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Copper and brass
Liquid cooled aircraft engines are not new. In fact the very first engine flown
by the Wright brothers and many of the earliest aircraft engines were water
cooled as well as some famous ones that were used during World War II such
as the P-51 Mustang, the P-38 and the Lancaster bomber. So why didn't
water cooling work for smaller general aviation aircraft? Well,
there are at least a couple of reasons; Weight and reliability.
However, in addition, the small piston engines that power GA aircraft today
were originally developed under military contract to power forward spotter
aircraft. The requirements for such engines had to be ease of maintenance and
the ability to survive being shot at. Thankfully today, GA aircraft aren't
shot at - so why do we still cling to air cooled engine technology with all
of its inherent limitations?
Back in the old days - well over 50 some years ago and even
up to the 1980s most radiators were made from copper and brass.
These metals were used because they were easy to work with and
could be readily soldered or brazed to form the tubes and fins
of the typical radiator. The problem is that copper/brass
radiators are both heavy and if you vibrate them enough they
tended to crack and leak. These were all issues that made it
very difficult to use them in light aircraft. Furthermore the
old copper/brass radiators were not very efficient from a
thermal standpoint. They required large radiators in order to
dissipate the heat generated by high powered engines.
Aluminum - Lightweight, Small and Super
efficient
Aluminum radiator technology has been refined to the point
were they are standard on virtually all automobiles manufactured
since 1985. New manufacturing techniques have been developed
that now make it possible to work with aluminum in such
intricate structures as a radiator. An aluminum radiator is up
to 60% more thermally efficient than a copper/brass radiator and
much more durable. Since aluminum is stronger than copper it has
been possible to manufacture radiators with even wider tubes
offering greater heat dissipation area than any copper/brass
radiator could possibly be made to do.
Aluminum fins can be made in such a way as to substantially
increase the amount of surface area that is in contact with the
passing air. The best news is the weight. Aluminum radiators
weigh less than half of their copper/brass counterparts. The
advancements in aluminum radiators technology is one of
principle reasons why liquid cooled aircraft engines are again a
viable solution.
In order to properly cool a 180HP, O-360 engine we have found
that a 12"x9" by 2 core (each core is 1.5" deep
for a total of 3" deep) radiator is all that is required.
This radiator weighs 7.75 lbs, dry. It holds 1.5 quarts of
water making the total weight 10.75 lbs.
Since such small radiators are possible, airframe designers
can now be creative about where they might locate a radiator
within the airframe or even the wings. It is these types of
options that open up to airframe designers that are simply not
possible with conventional air-cooled engines. One of the
reasons that there may be few pusher type airframe designs is
the difficulty on cooling an air-cooled engine located at the
back of the airframe. With water cooling such a configuration
no longer need be a major headache.
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