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Thread: Liquid Cooled Fighters? Or Air Cooled Fighters?

  1. #1
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    Default Liquid Cooled Fighters? Or Air Cooled Fighters?

    Okay, usual suspects, it's time for another pointless but fun debate ...

    If we look at the fighter arcraft of the various combatant nations of WW2, even at the end of the war we find first-rate fighter aircraft in both categories.

    Why is that? Shouldn't one technique be markedly superior to the other? I have an opinion which is a) liquid cooled is superior in principle but b) is inferior in practice if the aircraft is ever to be used in a close air support role because c) liquid cooled is vulnerable to ground fire and shrapnel.

    On the other hand, the P-38 is a clear counter example because it was used with great success for close air support in Italy and Southern Germany.
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    Liquid cooled engines are narrower and there fore faster, as P-51 and
    more fuel efficient, as P-51!!
    Liquid cooled engines are harder to manufacture!!
    Liquid cooled engines have more parts and take more maintenance!!

    Air cooled have less parts and are easier to work on!! This is why the
    Navy liked air cooled engines, they had to carry fewer parts on the
    ships which had limited space!! This left more space for fuel and
    bombs!! Also, carrier based planes did not need the range of land
    based as the runway could move closer if needed!!

    In battle damage, the air cooled has just a bit of advantage!!

    In large bombers, the water cooled engines would have required
    far too much hard ware and the weight would have reduced the
    bomb load!!
    Last edited by Kimber; 03-10-2008 at 12:17 PM.
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    Why is that? Shouldn't one technique be markedly superior to the other?
    Why does one have to be better than the other? I would put it down to using the right tool for the job.

    Another advantage for carrier based aircraft with air cooled radials is they tended to have a better view over the nose. Quite handy on approach to a carrier.

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    Also, the liquid cooled could fly higher with leaner settings and
    not over heat!!

    Air cooled engines have had cylinders shot off and still ran for
    some time!! Air cooled engines have extensive oil cooling systems
    that were easily damaged!!

    I comes down to,, the right tool for the job!! As said before!!

    It is nice to have a husband that teaches Aviation science and history!!
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    All aircraft design is a series of compromises of one sort or another, and engine style/design is no exception. Kimber's remarks above are on the money, but I thought I might add a tad to this.

    Air cooled engines have more drag, but are lighter for the same power, while liquid cooled engines are a bit more complex and tend to have more problems getting you home when battle damage occurs, especially being more vulnerable to small arms fire hitting the radiator. Speed and range requirements (and sometimes rate of climb) tend to favor liquid cooling, but cost and maintenance (along with ruggedness) tend to favor air cooling. So you might need 2000 HP in a radial (and greater fuel capacity) to get similar speed to an inline at 1300 HP. Radials were available in higher horsepower ratings (some were near 3,000 HP) than liquid-cooled engines (I'm not aware of any past 1700 or so HP), and that tended to dictate their use when heavy loads were to be carried (at some sacrifice in speed). Of course the radial drag penalty was more severe on a single engine aircraft than on a heavy bomber design, since it was a larger part of overall drag.

    So obviously, since both types were used in WW II, the mission requirements, engine and parts availability and designer preferences were among the factors deciding which type to use.

    Note that the P-51 (liquid cooled) was originally designed for ground attack. The P-39 was used extensively for ground attack, but was nearly useless above 15,000-20,000 feet, and certainly wasn't all that great for air to air. However the P-47 (air cooled radial) was a front line air to air fighter, as well as an excellent ground attack aircraft.

    Given the aircraft actually used in WW II, the Air Corps seemed to prefer the liquid cooled aircraft (P-51, P-38, P-40, etc.) for fighters, while the bombers were nearly all using the air cooled radials. The Navy, on the other hand, was pretty much all radials for their front line fighters, from the Wildcat and Hellcat to the Corsair, and for most anything operating from a carrier, as far as that goes.

    Note, too, that while the Japanese Zero was a radial, the ME-109 was liquid cooled, as was the Spitfire. But the FW-190 was a radial.

    So any way you slice it, engine choice wasn't so much a matter of which engine was better, per se, but which one was available in large numbers with the right power and weight (and maybe drag) for the specific aircraft mission design.

    Larry N.

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    Interesting ... Interesting ...

    Kimber, you wrote "In large bombers, the water cooled engines would have required far too much hardware and the weight would have reduced the bomb load!!"

    Yet we have the example of the Lancaster RAF bomber, powered by four Merlin engines, which was able to carry the 22,000 pound Grand Slam bomb. Is this simply an example of what lnuss suggested, that sometimes design simply favors components that are readily available? Or might a desire for increased airspeed have played a role in the design?

    (Your Honor, I was NOT leading the witness. I honestly don't know the answer. And while Google is my friend, sometimes it's more fun to speculate and let the rock throwers throw their interesting rocks.)
    Last edited by xxmikexx; 03-10-2008 at 04:06 PM.
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    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

    P.S. As OP, I hereby declare this thread open to discussion of the power designs of all types of aircraft, not just WW2 fighters.

    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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    The Lancaster with its Merlin engines is more complex to maintain (at least the engines are) than is a B-17.
    But that didn't matter to the RAF at the time. They had no aircooled engine with the required power and even if they had the expected lifetime of a Lancaster was not long enough to require engine overhaul to ever take place (a Lancaster was expected to last 3 weeks of bombing operations, so it was expected that the average Lancaster would be shot down on its 20th mission at best, earlier more likely).

    That's why it doesn't matter for landbased fighters to have liquid cooled engines, they weren't expected to ever need an overhaul.
    Carrier fighters needed more maintenance because of the salt water corrosion that sets in as soon as the carrier sets sail.
    And the shorter size of aircooled engines as stated is an advantage on a carrier when storing the aircraft, allowing for more of aircraft on the ship.

  9. #9

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    Quote Originally Posted by xxmikexx View Post
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

    P.S. As OP, I hereby declare this thread open to discussion of the power designs of all types of aircraft, not just WW2 fighters.

    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Okay,,,,,,,,,,,,,,

    In the experimental/kitbuilt/homebuilt market; the standard Lycomings/Continentals versus modified liquid cooled auto engines such as the Subaru is at least a weekly event of controversy.

    Basically, the aircooled Lyc's and Continentals are less draggy, because we don't have to stuff three radiators into the cowl. The aircooled engines are also lighter, less complicated electrical wise, and a bit better performance wise for the weight.

    Of course the fan's of auto conversions promote them as new technology, while claiming that the basic aero engine is 50 year old technology. Perhaps that's true, but the 50 year stuff still fits the mission almost perfectly!

    As to myself, the aircooled Lyc rules for our "little" planes, while the liquid cooled Merlin (P-51) is my favorite "sound" of all time!

    L.Adamson

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    What ever happened to the Porsche aircraft engine for GA.....was that 20 years ago? Don't remember if it was water cooled. I don't think it "took off" but I could be wrong.

    I'd be interested in hearing. Maybe it was too expensive? SPOFF

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