Received-SPF: pass
 receiver=logan.com; client-ip=64.102.122.149; envelope-from=echristl@cisco.com
Message-ID: <421F3532.8090505@cisco.com>
Date: Fri, 25 Feb 2005 09:24:50 -0500
From: Ernest Christley <echristl@cisco.com>
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20040929
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Racemate alt/water pump
References: <list-758518@logan.com>
In-Reply-To: <list-758518@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Finn Lassen wrote:

> I was looking for possible failure modes. We know that alternators 
> fail. What would be the possible fairure modes of this PM generator - 
> other than rectifiers, and series voltage regulator?
> Alternators failures: rectifiers, bearings, brushes, ?
> The envisioned PM generator would have which possible mechanical 
> failure modes?
>
> Finn
>
-No bearings.  In fact, if installed properly, no moving parts (at least 
in the sense that parts are rubbing against one another).  The stator 
bolts to something solid and doesn't (shouldn't) move relative to the 
mounting.  The rotor bolts to a shaft and doesn't (shouldn't) move 
relative to the mounting.

-You might be able to over-rev the engine enough for centrifugal force 
to force the magnets through the rotor housing.  I don't think it could 
happen before you drive the trochoid rotor seals into the side housings, 
but it would result in catastrophic (sp?) failure.  The rotor would 
'explode'.  This is, of course, a failure mode shared with any spinning 
device and is easy enough to design it so that it is more dependable 
than the wings.

-There are the typical electrical failures share with all electron 
pushers that you cited, burnt wires, shorted things, open things, etc.  
They are all the result of pushing electrons around and will be there 
regardless of what is doing the pushing.  Bill will help us out with an 
infallible regulator design 8*)

-No brushes.  As always, it can't break if it ain't there.

-Will the magnets weaken and wear out over time?  That's a question I've 
always had.  We are asking them to do work, after all.  If this does 
happen, it would be a very gradual process that would be taken care of 
at annual.

In the final analysis, the PM alternator is just a simpler design that 
does the job very well.  Standard alternators were made more complicated 
due to the operating environment, and along with that complexity comes  
a list of failure modes.  Even though the modern alternator is very 
robust, it'd be nice to leave that list on the ground.