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

Paul,

I knew I would get myself in trouble with my LAEV post. I am a retired
electroniker who got turned into a manager many years ago, not an electrical
machine type, but I can broadbrush a design so the group can understand the
idea and be involved in any development if they wish. Initially, assume the
use of the existing LAEV DC motor.

A design would start from a definition of the prop pitch change requirements.
If you must drive the prop pitch at low or 0 engine RPM, for ground test or
in-flight feather, then you will have to generate AC drive power (it can be a
simple square wave) on the airframe side and couple it to the prop side
through a rotary transformer. These are transformers with a circular air gap
between the primary and secondary so they can rotate relative to each other.
Somewhat inefficient due to the air gap but they can be overdriven for short
time pitch changes. We considered using these on the JPL/Galileo spacecraft
instead of sliprings for power and data transfer between the spun and despun
sections. These rotary transformers would definitely be custom devices.

For minimal changes to the existing LAEV, the AC power coupled into the hub
could be rectified, filtered, and regulated, within the spinner, to drive the
existing DC motor. AC power off - no motor drive. AC power on - motor drives,
but only in one direction. We also need a direction switch within the
spinner. Simple electronics but we also need a way to control the switch.
There are several non-contacting ways to provide a direction signal, another
rotary transformer or a higher frequency signal riding on the AC power
waveform or a substantial change in the AC frequency could be used as a
signal. Operation would be, AC power off - no drive, AC power on and signal
off - CW drive, AC power on and signal on - CCW drive.

If there is no requirement for 0 or low RPM pitch changes then the power
required can be supplied by a multipole alternator on the prop shaft.
Multipole to get the frequency up to a reasonable level, 1200 RPM is only 20
RPS or 20 Hz from a two pole device. The same electronics as above could be
used to to control the DC motor. This alternator would be an inside-out
device with DC excitation on the outside fixed part. Not a permanent magnet
type so the AC can be killed by shutting off the DC excitation. It probably
would have to be a custom device, but a good machinery guy might know of
something this old geezer never heard of. Again, the excitation could be
modulated for a direction signal.

Any interest ?

Fred O

 
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