On Mon, 28 Jul 2003 10:29:48 -0600, "Bill Daniels"
wrote:


"Jim" wrote in message
.. .
In his book Gliding, p100, Derek Piggott writes:

"In most modern gliders, the elevator power is not adequate to pull
the wing beyond the stalling angle in a steep bank and it is only just
possible to reach the pre-stall buffet with the stick right back.
This is very different from straight flight and gentle turns where a
movement right back on the stick would definitely stall the aircraft,
requiring a significant loss of height to pick up speed before full
control is regained."

If this is the case, what are the aerodynamics that account for
this? Does it have something to do with the elevator's limited
power to deal with the load factor resulting from a steep, level turn?

I'll give this one a try.

As we all know, the pitch stability/control system is like a seesaw with the
download produced by the horizontal tail balanced by the downward force of
the weight of the glider acting at the center of gravity with the center of
lift acting as the fulcrum.

In level flight the downforce at the center of gravity equals the all-up
weight of the glider and there is sufficient reserve up elevator authority
to stall the wing.

In a 60 degree bank, for example, the downforce at the CG is twice the
weight of the glider due to the centrifugal force of the turn. However, the
elevator effectiveness is the same as in level flight so it cannot overcome
the increased downforce at the CG and bring the wing to a stalling AOA.

As Derek points out, with most modern gliders in a steep turn, the wing
cannot be brought to a stalling AOA. The glider is, in effect, becoming
nose-heavy due to centrifugal force.

Bill Daniel

Your statement about the glider becoming nose-heavy from the load
factor in a turn gives me a very clear picture of what is going on.
Thank you.