---------------------------------------------------------- RV-List Digest Archive --- Total Messages Posted Fri 12/30/11: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 11:11 AM - Re: RV7-List: Re: Dynon Skyview Airspeed Calibration... (M. Marcotte) 2. 11:11 AM - Re: Dynon Skyview Airspeed Calibration... (David Carter) 3. 11:59 AM - Re: Dynon Skyview Airspeed Calibration... (Chris Welsh) ________________________________ Message 1 _____________________________________ Time: 11:11:31 AM PST US From: "M. Marcotte" Subject: RV-List: Re: RV7-List: Re: Dynon Skyview Airspeed Calibration... I think one can calculate from the GPS numbers that you had a 14 MPH (approx) wind from the WNW and you were doing 182 TAS. Your IAS would appear to be 12 MPH too high. From: Matt Dralle Sent: Thursday, December 29, 2011 10:33 PM rv7-list@matronics.com ; rv10-list@matronics.com Subject: RV7-List: Re: Dynon Skyview Airspeed Calibration... At 07:39 PM 12/26/2011 Monday, you wrote: Dear Listers, I've been flying the new 10" Dynon Skyview in the RV-6 for a few weeks now and it seems like the airspeed is reading maybe 10mph fast. The GS always reads 10mph or more slower than the True airspeed, no matter which way I fly with respect to the current wind. Looking through the configuration options on the Skyview, I'm not seeing parameters to calibrate the airspeed. If the airspeed were *slow* compared to the GS, I could envision making adjustments to the Pitot tube to get it in better alignment with slipstream. But *fast* is a head scratcher. If there's no electronic configuration parameters to adjust, what do you do? Are there Pitot line "attenuators" like for RF in coax? ;-) Matt Listers, I went flying tonight in the RV-6 around sunset and took some airspeed numbers flying the four points of the compass. I let each direction normalize for about 2 minutes before taking the readings. I've still got my little black-tape washer deals on the static ports that I detailed in a previous email. Do these numbers make any sense? I set the altimeter to 30.15 (KLVK ATIS). I compared the Dynon altitude with the Garmin 696 GPS altitude. The Dynon was high by 100 ft. I used the Dynon altitude adjustment to set it to match the GPS (-100ft). The readings above were after this adjustment. - Matt "Red Dawg" Dralle RV-8 #82880 N998RV "Ruby Vixen" http://www.mattsrv8.com - Matt's Complete RV-8 Construction Log http://www.mattsrv8.com/Mishap - Landing Mishap Rebuild Log http://www.youtube.com/MattsRV8 - Matt's RV-8 HDTV YouTube Channel Status: 172+ Hours TTSN - Rebuilding Fuselage After Landing Mishap... RV-6 #20916 N360EM "The Flyer" http://www.mattsrv6.com - Matt's RV-6 Revitalization Log Status: 48+ Hours Since Purchase - Upgrades Complete; Now In Full Flyer Mode ________________________________ Message 2 _____________________________________ Time: 11:11:31 AM PST US From: "David Carter" Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... My ears perk up when I read of people comparing "barometric altitude readings" with "GPS altitude". . . . In winter the atmosphere shrinks and in summer it expands. Worded differently, the "pressure lapse rate" is not standard in hot or cold weather, so your baro altimeter isn't going to accurately show "altitude above MSL". . . . Flying F-100s in the 132nd TFW at Des Moines, Iowa, in the 1970s we used gun camera film extensively to measure our actual dive angles on various dive bomb events (low, medium, and high angle). . . . We modified standard Air Force charts and added horizontal lines to show release altitude. Then we began noticing that we were releasing below preplanned release altitude in winter (bombs hit long) and were releasing higher in summer (bombs hit short of aim point). We worked with Offutt AFB Weather and learned to use a "D Value chart" to plot actual amount of deviation (D value) of a "baro altitude" (pressure level) from where it would be on a standard day (with standard day pressure lapse rate). . . . It will be difficult to give a tutorial via e-mail to properly treat this issue. Perhaps if there were interest, I could add something to a small web page I have. GPS altitude is based on a mathematical model of the theoretical shape of the earth (ellipsoid), which is not a round ball, i.e., the earths radius is larger at the equater than at the poles. . . . I'm not sure but suspect GPS math models use actual "digital terrain database" values to refine the local "ground" elevation (MSL).. Kevin Horton?? Bottom line, be aware that GPS altitude will probably be closer to "real altitude" above Mean Sea Level than "baro altitude" in winter and in summer (i.e., on non-standard days of temperature and pressure lapse rates). You'd have to have a D Value chart and call a local weather station to get data points from their latest weather balloon releases to plot the error between "baro" altitude (what you read with correct local "SURFACE" altimeter setting) and actual (like with a radar altimeter) altitude. David Carter cell 409-718-2268 RV-6A N164RS (great airplane built by Ron Smith of Goodyear, AZ) ________________________________ Message 3 _____________________________________ Time: 11:59:04 AM PST US From: Chris Welsh Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... Here's a link explaining in more detail what David just pointed out. http://rogallo.co.uk/tutorials:differences-between-pressure-and-gps-altitude -chris ________________________________ From: David Carter Sent: Fri, December 30, 2011 11:07:19 AM Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... My ears perk up when I read of people comparing "barometric altitude readings" with "GPS altitude". . . . In winter the atmosphere shrinks and in summer it expands. Worded differently, the "pressure lapse rate" is not standard in hot or cold weather, so your baro altimeter isn't going to accurately show "altitude above MSL". . . . Flying F-100s in the 132nd TFW at Des Moines, Iowa, in the 1970s we used gun camera film extensively to measure our actual dive angles on various dive bomb events (low, medium, and high angle). . . . We modified standard Air Force charts and added horizontal lines to show release altitude. Then we began noticing that we were releasing below preplanned release altitude in winter (bombs hit long) and were releasing higher in summer (bombs hit short of aim point). We worked with Offutt AFB Weather and learned to use a "D Value chart" to plot actual amount of deviation (D value) of a "baro altitude" (pressure level) from where it would be on a standard day (with standard day pressure lapse rate). . . . It will be difficult to give a tutorial via e-mail to properly treat this issue. Perhaps if there were interest, I could add something to a small web page I have. GPS altitude is based on a mathematical model of the theoretical shape of the earth (ellipsoid), which is not a round ball, i.e., the earths radius is larger at the equater than at the poles. . . . I'm not sure but suspect GPS math models use actual "digital terrain database" values to refine the local "ground" elevation (MSL).. Kevin Horton?? Bottom line, be aware that GPS altitude will probably be closer to "real altitude" above Mean Sea Level than "baro altitude" in winter and in summer (i.e., on non-standard days of temperature and pressure lapse rates). You'd have to have a D Value chart and call a local weather station to get data points from their latest weather balloon releases to plot the error between "baro" altitude (what you read with correct local "SURFACE" altimeter setting) and actual (like with a radar altimeter) altitude. David Carter cell 409-718-2268 RV-6A N164RS (great airplane built by Ron Smith of Goodyear, AZ) ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message rv-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/RV-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/rv-list Browse Digests http://www.matronics.com/digest/rv-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.