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Frozen Pitot line

jthocker

jthocker

Well Known Member
After practicing with the team this past weekend in Charlotte, two of us needed to fly north on Christmas eve to fulfill our Christmas commitments. There was a large system of moisture to fly thru on our way to Cincinnati and Detroit.
Both airplanes are G3X equipped with Dynon heated pitot tubes.
Both of us eventually suffered airspeed failures, with working pitot heats.
Pre flight showed pitot getting hot along with associated amp increase. Amp increase in flight was also verified.
I am theorizing that the copious amounts of rain we flew thru entered the pitot line and froze somewhere in the wing.
Has anyone else experienced this with a Dynon pitot, or any other heated pitot?
Is there a flaw in the Dynon pitot that allows water in?
Yes the pitot system passed the static check!
 
Jon,

I have a Gretz and performed extensive testing on it a couple years ago. I actually dipped it in a bucket of ice water and couldn't get it to freeze.

Thinking out loud for a moment:
  1. To what temp does Dynon heat the pitot?
  2. Where is the heater wire located? i.e. is it located in one 1/4" area or spread across several inches of the pitot tube
  3. By chance do you transition to a non metallic tube and how close to the pitot is that transition?
1 & 2 may be considered proprietary information by Dynon.

My thoughts on #3 is if the transition is to an aluminum tubing, perhaps some of the heat may be transfered a little futher along the tubing. Although the reverse could be true in that a cold wing could cause any water in the tubing to freeze.

In my RV, I have a 6" rise in my Gretz pitot before I transition to the aluminum tubing in the wing. I would suspect that if water froze, it would have to be internal to the pitot. I wouldn't think that water would flow past that vertical rise at the speeds we are flying. (but I could be wrong):eek:

bob
 
rleffler said:
Jon,

I have a Gretz and performed extensive testing on it a couple years ago. I actually dipped it in a bucket of ice water and couldn't get it to freeze.

Thinking out loud for a moment:
  1. To what temp does Dynon heat the pitot?
  2. Where is the heater wire located? i.e. is it located in one 1/4" area or spread across several inches of the pitot tube
  3. By chance do you transition to a non metallic tube and how close to the pitot is that transition?
1 & 2 may be considered proprietary information by Dynon.

My thoughts on #3 is if the transition is to an aluminum tubing, perhaps some of the heat may be transfered a little futher along the tubing. Although the reverse could be true in that a cold wing could cause any water in the tubing to freeze.

In my RV, I have a 6" rise in my Gretz pitot before I transition to the aluminum tubing in the wing. I would suspect that if water froze, it would have to be internal to the pitot. I wouldn't think that water would flow past that vertical rise at the speeds we are flying. (but I could be wrong):eek:

bob
Click to expand...

Hi Bob,
I used the Safe Air kit for my pitot plumbing, which transitions from the 3/16 in aluminum stub tubes in the Dynon pitot, to the green and blue nylon tubing that runs throughout the rest of the pitot static system. I would estimate that the aluminum line rises at least 8 inches from the pitot then curves inboard and down and then transitions to the nylon tubing via the push in quick connects.
Wondering if this thing might be an answer?

http://www.aircraftspruce.com/catalog/inpages/pitotstatic.php?clickkey=252315
 
Heated Pitot's have a drain hole in the back for just this reason, the moisture should not be getting past this drain point, if that hole freezes than you may have fluid blocked tube. When you landed was it immediately back to normal? (a frozen or blocked pitot line will show an airspeed indication)
 
Jon,

Good thread for me since I have bought a Dynon heated pitot for my RV that I have yet to install.

How did the G3X system handle the loss of airspeed?
 
We see these thread pop up each year when the cold weather swoops in.
Ill offer a few thoughts.
1. There is moisture in the system just as a matter of fact always. Our constant change in temperature up and down the altitudes and humidity levels means moisture in the lines.
2. Our systems were not designed well for draining. Every low point, both static and pressure, would require a drain to be useful.
3. I put less emphasis on the rain of the day and more emphasis on high moisture content air combined with headin in and out of now very cold air.

Net net my analysis, you did not get moisture from rain entering pitot and going up the lines. You were in high moisture content air up and down freezing levels and probably had already some drops in the system from months and years gone by.
 
Walt said:
Heated Pitot's have a drain hole in the back for just this reason, the moisture should not be getting past this drain point, if that hole freezes than you may have fluid blocked tube. When you landed was it immediately back to normal? (a frozen or blocked pitot line will show an airspeed indication)
Click to expand...

Walt,
In my case, I flew through moderate rain all the way from Charlotte to Detroit on Monday. IFR most of the way, temps around freezing at 8000 ft. Broke into the clear about 100 miles from destination, with temps coming down. Started seeing some odd airspeed indications but seemed to clear up on descent, shot the ILS into KPTK, landed and had FBO put plane in heated hangar for the night. Left Pontiac around noon and climbed up on top at 8000 again. I was amazed at my gradually increasing TAS as I flew into warmer air as I flew south! My LOP 60% pwr speed is 168 knots true. I watched as it went to 170, 176, 180, 186, 188! When I was given a descent clearance and nosed over guess what, airspeed began to fall off, until the GX pilot warned "min airspeed" at 70 knots, I clicked off the autopilot at that point because the tru track then pitched over to override the vertical speed mode to maintain 70 knots minimum. On further descent the airspeed finally went to zero and the G3X finally just gave me a red X over the airspeed window.
On a side note the G3X and GX pilot captured and flew a perfect ILS without the airspeed indication.
So I'm pretty sure I had a blocked pitot line, not sure if it's a Dynon problem or a system installation problem.
Also wondering if Garmin ought to take a page from the Dynon playbook and substitute a magenta GPS ground speed in the airspeed window when the airspeed is suspect?
 
It certainly is sounding more like water in another part of the line is freezing. Then that yields the question of how it got in there and how often should the pitot and static lines be checked for water? Blowing them out would be difficult since you would have to disconnect everthing before blowing into any of the tubing.

Your statement about TAS increasing after you left PTK was interesting. That would imply that the water re-froze after you left the heated hangar.

Please keep us posted as to what you find.

bob
 
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Definately sounds like a plugged pitot, it doesn't have to be frozen, a slug of water in the line somewhere can cause similar issues.
 
jthocker said:
Also wondering if Garmin ought to take a page from the Dynon playbook and substitute a magenta GPS ground speed in the airspeed window when the airspeed is suspect?
Click to expand...

Since its a TSO'ed part the FAA doest not want to give the pilot false information where we are used to or are required to get specific information.

However, Garmin could put that substituted speed in another location
 
Perhaps the static ports froze...no alternate static source? There is no air movement in the pitot lines so water can't get past the horizontal if there's an adequately sized drain hole in the passage in the pitot tube.
 
rocketbob said:
Perhaps the static ports froze...no alternate static source? There is no air movement in the pitot lines so water can't get past the horizontal if there's an adequately sized drain hole in the passage in the pitot tube.
Click to expand...

Can't rule anything out but, airpseed increasing/decreasing with altitude changes clearly points to a blocked pitot port.
 
drain hole size?

some drain holes need to be .035 to prevent freezing. .020 resulted in freezing over where .035 did not. however, I don't know how that would affect the airspeed indication.
 
So, if we can agree that moisture is collecting in the pitot line after the probe and then freezing. Is the problem a poorly designed pitot probe (inadequate drain) or improper pitot line placement/routing (possible water trap) ????
 
Walt said:
Can't rule anything out but, airpseed increasing/decreasing with altitude changes clearly points to a blocked pitot port.
Click to expand...

That and vertical speed would be zero, altimeter would freeze if the static ports were blocked.
 
There are actually two drain holes. One for the pitot line itself to drain inside the assembly, and another one for the assembly to drain. If both holes are not adequately heated and drained, well then they'll freeze. So it sounds like the Dynon's got some issues. The hole in the pitot has to stay as small as practical to not introduce a pitot error.
 
flare 60-90 degree away from drain hole

some recommend a 60-90 degree included angle flare away from drain hole to decrease surface tension to help prevent freezing. I'm not sure how to do this with a pitot tube.
 
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Just wondering did you notice any ice on your wings or canopy? I would suspect if the pitot tube had iced over, you would have seen at least some ice in the wing root area as well.

A couple of times that I inadvertently got into icing condition, I had no trouble with my Dynon Pitot tube but had ice on my wing root and glare shield. The one time that I got cut in it quickly, I did not have my pitot heat on and saw my speed decreasing fast without any apparent reason. I got my normal speed as soon as I turned the pitot heat on.
 
Bavafa said:
Just wondering did you notice any ice on your wings or canopy? I would suspect if the pitot tube had iced over, you would have seen at least some ice in the wing root area as well.

A couple of times that I inadvertently got into icing condition, I had no trouble with my Dynon Pitot tube but had ice on my wing root and glare shield. The one time that I got cut in it quickly, I did not have my pitot heat on and saw my speed decreasing fast without any apparent reason. I got my normal speed as soon as I turned the pitot heat on.
Click to expand...

Uh lets see, title to the thread is FROZEN PITOT LINE!!!!
Would it not be safe to assume that I might have been experiencing ICE somewhere!
Of course I had periods of ICE on the wings!
The PITOT HEAT and carb heat for that matter were on CONTINUOUSLY!

ARRRGHHH!
 
Soooo,pitot heat was on . . and the pitot gets hot?

I assume you checked, this, but did not see where it was stated that an actual check of the pitot temp rise on the ground was checked.

I am about to plumb my system so the cause/solution is of high interest, thanks for sharing.
 
BillL said:
I assume you checked, this, but did not see where it was stated that an actual check of the pitot temp rise on the ground was checked.

I am about to plumb my system so the cause/solution is of high interest, thanks for sharing.
Click to expand...

Bill,
I'm going to assume that you did not read my original post!
 
I've read a similar post to this one at some point in the past. He had a dynon heated pitot that kept icing up, switched out pitots with a certified heated and the problem went away. I can't seem to locate the thread, and perhaps it's the mad cow acting up again but I would swear I've read in here a thread with the same issue. Drain hole icing up and not enough heat back that far to thaw it, as I recall.
 
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ColoRv said:
I've read a similar post to this one at some point in the past. He had a dynon heated pitot that kept icing up, switched out pitots with a certified heated and the problem went away. I can't seem to locate the thread, and perhaps it's the mad cow acting up again but I would swear I've read in here a thread with the same issue.
Click to expand...

Yes you have and I had hoped that was a fluke....now I am not so sure!

I recently purchased a Dynon unit for my upgrade. Not sure what to do with it now.
 
jthocker said:
Uh lets see, title to the thread is FROZEN PITOT LINE!!!!
Would it not be safe to assume that I might have been experiencing ICE somewhere!
Of course I had periods of ICE on the wings!
The PITOT HEAT and carb heat for that matter were on CONTINUOUSLY!

ARRRGHHH!
Click to expand...
I don't assume, I ask!
 
I have 400 hrs flight time on a Gretz heated pitot and it has Performed as required every time the heat was needed.

Somewhere on this forum there is a thread about plumbing an alternate pitot from the aft bullhead of the engine cooling plenum. There may be small errors but perhaps better than no air speed indication.

Glad to hear the G3 run the ILS regardless!
 
jthocker said:
Also wondering if Garmin ought to take a page from the Dynon playbook and substitute a magenta GPS ground speed in the airspeed window when the airspeed is suspect?
Click to expand...

kinger said:
Since its a TSO'ed part the FAA doest not want to give the pilot false information where we are used to or are required to get specific information.

However, Garmin could put that substituted speed in another location
Click to expand...

Although the G3X system does not hold any TSOs, James's statement still agrees perfectly with the many cumulative lifetimes' worth of human factors experience that went into its design: the indicated airspeed tape is for indicated airspeed alone. However, as I'm sure Jon will be able to tell you, there is indeed a permanent display of GPS groundspeed on the G3X primary flight display, just an inch or two below the indicated airspeed tape. It's even magenta. :)

- Matt
 
It Appears You're Not the Only Dynon Pitot User With this Issue

Jon:
The heated pitot on my 9A is off of a Cessna. Never experienced the problem you describe with it or with the same mounted on factory aircraft. Based at KPTK and have spent a fair amount of time in icing conditions (most in factory aircraft). The few occasions I've experienced a frozen pitot have always been resolved by flipping the "on" switch. Before you start digging out the plumbing, you might check with Dynon to see where the heating element starts and finishes. Sounds like a heat/drain issue, as a couple of other posters have suggested. Please keep us posted on what you find.
Terry, CFI
RV9A N323TP
 
BillL said:
It is already made clear that I don't read well for comprehension, so this might be off, but it seems this is two additional posters' with apparently the same issue.

"Dynon heated pitot incident"
http://www.vansairforce.com/community/showthread.php?t=37974 OP

http://www.vansairforce.com/community/showthread.php?t=89650

Post #10

There maybe more using "site:vansairforce.com dynon +heated +pitot +icing" in a google search.
Click to expand...

Good one Bill!;)

Thanks for the threads. I don't do searches very well.
 
Worthy of note is the fact that some AN5812-type pitots have two heating elements, one at the fwd tip and one towards the rear where the drain is.
 
g3xpert said:
Although the G3X system does not hold any TSOs, James's statement still agrees perfectly with the many cumulative lifetimes' worth of human factors experience that went into its design: the indicated airspeed tape is for indicated airspeed alone. However, as I'm sure Jon will be able to tell you, there is indeed a permanent display of GPS groundspeed on the G3X primary flight display, just an inch or two below the indicated airspeed tape. It's even magenta. :)

- Matt
Click to expand...

Matt is correct and I just used that GPS ground speed and continued on the ILS.
Sorry Matt, old habits die hard. A few years ago I was elated that Dynon finally added GPS ground speed to their attitude solution when airspeed became unreliable. I am extremely happy with my G3X and it's more "robust" AHRS. I think I'll now ditch the Dynon pitot also.
 
Argh. You've got me worrying again Jon. I've got the exact same pitot and plumbing. Was most likely going to test fit everything this weekend as I build my wings.

Just out of curiosity, has anyone ever tried directly connecting the heater power lines to a circuit switch, completely bypassing the temperature controller? Maybe if we can determine that the heater element is strong enough, we could coerce Dynon into somehow updating the controller's heating firmware, even if you have to send the controller back?
 
sbalmos said:
Argh. You've got me worrying again Jon. I've got the exact same pitot and plumbing. Was most likely going to test fit everything this weekend as I build my wings.

Just out of curiosity, has anyone ever tried directly connecting the heater power lines to a circuit switch, completely bypassing the temperature controller? Maybe if we can determine that the heater element is strong enough, we could coerce Dynon into somehow updating the controller's heating firmware, even if you have to send the controller back?
Click to expand...

Scott,
I don't believe it's a heating issue, I think it's a faulty drain design.
 
I am perplexed as to how to explain a gradually (from normal to higher than normal) increasing airspeed indication while maintaining level flight at 8000'. Also, on descent to Charlotte, did the correct airspeed come back as the OAT went above freezing? This should have happened almost immediately if the blockage was in the pitot tube, but perhaps delayed if inside the wing.
 
jthocker said:
Scott,
I don't believe it's a heating issue, I think it's a faulty drain design.
Click to expand...

A little off subject.......

I have a Gretz pitot and am not aware of any situations in which it has frozen as long as the pitot controller circuit was functional. It also doesn't have a drain hole. This got me wondering. Perhaps the bore diameter is larger than the Dynon which might lesson the odds water freezing? Or perhaps the heater wire does a more effective job at heating the copper inner tube and the surrounding composite material?

My intent is not to slam the Dynon pitot, but to understand why one design may work better than another?

Bob
 
Brantel said:
Yes you have and I had hoped that was a fluke....now I am not so sure!

I recently purchased a Dynon unit for my upgrade. Not sure what to do with it now.
Click to expand...

I was in the same boat 6 months ago. I returned the dynon unit. While I won't intentionally fly into icing conditions...there isn't anything about the dynon that makes me want to overlook a lack of heating in a heated pitot. It only has two functions and appears to occasionally fail at one of them.

I have a dynon D6 as backup for the G3X system and I suppose the dynon AOA may have been easier to install than the AFS sport since the D6 is already present, but it only took a couple hours to install the AFS so it's a non-issue for me. The dynon also looks like cheap pot metal when compared to the many used certified units that are easily obtained on eBay. The cost is enough less than the dynon to drop the price of the AFS down to inconsequential (in airplane dollars). Aircraft Spruce charged me a restocking fee but I still don't regret the decision. One less thing to worry about.
 
Tonight I was looking at the heated Piper pitot on my Comanche and was surprised to see that there are no drain holes anywhere in it.

Hmmmm. Interesting!

After studying the shape of the inlet hole by shining a light down in the tip, their solution was so dang simple that I had to have a little bit of a chuckle. Basically there is a baffle at the forward end with a hole at the very top, out of the direct impact path of a water droplet. Since this hole is well above the inlet hole, water can never accumulate to where it would flow into the rest of the tube, since it would drain out the front first. Quite clever! It would be fairly simple to mod a Dynon pitot to mimic this setup and you may as well close up the drain holes.

The pitot on my C150, however, has a couple of drain holes. Apparently there were some sharper engineers at Piper.
 
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I wonder if the same could be achieved by simply mounting the pitot tube angled tip down by a few degrees. This way, any water that finds its way into the probe will, under the influence of gravity, flow forward toward the tip of the probe rather than toward the back. And in terms of affecting the measured ram air pressure, the pitot tube should not be terribly sensitive to angular differences of a few degrees, so I've been told.
 
Since this thread is primarily about our Heated AOA/Pitot Probe, I wanted to let you guys know that we have a big update on this issue, including a replacement program for any of you that currently have our Heated AOA/Pitot Probe. See this thread for more details.

Michael Schofield
Marketing Manager
Dynon Avionics
 
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