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Appendix
Myth: I can fully deflect the controls
below maneuvering speed!
WRONG! BELIEVE THIS AND DIE!
The wing structure in light planes is usually certified to take +3.8 G’s, -1.52 G’s (plus a certain safety
factor). Put more load on the wing than that and you should consider yourself dead.
But here is the nice part: Below a certain speed, the wing simply cannot put out a full 3.8 G’s of lift! It
will
stall
first! This speed is called
Maneuvering Speed
or
Va
.
Maneuvering Speed is defined as the maximum speed the plane can be flying at and still
stall
before the
wing breaks
no matter how much you pull back on the stick. If you are going
slower
than the
Va
and you pull the stick all the way back, the wing will stall
without braking physically
.
If you are going
faster
than the
Va
and you pull the stick all the way back, the wing can put out
so
much lift
that it can be expected to
break
. Therefore people think they can deflect the stick as much
as they desire below Maneuvering Speed and stay alive.
Wrong! The Maneuvering Speed is based on pulling back on the stick, not pushing it forward!
Note what was said above: The Va is defined as how fast you can fly and not be able to put out more
than 3.8 G’s of lift. But while the plane is certified for
positive 3.8 G’s
, it is only certified for a
nega-
tive G-load of 1.52 G’s!
In other words,
you can fail the wing
in the negative direction
by pushing
forward
on the stick well
below the Va!
Few pilots know this.
Also, for airliners, certification basis require that the rudder can be fully deflected below
Maneuvering Speed, but only if the plane is not in a sideslip of any kind! (e.g. crab method of ap-
proach) Does this make sense at all? Why would you need to fully deflect the rudder if not to
re-establish rightened flight?
In a wonderfully-timed accident shortly after Sept. 11
th
, 2001 of which everybody thought might be
an act of terrorism, an Airbus
pilot stomped the rudder
in wake turbulence while the plane was
in
a considerable sideslip
. The
combined loads
of the
sideslip
and the
deflected rudder
took the
vertical stabilizator to it’s
critical load
. A very simple numerical analysis based on the black box con-
firmed this. The airplane lost it’s vertical stabilizator in flight and you know the rest.
Also, if you are at your
maximum allowable g-limit
(e.g. 3.8) and you
deflect the ailerons
even
slightly
, you are actually asking for
more lift from one wing than the allowable limit!
Therefore combined elevator and aileron deflections can break the plane, even if the elevator
is positive only!
SO, WHEN YOU THINK THAT YOU CAN DO AS YOU PLEASE WITH THE CONTROLS BELOW
MANEUVERING SPEED, YOU ARE WRONG!
Please reconsider this myth and also look at the Vg diagram and the aircraft’s limitations to prove it
to yourself.
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