REFLECTOR: Need a topic... gear down check

[James Lotspeich]

Dave,

You can download digital terrain and elevation data (DTED) straight from
the USGS web page.  I believe they offer 10m post spacing to the public,
but it may be 100m.  You'd have to extrapolate between posts, but it's not
a bad start.  If you order the full data set for the US, they'll charge a
nominal fee to burn it and mail it to you.

James

On Thursday, January 24, 2013, Dave T Nelson wrote:

> 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<javascript:_e({}, 'cvml', 'jlotspeich34 at gmail.com');>>
> on Wed, 23 Jan 2013 22:28:08 -0600 -----
> *To:*
>
>    Velocity Aircraft Owners and Builders list <reflector at tvbf.org<javascript:_e({}, 'cvml', '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<javascript:_e({}, 'cvml', '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<javascript:_e({}, 'cvml', 'rich_ervin at hotmail.com');>>
>       on Wed, 23 Jan 2013 13:54:25 -0500 -----
>
>  *To:*
>
>    <reflector at tvbf.org <javascript:_e({}, 'cvml', '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<javascript:_e({}, 'cvml', '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<javascript:_e({}, 'cvml', '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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20130124/4360d46a/attachment.html>