Fred Osborn wrote:

Paul,

I?m a newbie and not sure this is the right address for this but the
posts on the LAEV prop have aroused my interest. I?m a retired aerospace
EE with 30+ years experience some of which involved use of various forms
of slip rings. Nasty things, prone to failure, cause of many headaches
and sleepless nights ;-). This is not to imply that the LAEV approach
lacks merit, make that considerable merit.

In the past I?ve given some thought to the problems involved in an
in-flight prop pitch adjustment and concluded that a electromagnetic
coupling would be the best approach. Something along the lines of a
pancake 2 phase or stepper motor generator with its rotor on the prop
shaft directly driving a 2 phase or stepper motor and gear train in the
hub. A switch would control the generator stator DC excitation (+ off -)
to determine the status and phase (direction) of the motor drive. It
seemed to me that this could resolve all of the wear and contamination
problems at a minimal weight penalty.

I don?t know if these thoughts are of any interest but I thought I would
toss them up for your consideration.

Fred Osborn

I would love to see a design for that. Can you get power to the motor
without contacts? I have no knowledge or experience in that area.
Can you do a schematic for us and upload it? Can we get the motor off the
shelf?

Paul Lamar

Yes, yes, YES!!!  Fred is on to something there.  We do this on the big
generators at work: brushless exciters.  I'm not sure just how to make a
small, light one for the LAEV, but I'm sure it could be done.  Basically,
use a static electromagnet mounted on the PSRU to create a field.  The field
can switched on or off, and polarity reversed manually or by the controller.

Mount a coil in the LAEV hub that "cuts through" the magnetic field of the
electromagnet.  This creates an AC voltage in the coil.  The voltage is a
function of the turns ratio, prop RPM, and field strength.  Now rectify it
into DC right in the hub, maybe use a zener diode to clip peaks, a capacitor
to remove ripple, and Voila!  You got a DC drive for the pitch motor.  No
physical contact, and the voltage & direction are all controlled by a fixed
coil.

On second thought, I think I can get direct DC in the hub.  The coil needs
to be wound in a torus, with the torus co-axial and encircling the prop
shaft.  Uni-directional "cutting" of the magnetic field gives DC.  No
rectifier needed.  Hmmmm.... I'm just a flange-head.  You sparkies out there
wanna chime in?

Tom Kendall

 
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