REFLECTOR: TAS calibration?

Wed Oct 2 09:12:59 CDT 2013

Last night, I put a 1/4" strip of aluminum tape ~1mm ahead of the static
ports on my pitot-static tube and took it out for a spin.  Before taking
off, I adjusted the barometric pressure on my altimeters (analog and Dynon
Skyview) so the indicated altitude exactly matched the GPS (field) altitude.

On takeoff, as I lifted of and accelerated, I could already see my
indicated altitude dip as my speed increased.  I climbed to 7000', leveled
off and established a cruise speed of 160kts.  My GPS altitude was
reading 6990ft
and my Dynon altimeter was reading 6620ft (at cruise speed).  I did two
passes with headings 180deg apart.  My GPS ground speeds in the two passes
were 168kts/182kts while holding a steady 158ktas airspeed.  Essentially no
change from readings I got with no aluminum tape ahead of the static port.

So, it doesn't seem like the one thin bit of aluminum tape was enough.
 I'll put a couple more layers on and see if it moves the needle in the
right direction.

Geoff

On Tue, Oct 1, 2013 at 3:22 PM, Laurence Coen <lwcoen at hotmail.com> wrote:

> **
> Geoff,
>
> Yes and yes.  In a previous post I showed that with a 10knt wind you would
> have to miss the actual wind direction by 28 deg. to cause an error of
> 1knt.  On a 180 heading you would also get a 1knt error but in the opposite
> direction thus canceling the original error.  A winds aloft report is more
> than enough to select your initial heading.  Most of the other stuff that
> was done was to determine the source of the TAS error.  The temperature
> error due to speed is less than 1 C at speeds less than 200MPH.  I have an
> RMI IAS,TAS, OAT, VSI, ALT, PALT, DALT that also corrects for OAT speed
> error.  I have rechecked my TAS reading against the above and it is within
> 1knt.  My altitude matches my WAAS GPS within +- 10 feet typically.
>
> Larry Coen
> N136LC
>
>  *From:* Geoff Gerhardt <geoff.gerhardt at gmail.com>
> *Sent:* Tuesday, October 01, 2013 11:35 AM
> *To:* Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> *Subject:* Re: REFLECTOR: TAS calibration?
>
> Thanks for the great article...the guy looks like George Carlin, tho.
>
> So, rather than cruising down the runway at low altitude, can't I just fly
> my plane at a constant GPS altitude and make sure my indicated altitude
> does not change with air speed?  Or, that my TAS matches my GPS average
> ground speed after two runs with headings 180deg apart?
>
> Might head out to the hangar after work and give it a go.
>
> Geoff
>
>
>
> On Tue, Oct 1, 2013 at 12:16 PM, Laurence Coen <lwcoen at hotmail.com> wrote:
>
>> **
>> That is an excellent article.  Since I don't think anyone actually
>> believed me in a previous discussion when I said that to determine your
>> TAS, Fly into the wind, record GPS ground speed, fly 180 degrees and take
>> the ground speed and average the two.  Read the last sentence in the second
>> paragraph.
>>
>> Larry Coen
>> N136LC
>>
>>  *From:* Henk van Ooijen <hjvooijen at yahoo.com>
>> *Sent:* Tuesday, October 01, 2013 9:37 AM
>>  *To:* Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>>  *Subject:* Re: REFLECTOR: TAS calibration?
>>
>>  A nice reading about this from Paul Lipps
>>
>> ------------------------------
>>
>>  Regards,
>> Henk van Ooijen
>>
>>
>>  Op 1 okt. 2013, om 11:40 heeft Geoff Gerhardt het volgende geschreven:
>>
>>  Dave,
>>
>> I have a Dynon Skyview.  It does the TAS calculation (using OAT) and
>> reports GPS speed in knots.
>>
>> Geoff
>>
>>
>> On Tue, Oct 1, 2013 at 12:23 AM, Dave Philipsen <velocity at davebiz.com>wrote:
>>
>>>  I'm just taking another wild stab...are you sure your GPS is reading
>>> nautical miles and not statute miles?  How is your TAS being calculated?
>>> Do you have an EFIS that does it for you or....?  Are you estimating OAT or
>>> actually measuring it?
>>>
>>> Dave Philipsen
>>> Velocity STD FG
>>> N83DP
>>>
>>>  On 9/30/2013 4:29 PM, Geoff Gerhardt wrote:
>>>
>>> Mine is a combination pitot static tube.  I wonder if I could calibrate
>>> it in a similar fashion by putting tape around the pitot tube before or
>>> after the static holes.
>>>
>>> Dave - yes, I realize that IAS changes with altitude.  I am observing an
>>> offset between my TAS and GPS ground speed (after accounting for wind).
>>>
>>> Geoff
>>>
>>>
>>> On Mon, Sep 30, 2013 at 4:24 PM, Scott Derrick <scott at tnstaafl.net>wrote:
>>>
>>>> I have a static port(3 vertical holes, 1/4 inch apart)  under the
>>>> carnard, about a foot, that works well. However it does need to be
>>>> calibrated. An uncalibrated static port will cause erroneous altitude and
>>>> IAS indications.
>>>>
>>>> You can calibrate the port by putting a 1/4 inch wide strip of aluminum
>>>> tape either right ahead of the the hole(s) or right behind them.  You can
>>>> add layers of the tape to increase the effect.
>>>>
>>>>
>>>> To determine if you need less pressure(tape before the hole) or more
>>>> pressure(tape after the hole).
>>>>
>>>>     Set your altimeter to field elevation, just before departure.  Fly
>>>> at cruise speed, ball in the center, 15-20 ft above the runway.  The people
>>>> on the ground love this!  Note your altitude.
>>>>
>>>>     If your indicating higher than 20 ft above field elevation, the
>>>> pressure is too low and you need tape behind the port. If your indicating
>>>> lower than 20ft above filed elevation, the pressure is too high and you
>>>> need tape ahead of the port.
>>>>
>>>>     If your within 50 ft, your good to go.  I did this after I bought
>>>> my plane, it was off 300ft. and after I painted, again off 300ft. The tape
>>>> lasts forever and looks like an embedded metal strip.
>>>>
>>>> my $.002, works for me.
>>>>
>>>> Scott
>>>>
>>>>  -------- Original Message --------
>>>> Subject: Re: REFLECTOR: TAS calibration?
>>>>  From: Geoff Gerhardt <geoff.gerhardt at gmail.com><geoff.gerhardt at gmail.com>
>>>> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org><reflector at tvbf.org>
>>>> Date: 09/30/2013 01:56 PM
>>>>
>>>> Guys,
>>>>
>>>> My pitot/static is positioned under the canard - I suspect it is seeing
>>>> increased pressure at high speeds thus giving me a low indicated airspeed.
>>>>  This weekend, I thought I was smart and put a small static port right
>>>> ahead of the dog house thinking that was a great place.  After a quick
>>>> flight where my air speeds were through the roof, I realized that that spot
>>>> was actually doing the opposite and was creating a low pressure region as
>>>> the air bends over the nose.  I see now that I need to find a place on the
>>>> flat section of the fuselage to put the static port.
>>>>
>>>> Where does everyone else have their static port?
>>>>
>>>> Thanks.
>>>>
>>>> Geoff
>>>>
>>>>
>>>> On Sun, Sep 29, 2013 at 11:43 AM, Kurt Winker <nmflyer1 at aol.com> wrote:
>>>>
>>>>> Sounds like a trip-strip may be in order.
>>>>>
>>>>> Kurt
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>>> > On Sep 29, 2013, at 6:47, Scott Baker <scottb33333 at gmail.com> wrote:
>>>>> >
>>>>> > I would assume that you are factoring altitude and temperature when
>>>>> calculating TAS. If so, airspeed error might be related to a pressurization
>>>>> of the static system (a common problem in Velocity aircraft that have their
>>>>> static port located forward of the entry door).
>>>>> >
>>>>> > Scott Baker
>>>>> >
>>>>> >> On Sep 28, 2013, at 8:29 PM, Geoff Gerhardt <
>>>>> geoff.gerhardt at gmail.com> wrote:
>>>>> >>
>>>>> >> Guys,
>>>>> >>
>>>>> >> Flying today I realized that my ground speed seems to be always
>>>>> greater than my TAS.  I figured at least some of the time it should be less
>>>>> (i.e. into a headwind).  But it always seemed to be greater.  So, today, I
>>>>> flew in a box, E, W, N, S and recorded my TAS and GS.  My TAS was constant
>>>>> at 159ktas on each leg, and my GS (GPS) was 185, 179, 171, 175 for the W,
>>>>> N, E, S legs.  If I add all those up and divide by four, I get 177.5kts,
>>>>> yet my TAS registered 158ktas.  Am I missing something?  Is my airspeed
>>>>> indicator reading too low?
>>>>> >>
>>>>> >> Thanks.
>>>>> >>
>>>>> >> Geoff
>>>>> >>
>>>>> >> _______________________________________________
>>>>> >> To change your email address, visit
>>>>> http://www.tvbf.org/mailman/listinfo/reflector
>>>>> >>
>>>>> >> Visit the gallery!  www.tvbf.org/gallery
>>>>> >> user:pw = tvbf:jamaicangoose
>>>>> >> Check new archives: www.tvbf.org/pipermail
>>>>> >> Check old archives:
>>>>> http://www.tvbf.org/archives/velocity/maillist.html
>>>>> >
>>>>> > _______________________________________________
>>>>> > To change your email address, visit
>>>>> http://www.tvbf.org/mailman/listinfo/reflector
>>>>> >
>>>>> > Visit the gallery!  www.tvbf.org/gallery
>>>>> > user:pw = tvbf:jamaicangoose
>>>>> > Check new archives: www.tvbf.org/pipermail
>>>>> > Check old archives:
>>>>> http://www.tvbf.org/archives/velocity/maillist.html
>>>>>
>>>>> _______________________________________________
>>>>> To change your email address, visit
>>>>> http://www.tvbf.org/mailman/listinfo/reflector
>>>>>
>>>>> Visit the gallery!  www.tvbf.org/gallery
>>>>> user:pw = tvbf:jamaicangoose
>>>>> Check new archives: www.tvbf.org/pipermail
>>>>> Check old archives:
>>>>> http://www.tvbf.org/archives/velocity/maillist.html
>>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>>>>
>>>> Visit the gallery!  www.tvbf.org/gallery
>>>> user:pw = tvbf:jamaicangoose
>>>> Check new archives: www.tvbf.org/pipermail
>>>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>>>
>>>>
>>>> --
>>>> Even if you're on the right track, you'll get run over if you just sit there.
>>>> Will Rogers
>>>>
>>>>
>>>> _______________________________________________
>>>> To change your email address, visit
>>>> http://www.tvbf.org/mailman/listinfo/reflector
>>>>
>>>> Visit the gallery!  www.tvbf.org/gallery
>>>> user:pw = tvbf:jamaicangoose
>>>> Check new archives: www.tvbf.org/pipermail
>>>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>>>
>>> Visit the gallery!  www.tvbf.org/gallery
>>> user:pw = tvbf:jamaicangoose
>>> Check new archives: www.tvbf.org/pipermail
>>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>>
>>>
>>>
>> _______________________________________________
>> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>>
>> Visit the gallery!  www.tvbf.org/gallery
>> user:pw = tvbf:jamaicangoose
>> Check new archives: www.tvbf.org/pipermail
>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>
>>  ------------------------------
>>
>> A nice reading about this from Paul Lipps
>>
>> Regards,
>> Henk van Ooijen
>>
>>
>> Op 1 okt. 2013, om 11:40 heeft Geoff Gerhardt het volgende geschreven:
>>
>>
>> > Dave,
>> >
>> > I have a Dynon Skyview.  It does the TAS calculation (using OAT) and
>> reports GPS speed in knots.
>> >
>> > Geoff
>> >
>> >
>> > On Tue, Oct 1, 2013 at 12:23 AM, Dave Philipsen <velocity at davebiz.com>
>> wrote:
>> > I'm just taking another wild stab...are you sure your GPS is reading
>> nautical miles and not statute miles?  How is your TAS being calculated?
>> Do you have an EFIS that does it for you or....?  Are you estimating OAT or
>> actually measuring it?
>> >
>> > Dave Philipsen
>> > Velocity STD FG
>> > N83DP
>> > On 9/30/2013 4:29 PM, Geoff Gerhardt wrote:
>> >> Mine is a combination pitot static tube.  I wonder if I could
>> calibrate it in a similar fashion by putting tape around the pitot tube
>> before or after the static holes.
>> >>
>> >> Dave - yes, I realize that IAS changes with altitude.  I am observing
>> an offset between my TAS and GPS ground speed (after accounting for wind).
>> >>
>> >> Geoff
>> >>
>> >>
>> >> On Mon, Sep 30, 2013 at 4:24 PM, Scott Derrick <scott at tnstaafl.net>
>> wrote:
>> >> I have a static port(3 vertical holes, 1/4 inch apart)  under the
>> carnard, about a foot, that works well. However it does need to be
>> calibrated. An uncalibrated static port will cause erroneous altitude and
>> IAS indications.
>> >>
>> >> You can calibrate the port by putting a 1/4 inch wide strip of
>> aluminum tape either right ahead of the the hole(s) or right behind them.
>> You can add layers of the tape to increase the effect.
>>
>> >>
>> >> To determine if you need less pressure(tape before the hole) or more
>> pressure(tape after the hole).
>> >>
>> >>     Set your altimeter to field elevation, just before departure.  Fly
>> at cruise speed, ball in the center, 15-20 ft above the runway.  The people
>> on the ground love this!  Note your altitude.
>> >>
>> >>     If your indicating higher than 20 ft above field elevation, the
>> pressure is too low and you need tape behind the port. If your indicating
>> lower than 20ft above filed elevation, the pressure is too high and you
>> need tape ahead of the port.
>> >>
>> >>     If your within 50 ft, your good to go.  I did this after I bought
>> my plane, it was off 300ft. and after I painted, again off 300ft. The tape
>> lasts forever and looks like an embedded metal strip.
>> >>
>> >> my $.002, works for me.
>> >>
>> >> Scott
>> >>
>> >> -------- Original Message --------
>> >> Subject: Re: REFLECTOR: TAS calibration?
>> >> From: Geoff Gerhardt <geoff.gerhardt at gmail.com>
>> >> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
>> >> Date: 09/30/2013 01:56 PM
>> >>> Guys,
>> >>>
>> >>> My pitot/static is positioned under the canard - I suspect it is
>> seeing increased pressure at high speeds thus giving me a low indicated
>> airspeed.  This weekend, I thought I was smart and put a small static port
>> right ahead of the dog house thinking that was a great place.  After a
>> quick flight where my air speeds were through the roof, I realized that
>> that spot was actually doing the opposite and was creating a low pressure
>> region as the air bends over the nose.  I see now that I need to find a
>> place on the flat section of the fuselage to put the static port.
>> >>>
>> >>> Where does everyone else have their static port?
>> >>>
>> >>> Thanks.
>> >>>
>> >>> Geoff
>> >>>
>> >>>
>> >>> On Sun, Sep 29, 2013 at 11:43 AM, Kurt Winker <nmflyer1 at aol.com>
>> wrote:
>> >>> Sounds like a trip-strip may be in order.
>> >>>
>> >>> Kurt
>> >>>
>> >>> Sent from my iPhone
>> >>>
>> >>> > On Sep 29, 2013, at 6:47, Scott Baker <scottb33333 at gmail.com>
>> wrote:
>> >>> >
>> >>> > I would assume that you are factoring altitude and temperature when
>> calculating TAS. If so, airspeed error might be related to a pressurization
>> of the static system (a common problem in Velocity aircraft that have their
>> static port located forward of the entry door).
>> >>> >
>> >>> > Scott Baker
>> >>> >
>> >>> >> On Sep 28, 2013, at 8:29 PM, Geoff Gerhardt <
>> geoff.gerhardt at gmail.com> wrote:
>> >>> >>
>> >>> >> Guys,
>> >>> >>
>> >>> >> Flying today I realized that my ground speed seems to be always
>> greater than my TAS.  I figured at least some of the time it should be less
>> (i.e. into a headwind).  But it always seemed to be greater.  So, today, I
>> flew in a box, E, W, N, S and recorded my TAS and GS.  My TAS was constant
>> at 159ktas on each leg, and my GS (GPS) was 185, 179, 171, 175 for the W,
>> N, E, S legs.  If I add all those up and divide by four, I get 177.5kts,
>> yet my TAS registered 158ktas.  Am I missing something?  Is my airspeed
>> indicator reading too low?
>> >>> >>
>> >>> >> Thanks.
>> >>> >>
>> >>> >> Geoff
>> >>> >>
>> >>> >> _______________________________________________
>> >>> >> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>> >>
>> >>> >> Visit the gallery!  www.tvbf.org/gallery
>> >>> >> user:pw = tvbf:jamaicangoose
>> >>> >> Check new archives: www.tvbf.org/pipermail
>> >>> >> Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >>> >
>> >>> > _______________________________________________
>> >>> > To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>> >
>> >>> > Visit the gallery!  www.tvbf.org/gallery
>> >>> > user:pw = tvbf:jamaicangoose
>> >>> > Check new archives: www.tvbf.org/pipermail
>> >>> > Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >>>
>> >>> _______________________________________________
>> >>> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>>
>> >>> Visit the gallery!  www.tvbf.org/gallery
>> >>> user:pw = tvbf:jamaicangoose
>> >>> Check new archives: www.tvbf.org/pipermail
>> >>> Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >>>
>> >>>
>> >>>
>> >>> _______________________________________________
>> >>> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>>
>> >>> Visit the gallery!  www.tvbf.org/gallery
>> >>> user:pw = tvbf:jamaicangoose
>> >>> Check new archives: www.tvbf.org/pipermail
>> >>> Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >>
>> >>  --
>> >> Even if you're on the right track, you'll get run over if you just sit
>> there.
>> >> Will Rogers
>> >>
>> >> _______________________________________________
>> >> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>
>> >> Visit the gallery!  www.tvbf.org/gallery
>> >> user:pw = tvbf:jamaicangoose
>> >> Check new archives: www.tvbf.org/pipermail
>> >> Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >>
>> >>
>> >>
>> >> _______________________________________________
>> >> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >>
>> >> Visit the gallery!  www.tvbf.org/gallery
>> >> user:pw = tvbf:jamaicangoose
>> >> Check new archives: www.tvbf.org/pipermail
>> >> Check old archives:
>> http://www.tvbf.org/archives/velocity/maillist.html
>> >
>> >
>> > _______________________________________________
>> > To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>> >
>> > Visit the gallery!  www.tvbf.org/gallery
>> > user:pw = tvbf:jamaicangoose
>> > Check new archives: www.tvbf.org/pipermail
>> > Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>  ------------------------------
>>
>> _______________________________________________
>> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>>
>> Visit the gallery!  www.tvbf.org/gallery
>> user:pw = tvbf:jamaicangoose
>> Check new archives: www.tvbf.org/pipermail
>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>
>> _______________________________________________
>> To change your email address, visit
>> http://www.tvbf.org/mailman/listinfo/reflector
>>
>> Visit the gallery!  www.tvbf.org/gallery
>> user:pw = tvbf:jamaicangoose
>> Check new archives: www.tvbf.org/pipermail
>> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>
>  ------------------------------
>
> _______________________________________________
> To change your email address, visit
> http://www.tvbf.org/mailman/listinfo/reflector
>
> Visit the gallery!  www.tvbf.org/gallery
> user:pw = tvbf:jamaicangoose
> Check new archives: www.tvbf.org/pipermail
> Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>
>
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