I agree; but the method I used was to fly one heading and compare GPS
with ASI and then
fly 180 degrees and repeat the comparisons. Then I repeated the
procedure 90 degrees from
that track.
Zero wind should be an average of the two as I see it.
Dan C
On Sep 5, 2008, at 8:39 AM, eaaflyguy wrote:
I recently bought an ercoupe this spring and posted the group with
the same problem/question.
During my first flight/checkout, everything seemed off when flying by
the numbers.. mainly because I was at minimum controllable speeds
because of the airspeed error.
In my case, the connector to the static line on the back of the gauge
looked ok but the fitting connections were leaking. (which made it
indicate 10-15mph to high). I tested with a spare airpseed gauge and
the old one, afterward, and both were dead-on. I would focus on
pitot/static troubleshooting before replacing the gauge.
Just for thought... I'm not sure if you have a model of GPS that has
a wind correction feature, but I assume most will indicate your true
speed relative to the ground, rather than your speed relative to the
air. The only time the compairison would be accurate between the GPS
and airspeed gauge is in an straight-and-level-cruise,
sea-level, zero-wind condition. (or when it is sitting still on the
ramp!).
On the pitot tube... the angle of wing incidence, and flow around the
wing at cruise may also play into the correct angle for the pitot
tube. These are factored in during certification. I'm curious now if
erco published any numbers that are still available.
-Brent Loveless
--- In [email protected], "Ed Burkhead" <[EMAIL PROTECTED]> wrote:
>
> Mike asks:
>
> > What is the 'direction of flight' when you are on the ground
>
> > under the wing looking at it?
> >
> > Photos I have of my Alon doing low passes at the airfield
>
> > show the nose attitude higher than on the ground, but
>
> > this was not at cruise speed, so to be expected.
>
>
>
> Mike,
>
>
>
> I think the airflow over the pitot tube part of the under-wing will
be very
> parallel to the wing's flat surface.
>
>
>
> I'd eyeball it from the side, making sure the pitot/static tube is
parallel
> to the bottom surface of the wing. This goes along with making
sure the
> tube is 3 7/8 inches below the wing as per the specifications.
>
>
>
> Then, I'd stand in front of the wing and pitot tube, trying to
judge as
> accurately as possible that I'm exactly in front of the pitot
tube. I'd
> eyeball the pitot/static tube to make sure it's not bent left or
right.
>
>
>
> There is some installation error in the Coupe's pitot/static tube
location
> but it's pretty minor. As I recall, it's designed to be right on
at 100 mph
> and the installation error at 50 or 55 mph is only about 3 mph from
true.
> That's pretty good.
>
>
>
> And, as always, you should determine the indicated airspeed at
minimum
> flying speed for your airplane with your airspeed indicator and use
that
> info to judge your approach and landing speeds.
>
>
>
> Ed
>
