I go out to the R/C field at Markam Park here in Broward county on occasion, and have seen that you really have to be good at getting those things on the runway from a high or low predicament, depending on where you are when the engine runs out of fuel!     Very impressive airmanship indeed.

A simple "airbrake" in a Twin Astir sailplane (and many
other types of sailplanes) is a panel that rises vertically out of the upper wing surface.

Simple as this sounds it produces a complex set of effects. The following is best observed at a full brake setting.

1. The airbrakes add a lot of form drag which is designed
   to "slow" the aircraft's speed.

2. The brakes act as spoilers, spoiling the lift over a
   significant portion of the wing. Radically reducing lift
   on an otherwise very efficient airfoil causes a
   tremendous increase in the aircraft's sink rate.

3. Despite what the flight manual states, deploying the
   airbrakes on a Twin Astir will cause a slight pitch down.
   This forward pitching, if flown hands off, will actually
   result in an increase in airspeed! (This effect played
    havoc on my circuit speed as a student pilot) 

Airbrakes on sailplanes are the primary rate of descent
control for landing, escape from proximity to cloud, and rapid height reduction. They may also be deployed when speed is getting too high during a mishandled aerobatic manuever, spin or spiral dive recovery. The Twin Astir's speed/air brakes are also a speed limiting
device to hold the aircraft below maximum allowable
speed in up to a 45 degree dive.

The airbrakes create such an increase in descent rate that the flight manual warns not to use full airbrake
during landing. (Sailplanes are ideally landed at a half
brake setting to allow adjustment for undershoot or
overshoot situations developing.)

At the recommended landing speed of 55 knots there is
absolutely no "hold off" at full brake setting in a Twin Astir. It lands instantly and there is no margin for error.
This can be overcome by inreasing the landing speed if a full brake landing is desired. But I digress.

I use aerodynamic braking a lot in my simming as well
as my real flying, combinations of effects can be used to
rapidly decrease speed or induce very high descent rates.

Aerodynamic braking is both essential in normal
flight ie. landings and can be a life saver in emergencies.

Without aerodynamic braking, many types of aircraft couldn't make the transition to the landing phase and
many landing grounds would be unsuitable for operations.

Note the auxillary drive unit on the glider below. This unit, when extended, causes such a lot of aerodynamic drag, ie. braking effect, that a suitable landing field close by is required before anyone dare extend the unit,
in case of some problem getting it to start. By the time you would get it stowed away in a situation like that, you may find yourself a bit too close to terra firma and
a serious predicament.

Does that help?