> The questions of this thread should center around:
>
> - Are high speed (50-80K RPM) alternators
available
OTS?
> - Can they be safely coupled to the turbo?  >Possibly replacing the compressor section?  >(U-joints are out!)
> - Are high efficiency electric motors available
OTS
that can be bolted to the e-shaft?
> - Can this be done to recover some exhaust energy,
or is this a waste of time?

First, turbocharging does not increase efficiency.
However, a carefully designed system using a
turboalternator might increase the torque.

I'm not aware of OTS high speed alternators, at
least
just yet, for the rotaries. Custom, they can safely
be
coupled to the turbo. The compressor section can be
replaced too.

High efficiency brushless electric motors are
available.

Given the notorious inefficiency of the rotary
engine,
any heat recovery would be of great value. A custom
turbo alternator has been done.

see Barber-Nichols site

http://www.barber-nichols.com/products/specialty_products/turbo_alternators/default.asp

To do this single design change in isolation would
make the engine prohibitively expensive. However, an
estimated 20-30% could be recovered assuming a base
efficiency of 40%.

However...one design takes the rotary engine and
eliminates the "bulkiness" of past and current
designs
in RX-7/8 and other rotaries.

Almost all rotating parts are placed on the main
rotary shaft including a starter/alternator, a
compressor, and a flywheel in line with the rotary
engine! Intake and exhaust would be designed to
assist
in cooling/heating.

The result is interesting since efficiency goes up
as
weight goes down. With the above changes, and by
using
other materials, the efficiency could reach 75% and
the weight could drop 50%. The gross increase in
power/pound would be a factor of 3 1/2, very
significant for airplane use.

Starter/alternators are already here and gives the
engine a bit more breathing room.

Instead of one turbo alternator, smaller multiple
turboalternators might be used for redundancy sake.
Also, there are scalability issues to address with
the
larger the rotating parts.

David Mathes

"Given the notorious inefficiency of the rotary
engine,"

It is not as bad as you think David. We are within
4% of a typical Lycoming BSFC. .47 for the rotary as
opposed
to .45 for the Lyc. Sure people are claiming .38 but
they
have no independent data to back it up. That is
diesel territory.

What more than makes up for that is the ability of
the rotary
to burn auto fuel. Most Lyc's now a days require 100
LL.
Typically there is a 50 cent a gallon saving or
about
$2.50 verses $3.00 or about a 17% savings in favor
of the rotary.

Paul Lamar

Paul

The gasoline rotary is an advantage in time. Diesel
used to be cheaper as well as propane and natural gas.
However, gasoline appears to be cheaper than any other
flight fuel, and allows one to fill at their favorite
low cost gas station.

I'm not sure a multi fuel rotary engine would be
desirable.

The rotary history has been one of lower "gas" mileage
than comparable. i was thinking autos at the time.

With all the recent improvements, and the rise of
competitors like Rotamax, there is a lot of work
moving the custom techniques onto the production
products.

The rotary wins on weight which translates to energy
density. Lycoming has solid engines but the 2% fuel
efficiency advantage can be eaten up by the heavier
engine.

Energy density is power per mass per volume

Energy density = P /(mass*vol.)

Volume is often ignored in improvements unless there
is a radical change since lighter weight parts are
usually form, fit and function replacements. An
example would be going from Aluminum housing to
magnesium housing, or using a lighter weight
alternator.

The advantage of putting everything in line and on
shaft especially in a plane is that we can actually
combine functions. For example, the turbo alternator
properly designed can combine starter, alternator and
turbo functions. Access may be easier; remove and
replacement may require removing the engine however.

David Mathes

A few years ago there was a lot of buzz about a starter/
alternator. Then reality apparently set in. If it has enough
HP to work as a starter it is too heavy as an alternator and the
idea never took hold. Also I think cost was a factor.
Hard to beat cost wise an established alternator and starter
infra structure. It is probably perfect however for a UAV.

One of the off setting factors as far as car mileage is concerned
is if you have 250 HP with a real smooth engine you are
likely to use it more. At 65 to 75 MPH cruise my RX8
gets 25 mpg.

The rotary is still in its infancy. We are just now getting
another ratio of rotor width to eccentricity ratio in the 16B.
First time in 34 years. How many zillion piston engine bore to
stroke ratios have been tried?

Don't hold your breath on Rotomax.

Paul Lamar ...No rotor no motor.

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