Airspeed indicator water in pitot
While returning home from a recent aviation event, I flew through some rain. Not long after this my indicated airspeed went up to 140 MPH while landing at an airport for fuel. After fueling I took off and the airspeed gauge indicated accurately. However I had to fly through more rain. Not long after flying through the additional rain, the indicated airspeed dropped to 40 MPH. I continued the 2.5 hour flight home.
Today me and my mechanic took the pilot tube loose from the back of the airspeed gauge and blew out several ounces of water.
The Stinson manual advises to remove the tube under the left side of the instrument panel connected to the pitot gauge to drain out water. I am surprised that there is not a container in this are of the low point of the pitot tube to catch water before it can become a problem. Also it would be extremely handy if there was a valve at the bottom of the container to drain water out. If this had been available I probably could have drained water out in flight during the cross country and would have alleviated the problem of not having accurate airspeed. How do other airplanes deal with water in the pitot tube system?
Bret C / N190C
I added a tee fitting in each line with a clear tubing and an AN plug and B nut under the instrument panel. It just sticks straight down so I can look up in there for water or drain it.
@resto108 That is a good solution. Do you know of something that I can mount which would allow it to be drained while in flight? Maybe something with a petcock valve? On your clear tube solution, do you find that it collects water while flying in rain? Thank you for your input.
I believe the correct plan of action would be to land if experiencing suspected pitot/static blockage and troubleshoot; at which point water could be observed through the clear tubing and drained. Don't have any info about flying in rain.
Cessna uses a small clear plastic bottle with 1/8" pipe thread at the ends. They often fail a static test because of cracks at the ends, so if you buy a used one, use some glue on the ends. Piper I think maybe, uses a quick drain, like in a fuel tank, under the dash, at a low spot.
Thank you Michael. It sounds like Piper has the best idea.
There should be a small hole on the bottom of your pitot tube to allow for water to drain in flight. Check to ensure clear.
So there should be an air leak in your pitot system?
I have a small hole at the bottom of the pitot tube, near front, circled in pic. I read this patten was filed in 1938.
Not sure if this helps but look for a clear water drain hole underside of pitot tube. Otherwise a drain valve under panel is likely best solution for the older designs.
This is a heated type pitot/static probe. I believe the holes are static ports. Ideally there should not be any leakage in the pilot system. Some of the aircraft I'm familiar with have a built-in reservoir to collect moisture. https://www.google.com/search?q=heated+pitot+static+tube&client=tablet-android-samsung-nf-rev1&prmd=sivn&sxsrf=ALiCzsaIA-rFtLm-ra9ku8hup_55qhAonA:1664297182953&source=lnms&tbm=isch&sa=X&ved=2ahUKEwi7yI-TtrX6AhWqEEQIHa79B4cQ_AUoAnoECAIQAg&biw=602&bih=964&dpr=1.33#imgrc=MRnEWUEENJOB1M&imgdii=fnKWnMq3lXq2IM
The three holes behind are static.
Thaks for the input. The pitot tube in your photo is not the same as mine. Mine is the standard twin tube on most Stinson’s. However I like yours and can see the benefits. But as others mention, yours must be a heated pitot tube which I don’t have.
I find it odd that Stinson did not have a better way to handle rain accumulation.
The manual states to remove a hose clamp on the pitot pressure tube, remove the tube and rain the water out. Obviously this is not going to work while flying.
I find it odd that I have flown through lite rain several times without any issues. However, the night before I departed there was a significant thunderstorm. I suspect the storm my have been driving rain in the direction of the pitot tube, thus opening the hinged pitot tube cover allowing rain to be driven into the pitot tube.
A partial fix would be to cover the pitot tube assembly while tied down outside, especially when rain is predicted.