Ethan - question of Drag comparisons between 109K and P-51D

[drgondog]

Perhaps it might've been a good idea if the different models of the Bf 109 are not lumped together. for example, it looks like the Bf 109F-4 have had the 'high speed Cd' (= Cd0?) of 0.023, as listed at the lower left corners of the tables from here: link

Tomo - I forgot to elaborate on this.

First the base CDo at relatively low RN for airspeed say ~100mph but well past laminar flow - when derived from wind tunnels is a compilation of contributions of each major component of the airframe (Wing, fuselage, cockpit enclosure, empennage, carb duct, radiator duct, exhaust stacks). Additional data is collected from contribution of gun ports/gun barrels, gaps in control surfaces, contribution of unfaired wheel wells, bomb racks, surface roughness, skin imperfections. These are part of the Base CDo but separate because they can be modified more easily. This is the Low Speed CDo.

CDo vs RN data is plotted on Log graph paper so that the plot starts at highest point at Lowest RN. The plot for all a/c will slope downward as a function of RN then at some point will level out (on log plot). I suspect that the phrase 'High speed Cdo) for the 109F-4 refers to that point at which the incompressible CDo levels out. I am absolutely sure that it does not reflect the Compressibility factored CDo

By contrast, the P-51B CDo at 1.84x10^^6 = .019 with compressibility factor of 1 at 29mph. At RN=20x10^^6 the P-51B CDo = .0155 at 319mph BEFORE compressibility factor applied. At 319mph at SL (@0.42M) the compressibility

 

[drgondog]

yes, but not to be confused with Ed Horkey or Bruce Boland or any long time aero pro.

 

[Peter Gunn]

Sez you.


Personally, I'm pretty impressed with your knowledge, and your willingness to share it.