[Rhodes22-list] Stupid people tricks

[Richard Smith]

<breakdown of how much of the heat in a
> 2-cycle engine is absorbed in vaporizing & heating up the incoming charge.
> Given the low heat capacity & latent heat of vaporization of air &
gasoline,
> I wouldn't expect it to be very much.  If that's how the 2-cycle engine
> cools itself, then it's a good thing they use almost twice as much fuel
per
> unit power than a 4-cycle engine because they would need to to reject the
> heat. >

In model aircraft practice the fuel is methanol and castor oil (in the
main.)  As you must know water vapor is produced when methanol is oxidized.
I am totally unfamiliar with the actual thermodynamics' of the alcohol
fueled 2 stroke cycle but I suspect that this water vapor plays a major part
in the cooling budget of an air-cooled model aircraft engine.

As far as fuel consumption goes you are totally correct.  A methanol fueled
model aircraft engine has a fuel consumption at least TWICE of a 4 cycle
engine of equal displacement.

On the other hand I suspect the power output of the two stroke engine is
more then double that of the four.  The issue with two stroke technology
(with model aircraft) is poor throttling and the difficulty of coupling the
engines hi-power output (developed at high RPM's) to a prop which would be
more efficient at 1/3 the RPM.  The history of add on or OEM gearboxes in
such engines is dismal.

Interestingly enough this fundamental difficulty has promoted the present
swing to electric power.  Here motors of modest power are able (via gearing)
to mate with a purpose designed prop to couple to the atmosphere  power
sufficient to compete rather successfully with a sport type glow engine of
much greater shaft horsepower.  In fact, in some areas of low speed
aerodynamics the internal combustion engine is totally outclassed by the
electrics.

There is little doubt that evolving battery technology will lead (rather
soon) to the obsolescence of 2 and 4 stroke IC engines as a power source for
all but the largest model aircraft..

Richard Smith