REFLECTOR: Static port stuff

Mon Mar 2 08:20:20 CST 2009

John,

In my experience with AP, you have an AP problem, not a static source
problem.

I fly two almost identical T210's,  with old but identical AP's. One
porpoises in turbulence, one is rock solid.  The rock solid one had the
AP completely reconditioned a few years ago. The porpoising one is
original 30 years old.

I had a connector to a servo cause a problem on my V, The ailerons would
over correct at times.   Cleaned the connector and all was well.

Had a Bonanza that had a porpoising AP. Finally figured out one of the
rod ends was seized and putting to much friction in the system.

A friend had an RV with a AP that course seeked, back and forth.  Like
porpoising but in the horizontal!  His aileron servo was to small for
how he had it set up.  That somehow confused the AP and it would
oversteer, then understeer, etc..  He could change the geometry of the
lever arms or increase the size of the servo.  He changed the servo and
no more problems.

Somebody on this list posted about resistor changes in his AP that cured
a problem. 

I think something in your AP system, be it mechanical or electrical is
out of wack..  Your system should have some kind of trouble shooting
procedure that will allow you to track down the problem.

Scott

aminetech at bluefrog.com wrote:
> Terry,
>  
> My AP seems to have a split personality.  Most of the time it works
> fine, making small corrections.  Infrequently it will start
> porpoising.  At first I thought it might be turbulence, but when I
> disconnect, the air is smooth.  Maybe it's the AP or maybe the static
> port.  I'll check the port next time it happens.
>  
> John
>
> --- terrence_miles at hotmail.com wrote:
>
>
>
> 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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