In article
,
"Flaps_50!" wrote:

The reason why I riase this is beacuse the variation of Cl with lift
is rarely shown at high AOA but I found some test diagrams and they
show that for typical foils, Cl at 45 is almost the same as the the
stall point. see:

http://www.aerospaceweb.org/question...s/q0150b.shtml

Clearly my understanding of this subject was inadequate. Thank you for
this link.

Now, as I understand/see it, with washout, the overall max lift in a
wing must be less than that given by just max Cl at stall and
planaform. This would not be the case with the 'flat plate lift'. for
a hershey bar wing with say 3 degrees washout, I'd say that flat plate
at 45 could generate at least as much lift as at the stalling point.
This may be a bit esoteric but I think it's interesting and might
indicate an even lower Va if vertical winds are anticipated.

Any vertical gust which approaches 45 degrees AoA is likely to destroy
your aircraft outright no matter what speed you're flying. We're talking
something near a 60kt vertical gust if you're flying at 60kts. That kind
of gust is beyond extreme. You're very unlikely to ever encounter such a
beast unless you're in a thunderhead or something of that nature.

Note that Va is set for a certain maximum vertical gust speed. For gusts
beyond that speed, no guarantees are made. My plane's manual explicitly
calls this out, saying:

"Note: According to the Regulations the term "severe turbulence" means
air movements which might be encountered in wave rotors, storm clouds,
visible whirlwinds and when overflying mountain ranges and ridges. As we
observed in Chapter II.1 this level of turbulence is reached when the
variometer indicates about 7m/s (+1378ft/min) momentary peak indication.
The experienced flyer knows that he can expect even more severe
turbulence in storms and in high mountain ranges."

So, yes, if you expect turbulence in excess of the numbers used to set
your Va, you should fly even slower yet. However I think this still
won't save you if it's as extreme as you describe, but fortunately such
extremes are very rare indeed.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon