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FM/DM threads Everything about FM/DM in CoD |
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#1
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Really did you read at least what I wrote on the last page?
(Edited on request). Last edited by TomcatViP; 10-15-2012 at 09:25 PM. |
#2
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Yes I did, assuming you are referring to this one. But it only states a few principles of aerodynamics, doesn't quantify them or provides a calculation illustrating that if this is taken into account, the numbers add up. I agree on the trend, but I doubt that they will account for the full difference.
Thank you for editing your post. |
#3
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However, generally there is no steep rise on the Cd until mach numbers well over 0.6 so the error caused by compressibility is very small given the speed differerences around 15kmh talked here. |
#4
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No Mig Sry but Mach nbr is the local mach, not the plane frwd speed.
At 15% thickness, the speed is in high subsonic when the plane is flying around 600kph. At this local speed, drag effects are not linear and raise sharply. Moreover, I think I was one of the first to put the dK/dt=SIGMA(P) eq around on forums. So don't nurse me with it. Thx in advance. Remind simply that this give only the max speed any increase of pow will give to a plane. At high speed, this is not linear. Generaly speeking: Incompressible theo apply only for M<0.3 Btw M0.3 to 0.8 effecst are sharp and results vary btw 6% to 100% Over 0.8, you hve shock waves and you need to apply according theo. Of course many guys rely only on incompressible, simply because they never really to get into the others case ![]() Last edited by TomcatViP; 10-18-2012 at 06:48 PM. |
#5
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I imagine this is what IL2FB did, though I'd be surprised if their correction factor was at all realistic. |
#6
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I don't think that anyone is relying on incompressible theory here, just giving a quick estimate of speed change due to power change at good enough accuracy. You can, of course, point out that compressibility is not accounted (nor Cl, prop efficiency etc.) but can you prove that there are significant errors? BTW that calculation method has been criticized earlier in this thread, actually well before Holtzauge used it and you posted your stuff. |
#7
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@Mig
Always the same, always bragging ... When did I post my "stuff" ? Tell me. If you gonna be insulting be precise, accurate and honest.. Your Holtzauge did not post detailed calculation or discuss his method. I pointed one source of error. Tht's it. This is the basis in Sciences. Put it down and submit to what ppl think. ANd you just hve to open a NACA chart to see the drag rise for the specific airfoil. You don't hve to pick bit of info here and there. It's free and available. But, huh, tht's what hurt the dark internet genius as always. And by the way, 10% of drag raise (outsourced from my memory) is equal to what a fully open rad will do on Seversky P-35. Tht's not negligeable my dear and will certainly not impact the max speed for only 1km/h Boring... @Doggle : you are right of course Last edited by TomcatViP; 10-19-2012 at 04:54 PM. |
#8
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Hoerner's number 10% is for entire speed range from mach 0.3 up to 0.55 ie speed changes 250-300kmh while we are talking here about 15kmh speed difference around mach 0.4, that means that drag rise is certainly certainly less than 2%, probably less than 1%. |
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