Pitot-Static system troubles

[jsbostwick]

Hi all,

 

Flew from KESN to KTTN the other night in relatively warm (above freezing) temperatures. Nice flight, all instruments normal. Refueled at KTTN, but upon restart, I noticed the ASI reading about 50-60 mph (while sitting still at the fuel pump). Was concerned, as I have never had that indication before (I've had my plane for 6 years). Flew it again the next day. On start-up the same thing occured (temps still well above freezing-nice for January here); at the suggestion of my instructor, I applied pitot heat, and surprisingly (given the warm temps) that seemed to help. By the time we were ready to take off, ASI was reading almost zero when we were sitting still. On take off and climb out the ASI seemed to be functioning properly (airspeed was what I normally get when pitched for climb out), but the VSI fluctuated erratically, and continued to do so in straight and level flight (almost like we were hitting pockets of turbulence), but air was glass smooth. Altimeter reading was within +/- 200 ft of independent GPS altitude. Variations on this theme presented themselves throughout the flight, so obviously I'm having this looked at, but I thought I'd throw this out here and see what any of you think the problem could be. Thanks/Jeff

[carusoam]

Sounds like something blocking the pitot part of the pitot static system...

Take a look inside the pitot tube for anything that may be stuck.

Definitely get it working prior to flying. Mooneys are too hard to estimate flying speed without one.

Welcome aboard. Are you familiar with the NJ Mooney group?

Best regards,

-a-

[takair]

You could have a kinked line or water in a low spot. A small amount of water can manifest itself as jumps in the instruments. It plugs the line and then, when there is enough pressure differential the slug of water lets air through suddenly. A kink can cause similar problems. If your altitude indication is stable, your plumbing may be such that you have a common line between the ASIand VSI. Best to have a look under the panel.

Also, check your pitot tube. There is a very small bleed hole on the aft bottom. If it is plugged, water will not drain. Pitot heat will boil it off. This would not explain a VSI problem.

[Ron McBride]

You should have 2 pitot/static drain in your plane, 1 under the left wing near the fuselage, and the other under the belly near the tail access panel. Try opening these to drain your lines. Welcome to the list. Ron

[takair]

You should have 2 pitot/static drain in your plane, 1 under the left wing near the fuselage, and the other under the belly near the tail access panel. Try opening these to drain your lines.

Welcome to the list.

Ron

Depends on the vintage. Not sure when they cut this in, but my 64 E does not have drains. Those drains can also be a pain and cause their own issues. They tend to accumulate dirt and don't seal. They can drive your avionics guy crazy when doing a leak check at your 24 month IFR check.

[jsbostwick]

Thanks for the feedback and advice. I am having this looked at, so when the verdict comes in I'll report the findings. In the meantime, I will check those pitot/static drains. To 'a' in NJ, no, I'm not familiar with the NJ Monney group. Where are you based? I tie down at TTN.

[testwest]

If, for some reason, your drains aren't sealing well, LASAR has a little kit of o-rings to reseal them, $7 a pop. This happened to us! But resealing the wing (pitot) drain will be a trick to get to, it is accessible from inside the cabin, you will need to remove the front seats and the cabin liners at the left wing root. Then there will be several wire bundles that need to be moved out of the way. Expect that the vampire airplane will want a blood sacrifice before further cooperation, so drip a little somewhere, and then the drain piston will come right out.

[carusoam]

DP

[carusoam]

JS,

PM sent.

http://njmooney.com/

Best regards,

-a-

[M20F]

Anyone know where to specifically fine the static drains on a 67F (pictures would be great!)

[Hank]

The easy way to find the rear one is to remove the tailcone access panel, shine a flashlight inside and follow the tubing from the static ports.

Should be another one on the belly just in front of the wing. On my C, they are both small, ~1/8" diameter.

[Yetti]

On the 75F one is below the battery access panel.  Kind of in the middle of the panel.   It is a smallish button.    The other is on the pilots wing below the wing root about 4 inches out from the fuselage.  There was enough water in the static port that we had to open the battery access panel.  remove the tubing nut at the drain and blow it out. Cover one static port then the other.   Use your mouth to blow on the tubing.   Then do the drain till no more water comes out.

[hoot777]

I have a 1968 G model. I keep it hangered. On two occasions I’ve had it outside on trips with a pretty good rain system moving through and got water in the static system. How does it get in ?.  I’ve got tons of hours in GA planes and have never had a problem before. It clears up but takes a flight or two to do it. VSI and altimeter jumping in iFR conditions will get your attention.

[takair]

4 minutes ago, hoot777 said:

I have a 1968 G model. I keep it hangered. On two occasions I’ve had it outside on trips with a pretty good rain system moving through and got water in the static system. How does it get in ?.  I’ve got tons of hours in GA planes and have never had a problem before. It clears up but takes a flight or two to do it. VSI and altimeter jumping in iFR conditions will get your attention.

I believe that it is getting in through the small static port holes and there is a simultaneous barometric pressure change that draws it in further. The Mooney static ports seem smaller than most so create a good seal with just a little water. 

[hoot777]

Thanks

[47U]

There’s a change to the location of the ‘T’ in the static plumbing in M20-43.  Not sure if it applies to the G, but some C, J, and K serial numbers are included.  Not sure why the G and F are not listed in the applicability.

https://cdn2.hubspot.net/hubfs/4147179/technical_documents/service_instructions/sim20-43.pdf

 

[carusoam]

The pic above has the static drain in it...

Many Mooneys of the day did not get static drains...

 

To get a bunch of water in the static system... all it takes is the right weather system... heavy rain on a windy day can force a lot of drops through the static port hole...

201er shot a video regarding the effects of water on his static system... around here somewhere.

 

If you have never seen this in GA planes... you would have to have dual static vents, and a static system drain to get a similar effect...

Then leave your plane outside in heavy weather...

PP thoughts only, not an instrument tech...

Best regards,

-a-

[RobertGary1]

On 1/11/2013 at 7:29 PM, Ron McBride said:

You should have 2 pitot/static drain in your plane, 1 under the left wing near the fuselage, and the other under the belly near the tail access panel. Try opening these to drain your lines. Welcome to the list. Ron

And the one on the back of the pitot tube. It’s small but sounds like a bit of water is trapped there snd heating it up moves it a bit. 
-Robert 

[PT20J]

I've had similar things happen with water getting trapped in the static system. The pitot tube has a drain hole and less frequently traps water. Did you try the alternate static?l

If you don't have drains, disconnect the static line at the instrument end and blow air through it toward the static port. 

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