X-Mozilla-Keys:                                                                                 

One important and often overlooked consideration regarding any rotor material
is the compatibility with the seal materials (coefficient of friction and
galling tendency). Cast iron is an excellent material for compatibility with
a wide range of mating materials. Titanium, as I recall, is not nearly so
good. At high power, the ability of the apex seal to move in the slot is very
important. I suspect that the reason two-stroke oils are in favor is more for
the seal-slot lubrication than for the seal-trochoid lubrication.

Another key consideration in rotor design is thermal stress. While a low
conductivity rotor material might reduce heat rejection and improve
combustion efficiency, it will also lead to larger thermal gradients through
the rotor. The gradients will induce large thermal stresses which can lead to
a) bearing bore distortion problems, and b) low cycle fatigue
failures.

This is only a theoretical discussion, I do not have any practical experience
with titanium rotors.

Jonathan Lauter Rotary Power Marine

Thanks Jon. You are on our list of the more experienced rotary
engine design engineers. How's the rotary boat engine  business going? 
My son is in the market for a 50 HP four cycle outboard engine for his
new McGregor. I wish there was a wankel rotary type available.

Paul Lamar
 
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