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1. 04:20 AM - Re: Pitot Tube angle (GARY PENNINGTON)
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Subject: | Re: Pitot Tube angle |
MessageBuz
You are a real prize. I've never met you, but, I really like you. Some
day I would enjoy the honor of meeting and talking to you.
Gary Pennington
----- Original Message -----
From: Colin J. Kennedy<mailto:cjk129@cox.net>
To: lightning-list@matronics.com<mailto:lightning-list@matronics.com>
Sent: Saturday, December 06, 2008 10:19 AM
Subject: RE: Lightning-List: Pitot Tube angle
Thanks Buz. I think that addresses my question too!
Colin K.
OK
Lightning # 52 under construction.
http://www.mykitlog.com/cojaken<http://www.mykitlog.com/cojaken>
-----Original Message-----
From:
owner-lightning-list-server@matronics.com<mailto:owner-lightning-list-ser
ver@matronics.com> [mailto:owner-lightning-list-server@matronics.com] On
Behalf Of N1BZRich@aol.com<mailto:N1BZRich@aol.com>
Sent: Saturday, December 06, 2008 9:23 AM
To: lightning-list@matronics.com
Subject: Re: Lightning-List: Pitot Tube angle
In a message dated 12/5/2008 10:39:46 P.M. Eastern Standard Time,
pequeajim@gmail.com writes:
I look at my airplane and notice that the pitot tube angles up a
little even when the aircraft is sitting straight and level; is this
correct? If not, what all did you do to correct the issue, shim it?
HI Jim,
The real key is to have the pitot tube aligned so that it is
perpendicular to the vertical axis and parallel to the longitudinal axis
of the aircraft when the aircraft is in flight - not when sitting on the
ground. Or in other words for practicable use, aligned with the
relative airflow in front of the wing. Since airplanes fly at different
angles of attack at different airspeeds, the actual alignment with the
airflow as it meets the wing obviously varies as you change speeds. So
in reality, the pitot tube alignment is important, with longitudinal
alignment being possibly more critical since we know that the other
alignment will change with angle of attack. So get it as accurate as
you can. But remember that it will only be exact at one angle of
attack.
What is probably more important is the placement of the static
ports. The pitot / static tube measures total pressure (or impact
pressure) at the nose of the pitot tube and the static pressure of the
air stream at side ports. The difference of these pressures, or the
dynamic or velocity pressure varies with the square of the gas velocity.
So static source is just as important, if not more so, than pitot
pressure measurement.
The Lightning kit uses a good pitot / static tube with the
static ports right on the tube, so generally your airspeed measurements
will be pretty accurate as long as you have the tube parallel to the
longitudinal axis and perpendicular to the vertical axis when the
airplane is at normal cruise speed. It should be that way when you
install it as the plans and build manual call for. The only problem
comes when some "delta alpha" (dumb ass) walks into it at an airshow and
bends it. Yes, that has happened to me at Oshkosh. I just bent it back
to a TLAR measurement and it seems to be OK. (TLAR = that looks about
right).
Hope all this helps.
Buz
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