Yes either the pancake or radial PM in the RE bell housing will be
used as a starter/gen. This is one item I will produce and offer it to
the group if interested. 12 or 24v versions. Don't know the weight
yet but it better be under 9Kgs. [19.9 lbs] Depends on what is
attached to it. Ie how to interface to Tracy's rubber donut flex plate
and how to incorporate a strain gauge into
its as well.
Doug in Japan
Tell me more about this-what is this we are talking about? The stock RE
bellhousing containing an alternator or what? Starter-gens are used only
in turbines that I know of.
Marc Wiese
Mark
I am having a 50mm or less thick motor combination generator made up. I
mistakenly called it a pancake motor. Sorry. The design specs are targeted
for at least 3 kw and the prototype unit will be able to fit in my the RE
bell housing. Last time I spoke with George he said it would fit but now I
am not so sure. It may have to be thinner. I've saw the prototype when I
was in USA in October. Unknown at this time is how it will link it to the
PSRU drive. Since the magnets are placed around the circumference of a
metal disc then cutting mounting holes in that disc shouldn't be a problem.
It will be design to slip on like a flywheel and the bell housing will have
to be machined to fit hold the stator.
A real pancake motor would have the magnets on the face of one disc and the
winding coils on the other. For several reasons that is not a good way to do
it for our needs.
Other designs points to look at. Çan or should the disc rotor be cut or
modified to act like a counter balance weight for the RE? IMHO.. no...
because of resonance problems but I would like to hear other thoughts. I
have seen flywheels cut that way but then again they are more torsionally .
stiff and a slight wobble it not noticable.
Wisdom dictates that aircraft engines should have a least two sources of
electrical generation to provide the spark to the engine. Magnetos are nice
and pretty reliable. So are permanent magnet generators. You can always have
another starter/alternator made by GM hanging at the usual mounting place
and make a little (very little) turbocompound system when the battery
becomes charged up. Actually these size of motors and generators are in the
high nineties in efficiency. Power controller however cuts the final figure
down to about 85% to 91% depending on load.
Doug in Japan
Where do you get that high 90's efficiency number Doug? What size coil wiring are you using
and how long is the wire for each coil. I assume all the coils are in parallel?
Please send me a schematic of the motor and the controller.
I have data on motors that claim over 90% efficiency but that is only initially
and for a short period of time until they warm up. Also if you are using this
for a generator you must also calculate the windage drag of a large diameter magnet
rotating at 5000 to 7500 RPM. Windage drag is proportional to tangential velocity squared.
A 12 inch diameter magnet is moving 15,708 feet per minute or 261 feet per second
or 180 MPH at 5000 RPM. If the drag is only one pound that is 261 pound feet per second
at 5000 RPM or about 1/2 HP. If the generator can output 3 HP or 2 KW than
the efficiency is 3.5 mechanical HP in and 3 HP out or 86% for this factor alone.
Also 2 Kw at 14 volts is 133 amps for a frame of reference. What is the size of
the magnet required to generate 100 amps at 14 volts?
At 6000 RPM cruise HP loss would be about 40% higher.
BTW it was discovered in WW I that windage drag limited the RPM of the rotary
radial engines then in use and started absorbing an excessive amount of HP at 1800
RPM or so. This is the main reason the otherwise elegant radial rotaries disappeared.
I am not saying it is not going to work. I am saying efficiency in the high
90's not counting the controller is unlikely.
Paul Lamar
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2004 All world wide rights reserved.