Airspeed Indicator problems

The original Schweizer airspeed indicator in my glider sticks.
Once on the ground I blew into the pitot and the indicator shows an
airspeed but then it takes 10 seconds to slowly go back down to 0.
On the back of the instrument there are 2 vertical ports.

I disconnected and blew through the top tube which runs to the static
ports. Blew just fine, no blockage.

The pitot line runs to the bottom port on the back of the instrument
but not direclty. It has a tee that routes it off to another
instrument also. I would have thought that the pitot should have an
uniterupted tube going directly to the airspeed indicator.

The diagram in the opertors manual shows a dedicated line going from
the pitot to the top port on the back of the instrument
and the static line going the the bottom port. Just opposite of my
particular installation.

Any advice would be appreciated.

Stan

Stan: First advice: STOP BLOWING IN THE ASI! That's the best way
there is to destroy it, which you might already have done. I've seen
people walk up to a pitot tube and put their mouth to it, and I cringe
at the thought of what they're doing to the internal workings. If you
disconnect the plumbing from the instruments you can check it's
continuity by drawing a slight vacuum on it and seeing if it holds.
I've seen plastic tubing chewed through by mice, and worse yet, I've
seen instruments incorrectly plumbed by someone who was "testing the
system." If neither of these is the problem you probably need to send
the instrument to a qualified shop. Fred

On Jun 18, 10:42 am, wrote:
Stan: First advice: STOP BLOWING IN THE ASI! That's the best way
there is to destroy it, which you might already have done. I've seen
people walk up to a pitot tube and put their mouth to it, and I cringe
at the thought of what they're doing to the internal workings. If you
disconnect the plumbing from the instruments you can check it's
continuity by drawing a slight vacuum on it and seeing if it holds.
I've seen plastic tubing chewed through by mice, and worse yet, I've
seen instruments incorrectly plumbed by someone who was "testing the
system." If neither of these is the problem you probably need to send
the instrument to a qualified shop. Fred

If it is an old instrument, it could be an accumulation of dirt,
especially if flown from turf or a dusty area. Repair or replace the
instrurment and check out the plumbing as Fred suggests.

Also, plastic tubing degrades over time and can become a problem with
leaks.

Chip F.

If you are interested, I have an old Schweizer airspeed without markings
that has been on a shelf since about 1965. Make me an offer.

Bill Daniels


"chipsoars" wrote in message
ups.com...
On Jun 18, 10:42 am, wrote:
Stan: First advice: STOP BLOWING IN THE ASI! That's the best way
there is to destroy it, which you might already have done. I've seen
people walk up to a pitot tube and put their mouth to it, and I cringe
at the thought of what they're doing to the internal workings. If you
disconnect the plumbing from the instruments you can check it's
continuity by drawing a slight vacuum on it and seeing if it holds.
I've seen plastic tubing chewed through by mice, and worse yet, I've
seen instruments incorrectly plumbed by someone who was "testing the
system." If neither of these is the problem you probably need to send
the instrument to a qualified shop. Fred

If it is an old instrument, it could be an accumulation of dirt,
especially if flown from turf or a dusty area. Repair or replace the
instrurment and check out the plumbing as Fred suggests.

Also, plastic tubing degrades over time and can become a problem with
leaks.

Chip F.

wrote:
Stan: First advice: STOP BLOWING IN THE ASI! That's the best way
there is to destroy it, which you might already have done. I've seen
people walk up to a pitot tube and put their mouth to it, and I cringe
at the thought of what they're doing to the internal workings.

Apart from the possibility of moisture ingress, the resulting pressure
is likely to be too high and can easily wreck the ASI.

After I've had the panel out of my Standard Libelle, which has the pitot
and TE probe on the fin and hence a lot of plastic tubing to leak, I use
the following simple check procedures:

- start with normal or cool air temperature
- place my thumb over the end of the pitot.
- with thumb remaining firmly in place I close my hand round the pitot
tube and wait.
- after 5 to 10 seconds the ASI comes off its stop and indicates
about 10 to 15 kts
- the reading remains stable as long as I care to retain my grip on
the pitot.
- the ASI returns to zero when I let go the pitot.

This shows that the ASI is in working order and that there are no leaks
between pitot and ASI. Of course it says nothing about the ASI
calibration but that gets checked during the annual C of A.

The only blowing I do is a trick shown me by an old hand. Turn the vario
on and the volume fully up. Hold your hands parallel to each other,
fingers together and bent slightly backward, on either side of the TE
probe and with your palms about 25mm (1 inch) apart. Blow hard between
your hands with your mouth about 100-150mm (4-6 inches) away from the
heels of your hands. If the system is operating correctly you'll hear
the vario signal a climb for 2-3 seconds and then go back to zero.

If both tests work OK I can be pretty sure that the pneumatic quick
connect at the panel was sealed correctly when I put the panel back in.

HTH


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

wrote in message
ups.com...
The original Schweizer airspeed indicator in my glider sticks.

The pitot line runs to the bottom port on the back of the instrument
but not direclty. It has a tee that routes it off to another
instrument also. I would have thought that the pitot should have an
uniterupted tube going directly to the airspeed indicator.


Any advice would be appreciated.

Stan



--
I agree with the other posters---send it in for cleaning, and calibration.

The tee is probably to a netto cappilliary, or possibly to a hidden
diaphragm TE compensator.

A 10 cc medical syringe is a good "air pump" for testing systems.


Hartley Falbaum

And then, there can be problems with sending instruments
in for a rebuild.

First, it was my altimeter. Off it went to a repair
shop in Kansas and came back with the glass cracked.
The crack went right to one of the screws. Damn.
Turn right around and send it back for 'warranty'
service. It has worked just fine since and that was
maybe three years ago.

Second, my airspeed indicator had a leak. I sent it
in to another shop in Kansas and authorized a check-up.
Turns out they tore it down and found it pretty much
all worn out and were in the process of starting to
totally rebuild it. Without my authorization. It
was going to cost around US$450. I told them to stop
and just send the instrument back to me. So, I bought
a new Winter airspeed indicator from Tim Mara at Wings
and Wheels for less than the rebuilt one would have
cost me.

I was hoping the old airspeed would just need a new
O-ring and a face cleaning.

Oh well.

Ray Lovinggood
Carrboro, North Carolina, USA
PS: The fairly new instruments didn't keep me from
landing out on Sunday



At 01:06 19 June 2007, Hl Falbaum wrote:


wrote in message
oups.com...
The original Schweizer airspeed indicator in my glider
sticks.

The pitot line runs to the bottom port on the back
of the instrument
but not direclty. It has a tee that routes it off
to another
instrument also. I would have thought that the pitot
should have an
uniterupted tube going directly to the airspeed indicator.


Any advice would be appreciated.

Stan



--
I agree with the other posters---send it in for cleaning,
and calibration.

The tee is probably to a netto cappilliary, or possibly
to a hidden
diaphragm TE compensator.

A 10 cc medical syringe is a good 'air pump' for testing
systems.


Hartley Falbaum