250 or point 65

It does not apply to ailerons or negative forces applied with the elevator either.

...and to the previous poster: what?

joepilot

Va applies to all control surfaces in either direction.

Airbus did not believe that they were required to make the tail strong enough to withstand a rudder reversal, i.e. full throw one way followed by full throw the other way. This is what happened with AA587, and the tail broke off.

Boeing always believed that the reg required the plane to be strong enough to take this kind of abuse.

Joe

Nevets

Va does not apply to negative forces.

250 or point 65

Wow, outright wrong information. Where do manufacturers get Va from? Look at a VG diagram. Va is derived from the speed above which a pilot is able to achieve enough G's to create structural damage before stalling. If the pilot is going slower than that, there is not enough control authority in the ELEVATOR to create the G's necessary to hurt the airframe. You'll also notice on a VG diagram that the curve that separates the normal operating range from the stall region is sharper on the negative G side...meaning you are not protected from a airframe damage at Va if you nose over quickly.

To add, when we speak of G's we are talking load factor. Since rolling and yawing do not directly effect the load factor, we are not guaranteed protection in the vertical or longitudinal axis'. Therefore, we are not necessarily protected from damage in a full aileron or rudder situation.

Let me know if this is different for a transport category aircraft.

FastDEW

What happens if you are flying at cruise speed and hit severe clear air turbulence? Since you are above maximum penetration speed does the aircraft become damaged?

rickair7777

Possibly. You will do a Mx writeup and they will inspect the airplane.

Structural damage does not necessarily mean the wings come off...airplanes will usually bend before they break.

I can't recall any CAT-induced breakup of a modern airliner.

rickair7777

The FAA required that you can put the rudder hard-over without breaking off the tail. They did NOT require that the tail stay attached if you go hard-over and then at the moment of max yaw (before it stabilizes) go hard-over in the opposite direction...that is what happened to AA. The pilot probably did not intend to go full deflection, the airbus controls produced full deflection with only a tiny amount of pedal travel in that flight regime.

Airbus designed to the letter of the law..saves weight and money. Boeing overdesigns vertical stabs relative to the FARs.

joepilot

I've been searching the web for a real FAA definition of what Va means, and I can't seem to find one.

I understand how the FAA uses the Vg diagram to establish one boundary for the elevator, but I can't find much else on an official web site or in my older books.

Note: I found quite a number of definitions, many of which contradict each other, but no OFFICIAL FAA definition.

Help?

Joe

rickair7777

I believe Va applies to more than just the elevator and pitch...never in years of training and instruction did I ever hear that rudder/ailerons were not included.

Even the airbus will hold togther with full rudder deflection...as long as you only do it once.

The VG diagram is only for pitch, but you could make a similar plot for each axis and I'm sure the designers do.

HSLD

Check out FAR Part 25.333

In transports, design maneuvering limits are based on airspeed AND load factor.