Altitude, flight height reading

What would be the cost effective but accurate way of reading flight height (altitude) of model aircraft and how this reading would relate the local
QNH
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Depends on the weight you can take. If you can take 120gms easiest way is a Garmin Geko 201 +-50mtrs but generally around +-25mtrs, or a Garmin Geko 301 +- 3 mtrs with proper calibration.
--

<Altimeter> wrote in message
news:408b72bb$0$16964$ snipped-for-privacy@news.optusnet.com.au...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Be advised, using a barometric device, you will need to "calibrate" it to local barometric pressure each time you attempt to make use of it. Otherwise the reading will be incorrect.<

< You may want to check out some of the search engines specifically in regards to model aircraft design, use, and operations. Cheers

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Record the pressure readings for the whole flight and you eliminate this need. Then you have even less work than with GPS to calculate the max. height AGL (within a similar degree of accuracy).
--kyler
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is not an option because I'm planning to build an autopilot to control the airplane for level flight which means that I need to measure the attitude in realtime an measure accurately.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sam wrote:

ahh.., then you'll need to use an absolute pressure sensor. uhmmmm. how much payload can your model carry ? (I mean, you'll need a battery, some sensors, possibly a radio link, a microprocessor and some actuators)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

** Not just any old pressure sensor, but one that responds to the infinitesimal changes so the model will fly level at heights of only a few tens of metres above the ground.
What he actually needs is a ground tracking radar system - like F111s use to fly low and fast.
............ Phil
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A radar altimeter will give height above the ground, but terrain avoidance radar will give you forward looking terrain info. Depending on how big the model is, and how much weight it can lift, you could use a radar altimeter from a GA aircraft. You'll need map of the earth if you want to hug the terrain. I believe the Tomahawk cruise missile uses a GPS and digital terrain map of its route, and some sort of sensor for double checking the course based on the digital map, but I'm not 100% positive. I don't think it's the same exact technology that is in the F111. Clearly it works though!
-- Shawn

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<Sam> writes:>> Record the pressure readings for the whole flight and you eliminate this

There's no need to calibrate it at all it if you just want to maintain level flight. This is common with autopilots on larger planes. You don't need to use an altimeter setting unless you have an altitude preselect.
(If something on the ground needs to communicate in terms of absolute altitude, make it do the conversion. That's how our transponders work.)

I'm not parsing this.
--kyler
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Only problem is the Gecko won't log the altitude for you. The easiest solution if you wanted a complete log is to use a GPSr which logs altitude as well. Then you'd have a complete self contained log of location and height which you can read back into your PC. No programming or design involved. If however you want to send the height info back via telemetry then a bare GPS module may be a better choice, as you'd have to interface to some sort of micro anyway. You can lower the weight of the GPS by using smaller batteries, as you wouldn't need 10-20 hours of operation that a regular GPSr would give you.
Regards Dave :)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Check the model rocketry pages. There are a number of lightweight altitude tracking devices out there.ask the question at rec.models.rockets
MMB <Altimeter> wrote in message> What would be the cost effective but accurate way of reading flight height

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 25 Apr 2004 18:11:30 +1000, <Altimeter> wrote:

The February 2001 isue of Circuit Cellar had an article about a low cost and low power altimeter project. It won second place in their Design2K contest.
http://www.circuitcellar.com/design2k/winners/third.htm#ea
Regards David
--
reply to

dmmilne at ozemail dot com dot au
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.