RV-List Digest Archive

Wed 01/04/12


Total Messages Posted: 5



Today's Message Index:
----------------------
 
     1. 03:47 AM - Re: Dynon Skyview Airspeed Calibration... (Kevin Horton)
     2. 08:35 AM - Re: Dynon Skyview Airspeed Calibration... (Jim Ayers)
     3. 10:06 AM - Re: Dynon Skyview Airspeed Calibration... (Kevin Horton)
     4. 03:01 PM - Need to find RV buiilder in Mississippi (David Swett)
     5. 07:38 PM - Re: Dynon Skyview Airspeed Calibration... (Ed Holyoke)
 
 
 


Message 1


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    Time: 03:47:36 AM PST US
    Subject: Re: Dynon Skyview Airspeed Calibration...
    From: Kevin Horton <khorton01@rogers.com>
    Jim, Yes, if the ridge is 2200 ft above the field elevation, and the temperature is 1 deg C below standard, the barometric altimeter would read approximately 9 ft high at the ridge. I believe that Dynon's statement that the pitot tube cannot be used for a leak check refers to the pitot drain that creates a very small leak internal to the pitot tube. In an ideal world, with no pitot leaks anywhere, in a constant airspeed condition there is no flow in the pitot system, and the pressure is the same everywhere in the pitot system. If there is a leak somewhere, air is escaping, and there must be air flow in the system to replace the air that is escaping through the leak. Air will only flow if there is a pressure differential, so the pressure at the leak (and from there to the ASI) must be lower than the pressure at the pitot tube and this lower pressure at the ASI causes the ASI to read low. But, if the leak is right in the pitot tube, and it is very small, as pitot drains should be by design, there is only a very short flow path between the pitot tube entrance and the leak location. Thus the pressure drop between the pitot entrance and the pitot drain should be so small as to be inconsequential. You could arrange some sort of test setup to measure the magnitude of this pressure drop if it still concerns you. Kevin Horton On 2012-01-04, at 24:10 , Jim Ayers wrote: > From your previous information, for my 2,200' foot altitude change from field 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 temperature at the field elevation. > > Does this sound about right? > > 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... > > > > > 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 > > > > To: rv-list < > rv-list@matronics.com > > > > Sent: Tue, Dec 27, 2011 11:50 am > > Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... > > > 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 > > >


    Message 2


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    Time: 08:35:30 AM PST US
    Subject: Re: Dynon Skyview Airspeed Calibration...
    From: Jim Ayers <lessdragprod@aol.com>
    I could just create an airspeed correction chart if I normally flew at a pa rticular altitude. For example, at 8.000' density altitude 194 KTAS is 201 Knots GPS TAS and 2 01 KTAS is 209 Knots GPS TAS. However, for cruise at 17,500' station pressure altitude which could be clo se to 20,000 density altitude, the IAS and dynamic pressure would be much l ower. A different TAS airspeed correction chart would be required. Could it be as simple as making a TAS airspeed correction chart based on IA S? Jim Ayers -----Original Message----- From: Kevin Horton <khorton01@rogers.com> Sent: Wed, Jan 4, 2012 3:48 am Subject: Re: RV-List: Dynon Skyview Airspeed Calibration... Jim, Yes, if the ridge is 2200 ft above the field elevation, and the temperature is 1 eg C below standard, the barometric altimeter would read approximately 9 ft igh at the ridge. I believe that Dynon's statement that the pitot tube cannot be used for a l eak heck refers to the pitot drain that creates a very small leak internal to t he itot tube. In an ideal world, with no pitot leaks anywhere, in a constant irspeed condition there is no flow in the pitot system, and the pressure is the ame everywhere in the pitot system. If there is a leak somewhere, air is scaping, and there must be air flow in the system to replace the air that i s scaping through the leak. Air will only flow if there is a pressure ifferential, so the pressure at the leak (and from there to the ASI) must b e ower than the pressure at the pitot tube and this lower pressure at the ASI auses the ASI to read low. But, if the leak is right in the pitot tube, an d it s very small, as pitot drains should be by design, there is only a very sho rt low path between the pitot tube entrance and the leak location. Thus the ressure drop between the pitot entrance and the pitot drain ! should be so small as to be inconsequential. You could arrange some sort o f est setup to measure the magnitude of this pressure drop if it still concer ns ou. Kevin Horton On 2012-01-04, at 24:10 , Jim Ayers wrote: > From your previous information, for my 2,200' foot altitude change from f ield levation to the ridge line, there is about a 9 foot altitude difference for ach degree C difference from the standard temperature change. Where the 2, 200' idge line temperature should be 4 degree C lower than the temperature at th e ield elevation. Does this sound about right? My aircraft has a Dynon Heated Pitot tube with the AOA port. It has a Dyn on -10A EFIS which provides TAS, OAT and Density Altitude read-out capability . For the Pitot/Static system test, Dynon specifically states that the Pitot ube CAN NOT be used as part of the Pitot pressure test.. It appears for the heated Dynon Pitot tube that Pitot pressure being accur ate ould be a bad assumption. I am trying to identify the sources of error in my Pitot/Static system and how uch each contributes to the error. The EFIS readout is 8 knots low at a 8.000' density altitude cruise compar ed o 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... > The classical test method that directly compares actual vs indicated altit ude s 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 determin ed rom the images, assuming the aircraft accurately tracks down the runway entreline. The aircraft instrumentation system records the altitude, with a very accu rate > time stamp. Ground instrumentation records the altitude and OAT at groun d level, and the camera images have an accurate time stamp. Post flight nalysis is used to determine the actual vs indicated altitude as the aircraft pass es y the tower at a range of airspeeds. This is used by some major test centres , ut it is not practical for us as it requires too much specialized equipment t o achieve reasonable accuracy. The method that is most practical for us is the speed course method (somet imes > called ground course method). It assumes that the pitot pressure is accu rate, > which is a reasonable assumption, and there are no static or pitot leaks, hich can be confirmed by ground test. The ASI instrument error must be measure d. The TAS is measured using one of several possible methods (GPS data from a our course box pattern is the current best method), and the CAS is back calcul ated > from the TAS, indicated altitude and OAT. The difference between CAS and IAS (corrected for instrument error) must be due to static source position err or. 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 coul d provide a correction for airspeed readout errors. > > Correcting airspeed readouts errors by changing the static vent geometer y leaves 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... > khorton01@rogers.com > > > > Checking altimeter accuracy against tops of ridge lines only works if th e > temperature is close to standard temperature. > > If the temperature differs from standard, the error is about 4 ft per 10 00 t > per degree C of difference from standard temperature. E.g., if the top of he > ridge line is 2000 ft above the airport where the altimeter setting came rom, > 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 alti tude. > > 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 > -= - 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 3


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    Time: 10:06:22 AM PST US
    Subject: Re: Dynon Skyview Airspeed Calibration...
    From: Kevin Horton <khorton01@rogers.com>
    Ignoring the small contribution due to weight (the AOA for a given IAS is affected by weight, which affects the flow field around the aircraft), the error in IAS will be a function of IAS. An X% error in IAS will translate into an X% error in TAS, so you could create a correction chart that gave the percent error in TAS as a function of IAS. Or, you could create a small table with TAS corrections for a number of cruise altitudes : TAS Correction for Altitude and IAS Corrected TAS = TAS from EFIS + correction Alt 80 90 100 110 120 130 140 150 160 170 180 0 +1.2 +1.1 +0.9 +0.6 +0.2 -0.2 -0.4 -0.9 -1.7 -2.3 -2.9 2000 +1.3 +1.1 +0.9 +0.6 +0.2 -0.2 -0.4 -0.9 -1.7 -2.4 -2.9 4000 +1.3 +1.2 +1.0 +0.6 +0.2 -0.2 -0.4 -1.0 -1.7 -2.4 -3.0 6000 +1.4 +1.2 +1.0 +0.7 +0.2 -0.2 -0.5 -1.0 -1.8 -2.5 -3.1 8000 +1.4 +1.3 +1.0 +0.7 +0.3 -0.2 -0.5 -1.0 -1.9 -2.6 -3.2 10000 +1.5 +1.3 +1.0 +0.7 +0.3 -0.2 -0.5 -1.1 -1.9 -2.7 -3.3 12000 +1.5 +1.3 +1.1 +0.7 +0.3 -0.2 -0.5 -1.1 -2.0 -2.7 -3.4 14000 +1.5 +1.4 +1.1 +0.7 +0.3 -0.3 -0.5 -1.1 -2.0 -2.8 -3.5 16000 +1.6 +1.4 +1.1 +0.8 +0.3 -0.3 -0.5 -1.2 -2.1 -2.9 -3.6 18000 +1.6 +1.5 +1.2 +0.8 +0.3 -0.3 -0.5 -1.2 -2.1 -3.0 -3.7 20000 +1.7 +1.5 +1.2 +0.8 +0.3 -0.3 -0.6 -1.2 -2.2 -3.1 -3.8 The above table is the actual errors in my aircraft, including EFIS ASI instrument error + static system position error. Many of the conditions are obviously not achievable in level flight. You'll need a fixed-width font to get the columns to line up. Kevin Horton On 2012-01-04, at 11:30 , Jim Ayers wrote: > I could just create an airspeed correction chart if I normally flew at a particular altitude. > > For example, at 8.000' density altitude 194 KTAS is 201 Knots GPS TAS and 201 KTAS is 209 Knots GPS TAS. > > However, for cruise at 17,500' station pressure altitude which could be close to 20,000 density altitude, the IAS and dynamic pressure would be much lower. A different TAS airspeed correction chart would be required. > > Could it be as simple as making a TAS airspeed correction chart based on IAS?


    Message 4


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    Time: 03:01:56 PM PST US
    From: David Swett <DSwett@arri.com>
    Subject: Need to find RV buiilder in Mississippi
    SGksDQoNCkZpcnN0IHRpbWUgb24gdGhlIGxpc3QuICBNeSBmcmllbmQgaXMgbG9va2luZyBhdCBh biBSVi0xMCBwcm9qZWN0IGluIE9saXZlIEJyYW5jaCwgTWlzc2lzc2lwcGkuICBXZSBsaXZlIGlu IFNvQ2FsLiAgQW55b25lIGluIHRoYXQgc3RhdGUgd2hvIG1heSBiZSBhYmxlIHRvIGhhdmUgYSBs b29rIGF0IGl0IGZvciBoaW0/DQoNClRoYW5rcyBpbiBhZHZhbmNlIGZvciB5b3VyIGhlbHAuDQoN CkRhdmUNCk5hdmlvbiBwaWxvdA0KDQoNCg0KRGF2aWQgU3dldHQNCg0KU3IuIEZpZWxkIFNlcnZp Y2UgRW5naW5lZXIsIERpZ2l0YWwgSW1hZ2luZyBTeXN0ZW1zDQoNCg0KDQpBUlJJIEluYy4NCjYw MCBOb3J0aCBWaWN0b3J5IEJsdmQNCkJ1cmJhbmssIENBIDkxNTAyDQpQaG9uZTogICg4MTgpIDg0 MS03MDcwDQpGYXg6ICAgICAoODE4KSA4NDgtNDAyOA0KDQpbQUxFWEFdPGh0dHA6Ly93d3cuYXJy aS5jb20vPg0KDQpGb3IgYWxsIHRoZSBsYXRlc3Qgb24gQUxFWEEsIHZpc2l0IHd3dy5hcnJpLmNv bTxodHRwOi8vd3d3LmFycmkuY29tLz4gYW5kIFlvdVR1YmU8aHR0cDovL3d3dy55b3V0dWJlLmNv bS91c2VyL0FSUklDaGFubmVsPg0KDQoNCg0KDQoNCg0KVGhpcyBtZXNzYWdlIGlzIGNvbmZpZGVu dGlhbC4gSXQgbWF5IGFsc28gYmUgcHJpdmlsZWdlZCBvciBvdGhlcndpc2UgcHJvdGVjdGVkIGJ5 IHdvcmsgcHJvZHVjdCBpbW11bml0eSBvciBvdGhlciBsZWdhbCBydWxlcy4gSWYgeW91IGhhdmUg cmVjZWl2ZWQgaXQgYnkgbWlzdGFrZSwgcGxlYXNlIGxldCB1cyBrbm93IGJ5IGUtbWFpbCByZXBs eSBhbmQgZGVsZXRlIGl0IGZyb20geW91ciBzeXN0ZW07IHlvdSBtYXkgbm90IGNvcHkgdGhpcyBt ZXNzYWdlIG9yIGRpc2Nsb3NlIGl0cyBjb250ZW50cyB0byBhbnlvbmUuIFBsZWFzZSBzZW5kIHVz IGJ5IGZheCBhbnkgbWVzc2FnZSBjb250YWluaW5nIGRlYWRsaW5lcyBhcyBpbmNvbWluZyBlLW1h aWxzIGFyZSBub3Qgc2NyZWVuZWQgZm9yIHJlc3BvbnNlIGRlYWRsaW5lcy4gVGhlIGludGVncml0 eSBhbmQgc2VjdXJpdHkgb2YgdGhpcyBtZXNzYWdlIGNhbm5vdCBiZSBndWFyYW50ZWVkIG9uIHRo ZSBJbnRlcm5ldC4NCg=


    Message 5


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    Time: 07:38:44 PM PST US
    From: Ed Holyoke <bicyclop@pacbell.net>
    Subject: Re: Dynon Skyview Airspeed Calibration...
    We just taped over the drain hole in the Dynon pitot tube while doing the biennial transponder and static check. Ed Holyoke On 1/4/2012 3:41 AM, Kevin Horton wrote: > --> RV-List message posted by: Kevin Horton<khorton01@rogers.com> > > Jim, > > Yes, if the ridge is 2200 ft above the field elevation, and the tempera ture is 1 deg C below standard, the barometric altimeter would read appro ximately 9 ft high at the ridge. > > I believe that Dynon's statement that the pitot tube cannot be used for a leak check refers to the pitot drain that creates a very small leak in ternal to the pitot tube. In an ideal world, with no pitot leaks anywher e, in a constant airspeed condition there is no flow in the pitot system, and the pressure is the same everywhere in the pitot system. If there i s a leak somewhere, air is escaping, and there must be air flow in the sy stem to replace the air that is escaping through the leak. Air will only flow if there is a pressure differential, so the pressure at the leak (a nd from there to the ASI) must be lower than the pressure at the pitot tu be and this lower pressure at the ASI causes the ASI to read low. But, i f the leak is right in the pitot tube, and it is very small, as pitot dra ins should be by design, there is only a very short flow path between the pitot tube entrance and the leak location. Thus the pressure drop betwe en the pitot entrance and the pitot drain ! > should be so small as to be inconsequential. You could arrange some sort of test setup to measure the magnitude of this pressure drop if it s till concerns you. > > Kevin Horton > > On 2012-01-04, at 24:10 , Jim Ayers wrote: > >> From your previous information, for my 2,200' foot altitude change fr om field elevation to the ridge line, there is about a 9 foot altitude di fference for each degree C difference from the standard temperature chang e. Where the 2,200' ridge line temperature should be 4 degree C lower th an the temperature at the field elevation. >> >> Does this sound about right? >> >> 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 P itot tube CAN NOT be used as part of the Pitot pressure test.. >> It appears for the heated Dynon Pitot tube that Pitot pressure being a ccurate 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 co mpared 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 >> The classical test method that directly compares actual vs indicated a ltitude is >> the "tower fly-by". Typically a camera is placed on top of a tower a bout 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 v ery well >> known so that the height of the aircraft above the runway can be deter mined from >> the images, assuming the aircraft accurately tracks down the runway ce ntreline. >> The aircraft instrumentation system records the altitude, with a very accurate >> time stamp. Ground instrumentation records the altitude and OAT at gr ound >> 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 cen tres, but >> it is not practical for us as it requires too much specialized equipme nt to >> achieve reasonable accuracy. >> >> The method that is most practical for us is the speed course method (s ometimes >> called ground course method). It assumes that the pitot pressure is a ccurate, >> which is a reasonable assumption, and there are no static or pitot lea ks, which >> can be confirmed by ground test. The ASI instrument error must be mea sured. >> The TAS is measured using one of several possible methods (GPS data fr om a four >> course box pattern is the current best method), and the CAS is back ca lculated >> 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 alime ter at >> cruise speed? >>> >>> The altimeter only has the static system for its input. >>> >>> Calibrating the static vents in cruise conditions for the altimeter c ould >> provide a correction for airspeed readout errors. >>> >>> Correcting airspeed readouts errors by changing the static vent geome tery >> leaves 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... >>> >>> --> RV-List message posted by: Kevin Horton< >> 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 t op of the >>> ridge line is 2000 ft above the airport where the altimeter setting c ame 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 a ltitude. >>> >>> 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 >>> > > =========== =========== =========== =========== > >




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