Airspeed reads low...

[vatkinson]

Just got the d100 going and the a/s reads consistantly low. I have a standby a/s and it reads correctly. they are hooked to the same lines. There are no leaks in the Dynon lines.... Transponder encoding altitude on the same static line reads correctly...
example;
dynon spare indicator
60kt 72kts
120kt 138kt
165kt 186kts
205kt 230kts

This aircraft has been flying for 22 years and the spare indicator appears right on and the Dynon is SLOW. As you can see, it gets progessively worse the higher you go in speed.

All the other parameters look good... heading was a snap and right on the money. (helps when you have an exact 090-270 degree runway).

Ive set the pressure to zero twice...... SUGGESTIONS?

 

[Mel]

Are you sure that your original indicator is knots? It is very suspicious that the error is very close to
a factor of 1.15 X. If you original indicator was reading in mph, the 2 would be very close.

 

[DBRV10]

I think the Min Equip List has hit the nail on the head!

MPH V knots.

I would almost bet someone elses house on it that the Dynon is 100% accurate and your old AI is a mile or two out!

Our D10 is 100% spot on in ALT and AI. now that it has a mag comp head its compass is also within 1 degree all round.

I hope my new D100 and D180 will be this good in the RV10!

 

[vatkinson]

Well... you could be right. I set the dynon with kts during the initial setting but have not checked it again to see if it has reverted. However if is not in knots, the airspeed difference would be worse. I will do that tomorrow.. and will ck the stdby a/s indicator to make sure its in kts...(its a digital readout also) and I originally set it in knots also, but will re check too.

But the fact remains the Dynon is not correct due to various flt characteristics I am seeing. I built this COZY 22 years ago and put 1900 hours on it. I know what it will indicate with a given fuel flow.

Typical would be 165kts to 170kts at around 3000' with 8 gallons per hour.....it aint there!! Again the Dynon shows 20kts low and the other A/S is right on. The other A/S is also new. I fly for a living and have 28,000 hours with the majority in 9 different jets, so Im attuned to the sound my plane makes at specific speeds. The clincher is you cant land the COZY at the speeds its showing...it would mush in or run out of elevator authority for the flair.

All my buddies are unavailable at the moment for an inflight airspeed check.

I was hoping to hear there is some sort of adjustment to the Dynon for A/S compensation that I havent come across, but I fear It will have to go back to the factory to have them look at it.

 

[dynonsupport]

There is no adjustment you can make to adjust the unit. It's fully calibrated at the factory, over temperature. The only adjustment we allow is the zero pressure, but that only adjusts speeds below 50 knots where the pressures are thousandths of a PSI.

If you decide to send it to us you can, but over the years, we've had probably 15 customers send them in with an airspeed complaint and I don't think we've ever found one off by more than 2 knots at 150 knots. There is always a first time, and we'd be happy to look at it.

The thing that makes me really doubt calibration in your case is that the error gets worse the faster you go. Any pressure error shows up as a smaller and smaller error the faster you go, so chances that the Dynon is out of calibration here are exceedingly small.

 

[vatkinson]

Thanks Dynon for the answer on SUNDAY of all things.... Found the culprit. The stdby airspeed indicator was in MPH. The Dynon was in knots. The pressure line from the pitot feeds the stdby first and it was fine. But the line then goes on to the Dynon and it had a very tiny slit in the end of it. Something I had failed to detect before. Replaced the line and they now read within two knots of each other !
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