What is the Va speed, what is different from Vx and Vy?

Answer 1

Va is maneuvering speed. This means that at and below this speed you can use full and abrupt control movements (e.g. move the yoke really fast) and the aircraft will stall before becoming overstressed. It changes with weight, increasing with increased weight and decreasing with decreased weight (that is, the weight of the aircraft, pax, fuel, etc).

Vx is the best distance to climb speed. In the shortest forward distance, the aircraft will have climbed the largest amount of altitude. This is not the fastest way to climb.

Vy is best rate of climb. This is the fastest time to climb speed, but will take more forward distance than Vx even though it takes less time.

Hope this helps.

Answer 2

Coolsounding's definition of Va is right out of the book.
The definition does not allow for repeated opposite full deflections of a control surface. It is assumed that if one is at Va, the stalled condition will in fact happen after the first abrupt or full deflection of the control surface.

What made the A-300 accident was the abrupt and repeated uncoordinated rudder usage by the pilot flying. As the aircraft was accelerating at the time, rudder effectiveness increased, hence the aerodynamic load on the structure increased. You can twist the tail off of any airplane. In small Part 23 certificated aircraft, however, it is pretty difficult to do that.

The AOPA article is somewhat misleading in that the author doesn't really understand the purpose of the rudder load limiter. It is there to allow for large and abrupt rudder input by the pilot. Were it to fail, you could easily overstress and damage the aircraft at cruise.

Answer 3

Design loads for the vertical fin and rudder at Va are limited to three simple conditions. They allow for full displacement of the controls, but they don't allow for repeated/reversed movements which can build the yaw angle to extra high values which can in turn result in overstressing the aircraft at maneuvering speed.

Answer 4

Sorry coolsoundingme, VA does not guarantee that you can't overstress the aircraft. AA587 augered in because that isn't entirely true. See the AOPA article in the link.

From the report:-
In a somewhat unusual move, the NTSB issued two critical recommendations to the FAA very early in the investigation. "For air carrier pilots, some training programs do not include information about the structural certification requirements for the rudder and vertical stabilizer on Transport category airplanes. Significantly, full opposite rudder inputs, even below the design maneuvering speed, may result in structural loads that exceed certification requirements."

So you can pull your own tail fin off below VA if you try hard enough.