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#71
07-14-2012, 11:17 AM
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P=nRT/V from perfect gazes theo.
The pressure output from the comp of a gaz depend of the volume V and the Temp T achieved before detonation* The less volume at the end, the more P. The temp T at which the gas will detonate under pressure is the leading factor here. The derivative energy (work) that someone can output of a compression work (isentropic**): dW=-dP/dV wich as you see is a function of the octane number for a specified eng design AS the Tot energy of a gas equate the sum of it's internal molecular energy that is in the theo of perfect gazes is the sum of the work done on that gas and the total output heat achievable (see the first law of thermodynamics (here : http://en.wikipedia.org/wiki/First_l...thermodynamics) Then I think I am right  - sry for the boring refreshing cursus - didn't do that pretentiously.You can read more here :http://en.wikipedia.org/wiki/Octane_rating Well now we are good to open another new thread *n is a ref numbers in moles (or molecules per volume at a specified state) and R is a cte defining the ratio btw the products **means here without any modification of the gazes's product state (which is never fully achievable in virtue of the second principle of thermodynamics) Last edited by TomcatViP; 07-14-2012 at 11:57 AM. 
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#72
07-14-2012, 12:39 PM
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Quote:
The end of argument.
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#75
07-14-2012, 02:09 PM
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and we have one resident expert of experts of everything....
(in his own mind anyway)
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#76
07-14-2012, 02:12 PM
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Quote:
I'm not a pilot (but I am a practicing physicist) perhaps others can confirm or refute the following suggestion: I strongly suspect that the RAF/Farnborough & Boscome Down used an Atmosphere that was representative of British conditions (particularly latitude), also probably spring/summer/autumn temperatures because aircraft would do most of their flying time at these times. I also suspect that the International Standard Atmosphere was not available until post-war. However I do not know whether the testing authorities normalised their measurements to some British standard atmosphere. SO - as long as the CloD atmosphere is reasonably representative of British conditions the speed or climb variations due to minor (day-to-day, or during the day) can be easily corrected by correcting for the density for a particular atmosphere in CloD without having to do anything more sophisticated. (As an aside - temperature DOES affect the compressibility in the supercharger, as well as input density, but it'll be fairly second-order because the two are coupled in a gravitationally stratified atmosphere) This is what I believe Klem has done (at least in some of his other posted data, I haven't checked this post). The differences between CloD data measured by Klem and measured performance (albeit slightly affected by local conditions on the day) are now so large (and even worse - inconsistent between 'plane variants - and even more worse, between red and blue) that issues of British atmospheric variations pale into insignificance. 56RAF_phoenix Last edited by phoenix1963; 07-14-2012 at 02:25 PM. Reason: clarity
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#77
07-14-2012, 02:17 PM
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Quote:
 But I am with you on that except for the suspected source of historic perfs (let me guess it's a website with the words "Spit" and "Performances"  )+1 so
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#78
07-14-2012, 02:25 PM
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The first versions of a standardised atmosphere model between nations was in the 1920's as far as I know, almost certainly those nations would have included the bulk of Europe.
Here check this NASA article.... http://ntrs.nasa.gov/archive/nasa/ca...2002153481.pdf
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#79
07-14-2012, 02:55 PM
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Now I haven't checked, but I have no reason to believe Spitfire Performance would post altered or faked data. However I would fully understand if the "blue side" wished to question the context of the data, or unpublished associated data that would be relevant to what was published. But that needs to be done in a reasoned way where the participants are prepared to accept they might be wrong when presented with evidence. It's called the scientific method. It is to your credit that your posts here at least seem to be trying to understand the physics. [ BTW: the conditions for detonation of the fuel-air mixture are not really to do with a particular temperature. Detonation happens because the sound-speed is higher on the high-pressure portion of a pressure pulse, so the pulse gradually sharpens-up until it becomes discontinuous - a detonation. So I'm afraid the run-length of the pressure pulse (i.e. the geometry of the cylinder) is a big factor. ] 56RAF_phoenix
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#80
07-14-2012, 02:58 PM
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56RAF_phoenix [EDIT] P.S. As is often the case with the English Internet, it's rather US centric. Have you got anything on British equivalents? Last edited by phoenix1963; 07-14-2012 at 03:14 PM. Reason: additional question
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