Mean Width Ratio & Disc Area Ratio
		Formulae
			MWR = average blade width / diameter
			DAR = ( Pi x (diameter squared)) / 4
	Disc area ratio.
		Ideal prop				Dia to fit prop				selected
		33%	"standard" DAR			16	max input prop dia			14
		14	diameter			51	sq/in blade area reqd			51
		51	sq/in blade area			25%	DAR reqd for dia			33%
	Mean width ratio								OK
		3	# blades			3	# blades
		0.22	MWR			0.16	MWR
		3	ideal prop av blade width			3 4/8	"to fit" prop av blade width