Model Forum / General / Rockets / June 2007

I read the Perfect Flite manual and it says the altitude for deployment
is AGL.  I believe the barometric unit takes a ground level reading for
a baseline and the algorithum calculates the approximate main deployment
AGL.  Jumper for 1000' and get 1000'feet above ground level.  I believe
this works fine as long as you are not pushing the altimeter close to
the rated level.  You could email them for particulars say if your model
is going to go close to the rated limit of the altimeter.

AGL = Above Ground Level.  MSL = Mean Sea Level  So if you have your
altimeter set to 1000' AGL it will fire 1000' above ground level
regardless of where you are.  If you have your altimeter set to 1000'
MSL it will fire 3000' below ground level (a very bad thing I should
imagine)  I believe all the PerfectFlite electronics use AGL and so
you shouldn't worry about how high you are unless your rocket is going
to fly above the ceiling the altimeter is configured for.  The MAWD is
good to 25,000' MSL and the HA45K is good to 45,000' MSL  The Alt15K
is configured to 15,000' MSL but that doesn't have deployment so I
doubt that you're using that altimeter.

You could always call/email/write PerfectFlite and ask them directly.

-aaron

The following information is provided
without warranty, since I have been wrong
nine times already this morning and it is only
8:00 AM:

In general, if you do not enter the elevation
into the altimeter during calibration, it has
no way of knowing where sea level is. This is the
case with the GWIZ units I am familiar with. (My
familiarity comes from other people's data - mostly
at ARLISS launches.) They use launch site elevation
as reference level. Altitudes are AGL; ambient
temperature correction is done with respect to launch
site temperature too.

The ALTACC (I am familiar with only the older
versions) was calibrated against sea level. Altimeters
associated with GPS units are normally calibrated
against sea level, because the GPS unit supplies the
launch site elevation. I don't know of other examples.

-Larry Curcio