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Essential and Dispensible WW2 aircraft.



 
 
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  #101  
Old October 19th 07, 07:35 PM posted to rec.aviation.military,rec.aviation.military.naval
Bill Kambic
external usenet poster
 
Posts: 57
Default Essential and Dispensible WW2 aircraft.

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.

  #102  
Old October 24th 07, 01:51 PM posted to rec.aviation.military,rec.aviation.military.naval
Peter Stickney
external usenet poster
 
Posts: 17
Default Essential and Dispensible WW2 aircraft.

guy wrote:

Responding late, but a few points:

On 18 Oct, 00:51, Dan Nafe wrote:
In article . com,

Eunometic wrote:
The modification would have required a lengtened nose to and
additional
radiator area to deal with the extra head and to dump heat from the
intercooler.


Liquid cooling an aircraft engine is like air cooling a submarine
engine...

;-


What has liquid cooled engines to do with intercoolers?

Nothing. Highly supercharged engines (Pressure Ratio of more than 3.0)
really benefit from removing as much of the heat that's generated by
compressing that air as possible, though. Some airplanes used cold air
(P-38, P-47, B-17, B-24, B-29) to do that, some (2 Stage Merlin) used
liquid.

And if liquid cooled engines are so bad why did every airforce want
liquid cooled engines for their fighters in WW2 (except the USN)?


Well, a couple or 3 reasons. With a smaller frontal area, it was felt that
an inline engine would be more streamlined, reducing drag.
It was also thought that a liquid cooled engine would have better heat
rejection - you just wouldn't be able to run an air-cooled engine at high
power due to insufficient cooling.
and last, but not least, fashion happens as much in Aviation as it does
anywhere else. Pointy airplanes look cool, so people like to design pointy
airplanes.

As it turns out, you lose most, if not all of the frontal area advantages of
a liquid cooled engine because you need to have radiators sticking out in
the breeze to keep the coolant temperature within tolerable limits.
As an example, consider a comparison between the aircooled P-47, and it's
liquid cooled British equivalents, the Typhoon and Tempest. They have
almost the same frontal area. In the case of the Typhoon and Tempest, half
of it is radiators.
It's possible to build low drag cooling systems, like that of the P-51
(Especially the B models and up), but it requires long ducting to act as a
diffuser, a large radiator that, because of the ducting, will have to be
buried in the structure, and a converging outlet to accelerate the heated
air.
The idea that an air-cooled engine couldn't get rid of heat fast enough was
based on the idea that you couldn't put enough fin area on a cylinder to
get rid of the heat. In the U.S., both Wright and Pratt & Whitney
developed methods of making fins thinner and closer together, and with
special shapes,to give more cooling area.

--
Pete Stickney
Without data, all you have is an opinion
 




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