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Ch-9 Weather TheoryV8-BAK_Basic Master Frame.qxd 12/19/2019 7:46 PM Page 76

9-76 Rod Machado’s Instrument Pilot’s Handbook
attitude change). Should you experience an uncommand-
ed roll due to ice formation forward of the ailerons you
should reduce the angle of attack and roll the wings level.
If the flaps are extended don’t retract them unless you can
determine that the upper wing’s surface is free of ice.
Retracting flaps in this instance raises the airplane’s stall
speed (which is probably a bit higher because of ice accre-
tion on the upper wing surface).
Tailplane Icing
It’s one thing to have ice form on the wings where you
have a chance to see it and do something about it. It’s
Fig. 139
another not to be able to see it because it’s on the tail (hor-
izontal stabilizer, elevator, stabilator, or T-tail surface) of
your airplane (Figure 137). At least when Burt Rutan
makes an airplane you can see the tail because he puts it
out in front of the machine where you can keep an eye on
it. So, why is tailplane (tail surface) icing so serious? Let’s
find out.

Tailplane Icing is Difficult to Detect Visually

Fig. 137 tail closer to its critical angle of attack. The result of this
configuration is that actions that move the wing away from
Downward Lift: What? Isn’t Lift stall, such as deployment of flaps or increasing speed,
Supposed to Act Upward? might move the tail toward its critical angle of attack, pos-
Most airplanes have a nose-down pitching moment gen- sibly resulting in a tailplane (or tail) stall (Figure 139). The
erated by the center of gravity (CG) being ahead of the disadvantage here is that a tailplane stall typically would
wing’s center of lift (Figure 138). It is the role of the tail occur during approach and landing—a time when the air-
surface to counteract this moment by providing lift that plane has less altitude to recover from a stall.
acts in a downward direction. Unfortunately, this arrange- Tailplane Stall: What? Another Part
ment often allows an application of flaps (as an intention- Of the Airplane That Can Stall?
al move to reduce the airplane’s stall speed) to increase As an airplane’s tail surface (also called tailplane) is
the negative angle of attack (AOA) on the tail. In other ordinarily thinner than the wing, it is a more efficient col-
words, the application of flaps might require slight aft ele- lector of ice. Because it’s often not possible to observe the
vator pressure (creating more downward-acting lift) to tail surface and see how well it is cleared of ice by any de-
maintain the desired attitude. Aft elevator pressure icing system, you must be alert to the possibility of a
increases the AOA (in the negative direction), moving the tailplane stall, particularly after full flap deflection. This

Fig. 138