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No there isnt any mention of the reasoning behind any of the V speeds. You
have to use your head. For instance all gear speeds must be above the stall
speed with flaps out, for obvious reasons. Va provides protection from
overstress from maneuvering loads. It says nothing about transient loads
caused by gusts and probably doesnt provide protection against certain
combinations of loads either. I doubt that Va provides protection if an
aircraft is maneuvering at the load limit and full aileron is applied.

Aircraft have inertia and that is what "gust loading" is all about. When
the aircraft encounters a change in wind speed or direction, it takes time
to accelerate to the new wind field. If the airplane was unaffected by
gusts then windshear would not be a problem. If you have taken off from a
small tree lined runway with a slight tailwind (that becomes a big tailwind
a treetop height) you know what Im talking about.

Yes, airplanes fly through hurricanes but they avoid the CBs as much as
possible. A P-3 experienced over 5.5Gs flying through one of the recent
hurricanes at really low altitude. A small airplane with a low wing loading
would not have survived.

As for the applicability of any of this to the thread, It was your
statement:

"Have you mentioned that you slow to Va in turbulence so that the wing
> will stall before it breaks? Once your airplane is at/below Va a
> vertical gust can only cause discomfort, not disaster"

that got things on the current tangent. The idea that Va is a guarantee
against structural failure is widespread and totally incorrect. Part 25
airplanes have a turbulence penetration speed Vb, but even that is not a
guarantee against failure. Vb is merely offers the best balance between
controllability and gust protection.

The B-29 was indeed pressurized.

Mike
MU-2

"Larry Dighera" wrote in message
news:svfY6.11204$c7.2739381@typhoon.we.rr.com...
> On Thu, 21 Jun 2001 02:02:53 GMT, "Mike Rapoport"
> wrote:
>
> >The certification requirement is that, at Va, the wing stall at the
design
> >load limit which for (normal category) part 23 airplanes is
> >2.1x(24,000/(W+10000)) where W is gross takeoff weight. I found this
on
> >the sight [sic] that you referenced.
>
> Was there any mention of Va in conjunction with "full control
> deflection" in that FAR?
>
> >No, I have not flown through a tornado! If you did, you would get a gust
of
> >up to 300mph which is enough to blow asphalt roads away.
>
> An aircraft moves WITH a body of air, it probably wouldnt encounter
> 300 MPH gusts in such a situation.
>
> > An airplane would not survive.
>
> The fly through the eye of hurricanes.
>
> >During the Sierra Wave Project an instrumented glider was flown into a
very
> >powerful rotor at 45mph IAS (well below Va). When the glider entered the
> >rotor the airspeed increased to 90kts even thought the glider was in a
nose
> >up attitude. Two stalls ensued one at 4G and another at 4.5G. When the
> >glider encountered the most severe turbulence the pilots chin was forced
> >against his chest and he blacked out from the Gs. The glider then broke
up
> >under the load which was estimated (by examination of the wreckage by,
well
> >know aeronautical engineer, Paul MacCready Ph.D.) to be +16G and -20G.
The
> >negative Gs were so great that all the capillaries in the pilots eyes
were
> >ruptured. The incident is believed to be the greatest G forces ever
> >survived in an uncontrolled setting.
>
> While that is very interesting information, it is not indicative of
> the conditions the original poster is likely to experience. How many
> pilots are fool enough to fly through the rotor of a standing wave in
> a GA aircraft?
>
> >In another incident a B-29 was intentionally flown into a powerful rotor
> >system and the fuselage was twisted so much that a window blew out. Look
at
> >a window on a pressurized airplane sometime and imagine how much force
would
> >be required.
>
> I wasnt aware that the B-29 was a pressurized aircraft.
>
> >A 747 had an engine fall of after an encounter with a mountain wave (out
of
> >Anchorage I think). I recall that the plane was climbing and was
probably
> >below Va or Vb. The load was over 4G.
>
> Ill agree with you that nature possesses awesome force, but I doubt
> that the original poster is contemplating flying in mountain wave.
>
> >A Cheyenne 400LS owned by Allied Signal had a horizontal stabilized bent
> >dramatically upwards in severe turbulence below Va.
> >
> >There is no way a small airplane with a low wing loading would have
survived
> >any of these events.
> >
> >A plane is no match for the worst that nature can dish out, no matter
what
> >the speed.
>
> Agreed. But, the original poster was concerned with "light chop."
>
> >The certification requirements are based on reasonable gust
> >loads, not on the maximum that could be encountered.
>
> While that may be true, it isnt really germane to the subject of this
> thread.
>
> >Mike
> >MU-2
> >
> >"Larry Dighera" wrote in message
> >news:vHbY6.10858$c7.2342302@typhoon.we.rr.com...
> >> On Wed, 20 Jun 2001 20:15:44 GMT, "Mike Rapoport"
> >> wrote:
> >>
> >> >This says that Va is the speed at which the wing will stall at the
> >maximum
> >> >load limit.
> >>
> >> Does it mention the load a stalled wing can support? Or, does that
> >> call for a little reasoning on your part?
> >>
> >> >It does not say or imply that an airplane flown at Va is not at
> >> >risk of a breakup in turbulence. If you fly into a tornado, for
> >instance,
> >> >it wont matter if you are at Va or not.
> >>
> >> Have you deduced this from firsthand experience, or conjecture?
> >>
> >> >At any airspeed, starting from 0, there is a gust intensity that will
> >> >cause structural failure.
> >>
> >> Please cite your source for that assertion. Can you quantify the
> >> vertical speed of such a gust? Can you please indicate the likely
> >> probability of encountering such a gust?
> >>
> >> >Mike
> >> >MU-2
> >> >
> >> >"Larry Dighera" wrote in message
> >> >news:s37Y6.9908$c7.1994460@typhoon.we.rr.com...
> >> >>
> >> >> Actually, youll find the true definition of Va here:
> >> >>
http://www.access.gpo.gov/nara/cfr/cfrhtml_00/Title_14/14cfr25_00.html
> >> >>
> >> >> On Wed, 20 Jun 2001 14:22:43 GMT, "Mike Rapoport"

> >> >> wrote:
> >> >>
> >> >> >Baloney! Va is the speed at which the wing will stall before
reaching
> >> >its
> >> >> >load limit with full control deflection. It says nothing about
> >ability
> >> >to
> >> >> >survive turbulence. You should read "Exploring the Monster" (my
> >favorite
> >> >> >aviation book). Near the end of the program, a glider broke up in
> >flight
> >> >> >after experiencing loads estimated a +16G to -20G.
> >> >> >
> >> >> >Mike
> >> >> >MU-2
> >> >> >
> >> >> >"Larry Dighera" wrote in message
> >> >> >news:AXTX6.4664$c7.927563@typhoon.we.rr.com...
> >> >> >> On 19 Jun 2001 11:45:40 GMT, jajohn@wnc0h0hm.bnr.ca () wrote:
> >> >> >>
> >> >> >> [snip]
> >> >> >>
> >> >> >> >However, as soon as we encounter turbulence, even as little as
what
> >> >> >> >most of us would consider light chop, she instantly turns into
> >> >> >> >a white knuckled flyer, her hands clenched around the seat belt
> >> >> >> >and any available handles as she stares straight ahead.
> >> >> >>
> >> >> >> [snip]
> >> >> >>
> >> >> >> Have you mentioned that you slow to Va in turbulence so that the
> >wing
> >> >> >> will stall before it breaks? Once your airplane is at/below Va a
> >> >> >> vertical gust can only cause discomfort, not disaster.
>
> I stand corrected. In extreme cases, it is evident from the
> information provided by Mr. Rapoport, that disaster is indeed possible
> at Va.
>

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