Pipistrel Virus 912 User Manual

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AppendixAppendix
Myth: I can fully deflect the controls
below maneuvering speed!
WRONG! BELIEVE THIS AND DIE!
The wing structure in light planes is usually certied 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 rst! This speed is called Maneuvering Speed or Va.
Maneuvering Speed is dened as the maximum speed the plane can be ying 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 deect 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 dened as how fast you can y and not be able to put out more
than 3.8 G’s of lift. But while the plane is certied for positive 3.8 G’s, it is only certied 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, certication basis require that the rudder can be fully deected 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 deect the rudder if not to
re-establish rightened ight?
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 deected rudder took the
vertical stabilizator to it’s critical load. A very simple numerical analysis based on the black box con-
rmed this. The airplane lost it’s vertical stabilizator in ight and you know the rest.
Also, if you are at your maximum allowable g-limit (e.g. 3.8) and you deect the ailerons even
slightly, you are actually asking for more lift from one wing than the allowable limit!
Therefore combined elevator and aileron deections 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.

Pipistrel Virus 912 Specifications

General

Brand	Pipistrel
Model	Virus 912
Category	Aircrafts
Language	English