From: Bes1612@aol.com
Date: Mon, 8 Feb 1999 05:39:56 EST
Subject: COZY: pitot tube extention

Greetings all;

Does the pitot have to extend past the surface?   Mine is slightly off center,
and was thinking that just a hole there would be better looking.  If so how
far must it extend? How big must the hole be? Can the end of the tube be
reduced?

Bob Smith.  (Looking forward to spending my refund on material!)

Date: Mon, 08 Feb 1999 16:47:29 -0500
From: Bulent Aliev <atlasyts@bellsouth.net>
Subject: Re: COZY: pitot tube extention

Jeff Russel has his pitot tube flush with the skin and works the same



From: cdenk@ix.netcom.com
Date: Mon, 8 Feb 1999 16:14:58 -0600 (CST)
Subject: Re: COZY: pitot tube extention

The pitot tube should extend to the point of being in relatively undistrurbed air flow. What the 
drawings show is a minimum probably. WHen you see test aircraft like CAFE tests, its much longer. I 
have seen them on booms a foot or 2 long. Therefore flush is not acceptable.

Date: Mon, 08 Feb 1999 21:06:31 -0500
From: Bulent Aliev <atlasyts@bellsouth.net>
Subject: Re: COZY: pitot tube extention

I had discussion with Jeff and had the same argument. He told me that
with or
without the extension of the PITOT tube, NOT the static source the readings
were the same. So he removed it permanently. I did not make this up.
Just the
facts .

cdenk@ix.netcom.com wrote:

> On 02/08/99 16:47:29 you wrote:
> >
> >Jeff Russel has his pitot tube flush with the skin and works the same
>
>
> Unless properly calibrated, I wouldn't think so. Put another airspeed with
> the pitot on a long boom. and compare. We are talking pitot tubes (ram air
> to the airspeed indicator), NOT the static source ???

From: Bes1612@aol.com
Date: Tue, 9 Feb 1999 02:30:13 EST
Subject: COZY: pitot extension

Looks like aesthetics wins out for now.  I can always put an extention on
later if there is any problems.  I like the idea of a small, slightly
elongated hole just off the nose.  Thanks to all the response.  

Bob

(Original question-  Should the pitot tube have an extension or can it be
flush with the surface?)  

From: ernie de goveia <edegov@iafrica.com>
Subject: COZY: Pitot extension
Date: Tue, 9 Feb 1999 13:51:19 +0200

Bob wrote "looks like aesthetics wins"

Aesthetics dont work, physics do. A pitot must be in a position to  measure
air pressure and not be affected by the slip stream. This is the reason
most aircraft have the pitot supported away from the structure on a mast.
the hole in the pitot faces directly at the airflow to measure all it's
pressure. A slightly elongated hole will be affected by the slip stream and
will  not feel the airflow directly ,it will only measure  part of the air
flowing  past this hole and will give low reading on the airspeed indicator.

Go with what works.

Ernie in Cape Town


Date: Tue, 09 Feb 1999 09:11:53 -0500
From: bil kleb <w.l.kleb@larc.nasa.gov>
Subject: Re: COZY: pitot tube extention

cdenk@ix.netcom.com wrote:
> 
> The pitot tube should extend to the point of being in
> relatively undistrurbed air flow.

true, but the nose _is_ in relatively undisturbed flow.

> when you see test aircraft like CAFE tests, its much longer.

this is because the pitot is typically mounted on the wing
which creates all sorts of disturbances ahead of it in subsonic
flow (upwash--see the latest sport aviation article about
how lift works).

> Therefore flush is not acceptable.

not true.

since we're putting the pitot port on the nose of the bird and
this location is a few chord-lengths away from the canard, we can
get away with quite a bit:

a flush pitot port will give _exactly_ the same reading as and
extended one IF the location of the port on the nose coincides
with the stagnation point on the nose.  note: the location of the
stagnation point varies with angle of attack.  to put it another
way, for the readings to be the same between a flush and extended
pitot inlet, your flush-mounted inlet must be located at the
stagnation point on the nose whereas the extended pitot is not
so location critical.

the extended (maybe only 2" or so) pitot probe inlet has it's own
stagnation point on its tip which remains useful up to angle of attack
deviations of about +/-15 degrees.  however, the flush mounted
inlet will start to experience errors as soon as the stagnation
point on the nose moves due to angle of attack.  note: the
sharper the nose, the less the stagnation point moves with angle
of attack.

so, if you manage to get your flush inlet located pretty close to
the stagnation point of the nose during cruise flight, then it
will read the same as an extended probe.  however, at different
angles of attack, it will be in error depending on how blunt the
nose is, but that is what cas is all about, right?  (cas is ias
corrected for position and installation error--see the poh of
your favorite spam can for a sample chart comparing the two.)

as mentioned earlier, those wing-mounted pitot probe people
have the same sort of angle-of-attack errors creeping in but this
time it is due to the upwash of the wing `disturbing' the incoming
flow to the probe inlet.

IAS is what you fly by, so as long as you know when stall (er,
minimum airspeed) is and the IAS is pretty close in cruise, then
it's the same situation that the little-wing-in-the-back people
have dealt with all along.

-- 
bil <mailto:w.l.kleb@larc.nasa.gov>

Date: Tue, 09 Feb 1999 09:06:24 -0600
From: vaatk@flash.net
Subject: COZY: pitot tube

<x-html>
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
I noticed a lot of talk about pitot tube location on the EZ types. In 1980
when I built my first VariEZ.&nbsp; I talked to Mike Melville about location
of the tube, (they were getting squashed and tromped on when parked) and&nbsp;
about a different location.
<p>Mike said " the best and most accurate location is where the plans show,
with the tube protruding into relative undisturbed air.&nbsp; Most other
arrangements will not be as accurate, (he didn't say how much the value
would be off) and the key would be a good static location and the pitot
located in undisturbed air.&nbsp; I took that to mean, at least get the
tube out there.
<p>In my COZY, I have flown with several other aircraft comparing airspeeds
(factory and home built) and most all are within 1 to 10 percent accurate.&nbsp;
If you change your tube location be aware, if you flush it in, the <i>relative</i>
angle of attack will have an effect on the readout, sometimes drastically,
like high angle of attacks when coming into land, or crosswinds, just when
you need accurate airspeed the most.......who needs it at cruise ?
<p>In the Jets (yes the factory makes experimental ones with EXPERIMENTAL
slapped on the side)&nbsp; the factory installs a huge 6 inch dia. airspeed
gauge marked in knots&nbsp; and a very long pitot tube, (on the order of
4 to 6 feet) just to get the truth.
<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
Vance Atkinson N43CZ&nbsp; 1300TT
<br>&nbsp;
<br>&nbsp;
<br>&nbsp;</html>
</x-html>
From ???@??? Wed Feb 10 16:49:05 1999
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From: "Melchinger, Klaus" <klaus.melchinger@daimlerchrysler.com>
To: "'Bulent Aliev'" <atlasyts@bellsouth.net>
Cc: cozy_builders <cozy_builders@betaweb.com>
Subject: AW: COZY: pitot tube extention
Date: Wed, 10 Feb 1999 08:13:38 +0100
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Why not have a look at todays high performance gliders ?
They all have the pitot tube inside the fuselage nose !?
Best
Klaus 

	> ...  Jeff  ... told me that with or without the extension of
the PITOT tube,
	> cdenk@ix.netcom.com wrote:
> > Unless properly calibrated, I wouldn't think so. 

