strange ASI readings on LXNAV s80 vs Winter ASI

[Matt Herron Jr.]

looking for some instrument debugging help.

I have a steam gauge ASI (winter) and an LxNav S80 sharing the same Pitot and static lines. In the air, the two gauges read ASI differently. The S80 reads about 10 knots higher than the Winter at 70 knots, and 5 knots higher at 40 knots. The error seems to scale with higher airspeeds

Back on the ground we used a syringe to pressurize the pitot line. Both instruments read within 2 knots of each other for the full speed range. they also held steady at the desired airspeed with the syringe, indicating no leaks in the Pitot system.

Back in the air, I tried opening and closing the vent, scooping air into the cockpit to pressurize it, etc. Neither instrument changed its reading, but the offset in speeds remained.

Ideas? Leak in Static?

Matt

[Dave Nadler]

On Wednesday, February 14, 2018 at 8:38:38 PM UTC-5, Matt Herron Jr. wrote:
> looking for some instrument debugging help.
>
> I have a steam gauge ASI (winter) and an LxNav S80
> sharing the same Pitot and static lines.

First, check your static for leaks.

Second, check the instruments against a 3rd reference.
See if they are consistent (doesn't matter if the 3rd
unit is off as long as its consistent).

Hope that helps,
Best Regards, Dave


PS: Once had a customer return an instrument TWICE because
he insisted his Winter ASI was correct -- and of course
when he finally checked it was way off. Winter 2 1/4" ASIs
are notorious (and why a back-seater once said
"gee, if I do this in Condor the wings come off").

PPS: I have a Chinese ASI in the shop that is WILDLY off,
but great for leak-checks...

[Paul Remde]

Are they connected to the same pitot and static sources? Some gliders use a triple probe in the tail for the soaring flight computer and vario and the pitot in the nose and statics on the fuselage for the airspeed and altimeter.

Also, make sure the S80 is set to display airspeed in knots, not mph.

Best Regards,

Paul Remde
_________________________

On Wednesday, February 14, 2018 at 7:38:38 PM UTC-6, Matt Herron Jr. wrote:
> looking for some instrument debugging help.
>
> I have a steam gauge ASI (winter) and an LxNav S80 sharing the same Pitot and static lines. In the air, the two gauges read ASI differently. The S80 reads about 10 knots higher than the Winter at 70 knots, and 5 knots higher at 40 knots. The error seems to scale with higher airspeeds
>
> Back on the ground we used a syringe to pressurize the pitot line. Both instruments read within 2 knots of each other for the full speed range. they also held steady at the desired airspeed with the syringe, indicating no leaks in the Pitot system.
>
> Back in the air, I tried opening and closing the vent, scooping air into the cockpit to pressurize it, etc. Neither instrument changed its reading, but the offset in speeds remained.
>
> Ideas? Leak in Static?
>
> Matt

[Brian[_1_]]

make a water manometer to calibrate them.
http://www.n56ml.com/airspeed_calibration/

Brian

[Matt Herron Jr.]

On Wednesday, February 14, 2018 at 6:39:45 PM UTC-8, Paul Remde wrote:
> Are they connected to the same pitot and static sources? Some gliders use a triple probe in the tail for the soaring flight computer and vario and the pitot in the nose and statics on the fuselage for the airspeed and altimeter.
>
> Also, make sure the S80 is set to display airspeed in knots, not mph.
>
> Best Regards,
>
> Paul Remde
> _________________________
>
> On Wednesday, February 14, 2018 at 7:38:38 PM UTC-6, Matt Herron Jr. wrote:
> > looking for some instrument debugging help.
> >
> > I have a steam gauge ASI (winter) and an LxNav S80 sharing the same Pitot and static lines. In the air, the two gauges read ASI differently. The S80 reads about 10 knots higher than the Winter at 70 knots, and 5 knots higher at 40 knots. The error seems to scale with higher airspeeds
> >
> > Back on the ground we used a syringe to pressurize the pitot line. Both instruments read within 2 knots of each other for the full speed range. they also held steady at the desired airspeed with the syringe, indicating no leaks in the Pitot system.
> >
> > Back in the air, I tried opening and closing the vent, scooping air into the cockpit to pressurize it, etc. Neither instrument changed its reading, but the offset in speeds remained.
> >
> > Ideas? Leak in Static?
> >
> > Matt

yes, they are connected to the same pitot and static sources. That's what is so weird about this

[Doug C[_2_]]

On Wednesday, February 14, 2018 at 8:38:38 PM UTC-5, Matt Herron Jr. wrote:
> looking for some instrument debugging help.
>
> I have a steam gauge ASI (winter) and an LxNav S80 sharing the same Pitot and static lines. In the air, the two gauges read ASI differently. The S80 reads about 10 knots higher than the Winter at 70 knots, and 5 knots higher at 40 knots. The error seems to scale with higher airspeeds
>
> Back on the ground we used a syringe to pressurize the pitot line. Both instruments read within 2 knots of each other for the full speed range. they also held steady at the desired airspeed with the syringe, indicating no leaks in the Pitot system.
>

> Back in the air, I tried opening and closing the vent, scooping air into the cockpit to pressurize it, etc. Neither instrument changed its reading, but the offset in speeds remained.
>
> Ideas? Leak in Static?
>
> Matt

Hi Matt:
I experienced the same problem when I received my S100 early last year. Uros sent me the following solution which autozeros the pressure sensors. His suggestions completely solved the problem for me.
Best regards
Doug
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Hello,
please check under setup-vario, that you have airspeed offset set to 0.

Please enter password 01043, to make autozero on pressure sensors.

Best regards, Uros
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

[[email protected]]

Paul's units suggestion would fit:

40knots = about 46mph. 70knots = 80mph.

[Matt Herron Jr.]

On Wednesday, February 14, 2018 at 10:27:22 PM UTC-8, Doug C wrote:
> On Wednesday, February 14, 2018 at 8:38:38 PM UTC-5, Matt Herron Jr. wrote:
> > looking for some instrument debugging help.
> >
> > I have a steam gauge ASI (winter) and an LxNav S80 sharing the same Pitot and static lines. In the air, the two gauges read ASI differently. The S80 reads about 10 knots higher than the Winter at 70 knots, and 5 knots higher at 40 knots. The error seems to scale with higher airspeeds
> >
> > Back on the ground we used a syringe to pressurize the pitot line. Both instruments read within 2 knots of each other for the full speed range. they also held steady at the desired airspeed with the syringe, indicating no leaks in the Pitot system.
> >
>
> > Back in the air, I tried opening and closing the vent, scooping air into the cockpit to pressurize it, etc. Neither instrument changed its reading, but the offset in speeds remained.
> >
> > Ideas? Leak in Static?
> >
> > Matt
>
> Hi Matt:
> I experienced the same problem when I received my S100 early last year. Uros sent me the following solution which autozeros the pressure sensors. His suggestions completely solved the problem for me.
> Best regards
> Doug
> XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
> Hello,
> please check under setup-vario, that you have airspeed offset set to 0.
>
> Please enter password 01043, to make autozero on pressure sensors.
>
> Best regards, Uros
> XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Thanks Doug, I will give that a try. As far as units go, both instruments indicate knots.

Matt