REFLECTOR: Static port stuff

Sat Feb 28 13:12:38 CST 2009

John,
Two things to look at.  You probably know this.  One is to know how
sensitive the a/p is about feet off target pressure altitude.  Is it chasing
it's tail over 1 foot?  The other is control displacement to correct the
internally sensed "off altitude" condition.  Is it taking a big bite or only
one commensurate to the needed correction?  I've got a GRT Horizon a GNS480
and like a said a TruTrac, and the Trutrak has settings you can change
yourself to both of these conditions.  I think for TruTrak anyway their
default settings out of the box are likely for RV's which could be different
than for us.  
Terry

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of aminetech at bluefrog.com
Sent: Saturday, February 28, 2009 10:00 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Static port stuff

Mine is an S-Tec 50 and Apollo GPS.  My porpoising happens in calm air,
straight and level.  Next time I'll switch to the heading bug and see if it
makes a difference.  I've tried adjusting elevator trim, but not sure if it
helps as the problem doesn't last that long.

John

--- cjensen at dts9000.com wrote:

From: "Chuck Jensen" <cjensen at dts9000.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: Re: REFLECTOR: Static port stuff
Date: Sat, 28 Feb 2009 09:28:10 -0500

Hi, John,

Is your AP a TruTrack?  I had, and still have, a problem similar to yours
with my AP; that being porpoising that can only be stopped by disengaging
the AP.  Sometimes in turbulence but most often when the AP is being
directed by the CNX-480 GPS to make a fairly sharp turn (>30 degrees), the
GRT EFIS will indicate a dive, followed by a climb follow by a compensating
dive.

I disconnected the static ports and let the static system communicate with
the cabin pressure.  The altitude displayed was still accurate in all flight
configurations, but it really didn't fix the porpoising, so I was interested
in your configuration of instruments feeding your AP?

Chuck Jensen

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of aminetech at bluefrog.com
Sent: Friday, February 27, 2009 6:25 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Static port stuff

Terry,

Interesting comment.  Sometimes my AP starts porpoising and I have to
disconnect it for a few seconds to get it lined out.  Next time it happens,
I'll open my alt static port which vents inside the cabin and see what
happens.

John

--- terrence_miles at hotmail.com wrote:

Have you considered just yanking
the static port line from inside and just using the ambient cabin pressure?
I have mine hooked up to outside and no problems to report, but I know guys
with autopilot alt hold issues that consider this as a possible fix.  Are
you up to date on this topic?
Terry

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of LAURA WALKER
Sent: Friday, February 27, 2009 5:41 PM
To: reflector at tvbf.org
Subject: REFLECTOR: Static port stuff

Just wanted to thank everyone for their excellent input on my pitot/static
situation. I tried the low altitude test at 200 kts over the airport, and
sure enough, my altimeter read almost 400 feet high. I have since added
three layers of metal tape behind the port, but have not had a chance to go
up and test the change.

The good news is that I now have 40.1 hrs on 36 Lost Vacations, so I am all
set to get it down to my home field at EYE this weekend. I have been doing
my Phase 1 testing at TYQ, and can't say enough good things about Dan
Montgomery and all the excellent staff at Montgomery Aviation. If you are in
the Indianapolis area, you will find a welcome like few others at this
airport. They are now well-versed in Canardness, and can speak pitch-buck
and flapless aviation with the best of them. 

I'll post my static change results as soon as I find out myself.

Bill 
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