Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: joeblogs on April 18, 2003, 10:18:02 PM
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Herschal Smith's book, History of Aircraft Piston engines (what else?) suggests that one reason why American water cooled fighters (ok the P40) was not competitive with the best British and German fighters was radiator size.
He argues that the US planes were engineered for a hotter climate and this required larger radiators, which induced more drag. This was particulalry true for the P40 which did not have a first rate radiatior installation.
In Africa, the European fighters had to be fitted with larger radiatiors and special filters. Smith argues that in this climate the speed disadvantage of the P40 was not as great as it would have been in Europe.
-Blogs
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If the P-40 still had a speed disadvantage in North Africa, then it simply wasn't as good as the Bf109 or Spitfire.
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Bf109 did not need a bigger radiator in the desert. The German sand filter especilly the one on Bf109F/G was tiny, imaparted virtually no extra drag and had no effect on performance. P40 simply was an outdated design.
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Gruen is correct The 109 didnt have a larger radiator. It had a Sand filter that was quite effiecient. Any aditional drag was minimal.
(http://bellsouthpwp.net/w/o/wotans/Info/TropFilter.jpg)
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I thought the P-40E was slightly faster than the Spit V but couldnt turn as well, and slightly slower than the 109F but turned a little better? Well, up to 15,000 feet anyway.
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Spitfire Mk V with standard air intake:
(http://perso.wanadoo.fr/christophe.arribat/model/filter.jpg)
Spitfire Mk V with the earlier Vokes Filter:
(http://perso.wanadoo.fr/christophe.arribat/model/vokes.jpg)
Spitfire Mk V with the Aboukir Filter:
(http://perso.wanadoo.fr/christophe.arribat/model/spit5-1.jpg)
As you can see the Vokes filter produced far more drag than the standard air intake. The Aboukir filter, while not as clean as either the Bf109F/G sand filter or the standard Spitfire Mk V air intake, did not produce nearly so much drag as the Vokes filter.
Urchin,
I'd not want to be in a P-40E against either the Bf109F-4 or the Spitfire Mk Vb. I think the P-40 would be at a large disadvantage against either.
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in the case of the P-40, one must take into account the powerplant itself, the Allison which, when compared to its contemporaries, the merlin and the DB's, just wasn't a world-class performer.
the early mustangs were fitted with Allisons and were rather ordinary planes until a merlin was installed. and the prototype mustang air intake under the fuselage was quite draggy until a design change that actually added thrust.
also, i believe the spit and 109 had their radiators under the wings.
edit to add - the filters on the 109 were for cleaning engine air, not cooling.
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I think what Smith meant was that the the engines of the European fighters would run hotter in the desert than would the P-40, because the P40 was designed with a larger radiator. If the engine runs hot, you get less air in the cylinders so you don't get as much HP out...
That said the P40 was hardly competitive in the desert let alone in Europe...
-Blogs
Originally posted by GRUNHERZ
Bf109 did not need a bigger radiator in the desert. The German sand filter especilly the one on Bf109F/G was tiny, imaparted virtually no extra drag and had no effect on performance. P40 simply was an outdated design.
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Hi Joe,
>If the engine runs hot, you get less air in the cylinders so you don't get as much HP out...
Actually, it's not engine temperature but charge temperature. As far as I know, neither P-40E, Spitfire V or Me 109F were equipped with aftercoolers, so if they were flying under the same conditions, they'd suffer the same from increased air temperature.
Regards,
Henning (HoHun)
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Yes it's the charge temperature that influences the HP you can get.
But if you can't dissipate enough heat from the block you can't supercharge the engine as much without detonation.
-Blogs
Originally posted by HoHun
Hi Joe,
>If the engine runs hot, you get less air in the cylinders so you don't get as much HP out...
Actually, it's not engine temperature but charge temperature. As far as I know, neither P-40E, Spitfire V or Me 109F were equipped with aftercoolers, so if they were flying under the same conditions, they'd suffer the same from increased air temperature.
Regards,
Henning (HoHun)
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Hi Joe,
>But if you can't dissipate enough heat from the block you can't supercharge the engine as much without detonation.
If you can't dissipate enough heat from the block, your engine overheats :-)
However, I'm not convinced the P-40 was less susceptible for overheating than the aircraft you compare them to.
Boscombe Down tests seem to indicate the Spitfire could come close to overheating on hot summer days, but that the temperature values stayed in the normal range nevertheless. An un-"tropicalized" Spitfire might not do so well in the African heat, but that's why there were modified, after all :-)
Regards,
Henning (HoHun)
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You may be right, I don't really know on what basis Smith made this argument...
-Blogs
Originally posted by HoHun
Hi Joe,
>But if you can't dissipate enough heat from the block you can't supercharge the engine as much without detonation.
If you can't dissipate enough heat from the block, your engine overheats :-)
However, I'm not convinced the P-40 was less susceptible for overheating than the aircraft you compare them to.
Boscombe Down tests seem to indicate the Spitfire could come close to overheating on hot summer days, but that the temperature values stayed in the normal range nevertheless. An un-"tropicalized" Spitfire might not do so well in the African heat, but that's why there were modified, after all :-)
Regards,
Henning (HoHun)
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How does this apply to the Merlin engined "F" & "L" model P-40's that fought in the Desert?
The Merlin's had about 100hp more than the Allison engines but I don't know what the heat would do to their respective plumbing.