REFLECTOR: Need a topic... gear down check

[Dave T Nelson]

I agree with everyone that a key shortcoming of my plan is in having to
guess at the altitude (i.e., subtracting the destination airport altitude
from the Dynon altitude).  Short of a laser based or radar altimeter, a
better solution would be to find a north American elevation database
referenced to lat/long.  A bit of background...

I researched homebrew radar systems, even going so far as to exchange
emails with several experimenters.  Unfortunately, there was no simple,
repeatable design to be had...  The other factor to consider is that the
architecture of what I'm implementing is very highly configurable... there
will be no big problem in retrofitting a better solution in the future.

Keep the input coming!

Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering

----- Message from James Lotspeich <jlotspeich34 at gmail.com> on Wed, 23 Jan
2013 22:28:08 -0600 -----
                                                           
      To: Velocity Aircraft Owners and Builders list       
          <reflector at tvbf.org>                             
                                                           
 Subject: Re: REFLECTOR: Reflector Digest, Vol 94, Issue   
          37                                               
                                                           

It's been a while, but I believe Cloudcap builds laser altimeters for
precision autopilot landings (UAV autopilot).  The cost six years ago was ~
$1k.  Worked pretty well when wings are level up to maybe 1000ft.  With an
IMU or AHRS unit, you can tell when you're level.  The laser will give a
good height above ground.  Both units feed serial data or CAN bus.  I'd
trust the laser over field elevation calculations.  Also could be used for
an auto gear down if you're feeling really experimental.

James

On Wednesday, January 23, 2013, Richard J. Gentil wrote:
  Hi Dave,

  I'm sorry I didn't make myself clear. I was going on the premise of
  building your own because the topic had mentioned building a single PCB
  computer to do what you needed. My comment was on how Avidyne handled it
  with the information from the Garmin and it was something that if you
  were thinking of designing on your own could give you some ideas on how
  to implement it. And I should add if you did build it, I would be happy
  to take one off your hands. ;)

  Richard

  Sent from my iPhone 5

  On Jan 23, 2013, at 2:43 PM, Dave T Nelson <dtnelson at us.ibm.com> wrote:



        I'll respond to Rich Ervin and Rich Gentil below...

        From:
        ----- Message from Rich Ervin <rich_ervin at hotmail.com> on Wed, 23
        Jan 2013 13:54:25 -0500 -----


                                                   
      To:       <reflector at tvbf.org>               
                                                   
 Subject:       Re: REFLECTOR: Need a topic...     
                gear down check                    
                                                   


        Any way to build this based on altitude or distance to ground? Some
        simple range detecting device that can measure the distance to the
        ground?

        What I'm planning is to use the Dynon altitude (referenced to MSL),
        and subtract the altitude of the destination airport (using the
        three letter identifier and a quick database look up)... to
        approximate the AGL altitude.  This is far from perfect... I've
        looked at trying to find an elevation database I could use and
        reference via lat/long... but so far no luck.

        From:
        ----- Message from "Richard J. Gentil"
        <richard at naples-air-center.com> on Wed, 23 Jan 2013 14:22:12 -0500
        -----
                                                           
      To:       Velocity Aircraft Owners and Builders list 
                <reflector at tvbf.org>                       
                                                           
 Subject:       Re: REFLECTOR: Need a topic... gear down   
                check                                      
                                                           

        Rich,

        You could use a radar altimeter. Also the Avidyne System in the
        Cirrus uses the GPS to give you TAWS terrain warnings when you are
        more then 5 miles from an airport and it calls out 500ft when you
        are on approach before landing at an airport.

        I would think that something like that would be what you are
        looking for in order to integrate with a gear warning if the gear
        is still up.

        Richard

        I've actually looked at homebrew radar altimeters for this
        application... complicated and expensive.  The Avidyne system in a
        Cirrus is quite different from my Garmin GNS-530W... my Garmin has
        terrain warnings, but unfortunately does not output anything usable
        regarding terrain warning or AGL altitude in the RS-232 data
        string.  As I'm not ready to by an Avidyne (or a Cirrus), I'm kinda
        out of luck on that front and working on my own solution.

        To all - thanks for the input!


        Dave

        Dave T. Nelson
        T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
        Program Director, ISC ECAT NPI & Test Engineering
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