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Va and turbulent air penetration speed.
Kershner's "The Advanced Pilot's Flight Manual" has the following
definition for Va. Va - The maneuvering speed. This is the maxiumu speed at a particular weight at which the controls may be fully deflected without overstressing the airplane. Now, Va is commonly taught as turbulent air penetration speed. But nowhere in the definition does it say that Va will protect the airframe from damage due to turbulence. Does slowing down even slower than Va protect the airframe from even more severe turbulence? Or is Va the best speed for turbulence penetration? Or is Va just used as a turbulence air penetration speed becauase of tradition or some other non-technically correct reason. |
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#4
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"Robert Moore"
As can be seen, Vb, the speed for the maximum gust has nothing to do with Va. How does one find Vb for most of the GA fleet?.....simple...just look for the top of the green arc on the airspeed indicator. By flying at Va during turbulence, one is flying un-necessarily close to stall and a possible upset. At Va, it would take a full, instaneous deflection of the controls to stall the aircraft. How is that un-necessarily close to stall? The aircraft can be loaded to a much higher value with the controls than by a 50 fps gust. Whicih is why it is recommended to fly at Va in turbulent conditions. That is, 1) because a full deflection of the controls, presumably commanded to recover from a turbulence induced upset, will result in a stall instead of a breakup, and 2) incidently because it is conservatively lower than Vb and therefore well within any expected maximum gust. I sense this is going to be a long one... |
#5
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"Doug"
Va - The maneuvering speed. This is the maxiumu speed at a particular weight at which the controls may be fully deflected without overstressing the airplane. Now, Va is commonly taught as turbulent air penetration speed. But nowhere in the definition does it say that Va will protect the airframe from damage due to turbulence. Does slowing down even slower than Va protect the airframe from even more severe turbulence? Or is Va the best speed for turbulence penetration? Or is Va just used as a turbulence air penetration speed becauase of tradition or some other non-technically correct reason. There should be no reason to go slower than Va for turbulence penetration. The case is made later in this thread for using the faster Vb for such conditions (I disagree but can be convinced). However, one point that is often overlooked is that the published Va is usally/always stated for max gross weight. At lesser weights, Va is lower and can be significantly lower. Va isn't marked on the airspeed indicator but it is an indicated airspeed. |
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On Thu, 08 Jan 2004 22:28:48 GMT, Robert Moore
wrote: By flying at Va during turbulence, one is flying un-necessarily close to stall and a possible upset. Which in my plane (SR20) is also 60% power at 50 degrees LOP, my normal cruise (120 IAS) and I am nowhere near stall which is 65 IAS. |
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"Maule Driver" wrote
At Va, it would take a full, instaneous deflection of the controls to stall the aircraft. How is that un-necessarily close to stall? A gust of sufficient value will also stall the a/c at Va. Whicih is why it is recommended to fly at Va in turbulent conditions. With the FAA saying that Vb is the speed for maximum gust intensity, who do find suggesting otherwise. 2) incidently because it is conservatively lower than Vb and therefore well within any expected maximum gust. This is true, but also closer to a stall I sense this is going to be a long one... Just post the documentation. :-) Bob Moore |
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ArtP wrote
Which in my plane (SR20) is also 60% power at 50 degrees LOP, my normal cruise (120 IAS) and I am nowhere near stall which is 65 IAS And I thought that every private pilot was taught that an airplane can be stalled at any airspeed and any attitude. I assure you that I, or a gust of sufficient value can stall your SR20 at 120 kts. Bob Moore |
#9
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Even if Vwhatever is "close to stall" (inasmuch as a gust could stall it), when
the gust is over, so is the stall. However, if that gust ripped your wings off, when the gust is over, you don't recover your wings. Jose -- (for Email, make the obvious changes in my address) |
#10
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On Fri, 09 Jan 2004 01:29:05 GMT, Robert Moore
wrote: And I thought that every private pilot was taught that an airplane can be stalled at any airspeed and any attitude. I assure you that I, or a gust of sufficient value can stall your SR20 at 120 kts. By my calculations, if I am flying in cruise it would take a tail wind gust of 56 knots to stall me. I suspect that would fall in the category of sever turbulence and I don't think there is any airspeed that would be safe under those conditions in a single engine normal category aircraft. In any case a stall at cruise altitude should not be a problem but parts (like the engine or the wings) falling off the aircraft would be. |
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