RV-List Digest Archive

Tue 01/03/12


Total Messages Posted: 2



Today's Message Index:
----------------------
 
     1. 09:18 PM - Re: Dynon Skyview Airspeed Calibration... (Jim Ayers)
     2. 09:47 PM - Re: Dynon Skyview Airspeed Calibration... (Kelly McMullen)
 
 
 


Message 1


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    Time: 09:18:48 PM PST US
    Subject: Re: Dynon Skyview Airspeed Calibration...
    From: Jim Ayers <lessdragprod@aol.com>
    >From your previous information, for my 2,200' foot altitude change from fie ld elevation to the ridge line, there is about a 9 foot altitude difference for each degree C difference from the standard temperature change. Where the 2,200' ridge line temperature should be 4 degree C lower than the tempe rature at the field elevation. Does this sound about right? My aircraft has a Dynon Heated Pitot tube with the AOA port. It has a Dyno n D-10A EFIS which provides TAS, OAT and Density Altitude read-out capabil ity. For the Pitot/Static system test, Dynon specifically states that the Pitot tube CAN NOT be used as part of the Pitot pressure test.. It appears for the heated Dynon Pitot tube that Pitot pressure being accura te could be a bad assumption. I am trying to identify the sources of error in my Pitot/Static system and how much each contributes to the error. The EFIS readout is 8 knots low at a 8.000' density altitude cruise compare d to the GPS TAS calculation. Jim Ayers -----Original Message----- From: Kevin Horton <khorton01@rogers.com> Sent: Mon, Jan 2, 2012 9:41 am Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... The classical test method that directly compares actual vs indicated altitu de is he "tower fly-by". Typically a camera is placed on top of a tower about 1 00 t high, with the tower abeam the middle of a long runway. The camera is ve ry ccurately aimed, and the geometry of the tower, camera lens, etc is very we ll nown so that the height of the aircraft above the runway can be determined from he images, assuming the aircraft accurately tracks down the runway centreli ne. he aircraft instrumentation system records the altitude, with a very accura te ime stamp. Ground instrumentation records the altitude and OAT at ground evel, and the camera images have an accurate time stamp. Post flight analy sis s used to determine the actual vs indicated altitude as the aircraft passes by he tower at a range of airspeeds. This is used by some major test centres, but t is not practical for us as it requires too much specialized equipment to chieve reasonable accuracy. The method that is most practical for us is the speed course method (someti mes alled ground course method). It assumes that the pitot pressure is accurat e, hich is a reasonable assumption, and there are no static or pitot leaks, wh ich an be confirmed by ground test. The ASI instrument error must be measured. he TAS is measured using one of several possible methods (GPS data from a f our ourse box pattern is the current best method), and the CAS is back calculat ed rom the TAS, indicated altitude and OAT. The difference between CAS and IA S corrected for instrument error) must be due to static source position error . More info: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/l ist/AC%2023-8B/$FILE/Final-Part8.pdf http://www.kilohotel.com/rv8/rvlinks/ssec.html Kevin Horton On 2012-01-02, at 10:35 , Jim Ayers wrote: > Do you have a test method that we can all use to calibrate the alimeter at ruise speed? The altimeter only has the static system for its input. Calibrating the static vents in cruise conditions for the altimeter could rovide a correction for airspeed readout errors. Correcting airspeed readouts errors by changing the static vent geometery eaves your altitude readings at cruise speeds as a total unknown. Jim Ayers -----Original Message----- From: Kevin Horton <khorton01@rogers.com> To: rv-list <rv-list@matronics.com> Sent: Tue, Dec 27, 2011 11:50 am Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > Checking altimeter accuracy against tops of ridge lines only works if the temperature is close to standard temperature. If the temperature differs from standard, the error is about 4 ft per 1000 ft per degree C of difference from standard temperature. E.g., if the top of the > ridge line is 2000 ft above the airport where the altimeter setting came from, > and the temperature is 15 deg C warmer than standard temperature, the ltimeter will read about 4/1000 * 2000 * 15 = 120 ft lower than the actual altitu de. See: http://bathursted.ccnb.nb.ca/vatcan/fir/moncton/WeeklyTopics/Archives/2004 0104/CurrentTopic.html http://44rf.com/misc/USAF_AIS_Cold_WX_Altimeter.ppt Kevin Horton On 2011-12-27, at 12:44 , Jim Ayers wrote: > An easy way to check the static side of the airspeed indicator is to use our altimeter. > > I flew along a ridge line at cruise speed that has a 2200 feet peak as s hown > on my sectional. > > I may not have been exactly at the same level. Could have been 10 or 20 eet off in hieght. My altimeter read 2,210 feet. > So, at that time, my static system was pretty close. > > Jim Ayers > Less Drag Special sn 1 (Modified HR2) > > -----Original Message----- > From: David Maib < dmaib@mac.com > > To: rv-list < rv-list@matronics.com > > Sent: Mon, Dec 26, 2011 8:03 pm > Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > dmaib@mac.com > > > > Maybe a static port error? Check out some of Kevin Horton's articles > in Kitplanes. Static port errors can, and do, cause "fast" errors. > IIRC, Kevin says that pitot alignment does not have to be very > precise to be pretty accurate. > > David Maib > Rv-10 40559 > Flying. > On Dec 26, 2011, at 10:39 PM, Matt Dralle wrote: > > dralle@matronics.com > > > > > > 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 > > > > - > > 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: 170+ Hours TTSN - Rebuilding Fuselage After Landing Mishap... > > > > RV-6 #20916 N360EM "The Flyer" > > > http://www.mattsrv6.com > - Matt's RV-6 Revitalization Log > > Status: 42+ Hours Since Purchase - Upgrades Complete; Now In Full > > Flyer Mode > > > > > > > > _blank>www.aeroelectric.com /" target=_blank>www.buildersbooks.com =_blank>www.homebuilthelp.com blank>http://www.matronics.com/contribution t=_blank>http://www.matronics.com/Navigator?RV-List p://forums.matronics.com blank>http://www.matronics.com/contribution http://www.matronics.com/Navigator?RV-List http://forums.matronics.com http://www.matronics.com/contribution -= - The RV-List Email Forum - -= Use the Matronics List Features Navigator to browse -= the many List utilities such as List Un/Subscription, -= Archive Search & Download, 7-Day Browse, Chat, FAQ, -= Photoshare, and much much more: - -= --> http://www.matronics.com/Navigator?RV-List - -======================== -= - MATRONICS WEB FORUMS - -= Same great content also available via the Web Forums! - -= --> http://forums.matronics.com - -======================== -= - List Contribution Web Site - -= Thank you for your generous support! -= -Matt Dralle, List Admin. -= --> http://www.matronics.com/contribution -========================


    Message 2


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    Time: 09:47:05 PM PST US
    From: Kelly McMullen <kellym@aviating.com>
    Subject: Re: Dynon Skyview Airspeed Calibration...
    Well, when a pitot is hooked up for a static system test, there is no pressure applied to the pitot. Rather it sees the same vacuum that the static port sees. This prevents the pitot from being exposed to much higher static pressure than the static side connection to the airspeed indicator. On old bellows airspeed steam gauge, you can damage the instrument by taking the static up to too high altitude causing the airspeed needle to peg at above max reading for the instrument. On 1/3/2012 10:10 PM, Jim Ayers wrote: > > My aircraft has a Dynon Heated Pitot tube with the AOA port. It has a > Dynon D-10A EFIS which provides TAS, OAT and Density > Altitude read-out capability. > For the Pitot/Static system test, Dynon specifically states that the > Pitot tube CAN NOT be used as part of the Pitot pressure test.. > It appears for the heated Dynon Pitot tube that Pitot > pressure being accurate could be a bad assumption. > I am trying to identify the sources of error in my Pitot/Static system > and how much each contributes to the error. > The EFIS readout is 8 knots low at a 8.000' density altitude cruise > compared to the GPS TAS calculation. > Jim Ayers > -----Original Message----- > From: Kevin Horton <khorton01@rogers.com> > To: rv-list <rv-list@matronics.com> > Sent: Mon, Jan 2, 2012 9:41 am > Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > > --> RV-List message posted by: Kevin Horton<khorton01@rogers.com <mailto:khorton01@rogers.com>> > > The classical test method that directly compares actual vs indicated altitude is > the "tower fly-by". Typically a camera is placed on top of a tower about 100 > ft high, with the tower abeam the middle of a long runway. The camera is very > accurately aimed, and the geometry of the tower, camera lens, etc is very well > known so that the height of the aircraft above the runway can be determined from > the images, assuming the aircraft accurately tracks down the runway centreline. > The aircraft instrumentation system records the altitude, with a very accurate > time stamp. Ground instrumentation records the altitude and OAT at ground > level, and the camera images have an accurate time stamp. Post flight analysis > is used to determine the actual vs indicated altitude as the aircraft passes by > the tower at a range of airspeeds. This is used by some major test centres, but > it is not practical for us as it requires too much specialized equipment to > achieve reasonable accuracy. > > The method that is most practical for us is the speed course method (sometimes > called ground course method). It assumes that the pitot pressure is accurate, > which is a reasonable assumption, and there are no static or pitot leaks, which > can be confirmed by ground test. The ASI instrument error must be measured. > The TAS is measured using one of several possible methods (GPS data from a four > course box pattern is the current best method), and the CAS is back calculated > from the TAS, indicated altitude and OAT. The difference between CAS and IAS > (corrected for instrument error) must be due to static source position error. > > More info: > > http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2023-8B/$FILE/Final-Part8.pdf > > http://www.kilohotel.com/rv8/rvlinks/ssec.html > > Kevin Horton > > On 2012-01-02, at 10:35 , Jim Ayers wrote: > > > Do you have a test method that we can all use to calibrate the alimeter at > cruise speed? > > > > The altimeter only has the static system for its input. > > > > Calibrating the static vents in cruise conditions for the altimeter could > provide a correction for airspeed readout errors. > > > > Correcting airspeed readouts errors by changing the static vent geometery > leaves your altitude readings at cruise speeds as a total unknown. > > > > Jim Ayers > > -----Original Message----- > > From: Kevin Horton<khorton01@rogers.com <mailto:khorton01@rogers.com>> > > To: rv-list<rv-list@matronics.com <mailto:rv-list@matronics.com>> > > Sent: Tue, Dec 27, 2011 11:50 am > > Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > > > > --> RV-List message posted by: Kevin Horton<khorton01@rogers.com <mailto:khorton01@rogers.com> > > > > > > > Checking altimeter accuracy against tops of ridge lines only works if the > > temperature is close to standard temperature. > > > > If the temperature differs from standard, the error is about 4 ft per 1000 ft > > per degree C of difference from standard temperature. E.g., if the top of the > > > ridge line is 2000 ft above the airport where the altimeter setting came from, > > > and the temperature is 15 deg C warmer than standard temperature, the > altimeter > > will read about 4/1000 * 2000 * 15 = 120 ft lower than the actual altitude. > > > > See: > > > > > > http://bathursted.ccnb.nb.ca/vatcan/fir/moncton/WeeklyTopics/Archives/20040104/CurrentTopic.html > > http://44rf.com/misc/USAF_AIS_Cold_WX_Altimeter.ppt > > > > > > Kevin Horton > > > > On 2011-12-27, at 12:44 , Jim Ayers wrote: > > > > > An easy way to check the static side of the airspeed indicator is to use > your > > altimeter. > > > > > > I flew along a ridge line at cruise speed that has a 2200 feet peak as shown > > > on my sectional. > > > > > > I may not have been exactly at the same level. Could have been 10 or 20 > feet > > off in hieght. My altimeter read 2,210 feet. > > > So, at that time, my static system was pretty close. > > > > > > Jim Ayers > > > Less Drag Special sn 1 (Modified HR2) > > > > > > -----Original Message----- > > > From: David Maib< > > dmaib@mac.com <mailto:dmaib@mac.com> > > > > > > To: rv-list< > > rv-list@matronics.com <mailto:rv-list@matronics.com> > > > > > > Sent: Mon, Dec 26, 2011 8:03 pm > > > Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > > > > > > --> RV-List message posted by: David Maib< > > dmaib@mac.com <mailto:dmaib@mac.com> > > > > > > > > > > > > Maybe a static port error? Check out some of Kevin Horton's articles > > > in Kitplanes. Static port errors can, and do, cause "fast" errors. > > > IIRC, Kevin says that pitot alignment does not have to be very > > > precise to be pretty accurate. > > > > > > David Maib > > > Rv-10 40559 > > > Flying. > > > On Dec 26, 2011, at 10:39 PM, Matt Dralle wrote: > > > > > > > --> RV-List message posted by: Matt Dralle< > > > > > dralle@matronics.com <mailto:dralle@matronics.com> > > > > > > > > > > > > > > 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 > > > > > > > > - > > > > Matt "Red Dawg" Dralle > > > > > > > > RV-8 #82880 N998RV "Ruby Vixen" > > > > > > > > > http://www.mattsrv8.com <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: 170+ Hours TTSN - Rebuilding Fuselage After Landing Mishap... > > > > > > > > RV-6 #20916 N360EM "The Flyer" > > > > > > > > > http://www.mattsrv6.com <http://www.mattsrv6.com/> > > > > > - Matt's RV-6 Revitalization Log > > > > Status: 42+ Hours Since Purchase - Upgrades Complete; Now In Full > > > > Flyer Mode > > > > > > > > > > > > > > > > > > > > > > _blank>www.aeroelectric.com <http://www.aeroelectric.com/> > > /" target=_blank>www.buildersbooks.com <http://www.buildersbooks.com/> > > =_blank>www.homebuilthelp.com <http://www.homebuilthelp.com/> > > blank>http://www.matronics.com/contribution > > t=_blank>http://www.matronics.com/Navigator?RV-List > > p://forums.matronics.com > > blank>http://www.matronics.com/contribution > > > > > > > > > > > > > > > > http://www.matronics.com/Navigator?RV-List > > > > http://forums.matronics.com <http://forums.matronics.com/> > > > > http://www.matronics.com/contribution > > > > > > > > > t=_blank>http://www.matronics.com/Navigator?RV-List > p://forums.matronics.com > blank>http://www.matronics.com/contribution > > > * > > > *




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