On Sat, 29 Nov 2003 11:32:36 -0800, Eric Greenwell wrote:

Here's an expanded expanation:

Gravity is pulling straight down, and so can not propel the glider
forward; drag is pulling the glider back, and so can not propel the
glider forward. So, what is left to counteract the drag? Lift, produced
by the wings. This forward force comes from the lift, which is not
vertical, but tipped forward a bit. Look at any diagram showing the
forces on a glider, and you will see how the lift, drag, and gravity
forces accomplish this.

It is not common to call this force moving the glider forward (without
it, drag would bring it to stop) "thrust", but the word is sometimes
used that way.

Sheesh! So many words and so little knowledge... Here's how it works,
guys.

For any aircraft in balanced flight, there are four forces acting on it.
All forces except gravity act only along the chord or perpendicular to it.
Gravity not only produces a force in opposition to lift, but a resultant
vector force which can be either thrust or drag, depending on the angle of
the chord in respect to earth (gravity). in other words; Gravity is the
'engine' in a glider that produces thrust.

For those that don't understand vector force components (or flunked trig),
don't worry 'bout it. Simply believe they exist.

As for the winglets, they only reduce drag. At the point where the
airfoil ends, air rolls to the other side of the wing due to the pressure
difference. The rolling air produces a vortex that kinda acts like vacuum
cleaner hoses grabbing the trailing tips of the wings. The winglets
interfere with the creation of the vortex(s) thus reducing drag. Smaller
vortex (smaller vacuum cleaner) means better L/D (slicker ship).

LittleJohn
Madison, AL