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Vb speed

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heidif created the topic: Vb speed

I got this question in a practice exam:
"turbulence penetration speed, Vb, is an indicated airspeed between -
(a) Vno and Vne
(b) Va and Vs
(c) Vfe and Vs
(d) Va and Vno

I chose (b), but the explanation says the following:
"Below Va you can be sure that maximum deflection of the elevator will not generate enough lift to cause any damage to the airframe. Vb - turbulence penetration speed is a higher speed which ensure that an encounter with severe turbulence will not cause damage. Vb is a higher speed than Va. So it is a speed between Va and the normal operating speed, Vno (the top of the green arc on the airspeed indicator).
The correct answer is: Va and Vno

When I did some more research for this question, I could only find information that Vb is less than Va. Can anyone shed some light?
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  • John.Heddles
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  • ATPL/consulting aero engineer
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John.Heddles replied the topic: Vb speed

I'll write up some notes on this question as Va, in particular, is full of OWTs throughout the piloting fraternity. In recent years the regulators have finally started to re-educate folks on the subject.

First, though, might I ask where you came upon the following suggestion ?

When I did some more research for this question, I could only find information that Vb is less than Va. Can anyone shed some light?

Engineering specialist in aircraft performance and weight control.
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Carello replied the topic: Vb speed

"When I did some more research for this question, I could only find information that Vb is less than Va. Can anyone shed some light?"

If you take a look through the POH or AFM, you will generally find nothing about Vb for most light aircraft. What you will most likely find is a reference to Va; the maneuvering speed; nothing else.

When I went through my flight training, many moons ago, we were taught to slow down to Va when flying through turbulent air. We thought of Va as a safety speed where the aircraft will aerodynamically stall before something broke.

The FAA and NTSB have since cautioned that “flying at, or below Va, 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.”

So, we have a situation where Va may not be safe and the aircraft manufacturer does not specify what Vb should be used.

Needless to say, Vb will lie somewhere below Va, and somewhere above Vs; Too slow and the aircraft will stall, too fast and it will bend.

I'll leave this question to the engineer - John H.
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heidif replied the topic: Vb speed

Thanks for your replies.

Carello, that's what I thought....that Vb lies somewhere between Va and Vs. That wasn't the answer in the Bob Tait practice exam that I did though, hence the further research.

John, I found the information I referred to at www.avweb.com/flight-safety/technique/turbulence-v-speeds/ under the heading "Load 'em up" paragraph 5.
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