Somewhat as a johny come lately, a few observations:
Quite a lot of dodgy Physics in this thread.
You can go at the OPs question using momentum if you like. You can also go at it using KE. Momentum is handy if you want to know how long a time a velocity change requires. KE is handy if you want to know how long a distance a velocity change requires.
(Generally, energy changes are easier to deal with because they are scalars.)
Bye, and gliding etc. Sorry Bye, but your Physics is full of holes.
In my experience people with a dodgy grasp of mechanics usually fail at Newton one. This is evidenced by trying to find some 'Thrust' to explain why the glider keeps moving. If you resolve forces on axes along/across the flight path then a component of weight is equal and opposite to drag, ergo there is no resultant force ergo the velocity is constant.
So, the gliders equivalent to thrust is a component of its weight, not it's momentum.
Pb