I had no idea Curtis Wright investigated aluminum
   rotors. I was going over some old 1963 booklets and
   tech papers Don Sherman sent me awhile back (his complete
   collection. Thanks again Don.) and ran across this illustration.
   The booklet was written by Max Bentele and was called "Curtis-Wright's
   Experimental Rotating Combustion Engines". Here is an excerpt.

   "A rotor made from an aluminum forging offers the benefits of
   lightweight and
   high thermal conductivity, but requires adequate cooling.
   One of the most successful aluminum rotor designs is cooled by forced
   circulation of oil from the engine lubrication system. The cooling
   circuit is
   schematically illustrated in Figure 18. Oil is supplied from the
   hollow shaft,
   through radial feed holes in the eccentric, and then to the rotor
   bearing
   central annulus. The oil then divides, one part to lubricate the
   bearing and the
   other to cool the rotor.

   Integral fins in each rotor lobe provide adequate cooling surface
   and a small
   hydraulic diameter. A recess at each end of these finned passes acts
   as a
   manifold for distribution of the oil. The oil from the rotor exit,
   after
   passing the bearing end annulus, is discharged from timed shaft
   eccentric
   passages directly into the housing drain annulus.

   The oil entering temperature, temperature rise, and period of
   contact with the
   metal are controlled to avoid coking or other lubricant
   deterioration. To date,
   we have had no evidence of adverse effects in this regard. While the
   oil flow of
   this design is continuous, the velocity varies as a function of the
   system
   dynamics: shaft and rotor inertia pumping superpose a roughly
   sinusoidal
   pressure increment onto the oil supply pressure. The cooling oil is
   metered at
   the exit; in this way, the rotor cavities are maintained full. Cast
   iron rotors
   can be made very much simpler than aluminum rotors but at present,
   not quite as
   light. Their cooling system is, however, different; it is adjusted
   to the lower
   thermal conductivity of cast iron and the thinner rotor walls. It is
   expected
   that by further design and casting improvements, the weight of iron
   rotors will
   approach that of aluminum rotors."

   Curtis Wright failed to take advantage of this weight reduction not
   realizing
   that someday the RPM of the rotary would be limited to 11,000 RPM by
   the weight
   of the rotor. Modern material, like Beryllium aluminum alloy, would
   make
   aluminum rotors even better. Be/Al alloy is three quarters the
   weight of just
   aluminum. My guess is the RPM of a two Be/Al rotor rotary (weighing
   180 pounds)
   would double to around 22,000 RPM and the HP would also double to
   about 1600 HP
   for an all out p-port turbo charged racing version. That would be a
   power to
   weight ratio much better than a pure turbine with about 1/3rd the
   fuel burn and
   1/10th the cost in a turbo compound rotary configuration.

   http://www.berylliumproducts.com/Attributes.aspx?id=AlBeMet162

   When this happens it is going to be an earth shaking event.
   A 300 HP car engine could shrink to below the size of a soccer
   (foot) ball.
   The empty weight of the car would also decrease as it is largely a
   function of
   the engine weight. The light aircraft industry would never be the
   same if these
   super power to weight ratio rotary engines were used in VTOL designs.

   Paul Lamar

   Paul, isn't there a major toxicity issue with machining beryllium?
   This was to be the super metal of the late 40's and 50's and it
   didn't happen.

   best,

   George W

   So? You want hi tech you deal with it. So is nuclear energy. Machining
   magnesium is dangerous as well.

   Paul Lamar

   Paul,
   Raw beryllium is dangerous, but alloyed much less so. The same reason so
   much mag is in mag-al alloy form. Mag is of course a physical problem,
   fire, rather than poisioning. Beryllium poisioning or berylliosis occurs
   more with long term contact.
   Bill Jepson

   So you stay out of contact with it. This is the age of automation.
   If you can reduce the weight of a car by 500 pounds what does that
   translated
   into initial energy savings and pollution? Once it is in the engine you
   will not be in contact with it. There are beryllium springs already in
   the Mazda rotary engine.

   Paul Lamar

   Yes Paul,
   I am with you on this. I think the BE/AL rotor is a GOOD idea. The
   machining of the material would be the only time that was worry some at
   all. I need to re-read the alloy information. The beryllium was the
   minor component of the alloy. Once alloyed the parts may pose no hazard
   at all. Kind of like salt, a compound made from 2 poisons, that becomes
   beneficial or even necessary for life! Be assured I am not fighting the
   idea.
   Bill Jepson


   Be is 62%

   Paul Lamar
   OK.  So for the sake of discussion, what happens if you take one of
   those single rotor 55 hp wankels from Renntech and go with the BE/AL
   rotor.   They already run at about 10-5  or  11 grand. What kind of
   output are we looking at?  110 hp?  Can you cool it?  How about
   bearings?  I agree that you can create a light-weight powerplant
   with high power density.  What I worry about are cooling and
   silencing issues.  The 65 hp Rotamax Wankels require a 32-36 inch
   stainless exhaust pipe before you get to the muffler.  You're going
   to have to gear it.  How much does the expense of the reduction unit
   go up with the increase in rotor rpm?  What is the cheapest way to
   do a technology demonstrator?  They already use Wankels for drone
   engines.  I wonder if DARPA would be interested in a techology
   demonstrator engine(s)?  They might also be interested in a compound
   version - high output and lower fuel consumption.

   best,

   george W.

I think you mean AIXRO rotary kart engines.  Renntech is just the U.S. distributor for those kart engines. All bets are off as that is a charged cooled engine. Charged  cooled rotors typically run 650 F or higher. I don't have any specific data on the AIXRO rotor temperature but I am willing to bet they have not measured it yet. It is a real instrumentation challenge to measure the rotor temperature with slip rings and all that stuff.

IMHO you need an oil cooled rotor to make Be/Al rotors work.
I am not a fan of charged cooled rotors. If it were me I would copy Mazda's oil cooled rotors for all rotary engines except for the cheapest low duty versions.

Where did you hear that about the Rotamax muffler? Rotamax engines have run with much shorter exhaust pipes. Come to think of it I have not heard from them since they crashed the Sadler. Also a charged cooled rotor design.

Paul Lamar

------------------------------------------------------------------------
NTSB Identification: CHI08LA274
14 CFR Part 91: General Aviation
Accident occurred Wednesday, September 03, 2008 in Findlay, OH
Aircraft: Sadler Vampire, registration: N333SV
Injuries: 1 Minor.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed.

On September 3, 2008, at 1257 eastern daylight time, a Sadler Vampire, N333SV, received substantial damage on impact with terrain during a forced landing. The airplane experienced a total loss of engine power after takeoff from Findlay Airport, Findlay, Ohio. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 test flight was not operating on a flight plan. The pilot sustained minor injuries. The local flight was originating at the time of the accident.

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