REFLECTOR: TAS calibration?

Tue Oct 1 04:40:29 CDT 2013

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 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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>>
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>>
>>
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>
>
>
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