would disagree that there's never any turbulence outside of a thunderstorm that you need to worry about, or that there's never any moderate turbulence in which newer planes might have a concern. Those kinds of absolutes seem troublesome to me. I don't plan to fly into thunderstorms any time soon ... so, do I even need to worry about manouvering speed if I am just flying in one of those gusty fall or spring Northeast VFR days? I would say that it's true that most of the time. Just make sure you are paying attention to winds aloft forecasts, especially comparing wind speed and direction changes over the various altitudes. Strong winds, or significant shear, can result in significant turbulence. I guess to me the thing to keep in mind is that continuous turbulence is unlikely to be the real issue. If you can stand the turbulence, the airplane can. Regardless of when it was built. The problem is that you could be flying along, tolerating the turbulence, and then run into something more significant. As Mike says, slowing down to match your comfort level is always a good thing. There's nothing worse than an anxious pilot. Even if you know the airplane can handle the turbulence, you need to be at ease. Even an older airplane is likely to be able to handle stronger turbulence than you feel comfortable with. The real question is whether you are potentially going to hit some strong turbulence without any warning. For this, the turbulence you're feeling now is less important than things like current and forecast weather and pilot reports. Bottom line: it's true that most pilots rarely, if ever, experience turbulence strong enough for Va to be a real issue. But it can happen, and usually it happens without warning. Furthermore, for both pilot and passenger comfort, it's helpful to slow down in turbulence, even if the airplane is in no danger of being hurt. As with all aviation decision making, being conservative is a fine thing with respect to flying at or below Va. For what it's worth, I think the chances of the wings falling off are the least of one's worries. More of an issue are all the other parts in the airplane that are important to a successful flight. It would still require some heavy turbulence to cause a problem, and I don't think this difference should mean that pilots should be braver in the face of turbulence. It's just an interesting academic aspect to the issue, IMHO. Pete |
#8
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"Gary Drescher" wrote in message
news:T_z9d.436094$8_6.136539@attbi_s04... Minor correction: the wings snap due to excessive lift (force), not due to excessive Gs (acceleration). Staying below Vne keeps the force from being excessive; staying below Va keeps the acceleration from being excessive. Vne does not vary with weight; Va varies in proportion to the square root of gross weight, becoming a stricter limit when weight is lower. That's because the less mass you have, the more acceleration is produced by a given force. IMHO, you are making things more confusing, not less. Yes, what will break the structure is force. But when we talk about "G's", typically we are describing a *factor* multiplied with the weight of the airplane, not "acceleration due to gravity". In that context, all "G's" means is "a factor increasing the nominal 1G force experienced by the airplane". For example, in a bank, lift needs to be increased in order to maintain vertical speed (i.e. prevent up or down acceleration), usually at zero. At a high enough bank angle (much higher than any normal operation would require), the "G's" exceed the certification limit. Those "G's" would be a static state, not due to acceleration of the airplane (if allowed to turn, the airplane would also be accelerating, but this acceleration isn't directly related to the "G's" experienced...if you could somehow counteract the lateral force caused by the increase in lift, the wings would still experience increased "G's", but the airplane would track straight ahead). Vne is not typically related to lifting force at all, but rather to other things like flight control flutter and longitudinal strength of airframe structures (e.g. drag pulling the wings backwards). In level flight, at any airspeed, the wing is generating exactly as much lift as there is weight of the airplane. The force (lift) is constant. Va, on the other hand, is related to a variety of other things. In the sense that those things have to do with rapid changes in airfoil loading, they are related to acceleration. But ultimately, those limits still have to do forces imposed on structure. The acceleration is relevant -- higher acceleration results in higher G forces on structure -- but the reason that Va changes due to weight has less to do with the distinction between "force", "G's", and "acceleration" and more to do with the fact that there are internal structures carrying loads that don't change with total gross weight of the airplane. It's true that "the less mass you have, the more acceleration is produced by a given force", but the reason this is relevant here is not because acceleration is the problem per se. Rather, it's because there are components in the airplane with a fixed load that, with the increase in total acceleration of the airplane, could experience loads higher than designed for. Because of these, the acceleration limit of the entire airframe needs to be held constant. If it weren't for that, increased acceleration would not be a problem, because the total load (force) at lower weights would be the same, and it's force that breaks things, not acceleration. As this relates to the original statement, Va is the only airspeed related to "keeping the force from being excessive". You can fly above Va and below Vne, and still create out-of-limit *force* on the airframe, enough to damage or even break the structure, simply by exerting too rapid a control movement (on the elevator, for example). Vne does nothing to prevent this; only Va does (and it's not perfect either...there exist gusts in nature than can still exceed the structural limits at or below Va). IMHO, arguing that Vne is only about force and Va is only about acceleration is misleading and only serves to confuse the issue. Ultimately, they are *both* about force imposed on various parts of the airframe structure; they just happen to be addressing different *force-related* issues. Pete |
#9
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Oops, major slip: I meant to say Vno, not Vne.
--Gary "Gary Drescher" wrote in message news:T_z9d.436094$8_6.136539@attbi_s04... "Marco Rispoli" wrote in message et... It is reccommended that if you encounter turbulence you slow down below Va (manouvering speed), so if you encounter an especially stiff gust the plane will stall before pulling enough Gs to snap a wing. Minor correction: the wings snap due to excessive lift (force), not due to excessive Gs (acceleration). Staying below Vne keeps the force from being excessive; staying below Va keeps the acceleration from being excessive. Vne does not vary with weight; Va varies in proportion to the square root of gross weight, becoming a stricter limit when weight is lower. That's because the less mass you have, the more acceleration is produced by a given force. If you don't feel more than 2G upward acceleration (or 1G downward) in turbulence, you're well within the acceleration design limits for a normal-category airplane. --Gary |
#10
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Marco Rispoli wrote:
If I am clear air (VFR), and I am not close to mountains (so I don't have to worry about mountain waves), and I am flying around in my little cutie Piper Cherokee 180 do I even need to worry about turbulence? First, mountain waves cause up and downdrafts, but they are as smooth as you can imagine. What you mean is rotor. Well, if you really want to know how turbulence really feels, go to your friendly glider operator somewhere in the mountains when there is wave and ask for a ride into a rotor. As a side effect, you will also learn what a "steep turn" is. Back to your question: There is no point in demonstrating how brave you are. If you feel uncomfortable, slow down to Va. there is nothing wrong in staying on the safe side. Stefan |
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