CZ,

Hmmm.  How about, I was in a rush and used a completely unsubstantiated aero analysis of the Legacy that I found on the web by Roadman, Chapelle and Emory.  And since you called me on it (you big meany), I suddenly woke up and went back to the excellent CAFE report.  They documented a glide ratio of 13.3 at 158mph CAS and 2127 lb.  With that, it's possible to deduce 160lb of drag force and a CDmin of .030, which includes the drag of the 2-blade prop on the prototype airplane in coarsest pitch (lowest rpm).  Again going mostly on gut feel, I'll say the near-streamlined prop can't be more than 1/4 of the drag, so airframe CDmin is probably closer to .025 than .014; and cruise drag would be a bit higher yet.  The delta CD of the open canopy is still a reasonable hack, at .002 or greater; which would put a 6-inch open canopy at 10% or greater drag increment (not 15%).  Still a significant effect on performance.

All of this is just quick hacks to put us in the ballpark.  I've neglected the pressure increase on the front of the open canopy, separation Cp on the upper aft fuselage, and incidentally the 6-inch opening is a totally arbitrary choice in a very non-linear drag-vs-opening function.  And of course the lift that gets dumped by the canopy calls for an increase in alpha, hence induced drag, that probably outweighs the profile drag increase.

CB

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On Mar 10, 2014, at 1:37 PM, Chris Zavatston wrote:

Charley,
How did you get that drag coefficient?  I don't know the Legacy area, but the number looks a wee bit low.
Chris

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