Newsgroups: rec.aviation.student
Subject: Re: question about electronic..
From: jbolinger@lintek.com (J L Bolinger)
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In article <70k33u$ip7$1@flotsam.uits.indiana.edu>, whchuang@indiana.edu 
says...
>
>Don't know much about mechanics and electronics...
>
>2 quick question about Cessna 150
>
>1. Why should we turn off all the electronics (radios and so on) before we 
lean the mixture to idle 
>   when we shut down the engine after flight? (according to the checklist in 
C-150)
>

I fly in a 172, which is the same way.

This is because there can be voltage spikes generated when starting/stopping
the engine that can damage the electronics.  Its a good idea anyway, to
get in the habit of doing things always in the same sequence.  Also, having the
radios on will drain the battery if you forget to turn off the master 
switch.  The batteries in airplanes are small, to save weight, so it is
a good idea to keep the drain to a minimum when the engine is off.

>2. Why does VOR need to "warm-up" to fully-functional? (at least in the 1975 
C-150 that I'm flying 
>   with, this is true..)


All electronics devices need to be warmed up.  It is that some warm up
faster than others.  They contain components whose values change with
temperature.  They could be adjusted to work when 'cold', but would then
be wrong after being on for a long time (that is, after 'warm up').  If you
where to look at the service manual for the VOR, it would probably say
something about 'allow to warm up for xx minutes before attempting alignment'.



(By the way, besides being a student pilot I am an Electrical Engineer.)


Jim

