"Charles Vincent" wrote in message
...
wrote:
On Jan 14, 11:10 am, "Peter Dohm" wrote:
wrote in message

...
On Jan 13, 10:06 pm, "Peter Dohm" wrote:

At the obvious cost of proving myself a heretic regarding VWs....
We could go back into the old debate about whether a nearly stock VW
engine
could be a reliable 50 to 60hp powerplant with the right sort of
pressure
cooling system. With all due respect to Bob, a/k/a Veeduber, I am still
convinced that it can
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Mybe it CAN. All I'm saying is that it never happened for me and I
gave it a pretty good go. Failures ALWAYS pointed to excessive
heating/lack of cooling.


Doubling the velocity of the air through a given cooling fin design only
gives a 60% or so improvement, but of course, the cost of accelerating
that air is operating on a curve going the opposite direction, i.e. it
takes 300% of the energy. Low horsepower designs use thick short widely
spaced fins with a turbulent air stream for the most efficient cooling
(i.e. least power) The fact that these are cheaper to build just happens
to work with the model that low horsepower designs are applied to. The
longer a fin is, the less efficient it is. So the VW head needs more fins,
not just longer fins, or even more air. All of this is exacerbated by the
fact that as load goes up, the percentage of heat in the cylinder head vs
the cylinder itself goes up disproportionately. Same thing happens with
RPM. So punching them and revving them to get more horsepower just
highlights the limitation of the original design. I can of course cite
sources for all of this, but real engineering textbooks are frowned upon,
so to go with the flow, I will ascribe it all to a friend of my cousin
named Mackerle and his partner Liston who has been building these things
for years and stuff and knows all about it.

Charles

I really had decided to let this whole matter slide; since, in the end,
everything that I might actually want to build would require 80 to 120
horsepower--and more if I really want the aircraft to have utility for
transportation. So this mostly an intellectual exercise.

However, since you phrase your response in the above manner:
1) To get from a thermal limitation of 45 horsepower to 60 horsepower looks
like a 33% increase. If you dissagree, please respond to
Hewlett-Packard--since I have been using their calculators for the past 25
years or so.
2) Doubling the velocity of airflow should require 400% (not 300'%) of the
energy, according to the old engineering texts that I can no longer find.
3) By the combining the above calculations, and using the latest trusty
Hewlett-Packard calculator, the 33% increase in cooling should require 177%
of the energy.
4) The basic point was that: if you climb at 60 (kph, mph, kts, or
whatever) and you would need to be climbing at 90 to adiquately cool the
engine; then the difference could be made up by the addition of a cooling
fan.
5) As to the real engineering textbooks: BRING 'EM ON.

Peter