On Tue, 15 Dec 2009 09:56:22 -0800 (PST), jimboffin
wrote:


Are you sure you are reading the manual right? I own a 27 and the aft
limit remains the same. Waibel argued that it was by design that the
CofG moves forward when adding ballast and that this automatically
made for more efficient high speed flight when flying with high wing
loading. He even stated that the fin ballast tank was unnecessary. It
is possible that the practical aft limit for CofG position when
ballasted is well forward of the position and aft limit when empty for
this reason.

Unfortunately he neglected the fact that especially the 27 with its
tiny horizontal tail is usually flown with very high wing loading,
hence especially the 27B really benefits from its tail ballast tank.


On the subject generally. I would recommend flying the glider (within
manufacturers limits) with a CofG that you find best suits your style
and ability. This can be achieved by experimentation.

100% agree.

As I understand
it, moving the CofG back improves efficiency at low speeds and in
thermals by reducing the necessity for the tailplane to produce
downwards lift (and drag) in those phases of flight.

In the 27 you can really notice this - flying a 27 with a forward CG
badly affects its climb performance, yet increases its perfomance the
more the fster you fly.



Bye
Andreas