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Chapter 2 - Your Flight Instruments: Behind the Panel 2-9

How Strong Are Those Wings? Should we have
Looking at the Mooney airplane to the right, you’re only seeing a portion of told the FBO
about this?
the force the wings on most small general aviation airplanes are safely capa- Naw!
ble of handling. As a matter of fact, it’s rare for a wing to fail because it’s over-
stressed by turbulence. Most wing failures occur because the pilot was flying
in or near IMC and lost control of the airplane, resulting in a dramatic increase
in airspeed. Too much speed increases the likelihood of damage by flutter or
excess stress caused by the pilot pulling too hard during a 200-300 mph
recovery. Take comfort in knowing that you’ll be lucky to find a single case of
a wing breaking off an airplane flown at or below its Vo/Va. Courtesy Mooney Aircraft Co.

before September 14, 1969). Operations above Vno within far reaches of the airplane’s envelope to folks who wear
the yellow arc are allowed only in smooth air (and this parachutes and are trained to do such things.
means smooth air, not air that’s less than the 30 or 50 FPS Three important speeds are not shown on the airspeed
limit values, either). To learn more about these vertical indicator: Va, Vlo and Vle. The first speed is called maneu-
gust values and how they may affect your airplane, you vering speed or Va, otherwise remembered as velocity (V)
might want to read the sidebar on page 2-11 and/or of acceleration (a). In turbulence, you should be at or
Chapter 21 of my Instrument Pilot’s Survival Manual that below maneuvering speed (my preference in serious tur-
covers this topic in much greater detail. bulence is to be below maneuvering speed, perhaps by
Your airplane has one speed that should never be 10–15 knots, since this is an indicated airspeed and a gust
exceeded. Coincidentally, it’s called Vne or velocity (V) can increase your indicated airspeed many knots over Va).
that you never (n) exceed (e). This is the red line on the Maneuvering speed is found well below Vno. Your
airspeed indicator. It’s also the maximum speed at which Pilot’s Operating Handbook or posted placards provide
the airplane can be operated in smooth air and going you with the airplane’s maneuvering speed. Since Va is
above it means all bets are off, and if you go past it you’re
a bit off, too. Exceeding Vne can cause aerodynamic flut-
ter, which, coincidentally, is something your heart valves Vo - Operating Maneuvering Speed
also do if you experience flutter. Aerodynamic flutter is
often an uncontrollable and destructive vibration of cer-
tain airfoil surfaces.
Dynamic divergence and aileron reversal are a couple of
the other bad boys associated with exceeding Vne. Don’t
go there. Many unprepared pilots have lost control of their
airplane in IMC (instrument meteorological conditions)
and reached, then exceeded, Vne. Many have paid a hefty
price for this error. Don’t exceed this speed. Period. No
exceptions and no excuses, unless you’re a test pilot and Fig. 18
getting test pilot pay, a bonus, and a free chocolate treat
for bringing the plane back undamaged. Consider this
your Surgeon General’s warning to avoid flying above the technically defined at the airplane’s maximum design
airspeed indicator’s redline. weight and since maneuvering speed decreases with a
Vne is 90% of the speed at which flutter occurs. decrease in weight, the FAA has added a new term refer-
Granted, Vne has a slight, built-in safety factor but who encing the maneuvering speeds associated with lighter
wants to count on that? General aviation flying isn’t the weights. This term is called Vo or operating maneuvering
test pilot business. If you’re looking for thrills, try speed. Some manufacturers provide one or more Vo’s for
tightrope walking during bee season. Leave exploring the weights less than max gross, as shown in Figure 18.

Divergent Flutter

A B C D
Courtesy NASA
The following video frame sequence (A to B to C) represents approximately one-fifth of a second in which the horizontal stabilizer and
the elevator are in the throes of divergent flutter. The test pilot on this Twin Comanche induced flutter at high speed by pulsing the con-
trol wheel with his hand then, when flutter occurred, he immediately reduced power and applied some back pressure on the elevator
to stop it. Frame D shows the range of surface movement as captured by a camera inside the cockpit.