Way back when ... there were terminal velocity dive brakes on gliders. (I
believe another term was DFS dive brakes, but am not sure about that).
These brakes would hold the glider below VNe in a vertical dive. At some
point, as air foils became thinner, manufacturers agreed that the air
brakes would be designed to hold the glider below VNe at a 45 deg. descent
angle. I believe this was sanctioned by JAR, IGC, or some such.

Spoilers will place no limit on speed and cannot be used in a steep or
High Parasitic Drag Approach, whereas airbrakes can be.

No one has mentioned an important difference between flaps and airbrakes
(whether spoilers, divebrakes, airbrakes, or your term of choice). This
difference is the effect had on closing them after having established a
stabilized descent under their use.

Retracting the airbrakes causes the stall speed to be lowered and the
glide angle to improve. If you are low and slow, retracting improves
EVERYTHING.

If you are low and slow and retract flaps, stall speed goes UP and you
might find yourself in the woods, creek, fence, or whatever is short of
the touchdown point.


At 13:53 17 May 2008, Tony Verhulst wrote:
>user wrote:
>> I'd continue to use them interchangeably .....
> > If during a positive control check the pilot corrects your call
>> of "spoilers," look under the wing for the extra
control surface.
>
>Yes, I've seen at least 2 books (FAA Glider Flying Handbook and
Russell
>Holtz's Glider Pilot's Handbook of Aeronautical Knowledge)where the

>writer claimed that if the ..um.. "device".. extended top
surface only
>it was a spoiler and if it extended from both survaces it was an air
>brake. Seems dubious to me.
>
>Tony V LS6-b "6N"
>