Speed doesn't come alive

[Camillo]

Hi, Dynon. I have a problem. I suspect that Dynon Pitot doesn't work.

My configuration is a SkyView system AND an analogic airspeed indicator. Tubes are safeair tubes (green for total pressure, blu for AOA and white for static). I had my system ramp-tested and it was OK (apart from Pitot).

Today I made two 7'' accelerations (just maybe 10/15 kts. before take off) on the runway and both airspeed indicators (SkyView display and United A/S indicator) signed zero.

I checked all the total pressure line and found that the system, bypassing the Pitot, loses only 5 kts. in 4 minutes. I guess this is average.

I then connected the same silicone tube on the Pitot and indication was zero (I previously covered the two small draining holes along the Pitot).

How does the Pitot work? Is it possible for a Dynon Pitot not to work? What may be the problem? Do I have to tighten something on the Pitot?
At what approx. speed the indicator on the EFIS comes alive?

Thanks.
Camillo

 

[jakej]

Sorry to ask the obvious - did you connect the green tubing to the forward aluminum tube on the AOA Pitot head ?

Did you blow air through the sam Pitot head tube to confirm air was coming out at the forward end of same ?

Jake J

 

[Camillo]

Jake, yesterday evening I was too frustrated to understand that I should have done the controls you were talking about.

So, no, I did not double checked the coerency of the two tubes and where the air exited if blowing into the total pressure tube. These controls will be the first things I will do on next Saturday.

Anyway, I checked my photos and the shorter aluminium tubing which comes from the forward part of the Pitot is connected to the green (Pitot) line.

I also blocked the tubing and blew inside the Pitot. It was not sealed, even if I plugged the two small draining holes with tape. I could neatly perceive a considerable amount of leaking air.

I was wondering how the AOA principle works. Is the AOA line basically the same line the total pressure is (so a line with potentially no leak) or is it an open tube? When checking for Pitot shall I plug the AOA entrance?

 

[dynonsupport]

Pitot comes alive at 20 knots. The Dynon AOA/Pitot is designed to leak to vent moisture, so you won't be able to pressurize it. It won't affect your IAS readings, however. To test that the pitot works at all, just have a friend watch the screen while you blow into the snout. Of thousands of AOA/Pitots we've sold, I think we've had one or two that have acquired a blockage between shipment and installation, so that's possible but unlikely.

The AOA has a second line that is connected to the opening on the beveled edge on the front of the pitot. Both the Pitot and AOA lines vent to a common cavity that drains through the holes in the rear. The designed leaks in each of those lines aren't enough to cause the pressure in the lines to interfere with each other.

If you wanted to check that there's no blockage in the AOA/Pitot, pop your lines off of it, and blow in each port and make sure air comes out each aluminum tube.

 

[Camillo]

Thank-you, Dynon. I will check for this next Saturday.

Once disconnected the lines, may I use an air gun to clean the inside of the Pitot tubes or will this ruin them?

Edit: problem was that I connected the green tube to the AOA aluminium tube. Surprisingly, the shortest tube was the AOA and not the standard total pressure tube. I switched the tube and now airspeed is OK.