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#31
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JLR-10 GPS Compass
http://www.jrcamerica.com/product.asp?Product_Id=17778 Furuno SC-50 http://www.maritech.com/satellite_compass.htm both around US$ 3500. And we complain about the cost of loggers! Ian "Bill Daniels" wrote in message news:eb3Cc.94362$Sw.26496@attbi_s51... "Dave Houlton" wrote in message ... Derrick Steed wrote: Isn't there some form of flux gate compass which can be used? The GPS's we use originated in the maritime market (after NMEA is a maritime standard), surely there is a flux gate compass with NMEA output. Rgds, Derrick. Hi, Bill. The Garmin eTrex Vista includes GPS, barometric altitude, and electronic compass. IIRC all the above data are output on the serial interface as NMEA or Garmin sentences. Can you get by with +- 2 degrees heading accuracy? No idea how big the dip error is when wings banked, but maybe your flight computer could be smart enough to use the compass when straight & level and switch to turning-base wind calculation when banked? http://www.garmin.com/products/etrexVista/spec.html Dave The "compass" on many handheld GPS units really shows ground track although I think some of them have electronic flux gate compasses. To compute true wind data you need four inputs: True Heading, True Airspeed, Ground Speed and Ground Track. We only need to add heading to get true wind info. There are fluxgate and other magnetoresistive sensors that use the earth magnetic field to determine heading. The $500 NMEA marine units would probably work but they suffer from all the problems that any magnetic compass has. There are other clever devices that detect the magnetic field in three axes and, with the GPS position data and a look-up table, subtract the variation and dip errors to output true north. I still like the idea of a double-headed GPS receiver with two antennas a meter apart on the fuselage centerline. These should be good to a half degree accuracy. If you add MEMS gyros for a "coast through" in the event of a GPS signal interruption, you have an elegant heading sensor. Bill Daniels |
#32
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#33
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Nope, thats a fluxgate compass and subject to all the normal magnetic
compass influences. What was suggested was a dual antenna GPS heading sensor, a completely different beast. Ian "Scott" wrote in message ... Here is what you are looking for. http://www.filser.de/main.php?dat=e_...7000pi#compass |
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