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#21
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TE probe up or down?
On Sep 27, 11:46*am, "Tim Mara" wrote:
Pete Russel (former SAGE Variometer maker) tested TE probes in all directions..Pete reported it worked equally as well off to the left or right as it did up or down.... Its completely dependent on the glider and the length of the probe... In general, UP is much preferred. See ya, Dave |
#22
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TE probe up or down?
"Rolf" wrote in message ... On Sep 27, 5:13 am, "kirk.stant" wrote: It's raining at the field today so here is a serious soaring question to ponder: Should the end of the TE probe on the fin point up or down? Informal surveys at recent contests seem to show a slight preference for up (not counting those "swingers" that go both ways). I've heard all sorts of reasons why each orientation is best - angle of attack during pull-ups, airflow in front of the tail, G-effects on the air column, blah blah blah... I point mine up so I don't snag it when taking off the tail dolly! Comments? Kirk Wet in IL Well, your very own Oran W. Nicks describes the development of the probe in your "Soaring" magazine of September 1976. He definitely has the probe pointing up. As he is the inventor and arrived at the configuration in extensive wind tunnel tests that settles it for me. Rolf And Professor Irving, who developed two different designs, shows his pointed down, and 20 degrees forward. Professor Irving also used wind tunnel testing. So there! Hartley Falbaum "KF" USA |
#23
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TE probe up or down?
This is pure speculation, but I wonder if Prof Frank Irving’s
preference for the probe pointing downwards is because in his day, and particularly in the UK, cloud flying was commonplace. It follows that accumulation of water droplets on the probe was also, common. After only a few minutes in cloud, it is usual to find that the vario starts misbehaving. (I find that typically, it suddenly stops displaying rate of climb accurately, and then flicks to a different reading, then settles back to something sensible for a few seconds, and then repeats the cycle. I put this down to water droplets accumulating, to the point that they block the tiny holes in the probe, then suddenly get freed, then repeat the cycle. I have no means of knowing whether my speculation in this respect is accurate.) Anything that can delay that, or at least get rid of surplus water droplets so that the vario returns to functionality for a few seconds at a time, is probably worth doing. If you're not flying where water droplets are likely to accumulate on the probe, other things being equal it seems to me that keeping it as far from disturbed air over the wings as possible is a good thing, hence up. Just my two cents worth. Chris N |
#24
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TE probe up or down?
On Sep 28, 10:45*am, Chris Nicholas wrote:
This is pure speculation, but I wonder if Prof Frank Irving’s preference for the probe pointing downwards is because in his day, and particularly in the UK, cloud flying was commonplace. It follows that accumulation of water droplets on the probe was also, common. *After only a few minutes in cloud, it is usual to find that the vario starts misbehaving. (I find that typically, it suddenly stops displaying rate of climb accurately, and then flicks to a different reading, then settles back to something sensible for a few seconds, and then repeats the cycle. I put this down to water droplets accumulating, to the point that they block the tiny holes in the probe, then suddenly get freed, then repeat the cycle. I have no means of knowing whether my speculation in this respect is accurate.) *Anything that can delay that, or at least get rid of surplus water droplets so that the vario returns to functionality for a few seconds at a time, is probably worth doing. If you're not flying where water droplets are likely to accumulate on the probe, other things being equal it seems to me that keeping it as far from disturbed air over the wings as possible is a good thing, hence up. Just my two cents worth. Chris N Gliders with short rear fuselage mounted TE probes often suffer from a flickering and false vario reading when flown at high angles of attack, as in a thermalling turn. I assume that this is because of interference from turbulent air coming off the wings. I have also experienced this effect with some fin mounted probes. I would point the probe upwards to keep it as clear as possible from any wing turbulence. Derek C |
#25
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TE probe up or down?
At 14:21 28 September 2010, Derek C wrote:
On Sep 28, 10:45=A0am, Chris Nicholas wrote: This is pure speculation, but I wonder if Prof Frank Irving=92s preference for the probe pointing downwards is because in his day, and particularly in the UK, cloud flying was commonplace. It follows that accumulation of water droplets on the probe was also, common. =A0After only a few minutes in cloud, it is usual to find that the vario starts misbehaving. (I find that typically, it suddenly stops displaying rate of climb accurately, and then flicks to a different reading, then settles back to something sensible for a few seconds, and then repeats the cycle. I put this down to water droplets accumulating, to the point that they block the tiny holes in the probe, then suddenly get freed, then repeat the cycle. I have no means of knowing whether my speculation in this respect is accurate.) =A0Anything that can delay that, or at least get rid of surplus water droplets so that the vario returns to functionality for a few seconds at a time, is probably worth doing. If you're not flying where water droplets are likely to accumulate on the probe, other things being equal it seems to me that keeping it as far from disturbed air over the wings as possible is a good thing, hence up. Just my two cents worth. Chris N Gliders with short rear fuselage mounted TE probes often suffer from a flickering and false vario reading when flown at high angles of attack, as in a thermalling turn. I assume that this is because of interference from turbulent air coming off the wings. I have also experienced this effect with some fin mounted probes. I would point the probe upwards to keep it as clear as possible from any wing turbulence. Derek C We use to use a nose mounted probe on a K18 I flew,not sure how good it was, but the yaw string mounted on it was much better as it didn't over react as much. Jon |
#26
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TE probe up or down?
You probably had the string tied around the holes that make the thing work.
The yarn sucked away the moisture from the holes so that they could continue to work and that moisture in the yaw string caused it to be heavier and thus not fluctuate so much. That is good theory! At 07:42 29 September 2010, Jonathon May wrote: At 14:21 28 September 2010, Derek C wrote: On Sep 28, 10:45=A0am, Chris Nicholas wrote: This is pure speculation, but I wonder if Prof Frank Irving=92s preference for the probe pointing downwards is because in his day, and particularly in the UK, cloud flying was commonplace. It follows that accumulation of water droplets on the probe was also, common. =A0After only a few minutes in cloud, it is usual to find that the vario starts misbehaving. (I find that typically, it suddenly stops displaying rate of climb accurately, and then flicks to a different reading, then settles back to something sensible for a few seconds, and then repeats the cycle. I put this down to water droplets accumulating, to the point that they block the tiny holes in the probe, then suddenly get freed, then repeat the cycle. I have no means of knowing whether my speculation in this respect is accurate.) =A0Anything that can delay that, or at least get rid of surplus water droplets so that the vario returns to functionality for a few seconds at a time, is probably worth doing. If you're not flying where water droplets are likely to accumulate on the probe, other things being equal it seems to me that keeping it as far from disturbed air over the wings as possible is a good thing, hence up. Just my two cents worth. Chris N Gliders with short rear fuselage mounted TE probes often suffer from a flickering and false vario reading when flown at high angles of attack, as in a thermalling turn. I assume that this is because of interference from turbulent air coming off the wings. I have also experienced this effect with some fin mounted probes. I would point the probe upwards to keep it as clear as possible from any wing turbulence. Derek C We use to use a nose mounted probe on a K18 I flew,not sure how good it was, but the yaw string mounted on it was much better as it didn't over react as much. Jon |
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