To be honest...
To be honest, I had to look up Vo. I wasn't familiar with that. It is not in Part 1 of the FAA definitions. But, thanks to Google, I learned it's the maximum maneuvering speed.
Yes, italia458, you are correct, this refers to only control surfaces and the supporting structure.
However, the Va does vary with weight...the basic premise is that at or below this speed the control surface "unloads" (stalls) before deformation an'/or structural failure occurs.
Source: FAA-H-8083-25A "Pilot's Handbook of Aeronautical Knowledge"
Pages 4-32 and 4-33.
Not only does it vary with weight, but with altitude, as well. (Above source) As the textbook states, there is one maneuverving speed for a given weight, altitude, and design load factor.
Further, you are correct regarding the turbulence issue. The "gust factor" provides no guarantee of safety.
And, again, italia458, you are correct regarding abrupt and oscillating control input. The American Airlines Airbus accident during departure from JFK brought that point to light.
Source: Airbus Flight Crew Bulletin FCB-FCB25 Use of Rudder on Transport Category Aircraft
And, once again, you are right....Turbulence is another issue. However, the point I was trying to make is that, in extreme conditions, speed reduction of speed to at or below Va affords additional protection against structural failure....with the admonition listed above in the Pilot's Handbook of Aeronautical Knowledge. (i.e. even if slowed to at or below this speed, gusts can bring the aircraft to a point beyond its structural capabilities.)
Again, the basic premise is that, at or below this speed, the surface will stall before it breaks. With the caveats you list regarding this, you are correct.
p.s. I just read your references... My comment:
The writer suggests that, in extreme turbulence, the pilot may need to use
full and abrupt control inputs to control the aircraft. As with the author, I agree, I'd hate to think about doing that.
But, cconsider this: You're in extreme turbulence. You're below your Va. And, you hold the control wheel totally static. That is to say, you make no control inputs. In other words, you let the aircraft do what it is forced to do at the mercy of the turbulence. In this hypothetical circumstance, gusts not considered, the control surfaces will stall before they're allowed to exceed their designed load factor limit.
Remember, stall is a function of, among several things, load factor.
Last edited by PantLoad; 2nd Mar 2013 at 03:47.