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Pitot system - odd event



 
 
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  #11  
Old May 24th 18, 08:43 PM posted to rec.aviation.soaring
Dave Nadler
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Posts: 1,297
Default Pitot system - odd event

On Wednesday, May 23, 2018 at 11:02:30 PM UTC-4, Del Jensen wrote:
Something clearly sent a shock through the pitot system


No... These exact symptoms can be caused....

Donkeys years ago I happened by a gliderport where I was assaulted by
an angry new glider owner. "Your instruments don't work worth crap!
P.O.S. !!! Go fly this glider and tell me what's wrong". And so forth.

I strapped on the shiny new plane and took off, noting incorrect ASI
on tow and general odd behavior. Enjoyed a nice flight and gave the new
owner some time to reflect on the error of his ways. Very peaceful
with no audio or instruments to distract from the pleasure of a nice
soaring day and the new-glider smell. Eventually I flew back home and
noted that as I rolled to a stop the ASI still read 45 knots.
New owner ran up and I pointed at the mechanical ASI...

The glider had been hosed down, and water was trapped in the low part
of the tube between the pitot probe and instruments. With enough airspeed
and agitation bubbles of air could get through the water, then the remaining
column of water acted like a water manometer. IIRC there was more than
a pint of water in the tube.

There was certainly no "burst diaphragm" in this instance but all other
symptoms match (including failure to correctly re-zero the electonic
ASI). Drying everything out (no compressed air EVER) cured all.

Please tell us the location of your pitot and the type of glider!

Hope that helps someone,
Best Regards, Dave
Ads
  #12  
Old May 24th 18, 09:55 PM posted to rec.aviation.soaring
Del Jensen
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Posts: 24
Default Pitot system - odd event

On Thursday, May 24, 2018 at 12:43:52 PM UTC-7, Dave Nadler wrote:
On Wednesday, May 23, 2018 at 11:02:30 PM UTC-4, Del Jensen wrote:
Something clearly sent a shock through the pitot system


No... These exact symptoms can be caused....

Donkeys years ago I happened by a gliderport where I was assaulted by
an angry new glider owner. "Your instruments don't work worth crap!
P.O.S. !!! Go fly this glider and tell me what's wrong". And so forth.

I strapped on the shiny new plane and took off, noting incorrect ASI
on tow and general odd behavior. Enjoyed a nice flight and gave the new
owner some time to reflect on the error of his ways. Very peaceful
with no audio or instruments to distract from the pleasure of a nice
soaring day and the new-glider smell. Eventually I flew back home and
noted that as I rolled to a stop the ASI still read 45 knots.
New owner ran up and I pointed at the mechanical ASI...

The glider had been hosed down, and water was trapped in the low part
of the tube between the pitot probe and instruments. With enough airspeed
and agitation bubbles of air could get through the water, then the remaining
column of water acted like a water manometer. IIRC there was more than
a pint of water in the tube.

There was certainly no "burst diaphragm" in this instance but all other
symptoms match (including failure to correctly re-zero the electonic
ASI). Drying everything out (no compressed air EVER) cured all.

Please tell us the location of your pitot and the type of glider!

Hope that helps someone,
Best Regards, Dave


Thanks guys. The glider is a glasflugel 304 (original version, 1980). Pitot is on vertical fin, static port on side of boom about 3/4 toward tail. Location is Arizona. Neither TE nor static was affected.

Glider is in hangar. I lost the pitot cover a couple of months ago, and have been meaning to get that taken care of. Maybe I should get on that.

It was a great soaring day, but I just puttered around locally for about an hour and a half after the airspeed failed, since I had to leave myself enough time to get behind the panel and pull the instruments once I got down.

Although I try to check things over one last time after belting in, I suppose it's possible the instrument was reading falsely at take off. I usually start rolling with flaps at -2 to get early aileron effectiveness, ease them back to neutral at about 45kts, so I usually take a glance at the airspeed well into the take off roll. I don't recall anything odd at that point. But who knows? That's a busy time, and most of take off is done by "feel," like everything else.

Landing without the instrument was a non-event. In some ways easier since I didn't feel any obligation to glance at the airspeed - easier to focus purely on attitude and wind noise, which is the we are supposed to do it. Landing with airspeed covered should be a part of training in my opinion.

P.S. I love my 304! The trailing edge spoiler/flap system is wonderful.
  #13  
Old May 24th 18, 10:14 PM posted to rec.aviation.soaring
Dave Nadler
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Posts: 1,297
Default Pitot system - odd event

On Thursday, May 24, 2018 at 4:55:39 PM UTC-4, Del Jensen wrote:
The glider is a glasflugel 304 (original version, 1980).
Pitot is on vertical fin, static port on side of boom about 3/4 toward tail.


Two places where the pitot tube could possibly get pinched
and transmit a shock to instruments:
- under the seat (hard landing, rolling over bump, heavy pilot)
- hinge-up panel (check tubing routing in this area carefully)

Let us know what you find!
See ya, Dave "YO"
  #14  
Old May 25th 18, 02:54 AM posted to rec.aviation.soaring
[email protected]
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Posts: 344
Default Pitot system - odd event

Excellent article by Lee Kuhlke in the July 2005 issue of Soaring magazine dealing with methods of troubleshooting your pitot/static/total energy system. I don't have the link available, but with the above information (Lee Kuhlke, July 2005, Title "How's Your Plumbing) you should be able to find it.Highly recommended.

Also, a great document from Mike Borgelt on the same subject.

https://www.dropbox.com/s/iqklz472pw...Leaks.pdf?dl=0
  #15  
Old May 25th 18, 05:00 AM posted to rec.aviation.soaring
Del Jensen
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Posts: 24
Default Pitot system - odd event

On Thursday, May 24, 2018 at 6:54:05 PM UTC-7, wrote:
Excellent article by Lee Kuhlke in the July 2005 issue of Soaring magazine dealing with methods of troubleshooting your pitot/static/total energy system. I don't have the link available, but with the above information (Lee Kuhlke, July 2005, Title "How's Your Plumbing) you should be able to find it.Highly recommended.

Also, a great document from Mike Borgelt on the same subject.

https://www.dropbox.com/s/iqklz472pw...Leaks.pdf?dl=0


Thank you so much. I've downloaded the Borgelt article and will track down the Kuhlke article. Also, appreciate Dave's advice; look under seat pan and tube routing through front hinge on panel/canopy. Makes sense. You've all been very helpful.
  #16  
Old May 25th 18, 01:51 PM posted to rec.aviation.soaring
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Default Pitot system - odd event

If the bellow ruptured, it seems like it would have made a path from the pitot to static which would have made the altimeter readings wierd.

From Dave's story, it might be worth putting the affected instruments in a sealed bag of fresh dessicant to dry them out. A cell phone that was run thru the wash takes about 24 hours, so a week should be more that enough time to know for sure if this will help.

Good luck.
  #17  
Old May 25th 18, 04:23 PM posted to rec.aviation.soaring
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Default Pitot system - odd event

This happened on my ASW-15 a few years back - when it was stored in the locked trailer in a garage over the winter. It was fine on the last flight of the year at the end of October and when I took it in for the annual in spring I noticed the ASI was off when I looked in the cockpit. The diaphragm had burst at the edge sometime during the off season. I think in my case it was just age.
  #18  
Old May 25th 18, 05:27 PM posted to rec.aviation.soaring
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Posts: 1,750
Default Pitot system - odd event

On Friday, May 25, 2018 at 11:23:52 AM UTC-4, wrote:
This happened on my ASW-15 a few years back - when it was stored in the locked trailer in a garage over the winter. It was fine on the last flight of the year at the end of October and when I took it in for the annual in spring I noticed the ASI was off when I looked in the cockpit. The diaphragm had burst at the edge sometime during the off season. I think in my case it was just age.


It is quite common that moisture builds up in the diaphragm and causes corrosion at the bottom edge, eventually leading to failure.
I've seen it a dozen times.
Any glider kept outside that has had a pitot blocked by water needs to be drained and dried. Obvious, but people don't do it.
UH
UH
  #19  
Old May 25th 18, 09:15 PM posted to rec.aviation.soaring
[email protected]
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Posts: 267
Default Pitot system - odd event

On Friday, May 25, 2018 at 9:27:39 AM UTC-7, wrote:
On Friday, May 25, 2018 at 11:23:52 AM UTC-4, wrote:
This happened on my ASW-15 a few years back - when it was stored in the locked trailer in a garage over the winter. It was fine on the last flight of the year at the end of October and when I took it in for the annual in spring I noticed the ASI was off when I looked in the cockpit. The diaphragm had burst at the edge sometime during the off season. I think in my case it was just age.


It is quite common that moisture builds up in the diaphragm and causes corrosion at the bottom edge, eventually leading to failure.
I've seen it a dozen times.
Any glider kept outside that has had a pitot blocked by water needs to be drained and dried. Obvious, but people don't do it.
UH
UH


I never leave my glider out BUT now that I think of it that particular autumn most of the flying days we had humidity around 90%+ and the temperature and dew point were frequently very close. Whenever I rolled to a stop on landing the wings were almost instantly covered in moisture, the face of my electronic vario had some moisture condensed on the glass face quite often and once the radio acted up and when I took off the top plate I saw that the top of the circuit board was covered in dew... It worked fine when I dried it out in a warm room but I wouldn't be surprised if moisture condensed in the ASI led to corrosion and failure.
  #20  
Old May 25th 18, 10:35 PM posted to rec.aviation.soaring
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Default Pitot system - odd event

My 14-year-old ASI failed at Uvalde mid-contest. One day it worked. The next morning apparently the diaphragm or some other internal part was open. Sometimes stuff breaks. Usually only one thing at a time, but not always.

Chip Bearden
 




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