So, I've been reviewing the spreadsheet linked earlier (http://www.southampton.ac.uk/~jps7/D8 website/homebuild aircraft design spreadsheet.xls) and finding some issues that I don't understand. 1) In the sheet 'As Drawn Performance' in cell H41, I recognize all of the variables except the 3600. Why is this there and where does it come from?In trying to use this spreadsheet, it shows that (H42) the range will be 1331 n.m. when it should really be 30% of that. 2) On the same sheet, cell D21 has some sort of calculation for "empty weight" which makes no sense to me. Until it aligns with everything else in the spreadsheet, I'm instead using cell G19 from the 'WeightSheet'. 3) On the 'Sizing Graph' the Wo figures don't make sense to me. In my spreadsheet, it keeps wanting to cross the lines at 1000 pounds, when everywhere else it computes to 1320 pounds (fortuitous for an LSA).I need some help on this one. 4) The Tail Volume coefficients already input onto the 'Initial Sizing Inputs' sheet (D40 and D42) seem low to me. Are these what Raymer usually recommends? It's a bit disconcerting to know whether the spreadsheet is truly original, since someone has input all the data for a particular twin-engine design of some sort (presumably his "Safety Twin", but not having the books, I don't know). Not sure how to know if any of the cells were purposefully/inadvertently changed. All in all, the numbers come pretty close to what we calculated for one of our designs. Thanks in advance for any enlightenment offered.