Dan_Thomas_nospam

On Jun 10, 9:29 am, Tina <tbaker27...@> wrote:
> One point about the lift fairy sitting on the tail I'd like to
> understand is this -- actually a serious question. As I understand
> it, nearly aways the tail is exerting a downward force, since the
> center of lift is aft of the center of gravity on general aviation
> airplanes (that is true, isn't it -- that the cg is forward of the
> center of lift?). If so the tail really is imposing an increased load
> on the airplane, adding to its effective weight. The question I have
> is, how many pounds of weight is imposed aerodynamically for an
> airplane that might be loaded with its CG at the forward limit? I
> don't know where the center of lift is on ga airplanes -- a third of
> the way aft of the leading edge of the wing is an ok approximation,
> but a few inches error on an airplane weighing what ours does at max
> could make a huge change in the required force to overcome the nose
> heavy moment.

CG range for most typical lightplane airfoils is 25 to 33%
of the chord, while the centre of lift is around the 40% mark. The
load on the stab/elevator isn't all that big, but it's enough that
we'll teach you in groundschool that the aircraft's stall speed is
lower when loaded to the aft limit than when it's loaded to the
forward limit, and that the cruise speed is a little better at the aft
limit.

Dan