Va-- can't wrap my brain around definition

TMetzinger said:
And it's also for ONE deflection of a control surface.
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I'm not sure this is accurate. Im pretty sure the aftermath of AA 587 was that Va applied only to the elevator and specifically didn't apply to the rudder. At a Va speed or below who cares how many times you go full back to full forward? Every time the loads are such that you wont over stress the plane.

The lesson I recall was its never safe to wildly kick the rudder full left to full right back and forth as that was never a design limitation of the rudder and is NOT protected by Va. only the elevator is protected by Va.

Btw, AA587 had the entire vertical stabiliser (rudder and all) separate from the plane due to the pilot kicking full travel of the rudder back and forth with flaps deployed (obviously well below Va).

I don't remember the lesson being ONE full travel. I think you can yank the elevator all you want and the ailerons and rudder (especially the rudder) need to be treated with respect...even at or below Va.
 
It is less than one control. In pitch you can pull back with maximum controls at Va and not break anything. But if you push forward with maximum controls at Va, the airplane is not necessarily designed to keep the wings on.
 
When you get in turbulence, the angle of the wind changes more abruptly than the inertia of the plane allows it to respond to. What this can do is have an immediate change on AoA which is directly followed by a large increase in vertical acceleration as the inertia catches up to the new relative wind direction. The faster you go, the less effect the increase in AoA from a driving gust right? Well, Va is the speed at which a 3.8 g (or whatever the number they use is, not sure, guessing due to other limitations) vertical acceleration will cause a change in AoA that will produce a stall condition at that load factor shedding off excess force in the form of drag. Any faster and you end up with a relative wind that will allow a greater load factor to be achieved.

Simple enough?;)
 
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Captain said:
American 587. That's the plane that crashed in New York right after 9/11. Everyone first thought it was another attack. Turns out AA was teaching pilots to kick the rudder as a wake avoidance techniguq.

I also seem to remember the FAA guidance after that was that Va only applied to the elevator and not the rudder or ailerons. I have no link for that though...
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http://rgl.faa.gov/Regulatory_and_G...62577b200495b5a!OpenDocument&ExpandSection=-4



The Federal Aviation Administration amends the airworthiness standards applicable to transport category airplanes to clarify that flying at or below the design maneuvering speed does not allow a pilot to make multiple large control inputs in one airplane axis or single full control inputs in more than one airplane axis at a time without endangering the airplane's structure.
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On November 12, 2001, American Airlines Flight 587, an Airbus Industrie Model A300-605R airplane, crashed shortly after takeoff from New York's John F. Kennedy International Airport. All 260 people aboard the airplane and 5 people on the ground were killed. The airplane was destroyed by impact forces and a post-crash fire. The National Transportation Safety Board (NTSB) determined "that the probable cause of this accident was the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design loads that were created by the first officer's unnecessary and excessive rudder pedal inputs."
The NTSB's investigation revealed that many pilots might have a general misunderstanding of what the design maneuvering speed (VA) is and the extent of structural protection that exists when an airplane is operated at speeds below its VA. VA is a structural design airspeed used in determining the strength requirements for the airplane and its control surfaces. The structural design requirements do not cover multiple control inputs in one axis or control inputs in more than one axis at a time at any speed, even below VA.
The NTSB found that many pilots of transport category airplanes mistakenly believe that, as long as the airplane's speed is below VA, they can make any control input they desire without risking structural damage to the airplane. As a result, the NTSB recommended that the FAA amend all relevant regulatory and advisory materials to clarify that operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time.1 After making our own assessment, the FAA agrees with the NTSB's finding and the resulting recommendation.
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http://www.aopa.org/advocacy/articl...info_about_what_maneuvering_velocity_spe.html
 
Thanks Andrew. Interesting read.
 
So... Basically what the FAA is saying is... VA ain't VA.. all because they were afraid to tell Scarebus Industries their " Airbus Industrie Model A300-605R airplane" was built too weak and could not stand the test of what VA is intended to designate... Other then this incident, can anyone else remember when a complete verticel stabilizer / rudder, broke clean off like this scarebus did. I briefly scanned the net looking for airframe failures caused by manuevering below VA speeds and I didn't see any Boeing, or for that matter any other brands who have had any documented issues..:dunno:
 
N801BH said:
So... Basically what the FAA is saying is... VA ain't VA.. all because they were afraid to tell Scarebus Industries their " Airbus Industrie Model A300-605R airplane" was built too weak and could not stand the test of what VA is intended to designate... Other then this incident, can anyone else remember when a complete verticel stabilizer / rudder, broke clean off like this scarebus did. I briefly scanned the net looking for airframe failures caused by manuevering below VA speeds and I didn't see any Boeing, or for that matter any other brands who have had any documented issues..:dunno:
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Va has always been about the main spars, you never 'stall' a rudder. The tail isn't built too weak, it's built too powerful for the dense lower air so it will work in the thin up near the tropopause.

If a NASCAR drives down pit row jumping on an off the throttle, he's gonna twist the driveshaft off. Doesn't mean the driveshaft was junk, it means the driver broke it by doing something the part was not designed to take because it is never operationally necessary.

In this case the problem was because the team manager coached the driver to do it. It worked as good as any half baked ideas that management comes up with do.
 
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Dan Thomas said:
I wouldn't go yanking hard on any controls even below Va in the average spam can. Va means the WING will stall and avoid damage at or below Va in turbulence. It doesn't mean I can abuse the airplane by inducing a hard accelerated stall just below Va.

Slippery airplanes like the Bonanza and 210 have been known to lose their elevators/ruddervators/stabilizers when the VMC pilot gets into IMC, loses contol and ends up in a spiral dive. He pops out of the clouds, see the ground coming at him, and pulls back hard. The tail surfaces fail first and with the loss of tail downforce the airplane tumbles onto its back and the wings then fail downward in negative G loading.

Dan
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This.

:yesnod:


Not all airplanes have a published (e.g. manufacturer flight test provided) Va.

In that case you can do the math (see more here: http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/8_Maneuvering.pdf) or just slow down.

Many pilots set power then bump along furiously in turbulence when a 15 knot reduction in speed can reduce the frequency and intensity of those bumps.
 
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Henning said:
Va has always been about the main spars, you never 'stall' a rudder. The tail isn't built too weak, it's built too powerful for the dense lower air so it will work in the thin up near the tropopause.

If a NASCAR drives down pit row jumping on an off the throttle, he's gonna twist the driveshaft off. Doesn't mean the driveshaft was junk, it means the driver broke it by doing something the part was not designed to take because it is never operationally necessary.

In this case the problem was because the team manager coached the driver to do it. It worked as good as any half baked ideas that management comes up with do.
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I agree with your explaination,,, BUT...When an airframe manufacurer sells a "certified" plane it comes with supposable "tested data" to back up specs the FAA sets out to prevent airframe failures.. I can understand anyone can break anything if given the time... my main concern over the scarebus is when they pulled that vertical stabilizer out of the water after the crash the thing had such a clean edge on it where it broke off the fuselage it actually looked like someone had unbolted it. No sign of skin wrinkling from aero sideloads at all... The vert really didn't fail, it was the measly attach brackets.. IMHO.... Hey, this is the internet,, I can have my own bizzarre theories can't I..:dunno::confused:
 
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N801BH said:
I agree with your explaination,,, BUT...When an airframe manufacurer sells a "certified" plane it comes with supposable "tested data" to back up specs the FAA sets out to prevent airframe failures.. I can understand anyone can break anything if given the time... my main concern over the scaebus is when they pulled that vertical stabilizer out of the water after the crash the thing had such a clean edge on it where it broke off the fuselage it actually looked like someone had unbolted it. No sign of skin wrinkling from aero sideloads at all... The vert really didn't fail, it was the measly attach brackets.. IMHO.... Hey, this is the internet,, I can have my own bizzarre theories can't I..:dunno::confused:
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I thought the carbon snapped, but never did read a reputable analysis.
 
Gotta keep up the myth that "Certification" of Transport Category aircraft equals "100% Safe". ;)
 
N801BH said:
And scarebus made DAMN sure the whole deal was clouded in a mystery...

And no... I don't own stock in Boeing...:no::no::no:
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I wouldn't either considering the 787.:rolleyes: I'm still not 100% that's not going to be the Carbon Comet. Just the other day a $1MM+ latest technology and best engineer's mast broke in what were rather benign conditions. Thing is they had take a brutal run in the Southern Ocean a few days prior.. All I hear coming from the Carbon Community about fatigue is denial. The first time I was introduced to structural carbon fiber, I had traded a short block for a 4-1/8" bore 348cuin SB Chevy for a set of carbon rods that GM made back in the 70s. I was the third owner of them new in the box their second year lol. I didn't have the balls to use them either (see Ron, there are risks even I won't take...:rofl:;)) so I traded them for a set of 6" Jet X titaniums. In the intervening years I have almost continuously had my hands in the fabrication and operation of carbon graphite equipment in either the marine or light experimental (although I built a cowling for an Arrow out of it once) aviation. In that time I have seen and experienced many failures of the pure carbon products regardless of the binding agent that have all the hallmark characteristics of fatigue involved failures.

Thing about carbon when it fails it dissolves, it looks like liquefaction on high speed. That's why a clean component next to a failed component would not be unexpected in a fatigue or overstress situation. Carbon doesn't crumple, it dissolves.
 
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