> >> > Jerry Hey wrote:

 >> > >
 >> > > I heard a new phrase (to me) in connection to the 13-B.  It is
 THERMAL RUNAWAY.
 >> > > What it suggests is that there is an operating rpm and hp above which
 >> > > cooling the 13-B becomes increasingly  much more difficult. Given the
 >> > > space available for radiators in my Tailwind, this  sets the limit on
 >> > > how much power I can hope to generate. Question:  Is 170 hp at 5500
 >> > > rpm continuous a realistic goal? I have Tracy's ignition and fuel
 >> > > injection.    Jerry

 >> > Not at all Jerry. 170 HP is well within reason and easy to achieve.
 >> > I think the term "thermal runaway" is misapplied to any internal
 combustion
 >> > engine. Are you putting the rad in the aft fuselage?

 >> > Paul Lamar

 >Dale Smith wrote:
 >>
 >> My $.02 worth ... the only time I have heard the term "thermal runaway"
 in connection
 >> with anything aeronautical is regarding ni-cad batteries.  An internal
 melt down
 >> starts to occur that is self feeding ... a little like the "china
 syndrome" of a
 >> nuclear reactor.
 >>
 >> Accordingly, ni-cad batteries should have temperature sensing systems ...
 which sure
 >> blows the KISS principle.  Most ni-cad systems get converted back to
 lead-acid or gel
 >> cells, by maintenance departments that would just not rather have to do
 all the
 >> ni-cad hassle ... drain the charge, recharge (in steps) ... monitor
 temperature, etc.

 >> Dale Smith

Howard wrote:

 Thermal runaway is an extremely poor term to apply to internal combustion
 engines.    Heat transfer ability increases tremendously as temperature
 differential increases.    Thus as waste heat dissipation increases with the
 application of power the engine temperature rises beyond where you want it
 to be, but it definitely does not run away because the transfer efficiency
 goes up.
     It is in no way appropriate to use a term that suggests something akin
 to neuclear meltdown for simple overheating......   If you exceed your
 cooling capacity your engine will just run hotter.... perhaps too hot.
 The idea of pressurized cooling systems it to allow the engine coolant temp
 to rize to a level where cooling  is more efficient, and where the engine
 operates more efficiently.....and of course to prevent coolant loss.
     If your temp exceeds the temp where pressure is greater than your
 radiator cap pressure you will blow all your coolant out and have a melt
 down......  that could be refered to as stupidity..... not thermal runaway.

                     H.W.

 My education continues.  Thanks, everybody.   Jerry

 
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