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JohnW
11-12-2006, 08:03 PM
For those of you that are running a Zlog, Eagle Tree or other units, I have a few questions. Have you had to take steps to deal with rotor-wash affecting your readings? Have you verified your altitude readings? Do your readings fluctuate significantly on the ground?

My Eagle Tree telemetry gives very odd readings on the ground. Once I power up the telemetry my altitude reading started at -1' and continued to decrease to -100' over a period of a few minutes. After roughly 30 - 40 minutes it read -286' (Indoors, no wind, 72 MHz transmitter turned off).

Has anyone else experienced this? The odd thing is that the readings seem reasonable after a flight, although I have not verified them. My flight data recorder sits inside the canopy but is not isolated from the rotor-wash.

catfight
11-12-2006, 08:50 PM
John,

Altimeters just measure the outside air pressure ( in very small amounts and are considered sensitive instuments) so if there is a change (i.e. a low pressure area moving thru your town = or a high pressure also) it will show as an altitude change. These instruments are subject to calibration errors also (just like in a real aircraft) so they are not very accurate over any length of time.

pyaresquared
11-16-2006, 08:05 PM
I've compared altitudes from my How High altimeter with altitudes calculated trigonometrically from oblique photos and found errors of about 200 feet. I put a Zlog altimeter on a heli for the first time a couple of days ago. I flew no more than 200-300 feet, and the Zlog told me I went to something like 1300 feet. I think I need to figure out a different mounting location.

AZ ChopperCam
11-16-2006, 08:26 PM
I'm going flying in my Cheetah this weekend and plan to bring my "How High" altimeter.

see it here:
http://rcreporter.com/howhigh.html

I'm going to note it's accuracy at 500' AGL, 1000' AGL, and..... why not test it's limit at 7,000' AGL. :D

I'll open my canopy to make sure the static air pressure is the same as outside. I'll let y'all know how it performs