airspeed indicator problem after TT2 transponder install

On Mar 3, 4:21*pm, Frank Paynter wrote:
On Mar 3, 10:26*am, Frank Paynter wrote:





I installed a TT21 transponder over the winter, and as per the
installation instructions, tapped into my ship's static line for
altitude reporting. *Yesterday I checked the transponder with Orlando
ATC and they reported a good signal and proper altitude reporting. *So
far, so good.

Then I noticed my airspeed indicator seemed to be reading
significantly higher than normal, and I confirmed this with a stall
series. *My Ventus 2bx, which normally stalls in the 40-45kt range
depending on bank angle, now is apparently stalling in the 50-55kt
range. *The ship actually feels pretty much the same as before,
although I haven't flown for 3 months so that's a bit hard to tell for
sure.

My dry flying weight is probably about 5-10lbs higher this year than
last, as I added the TT21 itself, plus a 5-lb battery to support it.
However, I'm pretty sure that by itself doesn't explain the
significantly higher apparent stall speed.

As a troubleshooting step, I removed and plugged the static line from
the airspeed indicator, so now the ASI takes it's static input from
cabin air, and everything else should be unchanged. *I haven't flown
it yet to try it out, but I will today. *I also have a spare airspeed
indicator that I can swap in if necessary.

Anything else I should be considering?

TIA,

Frank

Results of todays experiment:
* * * With the ASI static port open to the cabin, the problem remained
(reads too high by about 10-15kt). *I believe this eliminates the
plumbing changes associated with the TT21 install.

* * I happened to remember that my CAI-302 has an airspeed readout as
part of it's calibration/debug screens, and *I was able to get it to
that display while in flight today. *The CAI-302 (static also open to
cabin pressure) display was much more believable than the ASI, reading
about 38kt at stall in thermalling configuration, and consistently
about 10-13kt lower than the ASI at all airspeeds. *I believe this
eliminates cabin pressure differential as a possible cause, as both
the CAI-302 and ASI were using the same static reference, and the same
pitot line.

My conclusion (to be tested tomorrow) is that the ASI has decided to
depart for an extended lunch. *I happen to have a spare (actually the
original ASI for this ship) that was overhauled about a year ago. *My
prediction is that the replacement ASI and the CAI-302 will be very
close - any bets?

Regards,

Frank

PS: *Two nice streeting days here, but very windy (20+kt out of
east). *Got 3hrs in yesterday, and another 3 in today, all street
running.- Hide quoted text -

- Show quoted text -

Check the pitot line for a kink. if you have a kink it may be trapping
higher pitot pressure between the kink and the ASI and the kink wont
allow it to dissipate as you slow down.
JJ

Is this in a motor glider?
If it is and the motor was run with the Tail Pitot in use rather than the
alternate Pitot (some gliders will have front and rear Pitot and static
inputs if they come with motors today) you may have damaged the ASI from the
high pressure .......just a thought
tim
Please visit the Wings & Wheels website at www.wingsandwheels.comtim


"Frank Paynter" wrote in message
...
On Mar 3, 10:26 am, Frank Paynter wrote:
I installed a TT21 transponder over the winter, and as per the
installation instructions, tapped into my ship's static line for
altitude reporting. Yesterday I checked the transponder with Orlando
ATC and they reported a good signal and proper altitude reporting. So
far, so good.

Then I noticed my airspeed indicator seemed to be reading
significantly higher than normal, and I confirmed this with a stall
series. My Ventus 2bx, which normally stalls in the 40-45kt range
depending on bank angle, now is apparently stalling in the 50-55kt
range. The ship actually feels pretty much the same as before,
although I haven't flown for 3 months so that's a bit hard to tell for
sure.

My dry flying weight is probably about 5-10lbs higher this year than
last, as I added the TT21 itself, plus a 5-lb battery to support it.
However, I'm pretty sure that by itself doesn't explain the
significantly higher apparent stall speed.

As a troubleshooting step, I removed and plugged the static line from
the airspeed indicator, so now the ASI takes it's static input from
cabin air, and everything else should be unchanged. I haven't flown
it yet to try it out, but I will today. I also have a spare airspeed
indicator that I can swap in if necessary.

Anything else I should be considering?

TIA,

Frank

Results of todays experiment:
With the ASI static port open to the cabin, the problem remained
(reads too high by about 10-15kt). I believe this eliminates the
plumbing changes associated with the TT21 install.

I happened to remember that my CAI-302 has an airspeed readout as
part of it's calibration/debug screens, and I was able to get it to
that display while in flight today. The CAI-302 (static also open to
cabin pressure) display was much more believable than the ASI, reading
about 38kt at stall in thermalling configuration, and consistently
about 10-13kt lower than the ASI at all airspeeds. I believe this
eliminates cabin pressure differential as a possible cause, as both
the CAI-302 and ASI were using the same static reference, and the same
pitot line.

My conclusion (to be tested tomorrow) is that the ASI has decided to
depart for an extended lunch. I happen to have a spare (actually the
original ASI for this ship) that was overhauled about a year ago. My
prediction is that the replacement ASI and the CAI-302 will be very
close - any bets?

Regards,

Frank

PS: Two nice streeting days here, but very windy (20+kt out of
east). Got 3hrs in yesterday, and another 3 in today, all street
running.

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On Mar 4, 8:51*am, "Tim Mara" wrote:
Is this in a motor glider?
If it is and the motor was run with the Tail Pitot in use rather than the
alternate Pitot (some gliders will have front and rear Pitot and static
inputs if they come with motors today) you may have damaged the ASI from the
high pressure .......just a *thought
tim
Please visit the Wings & Wheels website atwww.wingsandwheels.comtim
[snip]

I don't see how the pressure at a tail mounted pitot in a motorglider
will ever be enough to damage an ASI. Not compared the pressure from
airspeed they'll experience from normal flight at different speeds.
And the main ASI would normally be permanently plumbed to the nose
pitot and the ships main static (not a TE or triple probe).

Darryl

On Mar 4, 12:22*pm, Darryl Ramm wrote:
I don't see how the pressure at a tail mounted pitot in a motorglider
will ever be enough to damage an ASI.

Agree - A pitot pressure high enough to damage the ASI would result in
an airspeed reading that would cause a change, perhaps several
changes, of underwear. No such event was reported

Andy

it's not just a simple pressure if it's in the tail and there's a fan
blowing on it, you don't find aircraft with the Pitot mounted behind an
engine either.there is a reason they put alternative Pitot and statics on
motor gliders today...most newer gliders do have the multi probes
(pitot-static-TE) in the fin.they all work typically "best" there but they
intend these to be switched to alternative sources when the motor is being
used.....
next time you ask someone to test your pitot are you going to ask them to
blow really hard ?? or just lightly?.and the reason for this would be????
tim



"Darryl Ramm" wrote in message
...
On Mar 4, 8:51 am, "Tim Mara" wrote:
Is this in a motor glider?
If it is and the motor was run with the Tail Pitot in use rather than the
alternate Pitot (some gliders will have front and rear Pitot and static
inputs if they come with motors today) you may have damaged the ASI from
the
high pressure .......just a thought
tim
Please visit the Wings & Wheels website atwww.wingsandwheels.comtim
[snip]

I don't see how the pressure at a tail mounted pitot in a motorglider
will ever be enough to damage an ASI. Not compared the pressure from
airspeed they'll experience from normal flight at different speeds.
And the main ASI would normally be permanently plumbed to the nose
pitot and the ships main static (not a TE or triple probe).

Darryl

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database 5926 (20110304) __________

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At 21:44 04 March 2011, Tim Mara wrote:
it's not just a simple pressure if it's in the tail and there's a fan

blowing on it, you don't find aircraft with the Pitot mounted behind an

engine either.there is a reason they put alternative Pitot and statics on

motor gliders today...most newer gliders do have the multi probes
(pitot-static-TE) in the fin.they all work typically "best" there but
they

intend these to be switched to alternative sources when the motor is
being

used.....
next time you ask someone to test your pitot are you going to ask them to

blow really hard ?? or just lightly?.and the reason for this would
be????
tim

Man who teach me to fly he say, "Never ever blow in pitot, altimeters are
not designed to deal with being blown"
If you must test it seal the tube with your finger and rub the tube. The
heat produced will warm the air enough to increase the pressure and cause
a small indication or better yet put a manometer on it, that will tell you
that the instrument is work AND if you have a leak. Of course if you have a
pot pitot gnore what I have written.

On Mar 3, 10:26*am, Frank Paynter wrote:
I installed a TT21 transponder over the winter, and as per the
installation instructions, tapped into my ship's static line for
altitude reporting. *Yesterday I checked the transponder with Orlando
ATC and they reported a good signal and proper altitude reporting. *So
far, so good.

Then I noticed my airspeed indicator seemed to be reading
significantly higher than normal, and I confirmed this with a stall
series. *My Ventus 2bx, which normally stalls in the 40-45kt range
depending on bank angle, now is apparently stalling in the 50-55kt
range. *The ship actually feels pretty much the same as before,
although I haven't flown for 3 months so that's a bit hard to tell for
sure.

My dry flying weight is probably about 5-10lbs higher this year than
last, as I added the TT21 itself, plus a 5-lb battery to support it.
However, I'm pretty sure that by itself doesn't explain the
significantly higher apparent stall speed.

As a troubleshooting step, I removed and plugged the static line from
the airspeed indicator, so now the ASI takes it's static input from
cabin air, and everything else should be unchanged. *I haven't flown
it yet to try it out, but I will today. *I also have a spare airspeed
indicator that I can swap in if necessary.

Anything else I should be considering?

TIA,

Frank

Too bad I didn't get any takers on yesterday's prediction, because
sometimes the cause of a faulty airspeed reading is just the airspeed
indicator. Replaced the indicator for today's flight, and lo and
behold, the airspeed dropped back to what it should be, matching the
CAI-302 indication almost exactly.

Interestingly enough, this little exercise taught me to trust what the
glider was telling me rather than what the ASI was saying. Before I
figured out the ASI problem, I was having trouble getting the glider
slowed down enough at -1 and -2 flaps - it seemed to want to run hands-
off at the fully ballasted speeds even though I was flying dry. Of
course today with the faulty ASI changed out, the glider wants to fly
hands-off pretty much in the correct (dry) speed range for all cruise
flap settings (-1 through S1)

So now all I have to do is figure out what to do with the 'extra'
posts associated with this topic. Do I still need to replace the
Dittel capacitor? Can I recover from the effects of the PW-5
sacrifice? Will the feds swoop down on me for replacing the ASI in my
experimental glider? Stay tuned for next week's episode ;-).

Regards,

Frank

On Mar 4, 1:44*pm, "Tim Mara" wrote:
it's not just a simple pressure if it's in the tail and there's a fan
blowing on it, you don't find aircraft with the Pitot mounted behind an
engine either.there is a reason they put alternative Pitot and statics on
motor gliders today...most newer gliders do have the multi probes
(pitot-static-TE) in the fin.they all work typically "best" there but they
intend these to be switched to alternative sources when the motor is being
used.....
next time you ask someone to test your pitot are you going to ask them to
blow really hard ?? or just lightly?.and the reason for this would be????
tim


Which manufacturer intends the ships's ASI to ever be connected to (or
switchable) to a tail mounted pitot and/or static? The ASI should only
be connected to the nose pitot and fuselage main static. A vario/
flight computer (like my C302) might be switchable between both (as it
is in my motorglider).

Even if it was connected that way, which still seems awfully wrong for
an ASI, I do not expect the "fan" wind speed plus actual airspeed
induced pressures to damage an ASI.


Darryl

several new gliders now have auxiliary nose and tail inputs



"Darryl Ramm" wrote in message
...
On Mar 4, 1:44 pm, "Tim Mara" wrote:
it's not just a simple pressure if it's in the tail and there's a fan
blowing on it, you don't find aircraft with the Pitot mounted behind an
engine either.there is a reason they put alternative Pitot and statics on
motor gliders today...most newer gliders do have the multi probes
(pitot-static-TE) in the fin.they all work typically "best" there but they
intend these to be switched to alternative sources when the motor is being
used.....
next time you ask someone to test your pitot are you going to ask them to
blow really hard ?? or just lightly?.and the reason for this would be????
tim


Which manufacturer intends the ships's ASI to ever be connected to (or
switchable) to a tail mounted pitot and/or static? The ASI should only
be connected to the nose pitot and fuselage main static. A vario/
flight computer (like my C302) might be switchable between both (as it
is in my motorglider).

Even if it was connected that way, which still seems awfully wrong for
an ASI, I do not expect the "fan" wind speed plus actual airspeed
induced pressures to damage an ASI.


Darryl

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database 5926 (20110304) __________

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AHEM - my T59D has a pitot on the tail fin - sharing space with the TE
probe...

That was way back in 1971 and is actually not that uncommon an arrangement.
Apparently they thought that it would spoil the laminar flow having a
pot pitot in the nose.

Bruce

On 2011/03/05 1:38 AM, Darryl Ramm wrote:
On Mar 4, 1:44 pm, "Tim wrote:
it's not just a simple pressure if it's in the tail and there's a fan
blowing on it, you don't find aircraft with the Pitot mounted behind an
engine either.there is a reason they put alternative Pitot and statics on
motor gliders today...most newer gliders do have the multi probes
(pitot-static-TE) in the fin.they all work typically "best" there but they
intend these to be switched to alternative sources when the motor is being
used.....
next time you ask someone to test your pitot are you going to ask them to
blow really hard ?? or just lightly?.and the reason for this would be????
tim


Which manufacturer intends the ships's ASI to ever be connected to (or
switchable) to a tail mounted pitot and/or static? The ASI should only
be connected to the nose pitot and fuselage main static. A vario/
flight computer (like my C302) might be switchable between both (as it
is in my motorglider).

Even if it was connected that way, which still seems awfully wrong for
an ASI, I do not expect the "fan" wind speed plus actual airspeed
induced pressures to damage an ASI.


Darryl

--
Bruce Greeff
T59D #1771 & Std Cirrus #57