Airspeed Indicator not zero at Rest

[Steveolyo]

During our annual for our 1969 M20F we were testing the gear retraction and had to apply pressure to the pitot tube. Apparently we applied too much and now the ASI reads about 30mph while the plane is at rest.

Is there an adjustment to zero the ASI or do we need to remove it and send it somewhere for servicing?

Any help would be appreciated.

[Piloto]

Try sucking in by mouth into the pitot tube. On ASI, altimeter and VSI you never apply more pressure/vacuum than that of your lungs.

José 

[Guest]

5 minutes ago, Steveolyo said:

During our annual for our 1969 M20F we were testing the gear retraction and had to apply pressure to the pitot tube. Apparently we applied too much and now the ASI reads about 30mph while the plane is at rest.

Is there an adjustment to zero the ASI or do we need to remove it and send it somewhere for servicing?

Any help would be appreciated.

You have damaged the sensitive inner workings, repair or overhaul is the only choice.

Clarence 

[Steveolyo]

I did try sucking

No Dice on that. 

Any recommendations on a shop to send it to?

Thanks.

[Marauder]

I sent mine to Mid-Continent. Paid $350 for the overhaul and to have the face redone.

Sent from my iPad using Tapatalk

[Steveolyo]

Oh nice. I wouldn't mind switching the face to knots.

 

[ArtVandelay]

Oh nice. I wouldn't mind switching the face to knots.

 

I was told you couldn't do that, if dual you can switch the scales and have knots on the outside scale instead of the harder to see inner scale.

[Piloto]

Check on Aircraft Spruce. I would replace with one with TAS

http://www.aircraftspruce.com/catalog/inpages/sigmatrueairspeed.php?clickkey=3020788

José

 

[Browncbr1]

I had this issue once with another plane.. sent it to Rudy Instruments and I recall it was in the $100 range to overhaul.  

I've had them overhaul a few instruments, and generally good prices..  He did a DG for me, which came apart after 2 or 3 hours, but warrantied it and has been good ever since.

[TTaylor]

Just had a VSI and manifold/fuel pressure gauges overhauled at Pressure Avionics in KS.  Very nice work on both.

http://www.pressureavionics.com/index.htm

 

[Steveolyo]

I sent it off to Rudy Avionics in Arkansas on Monday. They turned it around in one day and shipped it back. I had bent the long lever. I wonder if they replaced it or just bent it back.

 

[carusoam]

Great follow-up detail, Steve.

Best regards,

-a-

[SpamPilot]

FYI, I just had the same symptom on my M20F, but with a different cause, so I'll mention it here for those who might be searching on the same issue.  In my case, it was water in the static line that was holding the needle off zero.  If you plugged one static port, you could suck or blow into the other port and push the needle to a different location above or below zero, and it would stay there.  I then discovered there's a drain for the static line on the bottom of the aircraft, below the battery compartment door.  It looks like a small metal pushbutton sticking out from the bottom of the fuselage.  I pushed the button and several drops of rusty water dribbled out.  I had a helper blow into one static port (with the other plugged) and that forced even more water out.  Problem solved.  Obviously, if you remove the AI from the aircraft and it still doesn't read zero, then your AI has a problem, but draining the static line is a good thing to check first.

 

[Steveolyo]

Yes there are a couple of drains as shown on the attachment. One for the static and one for the pitot. I currently have a leak in my pitot lines so that's my next project. The fun never ends.

[carusoam]

201er reported a similar challenge a year or so ago, being tied down outside during a rain storm.

Best regards,

-a-

[mike_elliott]

On ‎4‎/‎26‎/‎2016 at 6:08 PM, Piloto said:

Try sucking in by mouth into the pitot tube

Last time I suggested that I got smacked

[PTK]

On April 26, 2016 at 6:00 PM, Steveolyo said:

...the ASI reads about 30mph while the plane is at rest.

Yes, a Mooney is never at rest! It can't sit still! 

It's in the Performane section of your POH. It has to do with the considerably reduced drag of the laminal flow wing and ground effect!!  

[N201MKTurbo]

On ‎5‎/‎10‎/‎2016 at 8:30 PM, Steveolyo said:

Yes there are a couple of drains as shown on the attachment. One for the static and one for the pitot. I currently have a leak in my pitot lines so that's my next project. The fun never ends.

 

My static system wouldn't seal last year. It turned out to be the drain valve. It was a ball of rust inside. To take them apart, remove both tubes from the tee, unscrew the tee from the fitting riveted to the skin. I wire brushed and then polished the pin, replaced the O-rings, used a dremel wire brush to clean the fitting in the plane. It then sealed up nice and tight and I passed my static test!

[Steveolyo]

How do you get at that drain? I tried from inside, from under the wing, from an access panel. Couldn't find a way to open that valve to clean it. Please share.

 

[Yetti]

I would not blow into a static port, you risk pushing water past the drain.  Which is accessed via the battery compartment door.   Better to push it out via removing the line and the drain then blowing it out the static port.

I tried using the drain, but there was too much water so had to remove the line.

There should be alt static valve under the dash, if you have water

[captainglen]

Most airspeed indicators have a feature called a gust lock this a hard stop around 30 MPH to keep the wind from bouncing the needle and wearing the gears causing hysteresis. Put a slight pitot pressure let it out slowly and see if it stops hard or soft at 30, it should stop hard. If however you have any doubt have someone do a pitot test; you just don't mess around with suspected significant airspeed indication errors.

[wishboneash]

On 4/26/2016 at 6:29 PM, Piloto said:

Check on Aircraft Spruce. I would replace with one with TAS

http://www.aircraftspruce.com/catalog/inpages/sigmatrueairspeed.php?clickkey=3020788

José

 

I don't understand why they put the moveable scale in mph instead of knots. I have to always go back and divide that by 1.15 to get to knots after applying the temp/altitude correction.

[PTK]

2 hours ago, Hyett6420 said:

I fully concur.  I has told by my a and p never to blow into the pitot...

I fully concur also. If my a&p saw me blowing into the pitot tube he would quietly try to persuade me to do that in a more private setting like inside the hangar!  

 

[Guest]

3 hours ago, Hyett6420 said:

I fully concur.  I has told by my a and p never to blow into the pitot or the static ports as the pressure we can exert doing that damages them. 

I too have a static leak on one of the ports on the side, but I was told by my nav com a and Omar annual tha was ok. As the aircraft is nor pressured if there is a leak in the static lines it will pick up the ambient pressure anyway in the fuselage which is the same as the outside air pressure.  Which makes logical sense to me.  The nav com guy is a bit of geek about this stuff so I trust him.  

Andrew,

I'm confused, are you saying that your static system has a leak beyond the accepted 100'/ minute?  If it is leaking, your contention that the pressure is the same inside the fuselage may be in error.  It's the equivalent of flying with the alternate static valve open.

Clarence

[Marauder]

8 hours ago, Hyett6420 said:

He just said there was a leak and signed it off. He would not have done I assume if it was outside limits.   I'll ask him to make sure. The leak is in the joints where the plastic tubes join the t drain valve in the battery box he said. 

I had the same thing happen when I went in to find out why my altitude was always 200' off. They address the calibration issue with altitude being off but noted a 700' leak in the static system. They signed the plane off and I found out the next day 100' was the limit. Their response was "it doesn't matter in unpressurized planes". I had them find and fix the leak. Their "fix" was to wedge grease into the static port because they couldn't get the seat ground down to seal correctly. I ended up replacing the static port and the avionics shop.