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
Hum,
Racemate makes a water pump mounted alternator. We need one that has that and
is a better fit for the low profile rotary. I'll talk to him. He's busy,
but.....if there is a market ? There is your second power source. Also, I
guess you want this starter-gen in the new 'smushed' bellhousing being done?
How many amps and how many gallons per minute does this device produce Marc?
If it is less than 35 gallons per minute it is unsuited to cooling the rotary.
Paul Lamar
Paul, I was referring to common alternators made by GM or Nippon Denso,
being in the high nineties. Seems like I might be misinformed.
I just got off of the phone this morning with our engineer.
The Zephyr's wind generator unit is claimed to be over 90% efficient.
Please understand Zephyr's wind generator technology is proprietary and the
whole unit was made with the help of 5 big institutions in Japan and funded
to the tune of over $500,000 by the Japanese government. It is state of the
art. But as you correctly pointed out as it heats up the efficiency will
come down. Like any electrical motor you have to know how it is rated. I
don't have the latest specs. mind you, but early on they were unhappy with
the engineers at Sumitomo Metals because the efficiency was ONLY 67%. at
full load. This prompted them to change engineers for the generator part of
the product. I only helped design a fail safe over spin mechanical brake.
I think the way they clamp the load is part of their patentable material.
I am not trying to be evasive, but perhaps I am:)
The bell housing motor project is just getting started. A different company
and an American engineer long time friend of mine is helping with this.
The 12" PM version (rotor about 8" inches or so dia. is now producing power
1 kW at 330 rpms. in a wind generator application. The design has been
motored as well. It has numerous magnets spaced around the perimeter of the
the rotor and is too heavy for our bell housing use. You can do the math
and understand what happens at 8K or 9K to the power outage. Suffice to say
we won't be flying anywhere.
He is making one with a thinner magnets (of less field strength and my
thinking is to keep the diameter as large as possible for good starting
torque.
Windage is an issue. Thanks for bringing it up. I don't follow your
estimate of one lb. of drag though. Was that arbitrary? Cooling will be an
bigger issue in the housing and may need some fins on the plate thus robbing
the generator of more power. The short answer is though we have plenty of
room to get a net 3Kw of power from a generator in there.
BTW in my late night verbiage I said another stupid thing. Hanging another
motor/alternator on the engine is just that. Redundant generator unless you
have something electrical you want to power. Charge the battery, and then
drain the battery motoring one unit again is a net loss situation. NG.
Obviously to make a little turbocompound unit the second generator needs to
be run by the turbo.
Funny I feel comfortable with electric mechanical motors or generators but
not for oil and water pumps, in airplanes. Call me silly.
One question for Vance. You mentioned homopolar motors once. I was curious
if you had ever meet Bruce DePalma or seen any of his work? For those of you
who don't know of him, Bruce was a very controversial physicist who lectured
at MIT and had many theories that didn't agree with Newton's laws of
physics. I as well as Bruce hesitate to say the words free energy. Actually
it is perhaps 'other energy' source. Before he died he made some interesting
(but heavy) motors.
Doug in Japan
Well it is easy to check the alternators with no electrical load. Just measure
the HP it takes to motor them at 10,000 RPM. I think you will find it significant.
Most of them have a built in centrifugal air pump for cooling.
The one pound was arbitrary. It is some finite number but I would need
some details to estimate it.
I'll buy over 90% but call me skeptical about high 90's.
Paul Lamar
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