REFLECTOR: TAS calibration?

[Geoff Gerhardt]

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 altitute and
> IAS indications.
>
> You can calibrate the port by putting a 1/4 inch wide strip of aluminin
> 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
>> >>
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>
>
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