On Sat, 10 Jan 2004 10:07:10 -0800, "Tarver Engineering"
wrote:


Ed Rasimus wrote:


There are all sorts of variations including Krueger flaps, Fowler
flaps, "BLC" (boundary layer control) blown flaps, flaperons that
combine both flap and aileron functions, and spoilers which disrupt
airflow across the top of the wing to reduce lift/increase drag.

Ed did not address the use of spoiler flap as used to cancel adverse Yaw,
produced by roll steering.

One can only say so much in a newsgroup response. There's little time
to address all possible options of control surfaces at all times. But,
since you brought it up, let us note that some aircraft use "spoilers"
(not spoiler flaps) as a control surface. It is an effective way to
counter adverse yaw--the tendency of the drag of a downward deflected
aileron to be greater than that of the upward deflected one, which
causes the aircraft to way opposite the direction of intended roll.

The B-52 for example uses spoilers for roll control and the F-105 had
eight spoilers on the top of the wing on each side for the same
purpose.

Not sure what "roll steering" is. Roll is defined as rotation around
the longitudinal axis of the aircraft. Yaw as rotation around the
vertical, and pitch as rotating relative to the horizontal. One
"steers" the aircraft by inducing bank, which then creates a lift
component to divert the aircraft from straight ahead flight.

Ed's description of the spoiler is refers only
to a spolier flap in a speedbrake configuration and while textbook in
nature, has been false for airliners since the 707;

Spoilers, surfaces that extend from the top surface of the wing are
used to "spoil" lift. They disrupt the smooth, accelerated flow over
the top surface of the wing which causes the low pressure area which
is different than the high pressure area on the bottom surface (maybe
wings don't lift, they "suck" the airplane up?) When these
lift-destroying devices are deployed, they help an aircraft descend
without gaining a lot of airspeed. Speedbrakes, are traditionally drag
devices, used to increase the form or parasite drag on the airframe.
Same thing gets accomplished but spoilers operate through induced
drag/destruction of lift while speedbrakes operate by parasite drag.
Got nothing to do with aircraft specific types.


except twins. (engine
out regulations for twins require a tall tail, so the mechinisation of a
spoiler flap carrys too large a weight penalty to be practical)

What does tail size have to do with weight lifting capability? Twins
don't always have a tall tail, and regardless, the mechanics of a
flight control system, whether spoilers, flaps, slats, slots,
speedbrakes, ailerons, flaperons, spoilerons, stabilizers,
stabilators, or whatever is about the same.

Ed Rasimus
Fighter Pilot (USAF-Ret)
"When Thunder Rolled"
Smithsonian Institution Press
ISBN #1-58834-103-8