From: soc1070                         
Subject: Re: Club Projects
News-Software: VAX/VMS VNEWS 1.41    
Organization: University of Minnesota CIS
Date: Fri, 11 Dec 1992 17:56:00 GMT

In article <1992Dec11.101635.2242@aio.jsc.nasa.gov>, jackson@sn.jsc.nasa.gov writes...
> 
>>
>>I can't see how the altimeter would be accurate except at peak altitude.
>>How can you get a shielded chamber that is open to ambient pressure?
>>It seems to me that if there was an air passage to the inside of the
>>rocket, the Bernoulli effect would lower the measured air pressure while
>>the rocket was ascending. If the air passage was constricted, there would
>>be a time lag, raising the measured air pressure. After ejection, the
>>altimeter should be accurate, but ejection altitude might not be the minimum
>>pressure recorded.
>>
>> How did you mount your altimeter? (Just inside
>>the rocket, or with an air passage to a hole in the side of the rocket?)
>>Can the altimeter detect and record the ejection charge?
>////
>The altimeter is mounted in a closed payload chamber except for a 
>sampling hole (or holes). 
>I know one has to isolate it from vacuum drawn by the lower part of the
>rocket and the ejection charge. Which is easy to do with a payload section.
>As to why it works so well, I dont know the technical reasons. 
>But many rocketeers have been flying fairly accurate altimeters in recent
>years. TRANSLOVE has had one on the market for years, I think there have
>been others. I belive they have been checked by tracking too. The little
>experiment I did with Adept's altimeter looked good to me.
>(This is all below mach speed.)
> 

Thanks to everyone who responded to thread (and the couple others that 
started as a result of my original post). After watching to tone of this
discussion on altimeters, I think I have devised a project:

Effects of Altimeter Chamber Design On Recorded vs. Optically Tracked
                      Altitude of a Model Rocket

Since no one can seem to agree on a chamber design that will result in
an accurate measurement of altitude based on atmospheric pressure, I 
thought this might be a good project. We could test various chamber
designs and see the altimeter's altitude vs. what observers measure
with theodelites. What I am working on is a way to check altitudes while
the model is in flight. There seems to be some agreement that electronic
altimeters will work accuratly for peak altitude, but cannot respond 
to changes in altitude during the asent because the speed of the model,
thus resulting in a flawd altitude vs. time curve. If we could somehow
measure the altitude at a specific time in the flight (say 2 sec.)
optically, then compare this to what the altimeter recorded as the same
instant, we could see how well the altimeter is responding.

My first thought was to use the altimeter with the timed switches to eject
a chalk cloud at a specific time and then track the cloud. Or maybe a
system that fires a .22 blank and we time it to the ground.

Any other ideas? Comments?

------
Tim Harincar				Millions long for immortality			
Central Minnesota 			who don't know what to do with
Association of Rocketry			themselves on a rainy Sunday 
soc1070@vx.cis.umn.edu			afternoon. -Susan Ertz