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#31
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Speed of a vario
Fast vario example: https://youtu.be/XAjwVPRTxQE?t=120
CNv set to "0.5s" for both pointer and audio. Panel is badly underexposed, but you can see the orange needle of the old CNv display on left side. I have the vario set to suppress sink tones (I don't need to be scolded when I'm not climbing). What the TC refers to in this case is the low pass filter on the back end of the data stream. 0.5s effectively turns the low pass "off". There is plenty of digital filtering in front of this, and imo, it works quite well. I think it is about as fast as is useful for sailplanes. There's a reliable, repeatable sequence of boot in the bum followed a couple tenths of a second later by the audio for real thermals. If the boot is missing, that's a gust. It's very easy to train yourself to detect this difference (a good vario helps). Not yet released CNv color display at upper right (it's quite visible in real life), should be out soon. OT: At 2:25 you get a nice look at the Appalachian Trail as it ascends Old Speck Mountain just before plunging into Grafton Notch. We fly this route fairly often... but normally a bit higher :-). T8 |
#32
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Speed of a vario
On Tuesday, August 11, 2020 at 8:54:37 PM UTC-7, Eric Greenwell wrote:
jfitch wrote on 8/11/2020 8:22 AM: On Tuesday, August 11, 2020 at 6:45:05 AM UTC-7, wrote: At 11:23 11 August 2020, s6 wrote: If I remember ok it is the time it takes to reach 80% of the thermal strength. Actually (1− 1/e) (approximately 63 percent) J. Also, the time constant of the electronics is after mechanical lags, so the delay may be somewhat longer. And then there is the time constant of the glider, which does not reach a steady upward speed immediately; ie, the glider is a mechanical filter for lift with, I'm guessing, a time constant between 1 second (low wing loading with stiff wings) and 3 seconds (high wing loading with bendy wings). Jon may have included the glider lag in his "mechanical lags". . -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 Yes, the glider is part of the mechanical lags. First a new angle of attack and/or airspeed has to establish over the wing. This itself has a time constant, as velocity gradients are always gradual. Then the wings bend. Then the fuselage begins to move - at that moment an inertial sensor can see it. After some movement the air in the tube from the triple probe begins to move. After some more time the hysteresis in the pressure sensor is overcome and it sends a signal to the electronics. From there the lags are electrical or software. I'm not convinced that your butt can tell the difference between a horizontal and vertical gust. Take as an example a gust from ahead. This will increase both lift and drag. A sharp edged 10 knot gust will give you approximately 1.36G kick. That is about the same as a 4 knot vertical gust. You may sort out which was which by differentiating airspeed, and I think that is what the Butterfly attempts to do in its inertial system. Your butt has no airspeed sensor. |
#33
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Speed of a vario
On Wednesday, August 12, 2020 at 12:35:39 PM UTC-4, jfitch wrote:
I'm not convinced that your butt can tell the difference between a horizontal and vertical gust. Take as an example a gust from ahead. This will increase both lift and drag. A sharp edged 10 knot gust will give you approximately 1.36G kick. That is about the same as a 4 knot vertical gust. You may sort out which was which by differentiating airspeed, and I think that is what the Butterfly attempts to do in its inertial system. Your butt has no airspeed sensor. Gusts, like the wind in general, are 3D. The "useless gusts" we've all encountered might well be horizontal plus vertical downwards. T8 |
#34
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Speed of a vario
On Monday, August 10, 2020 at 9:01:37 PM UTC-7, krasw wrote:
There seems to be a misconception about time constant of variometer. Many (all?) think that 2 sec time constant means that it takes 2 seconds after hitting thermal for variometer to show any lift. This is not true. Time constant means that within that time variometer needle reaches 100% of the pressure change signal. That does not mean that variometer needle does not start to show at least something (needle starts to rise) before that 2 secs. The traditional meaning of "time constant" is exponentially based: after one time constant you reach 63% of its final value, after two time constants this is up to 86%, after three it is 95%. You never reach the final value of 100%. |
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