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Does a Pitot need a Drain?

L

lr172

Well Known Member
I have a gretz heated pitot that came with my 10 kit that I was planning to use. However, I have realized this pitot does not have any drain holes. I fly IFR and have flown in the rain several times.

I am a bit concerned that without a drain, the internal tube will fill with water. I am concerned that if a slug of water develops in the tube it will impact the readings. I also suspect that if the water works its way up the vertical tube, the heating elements will not be able to keep ice from developing.

Does anyone have any experience with this pitot flying in rain or have any other input? Wondering if I should ditch it for a dynon or garmin pitot.

Larry
 
I'm using a Cessna heated pitot on my RV-9A and it does come with a drain hole for rain. I discovered this when an avionics tech tried to do a pitot/static re-cert on my Cessna 150 and thought I had an enormous leak in the tubing somewhere. After a lot of messing around we finally discovered the drain hole in the heated pitot (it's at the aft bottom). Plugged the hole with tape and the pitot/static re-cert went fine.
 
I shared your concern, but have noted no problems w my Gretz in 1100 hrs of flying, including VFR, IFR, and rain.
 
No issues with the pitot but do some reason my static lines get moisture in them after flying in rain or sitting in rain. I have to blow it out from time to time when I notice my airspeed is awol
 
If I recall correctly, Dynon heated pitot did not have a drain and they recalled and replaced those. I had one that was replaced by Dynon and if my memory serves me right, it was for the drain hole.
 
Tim Lewis said:
I shared your concern, but have noted no problems w my Gretz in 1100 hrs of flying, including VFR, IFR, and rain.
Click to expand...

That's encouraging. Maybe I will roll the dice and only replace it if I notice problems. I figure that the GPS speed will keep me out of trouble if I have a problem.

Larry
 
lr172 said:
That's encouraging. Maybe I will roll the dice and only replace it if I notice problems. I figure that the GPS speed will keep me out of trouble if I have a problem.

Larry
Click to expand...

Call Gretz and ask why they decided to forego the drain hole. Clearly a design decision. Or maybe they just took their non-heated and added a heater and didnt think about it.

Does seem a bit unusual for a heated.....
 
I'm curious about this as I didn't think much in the way of volume flows through the Pitot "side". Maybe the static because of some instrument bleed, but I wonder if "design" or "configuration" of the lines in from the Pitot/Static head has something to do with what was experienced??

(The use of "wonder" wasn't palliative, I truly haven't thought it out enough!)

mjb
 
Marc Bourget said:
I'm curious about this as I didn't think much in the way of volume flows through the Pitot "side". Maybe the static because of some instrument bleed, but I wonder if "design" or "configuration" of the lines in from the Pitot/Static head has something to do with what was experienced??

mjb
Click to expand...

The shape of the front of the heated pitot means that most of the airflow (and rain) flows around the outside of the tube, much like the leading edge of a wing. However, the airflow that is aligned with the opening in the heated pitot converts to pressure inside the tube, and any raindrop that is within this airflow can enter the tube. Since there is no "flow" in the tube or the lines going to the ASI, the raindrop will remain in the lowest part of the system, typically the end of the pitot tube where it takes a 90 degree bend to go inside the wing. If you get a lot of raindrops inside the pitot tube they can migrate up inside the wing and into the tubing to the ASI causing inaccurate readings.

The Cessna heated pitot has a small pinhole at the aft bottom end of the housing to allow rain to be pushed out of the tube and back into the atmosphere.
 
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