Bob, my current ratio is 1/.63.....which means nothing. Anyway, I'll be trying a smaller exit in the future. Recall I built the cowl so I could swap exit sizes at will, with a screwdriver.
Dan,
Concur with you that ratio, in and of itself, is meaningless. My query was strictly gathering a data point, to aid in viewing what appears to work in the field, and what does not (and just to clarify, the .63 is your exit, and you are going smaller, right?) I'm not working with a blank sheet, in that I'm looking at modifying an existing aircraft I didn't build...so I'm learning and going slow, so as to avoid unintended consequences (hmmm, wonder if I can move that gascolator out of the way...and what is it doing ther in the first place...stuff like that).
I know that there is no magic bullet, or ratio/number, that says "do this, and you will get that"...its all experimenting, and we each have, in a sense, a one-off design to try to optimize (no two engines, cowls, exhausts, etc. are exactly alike). There are just too many factors, from plugging leaks (plenum, prop shaft-to-cowl area, etc) to smoothing flow, to baffles and ducts...on and on. You and Tom (and others have been good about pointing that out...no quick fixes...its a system of systems approach. By the way Dan, how's your little baffle-like structure working to seal the air at the prop shaft...been weighing that versus Tom's fiberglass work at that area...both look innovative and effective.
I've listened a lot to Tom, and he has great advice. Have talked with Dave on his tail design (he and others have encouraged me to build an 8 tail for my S6, to get a counterbalanced rudder on board, due to the speed its running now). I hope to visit and look more at his modified tail, and now want to add a tour of his cooling mods as well...if he'll let me peek!
There are a lot of great posts and great info here, and I'm eatin' this up (along with Paeser's book and others y'all have recommended). You guys are an awesome braintrust, so I'm takin' notes, crawling under the hood and thinkin'. Little by little I'm learning, so thanks much!
And do my eyes deceive me, or are Howard and and Paul concurring!!
(All in fun, the debates here are very enlightening. Good stuff!)
Finally, Dan...that removable exit area you've designed is an awesome idea...I did notice it a long time ago! Still trying to figure how to retrofit something like that. Just takes time...and a little dab of courage to cut...perhaps when flying slows in the winter...having too much fun right now, and it is a balance...maintenance man-hours to RV grin hours...now that's a ratio we all want to keep high...or is it low...oh heck, I dunno, just keep the glass half full or better, right!
Cheers,
Bob