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#1
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String in the middle does not protect you from a spin
I think the recent threads on spinning have been wonderful. I find
them a great help to focusing on such an important issue. Somewhere in my dark student-pilot experiences I was shown that coordinated flight, with the yaw string kept carefully in the middle, does not guarantee against spin entry. As I recall, it was pointed out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. |
#2
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"Jim" wrote in message news I think the recent threads on spinning have been wonderful. I find them a great help to focusing on such an important issue. Somewhere in my dark student-pilot experiences I was shown that coordinated flight, with the yaw string kept carefully in the middle, does not guarantee against spin entry. As I recall, it was pointed out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. Your analysis is correct. Dick Johnson makes a persuasive case for flying thermals with the yaw string deflected slightly toward the high wing. Dick says this in not only safer, it is aerodynamically more efficient. Bill Daniels |
#3
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On Wed, 28 Jan 2004 10:57:47 -0700, Bill Daniels wrote:
Dick Johnson makes a persuasive case for flying thermals with the yaw string deflected slightly toward the high wing. Dick says this in not only safer, it is aerodynamically more efficient. Bill Daniels I would love to read that article, could you post a link please? Henry Irvine -- Those willing to give up a little liberty for a little security deserve neither security nor liberty. ---- Benjamin Franklin |
#4
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"Henry Irvine" wrote in message news On Wed, 28 Jan 2004 10:57:47 -0700, Bill Daniels wrote: Dick Johnson makes a persuasive case for flying thermals with the yaw string deflected slightly toward the high wing. Dick says this in not only safer, it is aerodynamically more efficient. Bill Daniels I would love to read that article, could you post a link please? Henry Irvine -- Those willing to give up a little liberty for a little security deserve neither security nor liberty. ---- Benjamin Franklin I didn't read an article, I just heard him say it at Hobbs. Bill Daniels |
#5
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Balanced flight (string in the middle) does not protect you from stalling or
a spin entry, but it helps. This is true both in straight flight and turning flight. Stalling is about angle of attack, above the critical angle you are stalled, below it you are not. Whether you are in balanced or unbalanced flight makes no difference to this. Spinning and spin entry are stalled manoeuvres, unstalled and they cannot happen, stalled and they may. If you are just below the stalled angle of attack, then unbalanced flight (slip or skid, string to one side) may stall part of the wing, so the glider will stall. If you are stalled and in unbalanced flight, then it is more likely that the stall will become a spin entry. Some types of glider will enter a spin even if stalled wings level in balanced flight, whether this happens may be affected by C. of G. position; different examples of the same type of glider may vary. Stalling in balanced flight when turning is more likely to result in a spin entry than when the wings are level. Any turbulence, roughness, gustiness or gradient in the air will increase the likelihood of stalling when close to the stall, and will increase the likelihood of a spin entry when stalled. Unbalanced flight makes it more difficult to sense and control the angle of attack, especially when close to the stall. Unbalanced flight can conceal the symptoms of the approaching stall. Derek Piggott wrote (5th February 1994): "I think lots of people still think that pro-spin controls means having a lot of rudder or aileron on and don't realise that the important thing is the stick position. If the stick is well back, spinable machines spin: without the stick being back they don't spin." In steady turning flight the stick will be further back for a particular angle of attack compared with straight flight. The angle of attack with the stick on the back stop in a steady turn will be lower than with the stick on the back stop in straight flight. These statements are not true when making a rapid entry into a turn. The change in stick position in steady turning flight is due to circular flow, as explained in "Understanding Gliding" by Derek Piggott, see chapter 2, use the index; the section is titled "Stalling in turns". However, note the section titled "The function of the elevator" earlier in the same chapter, note in particular where he says: "In a tight turn, the nose may even be a little lower than the normal cruising position but if the stick is being held well back near the end of its range, the angle of attack _is_ large and the aircraft _is_ close to the stall." When instructors are being trained in the U.K., a standard demonstration which every instructor must show is to get the glider to stall off a steep turn. The K13 shows this very well, it departs abruptly into a steep spin entry. Usually there is either only very subtle symptoms of what is about to happen, or no symptoms at all; other of course from the position and movement of the controls. The best book I know for basic "theory of flight", an understanding of angle of attack and the stall, and the importance of stick position and movement is still "Stick and Rudder" by Wolfgang Langewiesche published 1944. Fly safe, careful when you pull the stick! W.J. (Bill) Dean (U.K.). Remove "ic" to reply. "Jim" wrote in message news I think the recent threads on spinning have been wonderful. I find them a great help to focusing on such an important issue. Somewhere in my dark student-pilot experiences I was shown that coordinated flight, with the yaw string kept carefully in the middle, does not guarantee against spin entry. As I recall, it was pointed out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. |
#6
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W.J. (Bill) Dean (U.K.). wrote:
Balanced flight (string in the middle) does not protect you from stalling or a spin entry, but it helps. This is true both in straight flight and turning flight. Interesting problem. Reminds me of flying multi-engine noncenterline with one engine out, where to keep the string in the middle you have to fly with the ball to the side. So (my swag analysis) if you are in a right hand turn, the forces on the wings are as below, with the inner wing having more drag, because it is slower and must fly at a higher AOA (gained through aileron deflection). To counteract the forces now trying to rotate the aircraft, one must toss in some rudder. To then keep from side slipping, one must fly in what would feel like a skidded turn to balance all of the forces. | | | | | V H V ============================ H H H H --- ============ Does this make sense? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. true dat. |
#7
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At 18:00 28 January 2004, Bill Daniels wrote:
'Jim' wrote in message news I think the recent threads on spinning have been wonderful. I find them a great help to focusing on such an important issue. Somewhere in my dark student-pilot experiences I was shown that coordinated flight, with the yaw string kept carefully in the middle, does not guarantee against spin entry. As I recall, it was pointed out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. Your analysis is correct. Dick Johnson makes a persuasive case for flying thermals with the yaw string deflected slightly toward the high wing. Dick says this in not only safer, it is aerodynamically more efficient. Bill Daniels The yaw string is ahead of the line of the center of lift along the wing. This line is on the true radius of the turn. Any yaw string not directly on this line will be deflected to some extent in a turn. The two yaw strings on a two-seater will not show the same deflection in a turn; the one in front will be deflected further. |
#8
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Jim wrote:
out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. This is so, in theory, for a descending turn, and the other way around for a climbing turn. In power flying we are taught that from a descending turn you are more likely to spin in the direction of the turn and in the opposite direction from a climbing turn. All this is based on there being a certain amount of rotation around the longitudinal axis in a descending/climbing turn. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? A glider is of course always descending, in relation to the surrounding air mass, thus creating the effect described, but at the glide angles of modern gliders, as opposed to power planes, even in a steep turn, I'd expect the effect to be very small, perhaps too small to make any real difference (?), It would be interesting to hear whether anyone has been able to observe this in practice. And as somebody already pointed out somewhere in the spinning thread, in a steepish turn you can often (depending on the type of glider) fly with the stick on the back stop without ever slowing down to stalling speed, making it next to impossible to provoke this type of spin, even if possible in theory. CV |
#9
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This possibility was brought up deep in the bowels of another spin
thread. It a said, in essence, that the yaw string can be straight in a steep turn while the controls are crossed, to compensate for the overbanking tendency. If you are able to stall the aircraft in this condition, that may well lead to a spin. There are some mitigating factors, but I could see how one would develop. It will be at least 6 weeks before I can get out to experiment for myself, so any western or southern pilots who feel up to some flight testing, I'd be interested to hear your results. Be sure to let things develop for several seconds after the stall break so we know exactly what is going on. Insipient phases of spins and spiral dives are too easy to confuse. Jim wrote in message . .. I think the recent threads on spinning have been wonderful. I find them a great help to focusing on such an important issue. Somewhere in my dark student-pilot experiences I was shown that coordinated flight, with the yaw string kept carefully in the middle, does not guarantee against spin entry. As I recall, it was pointed out to me that even with the string in the middle, in a steep turn the inside wing is flying at a higher angle of attack than is the outer wing. If a stall is induced in such a steep turn the inside wing is likely to stall before the outside wing and thus will have higher drag than the outer wing and the glider will likely fall off over the inside wing. If confusion or inadequate skill or distraction get in the way of an immediate recovery the higher drag of the inside, falling wing may initiate an autorotation and possible spin entry. Does this seem like a real possibility? In any case, it instilled in me the knowledge that the yaw string is not an indicator of the relative angles of attack on the two wings. |
#10
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In article ,
Henry Irvine wrote: On Wed, 28 Jan 2004 10:57:47 -0700, Bill Daniels wrote: Dick Johnson makes a persuasive case for flying thermals with the yaw string deflected slightly toward the high wing. Dick says this in not only safer, it is aerodynamically more efficient. Bill Daniels I would love to read that article, could you post a link please? Henry Irvine Carl Herold mentions "slips in turns" at www.lvvsa.org/Training/LANDOUT-VER-2b.pdf briefly, but the rest of the article is WELL worth a looksie too...between Carl Herold, Dick Johnson, Jack Glendening, and Judy Ruprecht, this sport has really got some juice and some top-notch volunteers... |
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