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#11
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Eric Greenwell wrote in message ...
Charles Yeates wrote: Maybe it is simply an ergonomics thing --- I feel more comfortable circling to the right in clutch situations simply because it is easier to pull and adjust rather than push and adjust in right turns. For me, it's just habit: when I was learning to fly, we'd always get off tow in a thermal; since we'd always depart tow with a turn to the right, it was easiest to just continue turning right in the thermal. For a few flights before a contest, I'll make an effort to fly at least half my thermals to the left, so I'm ready for the left turns required at US contests near the start and at turnpoints. I know a few competition pilots that are definitely "handed", I will make it a point, when they are in my area, to turn in the direction, they least prefer. Thanks, Eric |
#12
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Two out of three thermals (very unscientific study on my part) favor a
right turn. This is the result of the internal circulation of the thermal. This adds yet another variable to the complexity of thermalling. I'll leave it up to you to figure out how lift strength, horizontal and vertical lift profile, vorticity, and turn direction affect climb performance. Suffice to say in this short note that they do. There was a discussion in Soaring (maybe 15 years ago) on this subject, with a nay sayer concluding, if thermals had spiral circulation, you could look up and see clouds rotating. Well, I spent an hour on my back the following weekend and found that they did, and favored clockwise 2 to 1. I use the right hand rule. By pointing my thumb up (lift) and curling my fingers (as in induction fields), I can determine with about 66% probability the direction of rotation of the thermal as a whole. A friend of mine (no longer an active glider pilot) used to keep a careful watch on his yaw string as he entered thermals. He felt that you could briefly see the direction of rotation and planned his centering turn in the same direction as its initial deflection. A talented pilot, I took careful note, though I admit I've defaulted to always using a right turn unless there are clear indications that I should turn left (noticeable yaw string deflection, birds, other gliders, visible shear beneath cloudbase, a dramatic surge up of the right wing, etc.) As a side note, I've found that reversing direction is a useful technique for climbing through a shear. This may be a result of reverasal of rotation at the top of the inversion layer, but that's just a guess. OC |
#13
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Eric Greenwell wrote in message ...
Charles Yeates wrote: Maybe it is simply an ergonomics thing --- I feel more comfortable circling to the right in clutch situations simply because it is easier to pull and adjust rather than push and adjust in right turns. For me, it's just habit: when I was learning to fly, we'd always get off tow in a thermal; since we'd always depart tow with a turn to the right, it was easiest to just continue turning right in the thermal. For a few flights before a contest, I'll make an effort to fly at least half my thermals to the left, so I'm ready for the left turns required at US contests near the start and at turnpoints. In Finland we consider it aerobatics to fly right turn in a termal. |
#14
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Chris OCallaghan wrote:
Two out of three thermals (very unscientific study on my part) favor a right turn. This is the result of the internal circulation of the thermal. This adds yet another variable to the complexity of thermalling. I'll leave it up to you to figure out how lift strength, horizontal and vertical lift profile, vorticity, and turn direction affect climb performance. Suffice to say in this short note that they do. There was a discussion in Soaring (maybe 15 years ago) on this subject, with a nay sayer concluding, if thermals had spiral circulation, you could look up and see clouds rotating. Well, I spent an hour on my back the following weekend and found that they did, and favored clockwise 2 to 1. Where do you fly? I've never seen clouds rotating, and I've been soaring for 25 years. I have seen dust and other objects in thermals rotating several thousand feet AGL. -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#15
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Agreed. Circling direction is more often dictated by other gliders in the thermal than meteorological phenomena and physics. The protocol I was taught was that unless you are first into the thermal, you follow the left or right pattern of the gliders already there. I've never had a preference of right or left. I was taught to turn into whichever wingtip went up. I was also taught that the most efficient technique, that is the highest rate of altitude gain, is in a 45-degree bank turn hopefully "coring" the thermal. Up here in the Mojave Desert flying out of IYK, I've been in a couple of 10 Knot thermals but 5 to 6 is the most common. I can't ever remember any kind of cyclonic rotation of any of them. That said, I did once, inadvertantly fly into a dust-devil. I NEVER want to do that again. If I had seen any dust indication that it was there I would definitely have avoided it in the first place. |
#16
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Chris OCallaghan wrote:
There was a discussion in Soaring (maybe 15 years ago) on this subject, with a nay sayer concluding, if thermals had spiral circulation, you could look up and see clouds rotating. Well, I spent an hour on my back the following weekend and found that they did, and favored clockwise 2 to 1. I use the right hand rule. By pointing my thumb up (lift) and curling my fingers (as in induction fields), I can determine with about 66% probability the direction of rotation of the thermal as a whole. Jack Glendening, among others, have discounted the idea that something as small as a thermal rotates in a particular direction due to any Coriolis forces. However, I carefully examined my .igc files for extended climbs in thermals, and found that my climb looks like a "corkscrew." I'm not talking about the path of the glider, but the center of the thermal at the various altitudes. As far as I can tell, this had nothing to do with the direction the wind rotates in the thermal, but is simply the thermal itself not going "up" straight (or even slanted evenly due to wind). So perhaps coriolis affects the thermal, or perhaps it affects the way the GPS readings are determined. In either case, I'll need to go back and look again at these traces. Has anyone else noticed that the core of the thermal they are climbing in seems to rise like a corkscrew with altitude? Does anyone have a hypothesis about if it is an effect on the thermal, or on the GPS? |
#17
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On Mon, 29 Dec 2003 02:02:43 GMT, "Casey Wilson"
wrote: That said, I did once, inadvertantly fly into a dust-devil. I NEVER want to do that again. If I had seen any dust indication that it was there I would definitely have avoided it in the first place. Could you tell more please? This is one of the things that I've been thinking about for a long time. Bye Andreas |
#18
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Casey Wilson wrote:
That said, I did once, inadvertantly fly into a dust-devil. I NEVER want to do that again. If I had seen any dust indication that it was there I would definitely have avoided it in the first place. No dust, no dust devil! But, of course, the thermal can still be there. Coming into one low can be dangerous, but up here in eastern Washington State, we use them frequently, especially on blue days. They are usually quite tame. Only the biggest are potentially dangerous, and then only when "near" the ground (say, less then 1500 feet AGL). What you are flying makes a difference, too: a 1-26 is going to be tossed around a lot more than an ASW 20 with ballast. Flying faster than the normal thermalling speed helps quite a bit if the thermal is rough. -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#19
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"Mark James Boyd" wrote in message news:3fefacf7$1@darkstar... Chris OCallaghan wrote: There was a discussion in Soaring (maybe 15 years ago) on this subject, with a nay sayer concluding, if thermals had spiral circulation, you could look up and see clouds rotating. Well, I spent an hour on my back the following weekend and found that they did, and favored clockwise 2 to 1. I use the right hand rule. By pointing my thumb up (lift) and curling my fingers (as in induction fields), I can determine with about 66% probability the direction of rotation of the thermal as a whole. Jack Glendening, among others, have discounted the idea that something as small as a thermal rotates in a particular direction due to any Coriolis forces. However, I carefully examined my .igc files for extended climbs in thermals, and found that my climb looks like a "corkscrew." I'm not talking about the path of the glider, but the center of the thermal at the various altitudes. As far as I can tell, this had nothing to do with the direction the wind rotates in the thermal, but is simply the thermal itself not going "up" straight (or even slanted evenly due to wind). So perhaps coriolis affects the thermal, or perhaps it affects the way the GPS readings are determined. In either case, I'll need to go back and look again at these traces. Has anyone else noticed that the core of the thermal they are climbing in seems to rise like a corkscrew with altitude? Does anyone have a hypothesis about if it is an effect on the thermal, or on the GPS? According to some published research by Wayne Angevine, http://cires.colorado.edu/ and NOAA, and the results of analysing thermic activity with lidar and IR methods in the mid-1990's, you might do better to think of thermals as plume-like. You may transit one or more plumes in a thermaling turn and plumes may merge into larger plumes while rising. Merging would seem to account for those lateral shifts, strengthening gusts, and some rotational effects. Transiting multiple smaller plumes might explain why some thermals appear to have two or more 'cores' or are hard to center. Wayne spoke at our club on this a few years back. His article was published in one of the model magazines and research presented at the CIRES gatherings. One of his grad student researchers was a collegiate member of our club during this period. Wayne's specialty is atmospheric boundary layer physics. Frank Whiteley |
#20
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http://www.rc-soar.com/tech/thermals.htm
Early version of Wayne's work. He presented us with quite a detailed display of a cubic mile of atmospheric activity. Frank "F.L. Whiteley" wrote in message ... "Mark James Boyd" wrote in message news:3fefacf7$1@darkstar... Chris OCallaghan wrote: There was a discussion in Soaring (maybe 15 years ago) on this subject, with a nay sayer concluding, if thermals had spiral circulation, you could look up and see clouds rotating. Well, I spent an hour on my back the following weekend and found that they did, and favored clockwise 2 to 1. I use the right hand rule. By pointing my thumb up (lift) and curling my fingers (as in induction fields), I can determine with about 66% probability the direction of rotation of the thermal as a whole. Jack Glendening, among others, have discounted the idea that something as small as a thermal rotates in a particular direction due to any Coriolis forces. However, I carefully examined my .igc files for extended climbs in thermals, and found that my climb looks like a "corkscrew." I'm not talking about the path of the glider, but the center of the thermal at the various altitudes. As far as I can tell, this had nothing to do with the direction the wind rotates in the thermal, but is simply the thermal itself not going "up" straight (or even slanted evenly due to wind). So perhaps coriolis affects the thermal, or perhaps it affects the way the GPS readings are determined. In either case, I'll need to go back and look again at these traces. Has anyone else noticed that the core of the thermal they are climbing in seems to rise like a corkscrew with altitude? Does anyone have a hypothesis about if it is an effect on the thermal, or on the GPS? According to some published research by Wayne Angevine, http://cires.colorado.edu/ and NOAA, and the results of analysing thermic activity with lidar and IR methods in the mid-1990's, you might do better to think of thermals as plume-like. You may transit one or more plumes in a thermaling turn and plumes may merge into larger plumes while rising. Merging would seem to account for those lateral shifts, strengthening gusts, and some rotational effects. Transiting multiple smaller plumes might explain why some thermals appear to have two or more 'cores' or are hard to center. Wayne spoke at our club on this a few years back. His article was published in one of the model magazines and research presented at the CIRES gatherings. One of his grad student researchers was a collegiate member of our club during this period. Wayne's specialty is atmospheric boundary layer physics. Frank Whiteley |
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