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Date: Wed, 23 Jan 2013 08:27:55 -0500
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Subject: Re: [LML] Re: the Legacy RG Static ports
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From: Charley Brown <browncc1@verizon.net>
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Guys, I don't doubt your experiences or question your data. I'll add a few t=
heoretical observations and maybe we can tease out some consistent conclusio=
ns.=20
1,  The main effect of extending a static port above the contour of the loca=
l skin is to lower the static pressure reading (which makes the altimeter re=
ad higher and the airspeed read higher). So if you were perceiving a tailwin=
d in every direction, and extended the static ports, that would make the err=
oneous tailwind go away.=20
2. I tried to find a Pressure distribution for the Legacy and couldn't;  but=
 because the fuselage is tapering so much, I'm sure that the pressure change=
s rapidly ( from below-ambient toward ambient) as you go aft, in the vicinit=
y of the rear windows.  In other words, static pressure accuracy depends a l=
ot on putting them in the right place. If you put them too far aft, you coul=
d compensate by making them stick out. I used the recommended placement, kep=
t them flush, and it worked. =20
3.  Mooneys and the Cessna 172 both have protruding static ports, to compens=
ate for off-ambient local static press. So there ARE airplanes where the por=
ts stick out by design.=20
4.  Pitot tubes like the basic, stock Legacy pitots, are very robust and tol=
erant of  angle of attack changes.  They HAVE to be out of the boundary laye=
r, but if they are, pitot errors are very rare.=20

CB from iPhone

On Jan 22, 2013, at 3:25 PM, Paul Besing <paulbesing@me.com> wrote:

> This was my exact experience with my RV-6=85.not sure why from an engineer=
ing standpoint that it's argued when there is ready available data such as y=
ours as to the effects of flush mounted static ports.=20
>=20
> On Jan 22, 2013, at 9:55 PM, Dennis Johnson <pinetownd@volcano.net> wrote:=

>=20
>> I have a Legacy RG and put my static ports flush with the outer skin, loc=
ated in accordance with the assembly manual.  During my flight test phase, I=
 pleasantly noticed that I always had a tailwind!  I knew I was lucky to be f=
lying such a wonderful airplane and just figured I was equally lucky to alwa=
ys have a tailwind.
>>=20
>> Eventually, logic prevailed and I realized nobody could be that lucky.  I=
 flew the four course GPS airspeed check and discovered that my indicated ai=
rspeed was reading low.  I added a tiny piece of machined aluminum, similar t=
o a domed head rivet, to both static ports and it solved the problem.  Other=
 Legacy builders who installed their static ports protruding slightly tell m=
e that their indicated airspeed is accurate.
>>=20
>> Dennis
>> Legacy 580 hours=20
>>=20
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