Originally posted by gripen
Therefore it's easy to figure out that there is something wrong in your or Badboy's EM curves in the case of the P-51D if compared to the real world data.
gripen
Hi Gripen,
I use a flight model in my analysis that allows me to add or omit various aerodynamic effects so that I can use it for different flight simulations, and the one I use for performance analysis of real world aircraft includes every relevant factor. If I compare the results with a simplified model, one that does not include the reduction in lift due to compressible flow, and does not include the increase in lift due to thrust or prop wash, the resulting curves are almost identical. It is, therefore, hardly surprising that some developers choose not to model those things at all. However, there isn’t anything wrong with the EM curves I’ve produced for any of the Aces High aircraft, based on extracted data, or the ones I’ve produced based on real world data.
The fact is that changes in the various coefficients are somewhat masked when the large number of parameters involved are all merged together numerically to produce the curves. I know this because the effects described in those reports have been included in my analysis and only appear to make a negligible difference to the EM curves for prop fighters, and in practice the reduction in the coefficient of lift due to compressible flow appear to be masked, to some extent, by other effects that increase the coefficient of lift, such as the contributions to lift from thrust and propwash, so that although those things have been modelled, they aren’t at all obvious on that type of diagram. In order to illustrate that I’ve attached an example of an EM analysis that shows the influence that Mach number would have on EM curves for a prop and subsonic jet.
This diagram was originally produced to help show how those factors influenced the variation in turn radius and explains why Shaw refers to a minimum turn radius that occurs below corner velocity, while most prop fighters have their minimum turn radius at their corner velocity. That happens because the results of the factors mentioned in those reports are more noticeable in the jet due to the higher Mach numbers involved, after all, its corner velocity is comparable with the maximum speed for the prop fighter. In the prop fighter the difference in corner speed, for example, caused by this is typically only in the order of a few mph, as you can see in the diagram, but in practice the factors I mentioned previously mask that shift and translate the curves back towards their original positions. I believe it would be impossible to see that anything was wrong with the curves on any of the relatively slow prop fighters by inspection. Even on the supersonic jets it takes dramatic variations in the various aerodynamic coefficients, such as those that occur in the transonic region, to distort the curves in a significant and readily noticeable way.
Badboy
