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Old Jan 10, 2012, 11:46 AM
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I would like to see it, especially the pitot device and how accurately it can measure airspeed. There has been some discussion on this in other threads and I remember a German guy involved with vario design for models posting that it is very difficult to get accurate airspeed with the small scale of the pitot device for model use. Maybe someone can figure out how to get accurate airspeed and incorporate it in our talking vario so the pilot can get that information.

I would rather have audio information than visual on screen info. My ideal telemetry system would be my Sky Melody with airspeed info and the ability to modify the talking and shorten it down considerably. My big complaint with the Sky Melody is the length of time it takes the talking lady to give me information, I just want her to spit it out fast, like "1000 meters, 25knots" the END, should'nt be more than 3-4 seconds. Also true AGL though that can be worked around by using a chase vehicle GPS and is not really a big problem except for the south end of the Cal Valley course when the team I was on landed out with the vario telling us we were still 900 ft high.

I agree with John that all telemetry info is good but automatic control is not acceptable. The Aloft team was unbeatable on certain days with huge lift but on days with limited ceiling to thermals they did not dominate. Also thier setup allowed complete autonomous flight with the sailplane finding and centering thermals very well and the straight line flight between TP's was amazing, no human could ever fly that efficiently, but then that is the challenge and a big part of what XC is all about.

I would still like to experiment with a gyro on rudder to see how it helps with tracking thru tree tunnels and cutting corners but those problems can be overcome with experience and pilot skill so a gyro is probably not really needed but could be a safety device for less experienced pilots.

Steve
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Old Jan 10, 2012, 12:15 PM
yyz
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Steve makes some good points. The Sky Melody product is a good one but it takes too long for the gal to spit out the information (there's an unintended joke hiding in there somewhere). I particularly hate it when I'm trying to center up a thermal and she "interrupts" the vario tone. There's probably a Sky Panel setting for that. Long story short, the utterances need to be fast and to-the-point.

I'm pretty sure the Sky Melody/Panel uses concatenated vs synthesized speech so tuning the prosody of the "speaker" is a reasonable thing to ask SkyMelody to do.

I don't think accurate airspeed is going to be that difficult. With cross-country sized gliders, we're at the lower end of the UAVs currently in service and they obtain/require accurate airspeed data. Want to say that it's "not rocket science" but it's along that path.

I'm working on heading-to-turnpoint direction (as in guidance) from the "vario". Something like "Left to course 15 degrees" if you were on a line 15 degrees right of the next turnpoint. I think that would be very handy.

Interesting discussion,

Mike
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Old Jan 11, 2012, 05:03 AM
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Originally Posted by Dudley Dufort View Post
This reply is somewhat related in that it pertains to the technological side of our sport.

I'm still hoping to see someone develop a split GPS system. One that takes the GPS location of a plane and transmits that information to an in-car Magellan Roadmate type of device. The purpose would be to have visual display of the plane, in relation to the road, so you can "see" where it is and when the plane has made the turnpoint.

Now, I'd buy one of those. As a matter of fact, I'm prepared to send a deposit to anyone who's working on such a device.

Dudley
David Beach made one that transmits to Google Earth. Can drive and watch the plane on the screen. Really cool.
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Old Jan 11, 2012, 06:16 AM
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Originally Posted by tbroeski View Post
David Beach made one that transmits to Google Earth. Can drive and watch the plane on the screen. Really cool.
He's using XBee 900 MHZ modules that I gave to him. :-)

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Old Jan 11, 2012, 06:17 PM
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Originally Posted by yyz View Post
........I don't think accurate airspeed is going to be that difficult.
I mounted my pitot tube/pressure sensor to the outside of my truck and took voltage readings wherever I went for weeks. My coworkers just shook their heads. Repeatability was good and I found out what speed vehicles are now programmed not to exceed... This was all predicate on me using the truck interior as a static source. There's no such luck with a glider. So from my experiments, I'd say that the pitot tube and sensor are not a problem for good readings, the problem is a reliable/consistent static source and whether that will work from glider type to glider type.

Anker did you already have that worked out ?

Mike
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Old Jan 11, 2012, 06:22 PM
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Originally Posted by ThermalSeeker View Post
I mounted my pitot tube/pressure sensor to the outside of my truck and took voltage readings wherever I went for weeks. My coworkers just shook their heads. Repeatability was good and I found out what speed vehicles are now programmed not to exceed... This was all predicate on me using the truck interior as a static source. There's no such luck with a glider. So from my experiments, I'd say that the pitot tube and sensor are not a problem for good readings, the problem is a reliable/consistent static source and whether that will work from glider type to glider type.

Anker did you already have that worked out ?

Mike
No Mike, I don't,

I asked on the diydrones.com forum whether anybody had calibrated the combination pitot tube/sensor voltage output to airspeed and haven't received a response yet. If I don't get one I'll have to do what you did. My pitot tube has both a dynamic and a static port, so that's not a problem.

I plan to calibrate and test this weekend if I don't find someone who already has done it.

Anker
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Old Jan 11, 2012, 06:31 PM
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...My pitot tube has both a dynamic and a static port, so that's not a problem.
That's an excellent fix. It'll be the same that way from glider to glider.

All of my data, ie...speed vs voltage fell on a fairly flat curve and did so consistently. I was either going to solve the curve down to a formula or just have a lookup table from say 20 mph to 80 mph in 2mph increments. That wouldn't eat up too much storage space. At any rate, good luck

Mike
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Old Jan 11, 2012, 07:47 PM
yyz
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Originally Posted by Anker View Post
No Mike, I don't,

I asked on the diydrones.com forum whether anybody had calibrated the combination pitot tube/sensor voltage output to airspeed and haven't received a response yet. If I don't get one I'll have to do what you did. My pitot tube has both a dynamic and a static port, so that's not a problem.

I plan to calibrate and test this weekend if I don't find someone who already has done it.

Anker
PM user "FAKHREALAM". He builds a small board that has the static/pitot sensor and A/D with an SPI or I2C interface. Super nice guy and very helpful.

M
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Old Jan 14, 2012, 09:13 AM
Stealth Plane Works
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Two versions

After giving the feedback some thought I'm going to work on two versions:

  1. A telemetry version that allows you to select the desired airspeed on a slider and returns a telemetry signal back to a receiver indicating whether you are flying at the desired airspeed. The telemetry can be visual or audio. I would prefer the audio signal with high- and low-pitched sounds indicating higher and lower than dialed air speeds.
  2. An automatic version as described earlier.
Version 1 will introduce a human into the feedback loop as many of you have said is essential. It would still introduce a safety factor by indicating over- and under-speed situations when the plane is speced out or lost.


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Old Jan 15, 2012, 04:46 PM
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Back in 2006, I put together a telemetry system for our XC team. Our biggest problem was getting a consistant data transmission; using at that time, some Aerocomm tranceivers on 900MHz. The project was shelved due to these transmission issues. The XBee modules from Digi are a better choice now.

I was working on the airspeed portion of the sensor system and found that the airspeed to voltage (from the pressure sensor) was not exactly linear so I developed a lookup table from the calibrated values. I've included that table, charted, as well as some other useful PDFs.

The airspeed sensor consisted of a 0 - 5 inch H2O pressure sensor driving the 10 bit A/D of a PIC processor. I was using a Pitot tube with a built in static port. This 5 inch pressure senssor had way too much range for actual use - I would go with a much smaller one now.

To calibrate the sensor and generate the table I bought a 0-120 MPH speed gauge from Airplane Spruce. I plumbed the gauge into a "Y" connector connecting the gauge, the pressure sensor, and 60cc syringe which provided the pressure. I had the PIC spitting out the A/D values to my PC. I then just applied the pressure until the gauge read say 20MPH and then recorded the A/D value. Continuing I ran it to 70MPH and that is the chart I've provided.

If I were to do it again, I would go with a different sensor, possibly the one I specified here.

I hope this helps.

Cheers,

- Bob -
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Old Jan 15, 2012, 08:47 PM
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Originally Posted by HLGNut View Post
Back in 2006, I put together a telemetry system for our XC team. Our biggest problem was getting a consistant data transmission; using at that time, some Aerocomm tranceivers on 900MHz. The project was shelved due to these transmission issues. The XBee modules from Digi are a better choice now.

I was working on the airspeed portion of the sensor system and found that the airspeed to voltage (from the pressure sensor) was not exactly linear so I developed a lookup table from the calibrated values. I've included that table, charted, as well as some other useful PDFs.

The airspeed sensor consisted of a 0 - 5 inch H2O pressure sensor driving the 10 bit A/D of a PIC processor. I was using a Pitot tube with a built in static port. This 5 inch pressure senssor had way too much range for actual use - I would go with a much smaller one now.

To calibrate the sensor and generate the table I bought a 0-120 MPH speed gauge from Airplane Spruce. I plumbed the gauge into a "Y" connector connecting the gauge, the pressure sensor, and 60cc syringe which provided the pressure. I had the PIC spitting out the A/D values to my PC. I then just applied the pressure until the gauge read say 20MPH and then recorded the A/D value. Continuing I ran it to 70MPH and that is the chart I've provided.

If I were to do it again, I would go with a different sensor, possibly the one I specified here.

I hope this helps.

Cheers,

- Bob -
Great stuff, Bob,

Thanks a bunch, very helpful.

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Old Jan 15, 2012, 09:01 PM
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Freescale MPXV7002DP

I got the Freescale MPXV7002DP which seems to have about three times the sensitivity of the one you used. The ADC is only 10 bit, so I lose a bit there.

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Old Jan 21, 2012, 08:51 AM
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I definitely would attribute a part of ALOFT's success at Cal Valley to efficient cruise speed regulation.

With the measurements of the speed polar, it was clear the SBXC had a fairly narrow efficient speed range (see page 10). Plugging the numbers into the Speed to Fly equations showed it took a fairly decent thermal (400fpm) ahead to suggest flying faster than 30 kts and a whopper thermal (1100fpm) to suggest flying faster than 40 kts. On that thought, it was intriguing to watch some teams blow by us on the cruise, sometimes to their success and sometimes to our advantage. We had lots of things that weren't optimum about our strategy, but did suggest to me at the time folks may have been flying generally faster with SBXC's than was useful.

Coming back to the thread topic, I'm certain that having an onboard speed regulation device would be useful to help optimize cruise performance. To no small extent, the combination of static margin, declage, and airfoil selection do this kind of speed regulation in any current aircraft at some drag penalty and tweaking effort. The major difference I see is the partial shift of requiring an XC pilot be even more well rounded, to include management of a new device. Using a vario is certainly an acquired skill...

I had hoped that the OpenAltimeter project would also put out an OpenAirspeed board for this very purpose. Thanks Anker for stepping up to the plate! Quite excited to see the progression!

Dan
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Old Jan 21, 2012, 12:07 PM
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Originally Posted by danstrider View Post
I definitely would attribute a part of ALOFT's success at Cal Valley to efficient cruise speed regulation.

With the measurements of the speed polar, it was clear the SBXC had a fairly narrow efficient speed range (see page 10). Plugging the numbers into the Speed to Fly equations showed it took a fairly decent thermal (400fpm) ahead to suggest flying faster than 30 kts and a whopper thermal (1100fpm) to suggest flying faster than 40 kts. On that thought, it was intriguing to watch some teams blow by us on the cruise, sometimes to their success and sometimes to our advantage. We had lots of things that weren't optimum about our strategy, but did suggest to me at the time folks may have been flying generally faster with SBXC's than was useful.

Coming back to the thread topic, I'm certain that having an onboard speed regulation device would be useful to help optimize cruise performance. To no small extent, the combination of static margin, declage, and airfoil selection do this kind of speed regulation in any current aircraft at some drag penalty and tweaking effort. The major difference I see is the partial shift of requiring an XC pilot be even more well rounded, to include management of a new device. Using a vario is certainly an acquired skill...

I had hoped that the OpenAltimeter project would also put out an OpenAirspeed board for this very purpose. Thanks Anker for stepping up to the plate! Quite excited to see the progression!

Dan
Thanks Dan,

I am waiting for weather that's warm enough to allow me to calibrate the pitot tube and pressure sensor by holding the pitot tube at arms length out my car window or on some kind of support.

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Old Feb 04, 2012, 05:06 PM
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Anker.

I read you are searching for calibration data for airspeed measurement.
Have you already finished the job?

I can offer you data and some additional information but it is important to realize, calibration isn't possible without professional equipment. Without these equipment, action will be limited to determine the air speed at theoretical 100 % signal of the electronic part.

In your case we can calculate that full range related to average barometric pressure, temperature and humidity of your environment and expected differential pressure of the pitot tube.

To have a real accurate measurement which is needed for your application IMO, your electronic differential pressure instrument and the pitot tube have to be calibrated, with use of master instruments at several signal levels.

Picture I show; airspeed transmitter I use in my replica Top Flite Taurus for air speed control! and data logging.

Cees
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