AviationBanter - View Single Post

**Bill Kambic**

On Fri, 19 Oct 2007 09:50:00 -0700, (Harry
Andreas) wrote:

In article , Dan Nafe
wrote:

Air cooled engines (in aircraft, not submarines) are lighter and less
complex to operate than liquid cooled engines.

WRT the weight...is that really true?
IME building liquid-cooled and air-cooled systems, the Liquid systems
are often lighter. Of course while glycol weighs more than air, usually
more aluminum is needed in an air-cooled system than in a liquid-cooled one.

From my reading it looks like you've got two issues:

Weight. It looks like early on the liquid cooled engines (like the
Merlin) could deliver more performance than single-banked radials
(like the R-1820). As time went on, however, the radials improved HP
output without much growth in weight. The version I'm most famliar
with, the R-1820-56 series, could put out 1525 hp (only slightly less
than an early Merlin). The double-banked radials (like the R-2800)
could significanly better the Merlin, but at a significant weight
penalty.

I've not looked at later liquid cooled models like the Griffin, nor
any of the Axis production engines.

Reliability. While you can probably get a better power to weight
ratio from a liquid cooled engine, the cooling system is an "achilles
heel" for the type. There are numerous stories (ranging from the
beginning of WWII to all the way to the end of the Viet Nam War's
A-1s) of radial engined aircraft coming back home with massive engine
damage (no oil, cylanders shot away, etc.).

Performance was certainly an issue and the larger frontal area of the
air-cooled engine puts it at a disadvantage vis-a-vis the liquid
engine. But, then, naval aircraft are generally at a slight
disadvatage when comparted to comparable land-based types due to the
additional weight penalty that navalization extracts (heavier overall
structure, heavier undercarriage, wing fold systems, etc.).

A liquid cooling system adds a significant level of complexity, and
thus maintenance cost (dollars and man hours). Ships cannot carry
unlimited numbers of mechs or spares so this complexity is a major
consideration.

A "quick and dirty" overview of the naval aviation establishments of
the WWII era demonstrates a dramatic favoring of air-cooled engines
over liquid cooled engines. The U.S. didn't have any liquid cooled
carrier aircraft; the British were mixed about 50-50 in type but I
can't get a firm grasp on numbers (large numbers of U.S. manufactured
aircraft like the Avenger and Corsair were used); the Japanese had a
very few liquid cooled types, but air-cooled predominated; I don't
have any good information on the French.

Overall, for naval use from carriers, the air cooled engine is the
clear winner.