snip

The steady state effect of spoilers, airbrakes, dive brakes, and even flaps
all do the same thing - they increase drag. * I carefully included the term
'steady state' to exclude brief transient effects that may occur as these
devices are deployed.

snip

You are correct in steady state the all pretty much do the same thing.
The difference in terms comes in the non steady state effects and how
they produce drag.

Take a glider at approach speed about 5 feet off the runway in steady
state (at least for a glider) level flight with all drag devices
retracted..

If you deploy the spoilers and do not change attitude the glider will
drop onto runway, speed will change very little.

if you deploy airbrakes the glider will slow and settle to the runway.

If you deploy flaps the glider will balloon up.


Brian CFIIG/ASEL