Bill Daniels wrote:

Both common sense and aerodynamics say that if the G-meter says 1.0 then
lift = weight. Applying 'spoilers' doesn't change that. Spoilers do not
'reduce lift' if the G-meter continues to say 1.0 - they increase drag.
The general formula is lift = weight x G

There is a nuance he opening the spoilers on most gliders does
diminish the lift of the wing section near the spoilers. To compensate,
the outer panels have to carry more of the weight of the glider. You can
clearly see this on an ASW 20 or open class ship, when the wings bend up
noticeably after the spoilers are open. So, in a steady state condition,
the lift is *decreased* over a significant fraction of the wing, but the
overall lift remains the same.

The reverse is true for flaps used for glidepath control: the lift in
the flapped section is increased. I can see this clearly on my ASH 26 E,
because now the outer panels are bent down slightly when landing flaps
are selected. So, in a steady state condition, the lift is *increased*
over a significant fraction of the wing, but the overall lift remains
the same.

Now, I'd say a true divebrake is what some fighters have: a panel(s)
that pop out of the fuselage, so they only add drag, and don't affect
the lift of the wing. Maybe we should consider our retractable landing
gear our "divebrake".

Of course, we glider pilots are a sloppy bunch and lump divebrakes in
with spoilers, and airbrakes. We pretty much stick with calling flaps,
well, flaps.

--
Eric Greenwell - Washington State, USA
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