Dynon Vs GPS Speeds

[yankee-flyer]

I've now completed all 5 Flight Test cards--or as much of them as I intend to do-- and all the 4-way speed boxes (different altitudes, airspeeds, RPM,s and the duplicate boxes give me the same thing.

IAS when converted to True compares VERY well with the Dynon TAS readout. Under all conditions the average of the converted IAS numbers and TAS readouts are 3-4 knots slower than the average GPS groundspeed. As I've mentioned earlier, all my indicated stall speeds are about the same amount below "book".

There is NO leakage in my pitot or static system. I've checked twice. I've done the "low speed calibration test" per the Dynon manual with no change. I've read the Dynon forum and talked with a Dynon tech. Their response is that airspeed errors are "almost always" the result of poor placement of the static ports and that Dynons returned for airspeed calibration are "almost never" incorrect.

Did anybody else who's done the FT cards find the same thing or is this unique to my airplane/Dynon?

Thans guys!!

Wayne 120241/143WM

 

[Brantel]

You can verify the accuracy of the Dynon's sensor by doing a simple manometer test. The error should be very small.

You would need to do this to determine if you have any static position error.

 

[Bavafa]

Or I would think a higher chance for inaccurate Pitot position. The length (blow the wing), direction and position of your pitot tube could be off enough to make a difference for the speed difference that you see.

 

[Brantel]

It's an RV 12.....

It sticks out the center of the spinner...

Static position errors are way more common than pitot problems as long as you stick with the normal methods.

 

[yankee-flyer]

Both the Pitot and static

positions were determined by Van's. We have to build the airplane exactly as per the prototype/plans.
That's why I want to know if other 12 builders have the same problem. If not, then it has to be my Dynon.

Wayne

 

[Mich48041]

Testing Dynon airspeed

Wayne,
Applying a known pressure to the pitot tube should result in a specific airspeed display on the Dynon. A syringe can be used as a pressure source and a manometer can measure the pressure. This website has a chart for converting pressure to airspeed:http://www.iflyez.com/manometer.shtml
If 9.4492" H2o is applied to the pitot tube, then the Dynon should display 120 knots. I have not actually tried this. Maybe someone who has can comment.
Joe
Additional links:
https://engineering.purdue.edu/~andrisan/Courses/AAE490F_S2008/Buffer/GPS%20PEC%20Method.doc

http://www.cockpitgps.com/other_articles/GPS_TAS/TAS_FNL4.pdf

 

[Brantel]

I suggest for you to do the test...its the only way to know for sure without sending it back possibly (and likely) for nothing......

I would say I built my RV7 like 90% of the others as well but mine had a major static position error. Why? I have no idea but it did and I had to fix it. My Dynon was very accurate out of the box.