Do winglets produce thrust?

Let's go back to the beginning. The FAA likes to teach four =
balanced forces, lift exactly cancelling gravity [weight] and thrust =
exactly cancelling drag. Unstated or widely ignored assumptions are a =
powered aircraft, constant altitude, constant speed, stationary airmass. =
This does not normally apply to a glider !

Starting with your Cessna flying per FAA model, take away the =
engine's thrust. Now something has to give - you can fly slower at =
constant altitude as drag exerts a decelerating force on you; lift would =
be reduced as airspeed drops, so to maintain altitude you increase angle =
of attack [until you stall, then you will descend]. Or you can choose =
to hold airspeed and descend by nosing down a little; then both the lift =
and drag vectors are tilted relative to gravity, and two things happen - =
a component of your total lift will resolve in the 'forward' direction =
90 degrees from the gravity 'down' direction AND a component of your =
total drag will resolve in the 'up' direction. Only three primary =
forces [lift, drag weight], resolved and summed in four directions. You =
stabilize at a new flightpath angle, same speed, same angle of attack =
[because your nose down input changed both fuselage angle and flight =
path angle by equal amounts after transients wash out] and therefore =
same drag, constant descent rate. That's how a glider works, I believe. =
The vectors can be drawn EITHER in space coordinates [true up and down] =
OR flightpath coordinates but please don't mix 'em together.

Note that of your three primary forces, weight is always there but =
lift and drag only exist because you have airspeed to begin with. And =
you need altitude as well, otherwise you can't fly down your slope.

To get to this stabilized state in the first place, you must have =
airspeed and altitude. Bungees, winches, towplanes, ramps off clifftops =
all supply the initial energy to get this altitude/airspeed to start you =
off.

Now soaring, that's a different matter, and really starts when the =
airmass motion comes into play..

Ian