D10A inaccurate airspeed - UPDATED INFORMATION

[tonyvaccarella]

Hi all,

I have updated information from my post dated 28th Aug about an inaccurate airspeed indication on my D10A.

I run a backup ASI and there is a huge difference between the two airspeeds indicated. When my old style ASI reads 100knots my D10A indicates 87 knots. At lower speeds the D10A under-reads by about 10knots.

Dynon kindly responded and said that they had checked thousands of these units and it almost always is the fault of the other ASI. Although I have used my GPS and conducted investigations that showed my old style ASI was more accurate, I took the information provided by Dynon to prove my old style ASI was faulty.

I constructed a water manometer that I found on the net http://www.iflyez.com/manometer.shtml

Today I ran some tests in-situ an with the D10A removed. Surprisingly I found my old ASI accurate according to the manometer and the D10A under-reads by 13 knots.

See images (I seem to only be able to insert 1 image. More available on request)


Is there anything I can do this end or does my D10A need a short holiday to the USA?

Many thanks to everyone who helped with my first post.

Regards to all

Tony

[/img][/img][/img][/img][/img]

 

[tonyvaccarella]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Hi,

Here are more images

Thanks
Tony

 

[tonyvaccarella]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Another image

 

[glasair]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

I have the D6 and likewise notice very good agreement with my analog ASI above about 120 kts but the D6 then starts to read increasingly lower than my analog ASI as the airspeed go lower and gets to the stall speed. My Glasair stalls at about 62 kts as listed in the performance specifications and have not questioned the accuracy of that speed since it has always agreed with what the analog ASI reads. By comparison, the D6 reads lower than 50 kts at the same stall.
I also think that the D6 is the instrument that is "wrong".
I have pressurized the aircraft pitot line on the ground to compare analog vs. D6 indications and see this discrepancy. If I plug the open end of the pressurized line both airspeed indications hold steady, inidicating there are no leaks in either the line to the analog instrument or to the D6, nor any internal leaks in the two instruments, so installation problems are eliminated as a cause. The D6 indicates increasingly lower airspeeds than the analog ASI as the speed decreases. I have not used the water manometer to verify which instrument is "wrong" but reading your post I now don't feel I have to. I am sure I will get similar results to yours.
It would be nice if Dynon could investigate this and see if a better calibration of their airspeed indicator could be achieved as a 20% error at the slower speeds is not very acceptable.

 

[dynonsupport]

Re:  D10A inaccurate airspeed - UPDATED INFORMATIO

Tony - your setup looks sound. Can you give us a call? We may want to see that unit.

Harvey - at what IASes are they diverging? Note that there is a zero airspeed calibration that you can do that can help with readings at very low IAS values.

 

[tonyvaccarella]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Hi Dynon Support,

Sorry to say but I called 4 times this afternoon and left voicemail messages (about 4 to 4:30pm your time) but no one has called back.

The Dynon dealer in Aust (Horsham Aviation) says he has seen something like this in firmware 5.1. He wants me to try a previous verion but Im not happy about taking a retrograde step. Do you feel going to 5.3 might help?

If I need to "downgrade" are you able to supply an older version of the firmware? - as I did not save a backup. Also is there a wiring diagram to construct a simple harness (because my D10A is now out of the aircraft) to enable me to install firmware on the bench?

Many thanks

Tony V

 

[dynonsupport]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

We're trying to nail down a problem with our phone system, so sorry about that. If you email a phone number to support at dynonavionics dot com with a link to this thread, and a time that works to call you (and what city/time zone you're in), and we'll try to get in touch with you. Note that our tech support closes at 4p pacific time.

 

[tonyvaccarella]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Left another 2 messages on your phone system (one at reception and the other with support). Time zones are a real problem as Sydney is GMT + 10. I have emailed my phone number.

Please call

 

[glasair]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Here are the numbers that I got when I pressurized the pitot line and compared our analog ASI with the Dynon D6. I first did the zero pressure airspeed calibration calibration of the D6 in my hanger with no wind or breezes.
All airspeed indications are in knots.
The numbers begin to diverge at about 150 knots and below. It is real obvious at 130 knots and lower.

Analog ASI Dynon D6
260 260
250 250
240 240
230 230
220 219
210 209
190 190
180 180
170 170
160 160
150 148
140 138
130 122
120 113
110 103
100 93
90 82
80 71
70 59
60 49
52 40

 

[Brantel]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Harvey,

The only way to know which one is correct is to do a water manometer test.

Details here:

http://www.iflyez.com/manometer.shtml

I did this on my D100 and it was dead nuts on from 20 to 230 knots.

 

[glasair]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

I will do the manometer test to put everything to rest. Only thing is I know that the Glasair stalls around 60 kts which is what the analog ASI has read for 20+ years and not 49 kts like the D6 is reading. There has never been a Glasair low wing that stalled at 49 kts!
We are having a pitot static transponder test next month come due and during that test he does pressurize the pitot line and compare our altimeter with his calibrated one. I will have him do that again and check the D6 that way also.

 

[Brantel]

Re:  D10A inaccurate airspeed - UPDATED INFORMATIO

With all that extra info, your most likely correct to assume the Dynon is the wrong one. I did not see your prior post cuz I always view the 40 most recent post....

One more question...

Do they share the same static source?

 

[glasair]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Yes, they share the same static source, tee'd off of the same line.
Different static sources could be a source of different measurements, certainlly, but not in my case.

 

[Brantel]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Looks like you are gonna have to call in for an RMA and get Dynon to look at it. Nothin you can do on your end to fix that issue.

 

[tonyvaccarella]

Re: D10A inaccurate airspeed - UPDATED INFORMATIO

Got to speak to Dynon this morning and they suggested I send the unit back. Cant do anything in the field with this type of problem.

Thanks to all who replied to this post.

Cheers and best regards,
Tony