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Old 10-20-2012, 05:05 AM
MiG-3U MiG-3U is offline
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Quote:
Originally Posted by TomcatViP View Post
No. Again lack of modesty in your assumption. Take a look on Youtube searching TcViP and related variables. You'll see that I posted that last time almost 3 years ago.
Well, I rely on what you have posted on this thread. At the post 519 you suggest that the calculation is ok "to estimate the time of accel from Stall speed to 200mph". But that is actually not true because the Cl and the hence Cd changes in large degree during acceleration as well as thrust. However, for a quick estimate for a small change as discused here, the calculation is good enough.

Quote:
Originally Posted by TomcatViP View Post
Didn't I say local mach number ???? Again when your plane is traveling at Mach 0.5, your wing see a peak of high subsonic speed for a 15% airfoil section. Same with the fuselage, especially the bottle neck effect at the rear par. Yes, the 109 was very well streamlined but your calculation need to be repeatable to other type
The testing of a whole airfame accounts all these and we know, based on Hoerner and other sources, that around Mach 0.4 the compressibility effects are minimal in the case of Bf 109G, there is no reason to believe that the Bf 109E is much different because the wing profiles are almost the same as well as the fuselage.

Quote:
Originally Posted by TomcatViP View Post
Compare to what ?
We can safely use the same rate of drag rise as given by Hoerner for assuming Cd change from 460 to 475kmh. And because the speed change is so small and we are around Mach 0.4, we can safely assume that the Cd rise is just a small fraction of that 10% given by Hoerner, probably less than 1%.
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