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Dynon Skyview Airspeed Calibration...
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khorton01(at)rogers.com
Guest

Posted: Mon Jan 02, 2012 3:31 pm Post subject: Dynon Skyview Airspeed Calibration...

John,



Modifying the static ports to reduce the error in IAS will also reduce the error in the indicated altitude, IF the static port is the source of your problem.  If the static port is not the source of your problem you could be introducing new errors in your altitude by modifying the static ports.  Be very sure that you have ruled out other possible errors before attacking the static ports.  



1. Be very sure that you don't have leaks in the static or pitot systems - do your own checks, rather than assuming the result from a month ago is still valid - you could easily have a new leak.  



2. Measure the ASI instrument error in your EFIS - don't simply assume it is zero - my Dynon EFIS has some ASI instrument error.  



3. And be sure your OAT is reasonably accurate.



If after doing the three items above without finding a problem, then you must have issues with the static ports, which will affect both airspeed and altitude.  Static port changes that reduce the ASI error will also reduce the altimeter error.



Kevin

On 2012-01-02, at 15:36 , Bubblehead wrote:



 	  Quote: 	
		   

 

 Kevin,

 

 I've been on your site a lot today reading about this.  Next weekend if weather permits I will collect a lot of Numbers to plug into your speadsheet to see about IAS and TAS. I suspect the TAS on my Skyview is significantly off because I am getting wind vectors that disagree significantly with forecast winds aloft and what I observe for a correction angle (crab angle) while flying. 

 

 In your experience if I correct my IAS and TAS by modifying the static port will I cause large changes and induce possible error on "indicated" altitude?

 

 As info i have the SafeAir1 system on my 8 including static ports and the static leak test was passed with flying colors just a month ago.

 

 I appreciate all the info you've share on this and other topics.

 

 John

 

 --------

 John

 Keller, TX

 RV-8 N247TD

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=362269#362269

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lessdragprod(at)aol.com
Guest

Posted: Tue Jan 03, 2012 9:18 pm Post subject: Dynon Skyview Airspeed Calibration...

 	  Quote: 	
		  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 

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Kellym

Joined: 10 Jan 2006
Posts: 1706
Location: Sun Lakes AZ

Posted: Tue Jan 03, 2012 9:47 pm Post subject: 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:     [quote]          

         

         

          

         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 

          

          

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

khorton01(at)rogers.com
Guest

Posted: Wed Jan 04, 2012 3:47 am Post subject: Dynon Skyview Airspeed Calibration...

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:



[quote] 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 

  

  

 --

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lessdragprod(at)aol.com
Guest

Posted: Wed Jan 04, 2012 8:35 am Post subject: Dynon Skyview Airspeed Calibration...

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?



Jim Ayers

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khorton01(at)rogers.com
Guest

Posted: Wed Jan 04, 2012 10:06 am Post subject: Dynon Skyview Airspeed Calibration...

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:



 	  Quote: 	
		   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?

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bicyclop(at)pacbell.net
Guest

Posted: Wed Jan 04, 2012 7:38 pm Post subject: 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:     [quote]       [quote]--> RV-List message posted by: Kevin Horton <khorton01(at)rogers.com> (khorton01(at)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:



         [quote]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      --

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