Airspeed Indicator Strangeness

Yesterday on the takeoff roll, I discovered my airspeed indicator was
stuck. I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. Then I verified that the airspeed indicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. OK, I'm an
experienced soaring pilot, and I don't need no stinking airspeed
indicator, so off I go cross-country. As luck (or lack of airspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. Tilt back down, ASI
sticks. Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.

This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. Anyone have any ideas?

TIA,

Frank

On Jun 2, 9:04 am, Frank wrote:
Yesterday on the takeoff roll, I discovered my airspeed indicator was
stuck. I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. Then I verified that the airspeed indicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. OK, I'm an
experienced soaring pilot, and I don't need no stinking airspeed
indicator, so off I go cross-country. As luck (or lack of airspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. Tilt back down, ASI
sticks. Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.

This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. Anyone have any ideas?

TIA,

Frank

Only time I had this happen was after I'd had the panel out of one of
my gliders. I had a four line quick connect for panel removal. All
appeared to work properly on the ground during pre-flight, but on tow
the ASI stuck at 90kts at all speeds. After flying around for a while
(watching the Blue Angels from a distance), I landed and reseated the
quick connect fitting. Worked fine after that.

Frank W

what did you get out of the Pitot tube when you blew it out? Mud Daubers?
Water?
water could be lying in a line that moves as the attitude of the lines
change.....mud daubers leave mud in the lines that hardens to solid dry dirt
(like cement) than could also be traveling in the lines with pressure.
also since the needle is very close to the glass faceplate check to see that
it isn't bent or have moisture inside the face that could cause enough
friction to cause it to stick
tim
Please visit the Wings & Wheels website at www.wingsandwheels.com



"Frank" wrote in message
...
Yesterday on the takeoff roll, I discovered my airspeed indicator was
stuck. I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. Then I verified that the airspeed indicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. OK, I'm an
experienced soaring pilot, and I don't need no stinking airspeed
indicator, so off I go cross-country. As luck (or lack of airspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. Tilt back down, ASI
sticks. Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.

This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. Anyone have any ideas?

TIA,

Frank

On Jun 2, 9:04*am, "Tim Mara" wrote:
what did you get out of the Pitot tube when you blew it out? Mud Daubers?
Water?
water could be lying in a line that moves as the attitude of the lines
change.....mud daubers leave mud in the lines that hardens to solid dry dirt
(like cement) than could also be traveling in the lines with pressure.
also since the needle is very close to the glass faceplate check to see that
it isn't bent or have moisture inside the face that could cause enough
friction to cause it to stick
tim
Please visit the Wings & Wheels website atwww.wingsandwheels.com

"Frank" wrote in message

...



Yesterday on the takeoff roll, I discovered my airspeed indicator was
stuck. *I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. *Then I verified that the airspeed indicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. *OK, I'm an
experienced soaring pilot, and I don't need no stinking airspeed
indicator, so off I go cross-country. *As luck (or lack of airspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. *I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. *So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. *Tilt back down, ASI
sticks. *Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.



Frank,
Check your static line, also. A blocked static (in the down position)
will block pitot pressure from exiting the ASI and it won't move. I'd
remove both lines and make sure you can blow back from the instrument
panel to the probe. Sounds like a mud-dauber problem to me. I have
seen these little buggers build a nest in one afternoon. I put in one
of Tim's plugs right after I remove the triple probe.
JJ
This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. *Anyone have any ideas?

TIA,

Frank- Hide quoted text -

- Show quoted text -

On Jun 2, 1:23*pm, JJ Sinclair wrote:
...I have
seen these little buggers build a nest in one afternoon...

I can top that - I've had them build two nests in a single afternoon.
I found the first one on pre-flight, cleaned it out, and mama wasp
built another nest before I launched.

"Frank" wrote in message
...
Yesterday on the takeoff roll, I discovered my airspeed indicator was
stuck. I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. Then I verified that the airspeed indicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. OK, I'm an
experienced soaring pilot, and I don't need no stinking airspeed
indicator, so off I go cross-country. As luck (or lack of airspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. Tilt back down, ASI
sticks. Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.

This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. Anyone have any ideas?

TIA,

Frank

Frank:
Isolate the problem stepwise--
Remove all lines from ASI
Get a small medical syringe or similar and tubing, and put in 2-3 cc of
air into the pitot line. Do this with panel down. If it works then, it is
plumbing. If not, it is ASI internal problem.
If ASI problem, remove from panel and retest.
If not ASI, remove all connections to pitot (electronic TE, etc) and plug
them. Use large syringe to pressurize the pitot line in reverse--i.e., from
instrument connection end to pitot probe end, but be careful--don't blow the
tubing off the internal connection to the probe.
Then check for static line obstruction, same way. You could also use the
large syringe to apply negative pressure at the instrument end and suck out
water etc.

This should diagnose it for you.

Hartley Falbaum
USA "KF"

Well, yesterday I replaced my old ASI with a new one from Eastern
Sailplane, and verified that the old one was defective. I could hold
the old ASI with it's face oriented vertically (normal orientation in
flight) and it would stick. Oriented with its face tilted up about 30
degrees (as if it was installed in the Ventus with the instrument
panel raised), and it worked fine. Gotta love Murphy's law!

Frank


On Jun 2, 11:04*am, Frank wrote:
Yesterday on the takeoff roll, I discovered myairspeedindicatorwas
stuck. *I got off tow a little early, and returned to the field to
sort things out.

Back on the ground, I visually inspected the pitot tube (in the
vertical fin on my Ventus 2bx), removed and blew out the short pitot
tube, and put it back on. *Then I verified that theairspeedindicator
responded correctly when I (carefully!) blew into the pitot tube.
Problem solved (I thought)

On tow again, I found I had the same problem - hmm. *OK, I'm an
experienced soaring pilot, and I don't need no stinkingairspeedindicator, so off I go cross-country. *As luck (or lack ofairspeed
indications) would have it, I landed out after 200km, about 30 miles
from home - ah well.

While waiting for my crew, I had plenty of time to troubleshoot the
ASI problem. *I repeated the steps I had done before, and verified
that the ASI responded correctly on the ground - how could this be?
Then I had the bright idea that the difference might be the position
of the instrument panel - tilted up or down in the Ventus. *So, I put
the panel down in the flying position, and voila - the ASI sticks!
Tilted it back up, and the ASI works fine. *Tilt back down, ASI
sticks. *Of course, the original ground check had been done with the
panel tilted up - lucky me!

After a number of other experiments, I was able to confirm to my
satisfaction that no tubing was being pinched when the panel was put
in the flying position, and the only variable was the orientation
(tilted or horizontal) of the instrument itself.

This is a fairly new instrument (circa 2002), so I'm puzzled by this
apparent failure. *Anyone have any ideas?

TIA,

Frank