John Mininger Posted March 8, 2018 Report Share Posted March 8, 2018 Soon after I bought my 77J, I started having problems with the airspeed indicator. The airplane lived in the Houston and the Florida Keys area for most of its life, so the first freezing temperatures we had in Pennsylvania the static tube was blocked with ice. Classic symptom: climbing airspeed until I pulled the alternate static source, then everything settled down. We put it in a heated hangar overnight, disconnected and blew out the static lines and things were fine. Some months after that when taking off, the ASI started sticking at zero, then poped up to 60K, then settled down to 40K and everything smoothed out. I've had the ASI out and sent to an instrument shop 3 times now and it's good for a few months then starts sticking again. It's sticking again now. I'm done with pulling this 41 year old instrument out and sending it off somewhere to be worked on. I'd like to replace it with a new true ASI and I'm thinking of United Instruments 8100 series model. Any recommendations for a new ASI? Any recommendations of which 8100 series model? Thanks, John Quote Link to comment Share on other sites More sharing options...
Hank Posted March 8, 2018 Report Share Posted March 8, 2018 Are you using the Static Drain Button during preflight? That should clear up many of these issues if there's actually water in the lines. That's the only advice I can provide . . . . . . 1 Quote Link to comment Share on other sites More sharing options...
John Mininger Posted March 8, 2018 Author Report Share Posted March 8, 2018 Thanks Hank, I am using the static drain button, and the pitot drain button now. When I had the problem with the water, I only had the Mooney about 4 months and didn't know about them. But I think the current problem is the ASI itself. After the initial sticking on takeoff, the airspeed indication becomes very smooth and seems to be spot on. Quote Link to comment Share on other sites More sharing options...
Piloto Posted March 8, 2018 Report Share Posted March 8, 2018 2 hours ago, John Mininger said: Soon after I bought my 77J, I started having problems with the airspeed indicator. The airplane lived in the Houston and the Florida Keys area for most of its life, so the first freezing temperatures we had in Pennsylvania the static tube was blocked with ice. Classic symptom: climbing airspeed until I pulled the alternate static source, then everything settled down. We put it in a heated hangar overnight, disconnected and blew out the static lines and things were fine. Some months after that when taking off, the ASI started sticking at zero, then poped up to 60K, then settled down to 40K and everything smoothed out. I've had the ASI out and sent to an instrument shop 3 times now and it's good for a few months then starts sticking again. It's sticking again now. I'm done with pulling this 41 year old instrument out and sending it off somewhere to be worked on. I'd like to replace it with a new true ASI and I'm thinking of United Instruments 8100 series model. Any recommendations for a new ASI? Any recommendations of which 8100 series model? Thanks, John John any good airspeed indicator will work fine. The United 8100 series are a little bit expensive. Get one with the speed ranges on the scale and with the true airspeed feature. Check with Aircraft Spruce. José Quote Link to comment Share on other sites More sharing options...
Vance Harral Posted March 8, 2018 Report Share Posted March 8, 2018 3 hours ago, Hank said: Are you using the Static Drain Button during preflight? That should clear up many of these issues if there's actually water in the lines. We live in a low-humidity area and have been fortunate never to have had problems with water in our static/pitot lines. However, I do press the drain buttons every few preflights just to make sure they're not stuck. The question I have is, how well do these drains actually work? The diameter of the passage with the button pressed in seems so small as to be insufficient to break the surface tension of any water in the lines. In the pitot line you at least have the benefit of a tiny amount of ventilation due to the vent port of the pitot tube itself. But the static system is supposed to be sealed. If I injected a small amount of water in the static lines, I can't imagine it draining out that button drain without somehow pressurizing the lines behind the slug of water. I'm starting to question whether there's ever any benefit in pressing these drain buttons during a normal preflight, or if they're only there to provide an opening when blowing the lines dry from some other point in the system. Quote Link to comment Share on other sites More sharing options...
Bartman Posted March 8, 2018 Report Share Posted March 8, 2018 I agree with Vance. I always push the buttons, but rarely if ever see or feel any water. Occasionally if I fly thru moisture or after washing the VSI needle will be jumpy for a while, but I am rarely able to get anything out thru the static drain, and I have never gotten anything at all thru the Pitot drain. Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 8, 2018 Report Share Posted March 8, 2018 (edited) Unless you can find the original model you’re going to have some paper work to do to replace it. Have you tested it with a pitot static tester? I’d be worried the real issue is water still trapped in the lines. They T in the tail so just blowing it out doesn’t get all routes -Robert Edited March 8, 2018 by RobertGary1 Quote Link to comment Share on other sites More sharing options...
Yetti Posted March 8, 2018 Report Share Posted March 8, 2018 There is a trap loop in the tail between the two static ports. A fair amount of water will not make it to the drain by the battery. under proper supervision blowing the water out from the tubing that connects to the drain is a working solution. Should cover one port, then the other. 1 Quote Link to comment Share on other sites More sharing options...
Marauder Posted March 9, 2018 Report Share Posted March 9, 2018 I replaced my static port when a local avionics shop decided the only way to pass the 100’/min leak portion of the static test was to fill the valve with grease. The seat on the valve will corrode and it can be ground down a few times and a new O ring installed. Sent from my iPhone using Tapatalk Pro Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 9, 2018 Report Share Posted March 9, 2018 201er posted a video a while back of the effects of moisture in the pitot static system in his J... The Problem, I believe, was a rain storm while being parked outdoors. Other stuff... The M20C doesn’t get a static drain, just a dead leg that gets emptied at annual... or as needed... The long body gets two drains, one static, one pitot... easy enough to push the buttons while walking around... it also gets a nicely integrated alternate static source valve in the cockpit... I think I got a few drops out of the drains after flying through the outer rings of a hurricane.... Kind of an important thing to have working when flying in IMC... or on short final in any weather... Compare OH prices to whatever else you are considering... The ASI is necessary until you get at least two color screens or more... having one that calculate TAS with the input of OAT is nice... need a decent digital OAT to make the best use of it though.... PP thoughts only, not an instrument guru... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Yetti Posted March 9, 2018 Report Share Posted March 9, 2018 Later model F got two drains also. Quote Link to comment Share on other sites More sharing options...
nels Posted March 9, 2018 Report Share Posted March 9, 2018 Where is the drain button? Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 9, 2018 Report Share Posted March 9, 2018 For the O... 1) Pilot side, fuselage right about where the N is on the tail... about a couple of feet back from the trailing edge of the wing... 2) Pilot side wing root a few inches back from the leading edge... Two small bumps... push to operate. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
John Mininger Posted March 9, 2018 Author Report Share Posted March 9, 2018 I appreciate all the advise guys. I'm 99.9% sure that the current problem is the ASI itself, not the pitot/static system. All these lines have been blown out numerous times in the last year and a half. What I find rather frustrating is that no one, including United Instruments seems to be able to give me a part number for a 8100 series ASI for a 77 M20J. John Quote Link to comment Share on other sites More sharing options...
RobertGary1 Posted March 9, 2018 Report Share Posted March 9, 2018 I wonder if your the first person to ask. I’ve never heard of anyone replacing the asi. It’s very unusual for it to be moisture prone itself. -Robert Quote Link to comment Share on other sites More sharing options...
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