Date: Fri, 25 Feb 2005 19:41:12 -0500
From: Finn Lassen <finn.lassen@verizon.net>
Subject: Re: [FlyRotary] Re: Racemate alt/water pump
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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That's why I'm interested in this PM generator. Looks nearly 100% bullet 
proof, especially with redundant rectifiers and regulators isolated with 
switches from the coils (at which point the switches become the weak link).

It appeared to me the primary mechanical failure would be the mags, 
unless some resonant frequncy could break off the stators or coils.

Finn

Ernest Christley wrote:

> 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.
>
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