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kbob(at)cox.net
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 Posted: Wed Oct 10, 2007 5:41 am Post subject: static port & altimeter error |
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My static ports were so far off I have had ATC ask me to turn off the
altitude reporting on my transponder. Investigation showed the convex
'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
ground the rivet head flat (on a painted plane!) and the error went away.
Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
altimeter reads high, consider this fix.
Kelly Patterson
RV-6A N716K
PHX, AZ 185 hrs
Time: 01:37:30 PM PST US
From: "John D. Heath" <altoq(at)cebridge.net>
Subject: Re: Altimeter error - ASI question
Doug,
That one has to go to the shop. I can say though, airspeed indicator errors
are generally in the Pitot/Static system. The main trouble spot seems to be
the Static Port position and height above the surrounding surface. There are
some very elegant solutions available for static ports, but in my opinion
they are just a fancy way to terminate the static tubing at skin level. A
cheap pop rivet with enough length to install the tubing on and a washer
placed between it and the head of the gun when it is installed has worked
for me many times. The washer is to make the rivet head flat and without the
slight oval shape they normally have.
John D.
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khorton01(at)rogers.com
Guest
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| Posted: Wed Oct 10, 2007 8:29 am Post subject: static port & altimeter error |
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How would ATC know your static system is not accurate? All they see is the altitude reported from your transponder, which should be that which is sensed at the static ports. They have no way to compare it against anything else.
GPS altitude is not the same thing as barometric altitude. There are many valid reasons why GPS altitude might differ by several hundred feet from barometric altitude, yet both could be correct (just as TAS may differ greatly from ground speed, yet both are correct, as they are measuring different things). GPS altitude is only the same as barometric altitude on the extremely rare day where the atmosphere perfectly matches a standard atmosphere.
Kevin Horton
On Wed, 10 Oct 2007 06:38:25 -0700
"Kelly Patterson" <kbob(at)cox.net> wrote:
| Quote: |
My static ports were so far off I have had ATC ask me to turn off the
altitude reporting on my transponder. Investigation showed the convex
'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
ground the rivet head flat (on a painted plane!) and the error went away.
Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
altimeter reads high, consider this fix.
Kelly Patterson
RV-6A N716K
PHX, AZ 185 hrs
Time: 01:37:30 PM PST US
From: "John D. Heath" <altoq(at)cebridge.net>
Subject: Re: Altimeter error - ASI question
Doug,
That one has to go to the shop. I can say though, airspeed indicator errors
are generally in the Pitot/Static system. The main trouble spot seems to be
the Static Port position and height above the surrounding surface. There are
some very elegant solutions available for static ports, but in my opinion
they are just a fancy way to terminate the static tubing at skin level. A
cheap pop rivet with enough length to install the tubing on and a washer
placed between it and the head of the gun when it is installed has worked
for me many times. The washer is to make the rivet head flat and without the
slight oval shape they normally have.
John D.
|
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acepilot(at)bloomer.net
Guest
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| Posted: Wed Oct 10, 2007 10:08 am Post subject: static port & altimeter error |
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Wouldn't ATC know if they assigned an altitude such as 6,500 feet and
the pilot of his RV flew at 6,500 feet according to his altimeter, but
his encoder was reporting 6,000 or 7,000 feet?
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)
Kevin Horton wrote:
| Quote: |
How would ATC know your static system is not accurate? All they see is the altitude reported from your transponder, which should be that which is sensed at the static ports. They have no way to compare it against anything else.
GPS altitude is not the same thing as barometric altitude. There are many valid reasons why GPS altitude might differ by several hundred feet from barometric altitude, yet both could be correct (just as TAS may differ greatly from ground speed, yet both are correct, as they are measuring different things). GPS altitude is only the same as barometric altitude on the extremely rare day where the atmosphere perfectly matches a standard atmosphere.
Kevin Horton
On Wed, 10 Oct 2007 06:38:25 -0700
"Kelly Patterson" <kbob(at)cox.net> wrote:
>
>
>My static ports were so far off I have had ATC ask me to turn off the
>altitude reporting on my transponder. Investigation showed the convex
>'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
>ground the rivet head flat (on a painted plane!) and the error went away.
>
>Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
>altimeter reads high, consider this fix.
>
>Kelly Patterson
>RV-6A N716K
>PHX, AZ 185 hrs
>Time: 01:37:30 PM PST US
>From: "John D. Heath" <altoq(at)cebridge.net>
>Subject: Re: Altimeter error - ASI question
>Doug,
>
> That one has to go to the shop. I can say though, airspeed indicator errors
>are generally in the Pitot/Static system. The main trouble spot seems to be
>the Static Port position and height above the surrounding surface. There are
>some very elegant solutions available for static ports, but in my opinion
>they are just a fancy way to terminate the static tubing at skin level. A
>cheap pop rivet with enough length to install the tubing on and a washer
>placed between it and the head of the gun when it is installed has worked
>for me many times. The washer is to make the rivet head flat and without the
>slight oval shape they normally have.
>
>John D.
>
>
>
|
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khorton01(at)rogers.com
Guest
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| Posted: Wed Oct 10, 2007 11:49 am Post subject: static port & altimeter error |
|
|
But, if his altimeter was connected to the same static source as the encoder (as it should), a servicable altimeter should read the same as the encoder is reporting (ignoring the effect of altimeter setting, which is accounted for by ATC). It wouldn't matter if a bad static port gave a 1000 ft error - both the altimeter and the encoder would have the same error. If the altimeter and encoder are connected to the same source, and they say different things, then one of them is unserviceable, or there is a large static leak between the two. The problem cannot be the static source.
Kevin
On Wed, 10 Oct 2007 18:04:18 +0000
Scott <acepilot(at)bloomer.net> wrote:
| Quote: |
Wouldn't ATC know if they assigned an altitude such as 6,500 feet and
the pilot of his RV flew at 6,500 feet according to his altimeter, but
his encoder was reporting 6,000 or 7,000 feet?
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)
Kevin Horton wrote:
>
>
>How would ATC know your static system is not accurate? All they see is the altitude reported from your transponder, which should be that which is sensed at the static ports. They have no way to compare it against anything else.
>
>GPS altitude is not the same thing as barometric altitude. There are many valid reasons why GPS altitude might differ by several hundred feet from barometric altitude, yet both could be correct (just as TAS may differ greatly from ground speed, yet both are correct, as they are measuring different things). GPS altitude is only the same as barometric altitude on the extremely rare day where the atmosphere perfectly matches a standard atmosphere.
>
>Kevin Horton
>
>On Wed, 10 Oct 2007 06:38:25 -0700
>"Kelly Patterson" <kbob(at)cox.net> wrote:
>
>
>
>>
>>
>>My static ports were so far off I have had ATC ask me to turn off the
>>altitude reporting on my transponder. Investigation showed the convex
>>'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
>>ground the rivet head flat (on a painted plane!) and the error went away.
>>
>>Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
>>altimeter reads high, consider this fix.
>>
>>Kelly Patterson
>>RV-6A N716K
>>PHX, AZ 185 hrs
>>
>>
>>Time: 01:37:30 PM PST US
>>From: "John D. Heath" <altoq(at)cebridge.net>
>>Subject: Re: Altimeter error - ASI question
>>
>>
>>Doug,
>>
>> That one has to go to the shop. I can say though, airspeed indicator errors
>>are generally in the Pitot/Static system. The main trouble spot seems to be
>>the Static Port position and height above the surrounding surface. There are
>>some very elegant solutions available for static ports, but in my opinion
>>they are just a fancy way to terminate the static tubing at skin level. A
>>cheap pop rivet with enough length to install the tubing on and a washer
>>placed between it and the head of the gun when it is installed has worked
>>for me many times. The washer is to make the rivet head flat and without the
>>slight oval shape they normally have.
>>
>>John D.
>>
>>
>>
>
>
>
>
>
>
>
|
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acepilot(at)bloomer.net
Guest
|
| Posted: Wed Oct 10, 2007 1:53 pm Post subject: static port & altimeter error |
|
|
I agree with that...I was making an assumption that the encoder OR the
altimeter was bad. The encoder could have one of the output pins open
or shorted to ground permanently giving a false number to the
transponder or the altimeter needs to be serviced...
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)
Kevin Horton wrote:
| Quote: |
But, if his altimeter was connected to the same static source as the encoder (as it should), a servicable altimeter should read the same as the encoder is reporting (ignoring the effect of altimeter setting, which is accounted for by ATC). It wouldn't matter if a bad static port gave a 1000 ft error - both the altimeter and the encoder would have the same error. If the altimeter and encoder are connected to the same source, and they say different things, then one of them is unserviceable, or there is a large static leak between the two. The problem cannot be the static source.
Kevin
On Wed, 10 Oct 2007 18:04:18 +0000
Scott <acepilot(at)bloomer.net> wrote:
>
>
>Wouldn't ATC know if they assigned an altitude such as 6,500 feet and
>the pilot of his RV flew at 6,500 feet according to his altimeter, but
>his encoder was reporting 6,000 or 7,000 feet?
>
>Scott
>http://corbenflyer.tripod.com/
>Gotta Fly or Gonna Die
>Building RV-4 (Super Slow Build Version)
>
>Kevin Horton wrote:
>
>
>
>>
>>
>>How would ATC know your static system is not accurate? All they see is the altitude reported from your transponder, which should be that which is sensed at the static ports. They have no way to compare it against anything else.
>>
>>GPS altitude is not the same thing as barometric altitude. There are many valid reasons why GPS altitude might differ by several hundred feet from barometric altitude, yet both could be correct (just as TAS may differ greatly from ground speed, yet both are correct, as they are measuring different things). GPS altitude is only the same as barometric altitude on the extremely rare day where the atmosphere perfectly matches a standard atmosphere.
>>
>>Kevin Horton
>>
>>On Wed, 10 Oct 2007 06:38:25 -0700
>>"Kelly Patterson" <kbob(at)cox.net> wrote:
>>
>>
>>
>>
>>
>>>
>>>
>>>My static ports were so far off I have had ATC ask me to turn off the
>>>altitude reporting on my transponder. Investigation showed the convex
>>>'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
>>>ground the rivet head flat (on a painted plane!) and the error went away.
>>>
>>>Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
>>>altimeter reads high, consider this fix.
>>>
>>>Kelly Patterson
>>>RV-6A N716K
>>>PHX, AZ 185 hrs
>>>
>>>
>>>Time: 01:37:30 PM PST US
>>>From: "John D. Heath" <altoq(at)cebridge.net>
>>>Subject: Re: Altimeter error - ASI question
>>>
>>>
>>>Doug,
>>>
>>>That one has to go to the shop. I can say though, airspeed indicator errors
>>>are generally in the Pitot/Static system. The main trouble spot seems to be
>>>the Static Port position and height above the surrounding surface. There are
>>>some very elegant solutions available for static ports, but in my opinion
>>>they are just a fancy way to terminate the static tubing at skin level. A
>>>cheap pop rivet with enough length to install the tubing on and a washer
>>>placed between it and the head of the gun when it is installed has worked
>>>for me many times. The washer is to make the rivet head flat and without the
>>>slight oval shape they normally have.
>>>
>>>John D.
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>>
>>
>>
>
>
|
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Doug Gray
Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia
|
| Posted: Wed Oct 10, 2007 3:49 pm Post subject: static port & altimeter error |
|
|
My alt encoder has a tag that reads:
"Replacement or re-calibration of the altimeter used for flight requires
re-calibration of the Altitude Encoder"
Doug Gray
On Wed, 2007-10-10 at 21:52 +0000, Scott wrote:
| Quote: |
I agree with that...I was making an assumption that the encoder OR the
altimeter was bad. The encoder could have one of the output pins open
or shorted to ground permanently giving a false number to the
transponder or the altimeter needs to be serviced...
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)
Kevin Horton wrote:
>
>
>But, if his altimeter was connected to the same static source as the encoder (as it should), a servicable altimeter should read the same as the encoder is reporting (ignoring the effect of altimeter setting, which is accounted for by ATC). It wouldn't matter if a bad static port gave a 1000 ft error - both the altimeter and the encoder would have the same error. If the altimeter and encoder are connected to the same source, and they say different things, then one of them is unserviceable, or there is a large static leak between the two. The problem cannot be the static source.
>
>Kevin
>
>On Wed, 10 Oct 2007 18:04:18 +0000
>Scott <acepilot(at)bloomer.net> wrote:
>
>
>
>>
>>
>>Wouldn't ATC know if they assigned an altitude such as 6,500 feet and
>>the pilot of his RV flew at 6,500 feet according to his altimeter, but
>>his encoder was reporting 6,000 or 7,000 feet?
>>
>>Scott
>>http://corbenflyer.tripod.com/
>>Gotta Fly or Gonna Die
>>Building RV-4 (Super Slow Build Version)
>>
>>
>>
>>Kevin Horton wrote:
>>
>>
>>
>>>
>>>
>>>How would ATC know your static system is not accurate? All they see is the altitude reported from your transponder, which should be that which is sensed at the static ports. They have no way to compare it against anything else.
>>>
>>>GPS altitude is not the same thing as barometric altitude. There are many valid reasons why GPS altitude might differ by several hundred feet from barometric altitude, yet both could be correct (just as TAS may differ greatly from ground speed, yet both are correct, as they are measuring different things). GPS altitude is only the same as barometric altitude on the extremely rare day where the atmosphere perfectly matches a standard atmosphere.
>>>
>>>Kevin Horton
>>>
>>>On Wed, 10 Oct 2007 06:38:25 -0700
>>>"Kelly Patterson" <kbob(at)cox.net> wrote:
>>>
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>>My static ports were so far off I have had ATC ask me to turn off the
>>>>altitude reporting on my transponder. Investigation showed the convex
>>>>'dome' of the Vans pop rivet was causing a vacuum as the air passed over. I
>>>>ground the rivet head flat (on a painted plane!) and the error went away.
>>>>
>>>>Use a GPS to see what your 'true' elevation is vs. the altimeter. If the
>>>>altimeter reads high, consider this fix.
>>>>
>>>>Kelly Patterson
>>>>RV-6A N716K
>>>>PHX, AZ 185 hrs
>>>>
>>>>
>>>>Time: 01:37:30 PM PST US
>>>>From: "John D. Heath" <altoq(at)cebridge.net>
>>>>Subject: Re: Altimeter error - ASI question
>>>>
>>>>
>>>>Doug,
>>>>
>>>>That one has to go to the shop. I can say though, airspeed indicator errors
>>>>are generally in the Pitot/Static system. The main trouble spot seems to be
>>>>the Static Port position and height above the surrounding surface. There are
>>>>some very elegant solutions available for static ports, but in my opinion
>>>>they are just a fancy way to terminate the static tubing at skin level. A
>>>>cheap pop rivet with enough length to install the tubing on and a washer
>>>>placed between it and the head of the gun when it is installed has worked
>>>>for me many times. The washer is to make the rivet head flat and without the
>>>>slight oval shape they normally have.
>>>>
>>>>John D.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>>
>>
>
>
>
>
>
>
>
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dale1rv6(at)comcast.net
Guest
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| Posted: Wed Oct 10, 2007 4:24 pm Post subject: static port & altimeter error |
|
|
In the US many or most approach control areas have radar altitude from their
ground system, independent of your on board encoder. Enroute seems to be a
different story.
Dale
Do not archive
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