Optimum CG Range

On Dec 14, 7:56*am, wrote:
On Dec 13, 9:19*am, JJ Sinclair wrote:



OR
A percentage of MAC behind the wing LE
Brian W

Errrrr, not neccessarily so; The wing leading edge will be the zero
MAC point only if the leading edge of the wing is a straight line,
otherwise as in the LS-8, zero MAC will be located behind the leading
edge. I know a guy that made this incorrect assumption on the first
flight of an RS-15 and he flew the whole flight (rather short) with
the stick full back because his CG was forward of the forward limit.
He considered bailing out, but found he could keep the nose up if he
flew 80 knots. He landed OK touching down at 80.

I like to refer to the CG in a percentage of the allowable range. The
Genesis likes to be about 85% of the allowable range which is; 0 to
5.25" aft of root rib and 85% is 4.5"aft. After adjusting the CG, give
her a test drive. If you find you are trimming forward when entering a
thermal, your CG is too far aft.
Cheers,
JJ

Another useful approach is start at about 66% aft using manufacturer's
CG range. When making the tightest turn you normally do, if you run
out of elevator, you need to shift CG back a bit. You will probably
end up around 75%.There isn't a huge benefit in having the CG way
back, but there is a significant deterioration of handling which
requires better pilot skills to offset.The last little bit of glider
performance costs quite a bit in pilot workload until you are very
proficient. I usually take a couple pounds out of the tail in the
Spring and put it back in when my skills are back up to snuff.
FWIW
UH

Here's another gem piece of advice: With my 3D model airplanes I roll
inverted and check if I need down elevator to stay level. If so, the
cg needs to be moved further back. A well set up model will happily
fly inverted without elevator movement! Haven't tried that in my LS8,
though.
Seriously, Hanks and Eric's methods will both work well. As long as
inside the book range, find the cg that gives you good handling and
enough up elevator to stall the plane in a steep turn. It'll be at
75%-90% aft.

Herb, J7