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Flying On The Ground: Remembering which way to turn the ailerons when taxiing in strong winds really shouldn't be so hard.

We all know what ailerons do and how to use them in flight. By changing the flow of air over the wing--either increasing or decreasing its lift and drag--we adjust the airplane's attitude about its longitudinal axis, also referred to as its bank angle. Most of the time, we may not think about using the ailerons on the ground unless we're flying on a windy day in a light airplane.

Your primary training probably included a diagram explaining where the elevator and aileron controls should be positioned based on where the wind is coming from while taxiing. When we have such wind conditions--and even when we don't, if we want to be honest--we can and should use the ailerons to help control the airplane on the ground. Alas, we don't always have that diagram available, and it's easy to forget whether the upwind wing's aileron should be down or up. (Hint: It depends.) Let's try to come up with a one-size-fits-all understanding of when and how to use ailerons on the ground.

WEATHERVANING

The most obvious need for aileron input on the ground is when flying a high-wing taildragger (or conventional-gear airplane, if you prefer). These airplanes are almost always on the light end of GA's weight scale, making them more susceptible to wind generally, and the ill-timed gust especially, right out of the box. Second, their high-mounted wing is another few feet higher off the ground, allowing that much more air between it and the ground. And wind coming generally from the front of a taildragger tends to want to get it light on its main wheels as it passes under the wing.

Finally, the wing's relatively higher angle of angle of attack on the ground--when compared to a similar tricycle-gear airplane--means more surface area is exposed when the wind is from the rear, like when we're taxiing downwind for takeoff. And let's not forget the taildragger's natural tendency to weathervane into the wind, which we use rudder to counter. In fact, one of the best uses of aileron on the ground is to help counter weathervaning tendencies with the necessary input to keep the upwind wing as low as possible.

To the extent there's any trick here, it's that any time you're in a taildragger and there's much wind, you may have a real chore trying to keep things pointed straight. And keeping things pointed in the direction you want to travel is a key part of taxiing anything, much less some pre-war design that wants to swap ends on you and head back to the hangar.

An equally important use of ailerons on the ground comes when taking off and landing a taildragger. Pretty much with any kind of wind at all, you'll want to coordinate your aileron input with the all-important rudder to help keep the upwind wing down. Yes, this is in stark contrast to how many pilots fly a tricycle-gear airplane in the same wind. But that tells us as much about a trike's forgiving tendencies as it does ham-fisted pilots.

Whether we're in a taildragger or a tricycle-gear airplane, we want to prevent the wind from raising the upwind wing while taxiing. Even raising it a small amount can alter the airplane's tendency to roll straight ahead and encourage it to go off on a literal tangent. To keep the upwind wing down in a stiff breeze or gusty conditions, we position the upwind aileron so that the wind itself acts to push down the wing, not raise it.

The diagram on the opposite page is a graphic explanation of how the wind can act on a deflected aileron and highlights that the correct position varies on the wind's direction relative to the wing. What that static diagram can't depict is that when the wind changes--like when we turn at a taxiway intersection or at the end of a runway--so must the aileron position if we're to keep the wing down.

It's not at all uncommon to go from one against-the-stops aileron position to the opposite in routine ground operations, and there should not be any hesitation or limitation in doing so. When turning, the rate we use to change the ailerons' positions should be as close as possible to the rate of heading change. On the ground, directional control usually is managed by our feet, either with a steerable small wheel or differential braking. But coordinating the airplane's attitude requires aileron.

SEAPLANES AND SUCH

It's probably not a huge coincidence that airplanes originally designed with conventional wheeled landing gear often make good seaplanes. Aside from generally being utilitarian in design, another reason might be enhanced aileron effectiveness. Just as with taildraggers, seaplanes--especially those of the high-wing variety--can use aileron quite effectively on the water. The caption and graphic above highlight what a skilled seaplane pilot can do, and we've seen no-power sailing of a seaplane in tight quarters up close and personal. It requires coordinated use of all the flight controls.

Of course, we haven't talked much about tricycle-gear wheeled airplanes. That's because the effects, benefits and traps of using aileron when we're not airborne are more pronounced with taildraggers and their kin. In those operations, aileron use is more important than with a trike, thanks in part to not having the luxury of the friction coefficient of tires on dry pavement. But it's quite obvious we can and should use a tricycle-gear airplane's ailerons to manage wind during ground operations. Using ailerons to keep the airplane upright and pointed in the right direction is a basic part of our stick-and-rudder skills.

Finally, be sure to observe glider landings sometime. As the sailplane rolls out, increasing aileron/spoiler may applied to keep a wing from dropping prematurely. That is one of the best examples of the fact is you still have to "fly" the airplane, and you do this by using the rudder, pitch and roll controls to keep it pointed where you want it to go. No exceptions.

We haven't talked about crosswind takeoffs and landings much because the case for using aileron on the ground during those operations is obvious, if for no other reason than the controls' effectiveness at higher-than-taxi speeds. But the same basic rationale for using aileron in crosswinds on the runway also applies to the taxiway.

BY THE AVIATION SAFETY MAGAZINE STAFF

We really do have to fly the airplane all the way to the hangar. While too many of us don't use the rudder enough once airborne, other pilots may be forgetting to coordinate all our control inputs on the ground.
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Title Annotation:STICK AND RUDDER
Publication:Aviation Safety
Date:Jun 1, 2019
Words:1096
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