Barry Kruyssen wrote: > Here is my work sheet http://users.tpg.com.au/barryk/Doco/My_W_and_B.xls . Please look at it and tell me what I've missed or got wrong.
Without looking at everything, and trying to follow every calculation, the one thing that stands out to me is the cg of the whole engine (+mount assembly) being 652mm (25.7") from the datum, which is said to be the front of the engine. That would make the engine somewhere around 45" long, which I don't believe. You might check into that. While getting the spreadsheet perfect is admirable, there's always the dirt simple method that I used. Weld up a temporary mount in the form of a tray, where you can just slide the engine fore and aft (or in the case of the Corvair, you could easily make a mount with several engine mounting points that would be "adjustable") and determine "empirically" where the CG is. No problem with errors that way, and welding up the mount with mild steel would be cheap and good welding practice. (See http://home.hiwaay.net/~langford/corvair/mount_fit.html , but I need to add my latest weight and balance to it). Other than that, most people make most of the numbers positive, and forward of the datum negative. That way is a little less confusing, and leaves less room for math errors. I'm sure you've taken care of this already, but your datum is something that moves (front of the engine). Maybe the firewall would be an easier place to use for a datum, since it doesn't move when the engine does. I probably missed some of your logic, and I'm not an Excel whiz...just pointing out the obvious from my standpoint. One other thing is you used 8" of CG range. It's been generally proven that you need to throw away the last 2" aft, as the plane will probably be textbook "unstable" in that range, if you built per the plans. That's something in the manual that cries out to be fixed. Somewhere in the middle of that 6" is probably best, or biased toward the front. Too far forward and your speed will suffer, too far aft and it'll be twitchier, which is probably OK after you get used to it, but better sneaked up on after you have KR flying experience. I will eperiment with that later. I'm sure others will have comments, but those are my few superficial ones... Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford
