[Camillo]

Hi. I have a big problem.

I decided to check if airspeeds indicators were working (SkyView indicator and United analogic ASI) and so today I made two 7'' accelerations (just maybe 10/15 kts. before take off) on the runway (15 kts front wind).

Both airspeed indicators (SkyView display and United A/S indicator) signed zero. 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 leaks). I double checked it yesterday, disconnecting the probe, and found that the system, bypassing the Dynon heated pitot probe, loses 5 kts. in 4 minutes. I guess this is average.

I then plugged the drain holes under the Pitot and connected the same silicone tube on the total pressure hole (the bigger central one in the probe) and ASIs indications were zero.

I would like to know:
1) at what average speed your ASIs get alive and particularly a Dynon EFIS;
2) if you have an idea on how to solve my problem, since my airplane was approved for flight and I have only 2 1/2 months left on my permit to fly.

The green total pressure line is connected on the shorter Dynon pitot tube (which should be the total pressure - and not the AOA - entrance) and the remaining part of the system is working. If I plug a silicone tubing on the system (Dynon probe disconnected) and fold it several times, speed reaches 80 knots and stays there for 1 minute. If I make the same with Dynon Pitot probe (drain hole plugged), the ASIs sign zero.

Thanks.
Camillo

 

[Camillo]

Ok. Got Dynon answer on their forum.
Airspeed indication comes alive @ 20 kts.

I guess my Pitot is blocked. Do you think that it is OK to shoot air with a gun from the inside to the outside (having disconnected lines)?

Thanks.
Camillo

 

[Bavafa]

I am not sure about Dynon, but many of the airspeed indicators do not come alive till about 30K or more. You can certainly disconnect the line from all your instruments and apply vacuum or blow air to see if it is any abstraction but make sure not to blow strong air into pitot tube when it is connected to your instruments.

 

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Switch AOA and pitot lines at the probe

Switch AOA and pitot lines at the probe and retest. My Dynon will come alive around 20 or so...

 

[Camillo]

Stephen, you were right!

My lines were inverted. For some strange reason, my Dynon shorter tube (which I assumed was the total pressure main entrance) is the AOA and not the "standard" total pressure.

Now it works @20-25 knots.