Hurricane hunters?

Stefan wrote
Actually, the maneuvring speed is the max speed at which full
deflection of the controls is still allowed and it is completely
unrelated to gusts.

Stefan...I've been fighting this common misconception here on
this newsgroup for years and the spam-can pilots just don't seem
to understand. It probably goes back to their basic instruction
and a few well intentioned but misguided magazine writers.

As you point out, maneuvering speed (Va) is related to pilot
induced loads and gust loads are related to Vno, the top of the
green arc on the airspeed indicator for small airplanes, it's Vb
for newer and larger airplanes.

There are actually two "g" envelopes for an airplane. One for
maneuver loads and another for gust loads. When overlayed, they
form the combined envelope. The gust loading envelope is required
to accomodate the most severe gust that it is anticipated that the
airplane will encounter in normal flying operations.

Although both of these loads are actual physical phenomena, the FAA
has defined them in the FARs via Part 23. The information is
scattered in several sections of Part 23, but when specifying the
gust loading requirements, nowhere is Va mentioned, and likewise,
when specifying the maneuver loading requirements, there is no mention
of Vb or Vno (the top of the green arc).

From the FAR:

Section 23.423: Maneuvering loads.
Each horizontal surface and its supporting structure, and the main wing
of a canard or tandem wing configuration, if that surface has pitch
control, must be designed for the maneuvering loads imposed by the
following conditions:

(a) A sudden movement of the pitching control, at the speed VA, to the
maximum aft movement, and the maximum forward movement, as limited by
the control stops, or pilot effort, whichever is critical.

Section 23.333: Flight envelope
(c) Gust envelope. (1) The airplane is assumed to be subjected to
symmetrical vertical gusts in level flight. The resulting limit load
factors must correspond to the conditions determined as follows:

(i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be
considered.........

(ii) Positive and negative gusts of 25 f.p.s. at VD must be
considered...........

Section 23.1545: Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b)
of this section, with the marks located at the corresponding indicated
airspeeds.
(3) For the normal operating range, a green arc with the lower limit at
VS1 with maximum weight and with landing gear and wing flaps retracted,
and the upper limit at the maximum structural cruising speed VNO
established under §23.1505(b).

Section 23.1505: Airspeed limitations.
(b) The maximum structural cruising speed VNO must be established so
that it is --
(1) Not less than the minimum value of VC allowed under §23.335


Quoted from Aerodynamics for Naval Aviators:

"As a general requirement, all airplanes must be capable of withstanding
an approximate effective +/- 30 foot per second gust when at maximum
level flight speed for normal rated power. Such a gust intensity has
relatively low frequency of occurrence in ordinary flying operations.
The highest reasonable gust velocity that may be anticipated is an
actual veritical velocity, U, of 50 feet per second."

Now, I ask, why, when flying in gusty conditions, do pilots slow to Va?
The airplane (by regulation) is designed to withstand the highest
reasonable gust velocity at the top of the green arc? Slowing to Va
presents a definate stall-upset possibility where the pilot is apt to
induce a maneuvering overstress during the recovery.

Bob Moore