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Originally Posted by Franek Grabowski
OK, so what is the point in underlining some of those figures? How about wetted area and the method it was calculated in each case? How about different AoAs or Res? Could you explain to us what is scientific value of the table while discussing aerodynamical characteristics of P-51?
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Franek - That is a report that should be very interesting to you and Graham. Gene Lednicer did a detailed analysis to get the geomety correct for both the B and D models as well as the Fw 190A and D , plus the Spit IX. He is a well respected Aerodynamicist that also used his models on a commission by the Strega Mustang Racing team to improve flow characteristics behind the wing on the lower radiator cowl/fairing.
His model is a finite panel, stream tube modelling approach which required several iteration to solve for the Potential Flow balance while introducing Boundary Layer separation for all the airframes investigated.
VSAERO is the model he used and that is why Crumpp used the references showing many of the documented studies and wind tunnel Tests as well as referencing the Reynolds numbers for wind tunnel tests. Look particularly at the Ames test as it was performed with a full scale production P-51. It was later compared with flight test data on a series of dive tests without power on another P-51 as a validation check against the Wind Tunnel and calculation methods - and found to be very close.
The .0053 wetted drag number is the one to be used in contrast to .0040-42 values as they are 'lower cowl/radiator fairing - less". The .0053 CDw is comprehensive in reducing all the factors associated with the surface geometry to one value, but assumes all the surfaces (including the Spit and FW) to be the same surface, but it does predict different stagnation flow regions contributing to drag for both the canopy areas as well as boundary layer separation. The model IIRC was compared to other profiles at 300+kts but I could be wrong about that.
These modelling techniques, with which I experimented with in the late 60's, have gone light years beyond state of art in those days and as a result yield much better performance predictions for a V-22 than for an F-102 in design stage.