Four Static Ports! Which to Use?

[John DeRosa Sky Soaring Chicago IL]

I need you opinion on which static ports to use on the DG. The
friendly folks at Glaser-Dirks provided me with two pairs of static
ports on my DG.

One pair is near my toes, the second pair near my knees. The only
difference is that the aft pair are on a surface that is almost
parallel to the line of the ship. The foreward pair are on a surface
that about +10-15 degrees away from parallel.

So which to use? It would seem to me that the forward pair, by virtue
of the fact that they are not on a parallel surface, might receive
some positive pressure. I assume that positive pressure would be bad
for a static port.

I should rig something up so that I can flip between the two while in
flight to see if there is any difference in instrument performance.
This makes the rash assumption that I would recognise the difference
if I saw it.

BTW: I am using the forward pair.

On a related question, why do static ports come in pairs? I assume it
has something to do with eliminating errors caused during slipping in
which the ports "see" different static pressures.

Thanks, John

[Bob Kuykendall]

Earlier, John Derosa wrote:

> ...It would seem to me that the
> forward pair, by virtue of the fact that
> they are not on a parallel surface, might
> receive some positive pressure. I
> assume that positive pressure would be
> bad for a static port...

That's not necessarily a valid way of looking at it.
I'd be inclined to look at it from a Bernoullian perspective,
and guess that the pressure there will more likely
tend to be lower than ambient.

> ... I should rig something up so that I
> can flip between the two while in flight
> to see if there is any difference in
> instrument performance.

That'd be an interesting experience.

What I'd suggest is: Look in the operation or maintenance
manual for guidance about which static ports to use
for the primary flight instruments. For a certificated
glider, it may specify one set or the other, and if
so you should heed it.

> On a related question, why do static
> ports come in pairs? I assume it
> has something to do with eliminating
> errors caused during slipping in
> which the ports 'see' different static
> pressures.

I believe that that is it. Or it could just be an unhealthy
Western fixation upon features of bilateral symmetry...

Thanks, Bob K.

[Nick Hill]

John DeRosa Sky Soaring Chicago IL wrote:
> I need you opinion on which static ports to use on the DG. The
> friendly folks at Glaser-Dirks provided me with two pairs of static
> ports on my DG.
>
> snip
>
> So which to use?

Look in the manual for the aircraft. I have a DG 100 and if I remember
correctly it states use the forward pair for ASI and the rearward pair
for soaring instruments.

Nick Hill

[John DeRosa Sky Soaring Chicago IL]

Thanks for the comments. I looked through both the DG-100 and DG-100G
(which I own) manuals and found nothing about the static port usage.
In fact I found nothing concerning ANY of the air lines within the
ship.

Could I ask you to look through your manual and see if you can find
the reference?

Thanks, John

Nick Hill > wrote in message >...
> John DeRosa Sky Soaring Chicago IL wrote:
> > I need you opinion on which static ports to use on the DG. The
> > friendly folks at Glaser-Dirks provided me with two pairs of static
> > ports on my DG.
> >
> > snip
> >
> > So which to use?
>
> Look in the manual for the aircraft. I have a DG 100 and if I remember
> correctly it states use the forward pair for ASI and the rearward pair
> for soaring instruments.
>
> Nick Hill